Making Polycarbonates without Employing Phosgene - American

Ind. Eng. Chem. Res. 2004, 43, 1897-1914

1897

REVIEWS Making Polycarbonates without Employing Phosgene: An Overview on Catalytic Chemistry of Intermediate and Precursor Syntheses for Polycarbonate Won Bae Kim, Upendra A. Joshi, and Jae Sung Lee* Department of Chemical Engineering and School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31 Hyoja-dong, Pohang 790-784, Korea

Conventional production of aromatic polycarbonates (PCs) involves interfacial polycondensation between phosgene (COCl2) and bisphenol A (BPA). This COCl2 process has several drawbacks such as environmental and safety problems involved in using the highly toxic COCl2 as the reagent, which resulted in the formation of chlorine salts of a stoichiometric amount, and in using copious amounts of methylene chloride as the solvent. For these reasons, environmentally friendly processes for PC production without COCl2 have been developed such as melt transesterification of BPA and diphenyl carbonate (DPC). However, COCl2-free production of DPC is not easy yet because of its severe equilibrium constraint, and therefore obtaining DPC efficiently is the most important step to develop a successful COCl2-free PC process. DPC can be obtained via two methods without using COCl2: two-step synthesis of DPC from dimethyl carbonate (DMC) and phenol and direct oxidative carbonylation of phenol. The DPC reacts with BPA to form PC precursors, which are amenable to the subsequent polycondensation step to obtain high molecular weight PC. Alternatively, BPA can be directly carbonylated with DMC or CO. In this work, we review and discuss different reaction routes and the involved catalytic chemistry of possible COCl2-free PC syntheses based on literature as well as our own experimental results. We compare reaction characteristics and the nature of PC precursors produced from different synthetic routes and provide a perspective on an improved COCl2-free PC process. 1. Introduction Market growth for aromatic polycarbonates (PCs) has been more than 10%/year from the late 1990s. Currently, the worldwide production capacity of PC is more than 1.5 million t/year, and the construction of new PC plants is likely to continue. However, the commercial PC has been produced mostly by phosgene (COCl2) processes, which are based on an interfacial polycondensation of bisphenol A (BPA) and COCl2.1 The major drawbacks of the conventional COCl2 processes are environmental and safety problems involved in using highly toxic and corrosive COCl2 as the reagent and copious amounts of methylene chloride as the solvent (ca. 10 times the weight of the final products).1 When COCl2 is used, the formation of salts such as NaCl or HCl in stoichiometric amounts cannot be avoided. Thus, a number of recent researches have been focused on alternative routes to PC synthesis without employing COCl2 or chlorinated chemicals, turning these stoichiometric processes into catalytic reactions. The recently commercialized COCl2-free PC process consists of a number of reaction steps starting from CO to the final polymer, which is illustrated by the boldface arrows in Figure 1. The first step is to synthesize dimethyl carbonate (DMC) via oxidative carbonylation * To whom correspondence should be addressed. Tel.: 8254-279-2266. Fax: 82-54-279-5528. E-mail: [email protected].

of methanol,2-17 and then diphenyl carbonate (DPC) is synthesized from a two-step reaction of transesterification of phenol and DMC into methylphenyl carbonate (MPC) followed by disproportionation of MPC.18-37 The DPC is transesterificated with BPA in the melt phase,38-64 resulting in the formation of PC precursors, which are amenable to polymerization in the subsequent polycondensation step. The polycondensation step is carried out under a vacuum condition to remove phenol produced as a recyclable byproduct. The precursors obtained by this route have phenyl carbonate and/or hydroxy (of bisphenol) end groups.45 As a potential substitute for DPC, DMC could carbonylate BPA into PC precursors,45,65-73 as depicted on the right-hand side of Figure 1. In this case, the precursors have methyl carbonate and/or hydroxy end groups.45 This reaction scheme is similar to the transesterification of phenol and DMC that involves ester exchange between phenolic and carbonate compounds and thus, like that reaction, is subject to serious constraints on chemical equilibrium for the forward reaction.45 A direct insertion of CO into the para position of BPA74-83 is also possible and, in theory, it would be the most desirable method to obtain PC precursors without using COCl2 or chlorinated reagents. It involves the least number of reaction steps from CO to PC precursors and, in fact, it is a direct one-step reaction, as shown in Figure 1 on the left-hand side. It is a

10.1021/ie034004z CCC: $27.50 © 2004 American Chemical Society Published on Web 03/31/2004

1898 Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004

Figure 1. Possible routes for PC synthesis without employing COCl2 and chlorinated reagents. The boldface arrows indicate the commercialized COCl2-free PC route. Section numbers describing each route are indicated.

reaction scheme similar to the direct oxidative carbonylation of phenol into DPC,84-120 which aims to obtain DPC directly without involving DMC, as described in Figure 1. In this work, reaction characteristics of each route in Figure 1 are reviewed and advantages and disadvantages for these possible routes for PC synthesis are discussed on the basis of experimental results obtained by us and other investigators for each reaction. We focused on the catalytic chemistry of each reaction to compare intrinsic catalytic aspects under similar conditions with a limited attention to the engineering aspects of the processes. Polymerization to obtain high molecular weight PCs is also excluded from the scope of this review. 2. Methods for Investigations This section describes briefly typical experimental procedures that we employed to obtain results discussed in this review. Similar procedures were also used in most of the other cited works. 2.1. Preparation of Catalysts. All catalysts were prepared by an impregnation method, and the detailed procedures were described elsewhere.25-27,83 For example, to prepare TiO2/SiO2 or TiO2/C catalysts, SiO2 and activated carbon were impregnated with a solution of tetrabutoxytitanium dissolved in toluene. Samples (10 wt % by metal) were dried in an oven at 383 K for 12 h to remove the organic solvent and calcined in a quartz reactor at 773 K for 4 h with an air stream of 89 µmol s-1. For the preparation of 5 wt % Pd on activated carbon (denoted as Pd/AC), activated carbon was mixed with a solution of Pd(CH3COO)2 [denoted as Pd(OAc)2] dissolved in acetone. This slurry was dried at 333 K for 1 h to remove the acetone, followed by further drying under a reduced pressure of ca. 100 Torr, and then

reduced at 473 K for 4 h with a dihydrogen stream of 37 µmol s-1 at atmospheric pressure in a U-type Pyrex reactor. 2.2. Procedures of Catalytic Reactions. Transesterification of DMC and Phenol. For a gas-phase reaction, the mixture of DMC and phenol in a 5:1 mole ratio was vaporized in an evaporation chamber prior to delivery to the catalytic reactor. The reactants were introduced into the flow of nitrogen gas of 15 µmol s-1. The detailed procedure for the gas-phase reaction was reported elsewhere.26,27 For a liquid-phase reaction, a 300 cm3 autoclave (Parr) was employed as the batch reactor. A catalyst and a mixture of DMC and phenol were charged into the reactor. With stirring, the reactor was flushed with nitrogen gas several times and pressurized with nitrogen gas, and then the reaction temperature was adjusted to the desired temperature.25 Disproportionation of MPC. Using a mixture of 94.3 wt % MPC containing 5.7 wt % of phenol, which was synthesized by an organochemical method described elsewhere,121 the disproportionation of MPC was performed in gas and liquid phases in a manner similar to that of the first transesterification step.25 In the liquid-phase reaction, an excess amount of n-hexane was employed as a solvent. Oxidative Carbonylation of Phenol. For a given amount of Pd catalyst, an inorganic cocatalyst, tetrabutylammonium bromide (TBAB), 1,4-benzoqiunone, and dried phenol were charged into a 200 cm3 autoclave reactor (Parr). After the reactor was purged with CO, 7.7 MPa of CO and 0.58 MPa of O2 were successively charged and the reaction temperature was adjusted to 381 K.88 Transesterification of BPA with DPC or DMC. BPA and an aqueous catalyst solution of alkali-metal hydroxides (or carbonates) were added into a 100 cm3 autoclave (Parr) containing molten DPC. After the reactor was purged by dinitrogen three times and pressurized to 1 MPa, the temperature was ramped to 433 K with an electric heater.45 In the case of transesterification of BPA and DMC, the reaction was carried out in the same manner as the reaction between BPA and DPC.45 The catalysts of titanium alkoxides or silicasupported titanium oxides, which have been found to be effective for the transesterification of phenol and DMC, were employed in this case.25-27 Oxidative Carbonylation of BPA. For the direct oxidative carbonylation of BPA, a homogeneous Pd(II) complex or a heterogeneous Pd/AC catalyst, an inorganic cocatalyst quaternary ammonium halide as the base, quinones as organic cocatalysts, methylene chloride or tetrahydrofuran as the solvent, and BPA were charged into the 100 cm3 autoclave (Parr). After the reactor was purged with O2 three times, 5 MPa of CO and 0.5 MPa of O2 were charged successively and the reaction temperature was adjusted to 373 K. The reaction was quenched after a desired reaction time by cooling the reactor with ice water.45,81-83 Identification and Quantitative Analysis of Reaction Products. Reaction products were analyzed by high-performance liquid chromatography (HPLC), gas chromatography (GC), and GC/mass spectrometry (GC/ MS) in order to identify and quantify intermediates, PC precursors, and byproducts. The GC analyses were carried out by a HP 5890II gas chromatograph equipped with a flame ionization detector (FID) and by a HP 5890II/HP5972MSD gas chromatograph/mass spectrometer . The HPLC analyses were performed by a reversedphase method on a Waters 2690 separation module

Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 1899 Scheme 1. Oxidative Carbonylation of Methanol into DMC

Scheme 3. Oxidative Carbonylation of Methanol Using Cupric Chloride Supported on Activated Carbon in the Gas Phase14

Scheme 2. Oxidative Carbonylation of Methanol Using Cuprous Chloride Catalyst in the Liquid Phase5

equipped with an autosampler. As an UV detector, a Waters 2487 dual λ absorbance detector was used at a UV wavelength of 240 nm. The reversed-phase liquid chromatography (LC) column was a Waters Lichrosorb RP18 analytical column (5 µm particle size, 4.6 × 250 mm). A mobile-phase flow rate of 1 mL min-1 was adjusted with a gradient mode of acetonitrile and water from 65:35 to an isocratic mode of acetonitrile. The detailed procedures were described in previous papers.45,82 3. Synthetic Processes of Intermediates and Precursors to PCs 3.1. DMC Synthesis from Methanol and CO. DMC has been regarded as a safe alternative to the use of toxic and corrosive intermediates such as COCl2 in carbonylations and methyl chloride and dimethyl sulfate in methylation reactions. It is also being considered as a component of reformulated fuels, owing to its high oxygen content and good blending properties.5 The two most attractive routes for industrial syntheses of DMC were found to be oxidative carbonylation of methanol and carbonylation-transesterification of ethylene oxide via ethylene carbonate. However, on the basis of technical and economical considerations, the former process has advantages because the latter has a major drawback of the coproduction of ethylene glycol.5 The oxidative carbonylation of methanol to DMC is described in Scheme 1. There is an excellent recent review15 on the DMC synthesis; thus, we will briefly discuss here the catalytic chemistry of the DMC synthesis from oxidative carbonylation of methanol catalyzed by copper and Pd/ C. The copper-catalyzed process developed in 1983 adopted the oxidative carbonylation of methanol in the liquid phase with a slurry reactor employing cuprous chloride as the catalyst.5 According to a simplified scheme, the reaction proceeds initially through CuCl oxidation by O2 in the presence of methanol to cupric methoxychloride, and then the latter is reduced by carbon monoxide to DMC, restoring CuCl and completing the catalytic cycle as shown in Scheme 2.5 Most of the metal ions suitable for oxidizing CO in water to CO2 are also effective in Scheme 2 because of their similarity in involved catalytic chemistry. The copper-containing catalyst developed by Dow was a cupric chloride supported on activated carbon promoted with a variety of other metal chlorides. The oxidative carbonylation of methanol proceeded in the vapor phase, and the catalysts were regenerable.14 The proposed mechanism is coordination of the methoxy groups to divalent copper atoms as the initial step, followed by CO insertion into a Cu-O bond to form a labile carbomethoxide species, which couples with a neighboring methoxy group to form DMC. The reductive elimination produces two Cu(I) species, which reoxidize

to Cu(II) with molecular oxygen. The Cu(II) atoms are remethoxylated, and two protons combine with atomic oxygen to form byproduct water.14 The scheme is described in Scheme 3 as suggested, but the redox mechanism between Cu+/Cu2+ and the state of Cu2+ supported on activated carbon is not clear. A similar scheme for the gas-phase oxidative carbonylation of methanol was reported using the same catalyst of CuCl2 supported on activated carbon by Tomishige et al.8 They studied structural changes of copper during the reaction and suggested that the formation rate of DMC was strongly related to the Cl/ Cu ratio and cupric chloride was changed to Cu-ClOH compounds (such as Cu2Cl(OH)3, CuCl2‚3[Cu(OH)2], etc.), followed by copper oxychloride compounds. Also CuCl2 supported on polymers, such as poly(2,2′-bipyridine-5,5′-diyl) or poly(vinylpyridine), was reported as the active catalytic system for the synthesis of DMC in the liquid-phase reaction.6 The reaction mechanism was proposed to be a typical Cu+/Cu2+ redox system except that the pyridine compounds as the supports played the role of ligand for the copper. An additional oxidant is often introduced to reoxidize the metal ion more efficiently, and the redox is preferably carried out in situ. The oxidative carbonylation also takes place in the presence of nonmetal redox pairs such as Se2-/Se0 and Br-/Br2.5 Particular attention has been devoted to the catalytic activity of palladium (Pd0/Pd2+) pairs, mostly because of their high reactivity even under mild conditions. The reoxidation of Pd0 with molecular oxygen can be easily performed in situ if a suitable cocatalyst such as copper salts is used.2,5 Aminecopper(II) complexes were also reported as efficient catalysts in the reaction.5 Another commercially practiced process developed by Nishihira et al.16 uses a nitric oxide catalyst system for oxidative carbonylation. They develop this technology from the process operated by them for the last 12-14 years for the synthesis of dimethyl oxalate (DMO), where DMC is the byproduct. Their process has the advantages of less reactor volume, less severe catalyst deactivation problems, and higher conversion compared to copper-catalyzed processes. In early work, Nishihira et al. focused on the production of DMO, using a tworeactor system with a Pd/carbon catalyst in one of the reactors. The catalyst system used for DMC is a simple modification of the oxalate catalyst. A typical catalyst used was palladium chloride and a second metal chloride (Bi, Fe, or Cu) coimpregnated on active carbon. The activity of the catalyst was tested in the vapor phase in a fixed-bed reactor of 1-20 atm and 323-423 K. High pressure favors the formation of oxalate. The palladium catalyst converts methyl nitrite (MN; CH3ONO) to DMC in the presence of CO. Scheme 4 shows a block diagram for this process. A two-reactor setup was employed. The overall catalytic chemistry proceeds as follows. In the first step (reactor 2), methanol is reacted with oxygen and NO without any catalyst to give MN and water. In the second step (reactor 1), gaseous MN reacts with CO over

TiO2/SiO2, TiO2/C Kim and Lee26,27

a There are two synthetic methods: a two-step reaction of transesterification of DMC and phenol (denoted as the “1st step”) followed by disproportionation of MPC (denoted as the “2nd step”) and a one-pot reaction of DMC and phenol to DPC.

various supported solid catalysts were screened in the gas-phase reaction; formation of various side products depended on the catalytic systems

Bu2SnO Murata et al.22

423-473 K, 26 kPa 723 K

19.7% MPC yield (1st step), 84% MPC conversion (2nd step) 31.7% MPC yield (1st step)

mechanism of the carbonate interchange reaction was proposed effect of the reactant ratio was studied in a continuous process many catalytic systems were studied in a continuous process integrated with multistage reactive distillation various reactive distillations were studied in continuous process. 44% DPC yield 21% MPC yield, 23% DPC yield 91.2% DPC yield Shaikh and Sivaram20 Harrison et al.23 Fukuoka et al.21

463 K, 12 h

samarium trifluoromethanesulfonate n-Bu2SnO titanate esters Pb(OPh)2 Fuming et al.34

383-393 K, 48 h 523 K 467 K, 12 kPa

catalyst could work in moisture or in the presence of O2 without deactivation

effect of calcination temperature on catalyst performance was studied anisole and cresol were byproducts in the 1st step; no byproducts in the 2nd step MoO3/SiO2 TiO2/SiO2, MoOx/C Oh et Kim and Lee25

473 K, 4 h 433 K, 3 h

17.1% MPC yield (1st step), 44.2% DPC yield (2nd step) 19.2% phenol conversion. (1st step) 7% MPC yield (1st step), 47% DPC yield (2nd step) 31.1% DPC yield 433 K, 4 h MoO3/SiO2

al.33

Fu et

remarks conversion and yield reaction conditions catalyst ref

Table 1. Some Examples for Catalytic DPC Synthesis from DMC and Phenola

the bimetallic catalyst to produce DMC and NO. The overall productivity of this process, to some extent, depends on the reaction in reactor 2. An initial high reaction rate for the reaction in reactor 1 [0.5 L of DMC/ h/L (selectivity ) 97%)] deactivates in the first 10 h to the steady-state rate of 0.3 L of DMC/h (selectivity ) 92%). No further deactivation was noticed up to 100 h.16 The major advantage of this process compared with the copper-catalyzed process is the dual reactor system, which never allows the feed methanol and byproduct water to pass over the metal chloride catalyst, which deactivates the catalyst in the case of the coppercatalyzed process. In addition, product separation should be relatively simple because the two azeotropes that cause problems in the copper-catalyzed system are never formed. The ease of vapor/liquid separation compared to solid/liquid separation benefits the PdFe/C-catalyzed process. 3.2. DPC Synthesis from DMC and Phenol. DPC is an indispensable intermediate for the currently commercialized COCl2-free PC process and has often been synthesized via a two-step reaction from DMC and phenol24-27 because the direct synthesis of DPC [simultaneous reactions of (1) and (2) (Scheme 5) in one reactor] is limited because of a very low equilibrium constant for the forward reaction.23,25 Hence, DPC is obtained efficiently with two reactions of transesterification of DMC and phenol (reaction 1), followed by disproportionation of formed MPC into DPC and DMC (reaction 3). Table 1 represents a brief summary of the catalytic DPC synthesis, which involved a single or combined reactions of (1)-(3) over a homogeneous or heterogeneous catalyst system. Generally, reactions (1) and (3) are carried out in the liquid phase using homogeneous catalysts such as organic Pb, Sn, or Ti compounds. However, an active solid catalyst is more desirable in the aspects of separation and regeneration of catalyst. As one of a few reports on the development of active solid catalysts, Fu et al.12 reported that molybdenum oxide supported on silica showed the highest activity for both transesterification (eq 1) and disproportionation (eq 3) in the liquid-phase reaction. Nevertheless, there exists a critical thermodynamic limitation for the synthesis of DPC from DMC and phenol, especially in reaction (1). The reaction of DMC and phenol shows another problem of side reaction such as methylation due to the reactivities of DMC in the liquid phase as suggested in Scheme 6. Much effort has been devoted to increasing the yield of MPC by employment of complicated reaction processes such as catalytic distillation,21-23 but it is desirable to devise a

al.24

Scheme 4. Two-Reactor System for DMC Synthesis15

anisole as the sole side product; a number of supported solid catalysts were screened


Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 1901 Scheme 5. DPC Synthesis from the Reaction of DMC and Phenol

Scheme 6. Reactivities of DMC in the Liquid Phase

Table 3. Transesterification of DMC and Phenol in the Gas-Phase Reaction25,a catalyst MoO3/SiO2 TiO2/C TiO2(B)/SiO2 TiO2(E)/SiO2d TiO2(I)/SiO2d TiO2(C)/SiO2d

Table 2. Transesterification of DMC and Phenol in the Liquid-Phase Reaction25,a catalyst

MoO3/ SiO2b

TiO2(B)/ SiO2c

TiO2(I)/ SiO2c

TiO2(C)/ SiO2c

PhOH conversion (%) MPC selectivity (%)

7.1 99.7

6.3 99.3

5.7 99.4

6.7 99.7

a Charge of DMC, 595.0 mmol; charge of phenol, 119.0 mmol; catalyst loading, 1.0 g; reaction temperature, 433 K; reaction time, 3 h. b 20 wt % Mo loaded MoO3/SiO2 catalyst. c 10 wt % Ti loaded TiO2/SiO2 catalysts derived from the different precursors of tetrabutoxytitanium (B), tetraisopropoxytitanium (I), and tetrachlorotitanium (C).

more improved catalytic system that could increase the yield of MPC from the reaction itself under novel reaction conditions. Tundo et al.19 reported the reaction of DMC with phenol under continuous flow of gaseous reactants over a solid bed supporting a liquid-phasetransfer catalyst, which was a spherical macroporous R-alumina coated with 5 wt % of potassium carbonate and 5 wt % PEG 6000. However, anisole was the sole product. They suggested that transesterification between DMC and phenol was not favored thermodynamically, with Keq of ca. 3 × 10-4 at 453 K. Table 2 shows the activities of MoO3/SiO2 and TiO2/SiO2 catalysts (the latter prepared from three different Ti precursors) for the liquid-phase transesterification reaction (1) in a batch reactor. MPC yields of ca. 7% were obtained, which were believed to be the equilibrium yield. The reaction rates were so fast that the highest yield of MPC was obtained within 1 h with minimal formation of anisole as the sole byproduct. In the liquid phase, transesterification of DMC and phenol has a critical thermodynamic limitation in obtaining high MPC yields. The equilibrium yield of MPC was less than 7% under the present conditions, although the reaction rate was fast. Hence, the development of a more efficient catalyst system for the liquid-phase reaction would not exert any

conv yield (%)b (%)c BZ TN 20.5 30.4 37.2 30.4 28.9 32.4

8.4 27.7 31.7 25.8 23.2 28.5

1.9 0 0 0 0 0

selectivity (%) AN

Cr

0.7 29.3 17.3 0 5.9 1.6 0 8.8 4.0 0.4 6.6 5.6 0 7.7 8.4 0 8.2 2.5

MPC MMB DPC 40.8 91.2 85.1 84.9 80.4 87.9

5.1 0 0.4 0 1.0 0

5.0 1.2 1.7 2.4 2.5 1.4

a Reactant mixture feeding rate, 1.0 cm3 h-1; mole ratio of DMC to phenol, 5; N2 flow rate, 15 µmol s-1; catalyst (10 wt % metal loaded) loading, 0.48 g; temperature, 723 K. BZ: benzene. TN: toluene. AN: anisole. Cr: cresol. MMB: multimethylbenzenes. b Based on phenol converted. c Yield of MPC. d Silica-supported titanium dioxide catalysts derived from tetraethoxytitanium (E), tetraisopropoxytitanium (I), and tetrachlorotitanium (C).

significant impact on the improvement of the MPC yield. Because reaction (1) is endothermic,25 higher temperatures are desirable for higher MPC yields. Because of the boiling point of phenol (454 K), however, the hightemperature reaction should be carried out in the gas phase and development of a new catalyst that worked effectively under the drastically altered reaction conditions was required. We found that TiO2/SiO2 or TiO2/C employed in a continuous-flow gas reactor was a suitable catalyst for this purpose. The detailed results of catalyst characterization26,122,123 and the role of coking27 for the gas-phase transesterification over TiO2/SiO2 were described elsewhere. Table 3 shows the activities of various catalysts at 723 K in the gas-phase reaction at a time on stream of ca. 8.5 h. The catalyst systems of titania supported on activated carbon and silica reached steady-state activities within 6 h, but the other catalysts were deactivated by coking until the end of the reaction. Major byproducts were anisole and cresol, which could be formed via methylation of phenol by DMC. The most efficient catalyst was TiO2 supported on activated carbon or silica for this gasphase reaction. Furthermore, the performance of TiO2/ SiO2 was similarly independent of the titanium precursors employed for the catalyst preparation.27 Selectivity to MPC could be increased to 94% with 29.5% phenol conversion at 673 K over a 10 wt % TiO2/SiO2 catalyst. Anisole was produced with about 3.5% and DPC with 1.5% of selectivity values. The gas-phase reaction (1) over TiO2/SiO2 catalyst showed an interesting feature of an induction period for the selective formation of MPC, which was caused by carbon deposition on the catalyst surface that deactivated selectively the highly reactive catalytic sites responsible for the side reactions.27 The reactivity of DMC in the gas phase was quite different from that of the liquid phase. It was more

1902 Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 Scheme 7. Proposed Reaction Pathways of DMC on the Surface of 10 wt % TiO2/SiO2 Catalyst in the Gas Phase27

Figure 2. Disproportionation of MPC over 10 wt % TiO2/SiO2 and 20 wt % MoO3/SiO2 in the liquid-phase reaction:25 charge of MPC, 31.2 mmol; catalyst loading, 0.5 g; temperature, 433 K.

complicated, as illustrated in Scheme 7, and is responsible for much of the byproduct formation and the presence of the induction period in the gas-phase reaction between DMC and phenol. Figure 2 represents time courses of the disproportionation of MPC [reaction (3)] in the liquid phase over TiO2/SiO2 and MoO3/SiO2 catalysts. In both cases, MPC disproportionated into DMC and DPC with a selectivity of 99.8% or better. The TiO2/SiO2 catalyst showed the equilibrium conversion of ca. 47% within 20 h, but the MoO3/SiO2 catalyst showed a slower rate, giving 20% conversion in 25 h. Apparently, disproportionation of MPC [reaction (3)] is too slow compared with reaction (2). However, the rate should be increased without solvent or through control of the mass-transfer constraints by modification of the void volume of supports.124 From the above results, a new process could be proposed for the synthesis of DPC from DMC and phenol that employed the unprecedented gas-phase transesterification of DMC and phenol, followed by the liquid-phase disproportionation of MPC. Both reactions can proceed over TiO2/SiO2 or TiO2/C catalysts, which perform better than catalysts reported previously in the literature to be active in similar reactions. This process alleviates the severe equilibrium limitation on the DMC/phenol route. Therefore, we can consider two methods to overcome the serious equilibrium limitation on the first step: a high-temperature gas-phase reaction or a liquid-phase reaction with a reactive distillation process. 3.3. DPC Synthesis from Direct Oxidative Carbonylation of Phenol. The oxidative carbonylation of phenol82-120 has been considered as one of the promising candidates for DPC synthesis without using COCl2 because it achieves direct synthesis of DPC from carbon monoxide and phenol. Hallgren et al.95-97 reported that oxidative carbonylation of phenol to DPC could be accomplished using the catalytic system composed of a palladium complex, oxidation cocatalysts, a base, and a dehydrating material (Scheme 8). Hallgren et al.95-97 studied the interaction of phenols with CO under ambient conditions of atmospheric pressure and room temperature with palladium chloride and a tertiary amine. It produced DPC and phenyl salicylate depending on the state of Pd.97 Scheme 9 could account for the salicylate formation. DPC might not be formed from Pd(II) halides but rather from Pd(I) carbonyl halide species. This reaction by a Pd(I) species to form carbonates through formally a two-electron transfer was quite unusual; therefore, it involved possibly two metal centers in the transformation. DPC formation by a two-

Scheme 8. Oxidative Carbonylation of Phenol into DPC

Scheme 9. Phenyl Salicylate Formation under Bis(benzonitrile)palladium(II) Chloride with CO and Phenol97

metal-center mechanism is shown in Scheme 10. Evidently, in structures a and/or b the carbon monoxide ligand is activated toward nucleophilic attack by phenoxide. The transformation of b to c involves an internal redox reaction promoted by carbon monoxide. Although this reaction was quite specific and a high yield of DPC was obtained, a stoichiometric amount of Pd metal was produced. Conversion of this reaction into a catalytic process requires oxidation of the reduced Pd and regeneration of the active palladium species. The direct oxidation of Pd metal with gaseous oxygen has been reported to be slow; therefore, Pd usually needs cocatalysts such as Cu, V, Co, and Mn salts to achieve a rapid reoxidation of its metallic form.95 Aqueous sodium hydroxide in combination with a phase-transfer catalyst such as quaternary ammonium or phosphonium halide salt was found to be an effective base for the palladiumcatalyzed synthesis of DPC.96 The success of these bases even with a small amount was attributed to the combined contributions of high basicity, which resulted in substantial ionization of phenol, and low nucleophilicity, which prevented their coordination to Pd followed by oxidation. With palladium bromide, differences in the reaction rates were observed as a function of the phasetransfer anion. Apparently, chloride or bromide ion was required for reoxidation of palladium under the basic reaction conditions.95

Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 1903 Scheme 10. DPC Formation by a Two-Metal-Center Mechanism97

Scheme 11. Phenyl Acetate Formation under Palladium(II) Acetate with CO and Phenol84

Scheme 12. Multistep Electron-Transfer Catalytic Cycle of the Oxidative Carbonylation of Phenol under the System of Pd(II) with Organic and Inorganic Cocatalysts85

Moiseev et al.84 reported that giant palladium-561 clusters were effective catalysts for the oxidative carbonylation of phenol, which was conjugated with the reductive carbonylation of nitrobenzene. Their lowvalent Pd clusters could serve as catalysts because of the expected capability of both facilitating the nucleophilic attack of phenol to CO and acting as the electron reservoir for the reduction of nitrobenzene. Phenyl acetate was also found in the carbonylated products of DPC together with phenyl salicylate and palladium(II) acetate catalyst (refer to Scheme 11). Vavasori and Toniolo85 studied the oxidative carbonylation of phenol with components of a Pd(II) salt as the main catalyst, inorganic cocatalyst, organic cocatalyst, and surfactant such as TBAB. They reported the role of each component in the catalytic system based on the so-called “multistep electron transfer catalytic system”. Benzoquinone (BQ) alone as the organic cocatalyst could be an effective reoxidation agent. They confirmed that BQ played an important role in the catalytic cycle. It acted also as a ligand and prevented effectively the aggregation of Pd metal by the formation of BQ/Pd complexes, followed by easy transformation to the active Pd(II) complex by the metal redox agent.85 When an excess of TBAB was added, Pd metal formation was avoided. They supposed that the presence of bromide led to an in situ formation of a more stable Pd(II) catalyst of the type PdBr42-, thus easing the reoxidation step. Furthermore, the TBAB cation played an important role, probably because of its surfactant property. In fact, the surfactant led to nanostructured R4N+X--stabilized metal clusters.85 According to the results, their proposed catalytic cycle is given in Scheme 12. A combination of an organic redox cocatalyst (hydroquinone, HQ) and an inorganic cocatalyst [copper(II) acetate] was reported to be effective for in situ regeneration of active homogeneous Pd species.86,87 HQ

mainly assisted reoxidation of Cu(I) to Cu(II), and the latter, in turn, helped regeneration of reduced Pd species. On this basis, Goyal et al.87 proposed a redox mechanism quite similar to that of Vavasori et al.85 except for the water formation cycle and the role of the organic cocatalyst. Goyal et al.86,87 suggested that BQ produced from the oxidation of HQ with molecular oxygen did mainly oxidize the reduced Cu(I) formed after the oxidation of Pd(0), while Vavasori et al.85 suggested that BQ oxidized the reduced Pd(0) directly. It was reported that o-phenylene carbonate (o-PC) was the major side product on their catalytic condition of PdCl2-Cu(OAc)2. Ortho oxidation of phenol with Cu(I) yielded copper catecholate, which, in turn, was converted to o-PC by Pd(II).87 A number of various Pd catalysts assisted by various cocatalysts have been reported to simplify the complicated catalytic system or to increase the reaction rates. Also, the easy recovery of the expensive palladium catalysts is one of the main concerns in homogeneous Pd chemistry. Pd/Sn heteronuclear complexes, such as Pd2(dpm)2(SnCl3)Cl, with assistance from Mn(TMHD)3 produced DPC even in the absence of ammonium halide, where dpm is bis(diphenylphosphino)methane and TMHD is 2,2,6,6-tetramethyl 3,5-heptanedionate.103,104 Modified Pd complexes with a phosphine or pyridine ligand99-101 and a Pd/pyridyl complex tethered on a polymer support of polystyrene105 were also reported by the same workers. Heterogeneous Pd supported on activated carbon (Pd/C) has also been studied for the oxidative carbonylation of phenol to DPC.83,88-92,98,125 Takagi et al.98 reported a Pd/C-Pb-NMe4Br catalytic system and suggested that the Pd species seemed to work as a homogeneous catalyst because the inductively coupled plasma atomic emission spectrometry (ICPAES) measurement of the reaction mixture after the reaction indicated the presence of dissolved Pd species although activated carbon supported metallic Pd was used as a palladium source. Despite the potential advantage in practical applications, the heterogeneous Pd catalysts have not been examined intensively compared with homogeneous ones. Table 4 gives a summary of some work done on this reaction. Song et al.88 studied the effects of the amount of various inorganic cocatalysts and bases coupled with Pd/C catalyst and investigated an optimized catalytic system for the reaction. To find out the optimized catalyst compositions with the heterogeneous Pd/C catalyst system, DPC yields were compared with different ratios of Ce(OAc)3/Pd and Bu4NBr/Pd. As shown in Figure 3, the DPC yield increased as the amount of promoters was increased at low ratios of Ce(OAc)3/Pd and Bu4NBr/Pd and became flat at high ratios. From these optimum ratios of catalytic components, the highest DPC yield of ca. 20% could be obtained at a

giant Pd clusters of Pd-561 familya

Pd diacetate/Co diacetate/TBAB/BQ

Moiseev et al.84

King et al.107-109 and Joyce et al.110 Ishii et al.99-106

a

381 K, 77 kg/cm2 CO, 5.8 kg/cm2 O2, 4 h

Such as Pd501Phen60(OAc)180 (GPC I) and Pd561Phen60(PF6)60O60 (GPC II).

Song et al.88

373 K, 2.5 h

Pd acetylacetonate/Cu(acac)2/TiO(acac)2/ tetraethylammonium bromide/NaOH 5% Pd/C-Ce(OAc)3/Bu4NBr/BQ

Offori et al.120

373-393 K, 3 h, 7.1% O2 in CO, 1650 psi 423-472 K, 3 h, 10 bar (CO + O2) 373 K, 2 h, 60 kg/cm2 CO, 30 kg/cm2 dry air 353 K, 5 h

373-423 K, 5 h, 400 psi O2 and 600 psi CO 373 K, 3 h, 0.50 MPa CO, 0.25 MPa air

393 K, 3 h, 100-150 atm

Pd(II) nitrate/Cu(II) acetylacetoniate/Ti(IV) 373-423 K, 2.5 h, 10.342 oxide/NaOH/NaBr, tetraglyme (6-12%) MPa (9% of O2 in CO)

5% Pd/C-Ce(III) acetate monohydrate/ TBAB/HQ 5% Pd/PbZrO3

CO,

373 K, 3 h, 60 kg/cm2 CO, 3 kg/cm2 air 373 K, 5 h, 60 atm (CO/O2 ) 10/1)

373 K, 24 h, 60 3 kg/cm2 O2 523 K, 96 h, 1 atm

kg/cm2

reaction conditions

Shalyaev et al. 119

Yoshisato et al.118

Iwane et al.91

Pressman et al.111-114 Pd diacetate/Co [di(salicylal)-3,3′-diaminoN-methyldipropylamine]terpyridine Buysch et al.116,117 Pd bromide/Mn acetylacetonate/TBAB

Pd2 [bis(diphenylphosphino)methane]ammonium halide

Pd(OAc)2/Cu(acac)2/BQ

Vavasori et al.85

Takagi et al.98

PdBr2/Mn(2,4-pentanedione)3/ diisopropylethylamine 5% Pd/C-Pb-NMe4Br

PdCl2/Ce(OAc)3/HQ/TBAB

catalyst

Hallgren et al.95,96

Goyal et

al.86,87

ref

conversion and yield

various combinations of perovskite-supported Pd catalysts in the continuous-flow gas reactor two consecutive batch reactors (batch-batch regime) were used to carry out the reaction; a 3A molecular sieve was used as a desiccant no molecular sieves

effect of various pyridine and phosphine ligands, halide, and Pd complexes such as Pd dinuclear, Pd-Sn complexes were studied; CO2 and phenyl salicylate as major byproducts molecular sieve was used as a desiccant; the products were recycled to improve yield in the continuous process a bubble column reactor was used; CO was passed before reaction to activate catalyst; CO2 generated acted as a desiccant effect of various halides was studied in the batch reactor

various Ce and Cu complexes as inorganic redox cocatalysts; a 3A molecular sieve was used to remove water studied various Mn and Co complexes; a stoichiometric amount of Pd was used phenyl salicylate, bromophenol, and CO2 were reported as byproducts; mechanism was proposed for the catalytic system effect of different cocatalysts was studied; phenylsalicylic oligomer was produced as a byproducts; multistep electrontransfer mechanism was proposed; excess BQ led to high yields oxidative carbonylation of phenol coupled with nitrobenzene reduction; mechanism was proposed CO2 was used as a desiccant in the batch process

remarks

37.6% PhOH carbon-supported Pd catalyst showed a better DPC yield than conversion, the best homogeneous system with Pd(OAc)2 for the 26.8% DPC yield same amount of palladium

30.3% DPC yield

27.6% DPC yield

21% DPC yield

26% DPC yield

23% DPC yield

74% DPC yield

1.7% DPC yield

26% DPC yield

42% DPC yield

89 mol of DPC/mol of Pd

75% phenol conversion 9.5% DPC yield

76% DPC yield

Table 4. Some Examples for Catalytic DPC Synthesis by Oxidative Carbonylation of Phenol


Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 1905

Figure 3. Effects of the amount of Ce(OAc)3 and Bu4NBr as an inorganic cocatalyst and a base, respectively, on the oxidative carbonylation of phenol to DPC:88 1 wt % Pd/AC, 2 g; phenol, 0.53 mol; time, 4 h; temperature, 381 K.

Scheme 13. Transesterification of BPA and DPC

phenol conversion of 30% and a DPC selectivity of 67%. The synthesis of dialkyl carbonates such as DMC via oxidative carbonylation of methanol has been promoted by transition-metal compounds such as CuCl2 or CuCl and well-established in a commercial plant. However, an analogous reaction of phenol to DPC seems to be less feasible because of the lower basicity of phenol and the ease of phenol oxidation to various side products. Limited success has been reported for a number of different Pd catalysts assisted by various cocatalysts simplifying the complicated catalytic system or increasing the catalytic activity. Also, the easy recovery of the expensive palladium catalysts would be the significant advantage for heterogeneous Pd catalysts in this reaction. 3.4. PC Precursors from DPC and BPA. COCl2free processes for PC have been proposed that employ melt transesterification38-41,47-54,58,61-64 or solid-state polymerization1,42,44,57,60,61 using BPA and DPC, with the latter synthesized in a COCl2-free process. They are mostly two-stage processes with the prepolymerization step of BPA and DPC (degree of polymerization of 1-10) and the subsequent polycondensation step of the prepolymers while removing phenol under the conditions of increasing temperature (450 K to higher than 570 K) and decreasing vacuum pressure (100 mmHg to less than 1 mmHg). The basic catalysts are usually alkalior alkaline-earth-metal hydroxides, carbonate, or oxides. Besides those, sodium acetate with 4-(dimethylamino)pyridine43,51 dibutyltin oxide with the copresence of an organosilicon compound52 were claimed. Also, there are patent works that describe melt transesterification of BPA and DPC in the presence of a transesterification catalyst such as a quaternary phosphonium salt compound53 or a quaternary ammonium salt.44 There is an interesting report about the influence and effect of the construction materials of the reactors in the preparation

of a PC using transesterification on the physical and chemical properties of the final polymer.54 Some examples for the synthesis of PC precursors from BPA and DPC are given in Table 5. Transesterification of BPA and DPC in Scheme 13 occurred readily. About 10% of BPA was converted into MpC(1) without any catalyst in 3 days after just equimolar mixing of BPA and DPC in acetonitrile at 298 K. At 523 K without a catalyst, 6 h of reaction also produced yields of 26.7 wt % MpC(1) and 17.4 wt % DH(1). Note that DH(n) has no available end-group functionality in the polycondensation step and DpC(n) requires the removal of DPC coproduced in the step. Kim et al.40,41 studied the kinetics of batch and semibatch melt transesterification of BPA and DPC in the presence or absence of a LiOH catalyst at temperatures of 150-300 °C. They assumed that the reactivities of the functional end groups were independent of the chain length and demonstrated a quite satisfactory agreement between the model predictions and experimental results. We studied several alkali-metal hydroxides and carbonates for the melt transesterification of BPA and DPC as shown in Figure 4. A pseudoequilibrium state was reached within 1 h except with LiOH, which showed a slower rate. However, the secondary reactions between oligomers continued. It was found that oligomers reacted with DPC more often than with BPA. Melt transesterification of BPA and DPC occurred readily to reactive precursors of phenyl carbonate ended oligomers without a serious equilibrium constraint. Alkali-metal carbonates were more efficient catalysts than other alkali- and transition-metal compounds especially at low temperatures.45 One of the problems in this process is that a high molecular weight PC is difficult obtain because the removal of condensation byproducts (phenol) becomes more difficult as the molecular weight increases because of the high melt viscosity.40 Therefore,

a Viscosity-average molecular weight determined by GPC with polystyrene standard. b Number-average molecular weight determined by GPC with polystyrene standard. c Reactor material contained 19-22 wt % Ni, 24-26 wt % Cr, less than 0.25 wt % C, less than 1.5 wt % Si, less than 2 wt % Mn.

bis(epoxide)s were used instead of BPA; effect of amount of TBPC on yield was studied; reaction carried out in a sealed tube Mn ) 28 300 373 K, 48 h Yashiro et al.56

LiOH‚H2O LiOH‚H2O 4-(dimethylamino)pyridine/ potassium acetate tetrabutylphosphonium chloride (TBPC) Brunelle et al.55 Gross et al.60,62 Yamamoto et al.51

503-533 °C, 1 atm N2 423-503 K, 20-25 mmHg vacuum 553 K, 0.2 Torr vacuum

Mw ) 50 400 Mw ) 36 000 Mw ) 35 000

some reactor materials increased catalyst activity, so reactors with different materials of construction were used instead of DPC, bis(o-chlorophenyl) carbonate was used PC by this catalyst showed high thermal stability; kinetics of reaction studied various dihydroxy compounds were studied Hayashi et al.54

2-methylimidazolesodium acetate dibutyltin oxide/methyl hydrogen polysiloxane SUS-310c/NaOH Yamato et al.43 Yokoyama et al.52,53

533-553 K, 2 Torr vacuum 473-523 K, 20 Torr vacuum

Mw ) 28 000

thermodynamics of vapor-liquid equilibrium; effects of DPC/BPA ratio and reflux temp were studied in a semibatch reactor high Mn was obtained due to removal of phenol through distillation 5% weight loss reported was above 733 K process temperature Mw ) 16 000 LiOH‚H2O Woo et al.50

453-553 K, 100 mmHg vacuum

PC by this catalyst showed a high thermal stability; kinetics of reaction studied Mw ) 31 500

473-533 K, 2 h, 20-25 mmHg vacuum 503 °C, 5 mmHg vacuum La(acac)3 Ignatov et

al.58,59

Mnb ) 32 000 Mw ) 20 900

remarks

a

conversion and yield reaction conditions catalyst ref

Table 5. Some Examples for the Synthesis of PC Precursors from BPA and DPC


a number of process advances have been reported. Multistaged melt-polycondensation processes vary temperatures and pressures progressively at each stage to distill off phenol efficiently.40,43,51-54 Forced gas sweeping processes remove phenol by forcing inert gas bubble.48,49 A solid-state polymerization process1,42,44,57 is expected to be an innovative technology to solve the drawbacks of the conventional melt-transesterification process. This involves a crystallization step of the prepolymers (PC precursors) that have a ca. 30% crystallinity with a specific surface area of a few square meters per gram. A very broad range of molecular weights of the final PC could be obtained up to a special grade polymer. Because this process proceeds at relatively low temperatures of 483-493 K, the final polymer has no discoloring that might be caused by a higher temperature in the melt process. 3.5. PC Precursors from DMC and BPA. As a potential substitute for DPC as a carbonylating agent, DMC could react with BPA into PC precursors. This has the advantage that there is no need to obtain DPC, whose economical synthesis by a COCl2-free method is not easy yet. There are a few reports on the synthesis of PC precursors from BPA and DMC.46,65-73 However, DMC-ended oligomer [DmC(n)] is supposed to be the sole precursor that is amenable to the subsequent polycondensation. Monomethyl carbonate ended oligomer [MmC(n)], which is the first transesterification product between BPA and DMC, favors more its disproportionation into dihydroxy-ended oligomer [DH(n)] and DMC rather than further transesterification with DMC into DmC(n) because of chemical equilibrium constraints.45 Also, the heavier oligomers, whose repeating unit of n is higher than 2, are not generally formed under a typical liquid-phase reaction condition. Therefore, this method seems to require a very large excess amount of DMC to obtain the reactive DmC(n) by driving the reaction forward and/or an efficient and selective removal of coproduced methanol from products by adopting reactive distillation or using adsorbents. The scheme of the transesterification of BPA and DMC is illustrated in Scheme 14. It is generally recognized that the structure of oligomers plays a key role in determining the efficiency of the polymer-forming reactions.46 A number of patents describe the synthesis of PC precursors, which can be subject to postpolycondensation to yield high molecular weight polymers.66-69 Shaikh et al.46 studied, by using a fast atom bombardment mass spectrometer (FAB-MS) and mass spectral pattern, reactivities of oligomers with different end groups obtained from the reaction using di-n-butyltin oxide and 1,3-diphenoxytetrabutyldistannoxane as catalysts at the temperature range of 383-513 K. They observed that MmC(n) were far less reactive to chain growth polymerization compared to DmC(n). It could be attributed to their reactivity differences; i.e., MmC’s tend to disproportionate to OH rather than to transesterify45 further to DmC. This method seems not technically easy for obtaining high molecular weight PCs. The hydroxy-ended groups of PC oligomers are far less reactive with the methyl carbonate ended group because of the high basicity of a methoxide anion in comparison with a phenoxide anion.65 Furthermore, the synthesis of DmC(n) with high yields is difficult because it is a thermodynamically unfavorable process. To overcome the problems, Haba et al.65 carried out the DmC(1) synthesis with continuous removal of the byproduct methanol using a very large amount of molecular sieve. They reported that 22%


Figure 4. Melt transesterification of BPA and DPC with alkali-metal hydroxides and carbonates as catalysts:45 concentration of catalyst, 5 × 10-5 mol of catalyst/mol of BPA; DPC/BPA, 2; temperature, 433 K; time, 1 h.

Scheme 14. Transesterification of BPA and DMC

yield of DmC(1) could be obtained with 2 g of BPA, a DMC/BPA ratio of 68, 7 g of molecular sieve 4A over (Bu2SnCl)2O, and (dimethylamino)pyridine catalysts in 48 h of reaction.65 However, these conditions should involve a few problems such as regeneration of a large amount of molecular sieve and slow reaction rate as well as separation of the excess amount of DMC unreacted. Considering all available literatures, the high yield synthesis of DmC(1) seems to be quite difficult because of small equilibrium yields and the narrow difference of boiling points between DMC and byproduct methanol. There are other attempts to obtain PC precursors from the reactions of bisphenol A diacetate72,73 or 1,4-bis(hydroxymethyl)cyclohexane70 with DMC. These works aim to overcome the low activity of transesterification of BPA and DMC or to obtain biodegradable and biocompatible polymers,70 respectively. Table 6 summarizes some of the work on the synthesis of PC from BPA or bisphenol A diacetate and DMC. Lewis acids such as titanium phenoxides or alkoxides are well-known transesterification catalysts, and it was found that solid catalysts of titania supported on silica or activated carbon could efficiently catalyze transesterification of phenol and DMC.25,24 As shown in Figure 5, the conversion of BPA approached ca. 11% during 55 h, which is believed to be the equilibrium conversion. The first product of transesterification of

BPA and DMC was MmC(1) with an amount of 10% of initial BPA. The further transesterification of MmC(1) by DMC produced DmC(1) in amounts of less than 10% of MmC(1) produced, indicating that a similar degree of equilibrium limitation is imposed on both reactions. Unlike the cases of BPA and DPC, further transesterifications of MmC(1) and DmC(1) to heavier oligomers seemed not to occur readily. There was no heavier product like MmC(2) or DH(1) in a level detectable by GC, GC/MS, and HPLC. The activity of transesterification of BPA and DMC using 1 wt % TiO2/SiO2 was investigated with different reactant molar ratios of DMC/BPA as shown in Table 7. The formation of heavier oligomers with n g 2 were not detected although the DMC concentration increased, but the BPA conversion at 7 h increased because of a shift in equilibrium. Byproducts of methylated bisphenols were produced in a large amount at DMC/BPA ) 2, suggesting that the lower DMC concentration gave a negative effect on this transesterification. Above DMC/BPA ) 5, the product distribution remained invariant, except a slight increase of DmC(1), and the selectivity of MmC(1) + DmC(1) stayed around 95%. The beneficial usage of DMC has been well established as an environmentally benign agent for carbonylation as well as methylation reactions. Transesterification of BPA and DMC was expected to show

74% BPA conversion, a large amount of molecular sieves was used; both transesterification 22% PC oligomer yield and melt polymerization studied TiO2/SiO2 473 K, 7 h 10-20% BPA conversion, effects of temperature and reactants molar ratio 10-20% PC oligomer yield 1,3-diphenoxytetra-n-butyldistannoxane 393 K, 5 h 54% PC oligomer yield aliphatic diols were used instead of BPA; different diols showed different properties of PC precursors bis(4-chlorocarbonylphenyl)dimethylsilane 0 °C, 1 h 94% PC monomer yield poly(ester carbonate) was obtained and monomethyl carbonate of BPA was used instead of BPA; the high yield because of disproportionation Ti(OPh)4 493 K, 1 h 60% PC oligomer yield BPA diacetate was used instead of BPA; critical role played by the nature of end groups in the first stage oligomers tetraphenyl titanate 493-513 K, 1 h Mw ) 25 000 BPA diacetate was employed instead of BPA di-n-butyltin oxide and 1,3383-513 K Mw ) 25 000 characterization of oligomer with FAB-MS of BPA diphenoxytetrabutyldistannoxane Bolon et al.73 Shaikh et al.46

Deshpande et al.72

Shaikh and Sivaram71

Pokharkar et al.70

Kim and Lee45

Haba et

al.65

(Bu2SnCl)2O

48 h


Table 6. Some Examples for Catalytic Synthesis of PC Precursors from BPA and DMC

remarks


Figure 5. Transesterification of BPA and DMC with various Ti catalysts:45 catalyst loading, 6 × 10-2 mmol of TBOT or 0.5 g (1 mmol of Ti) of solids; charge of BPA, 120 mmol; DMC/BPA, 5; temperature, 433 K. Table 7. Effects of Reactant Molar Ratio on the Transesterification of BPA and DMC45,a selectivity (%) mC(1) DMC/ conversion BPA of BPA (%) MmC(1) DmC(1) byproductsb yieldc (%) 2 5 10 20

7.4 13.2 16.0 21.2

83.3 90.5 87.4 86.2

4.8 5.4 7.8 7.6

11.9 4.1 4.8 6.2

6.5 12.6 15.2 19.9

a Ti loading per initial charge of BPA, 8.76 × 10-4 mol of Ti/ mol of BPA; DMC/BPA, 5; temperature, 433 K; time, 7 h. b Byproducts were methylated bisphenols. c mC(1) yield is a sum of MmC(1) and DmC(1) yields.

similarity to transesterification of BPA and DPC, but it was closer to transesterification of phenol and DMC in light of reaction characteristics and particularly a severe equilibrium limitation in the liquid-phase reaction.45 Recycle and reflux of excess DMC could be employed to improve the yield by shifting the equilibrium toward the forward reaction. However, any recycle scheme involving fractionation should be inefficient because of the small difference of boiling points between DMC and methanol. 3.6. PC Precursors from Direct Oxidative Carbonylation of BPA. There has been some effort to develop a COCl2-free PC process without employing the expensive DPC or DMC as intermediates. One such route is a direct oxidative carbonylation of BPA into PC oligomers29-37 in a manner similar to that employed for an oxidative carbonylation of phenol to DPC (Scheme 15). Researchers filed patents 2 decades ago about the oxidative carbonylation of BPA into PC precursors.74,75 The reaction scheme was demonstrated in the last example, followed by 15-20 results that dealt with the preparation of 4,4′-(R,R-dimethylbenzyl)diphenyl carbonate from an oxidative carbonylation of p-cumylphenol. The oligomeric PC was prepared by contacting BPA, CO, aqueous NaOH, PdBr2, Mn salt, type 3A molecular sieve, and TBAB as a phase-transfer agent at room temperature while CO and air were bubbled slowly. The number-average molecular weight of the PC obtained after 42-90 h was estimated in the range of 600-2800 by LC.74,75 These patents showed the possibility of preparation of PC from the direct oxidative carbonylation of BPA. Recently, Goyal et al.76-78 reported a successful synthesis of PC oligomers using a catalyst system that

an alcohol-free solvent was employed; many of the noble metals were studied

effects of use of molecular sieve on yield were clearly observed 89% oligomer yield

50% oligomer yield 373 K, 4 h Chaudhari et

al.80

Hallgren et al.74

Pd(I) monocarbonyl monobromide/ Cu dibromide/2,2,6,6,N-pentamethylpiperidine/methylene chloride Pd(II) dibromide/Mn(II) bis(acetylacetonate)/ TBAB Pd(II) 2,4-pentanedionate/Co salt of bis[3-(salicylamino)propyl]methylamine/ hexaethylguanidinium bromide/ N-methylpyrrolidinone Chalk et al.75

298 K, 18 h

various redox components were reported 26% oligomer yield

Pd/6,6′-dimethyl-2,2′-bipyridyl complex, Mn(TMHD)3/HQ/(Ph3Pd)2NBr Ishii et al.79

remarks

a high yield of PC with high molecular weight was obtained 86% oligomer yield; Mn ) 3300

50% PC yield

373 K, 24 h, 60 kg/cm2 CO, 3 kg/cm2 O2 373 K, 24 h, 6 MPa CO, 0.3 MPa O2 323-473 K, 1-10 h PdCl2/Cu(OAc)2/TBAB/HQ Goyal et al.76-78


Table 8. Some Examples for Catalytic Synthesis of PC Precursors from BPA and CO

has been found to be effective in the extensive work on the synthesis of DPC from phenol and CO. It was claimed that DHs having an average molecular weight of ca. 3600 could be synthesized with the PdCl2/Cu(OAc)2/ HQ catalyst system and a substantial amount of molecular sieve 3A to remove coproduced water.76 While o-PC and salicylic acid ended oligomers were also formed using this catalytic system, they claimed that replacing Cu with Ce salts could eliminate o-PC completely and usage of bis(triphenylphosphoranylidene)ammonium bromide instead of TBAB resulted in the absence of acid-type byproducts as determined from polymer characterizations by IR, NMR, and MALDI TOFMS.77 They also demostrated that a hydroxyterminated precursor [DH(n)] could be further polymerized via multistep oxidative carbonylations to obtain high molecular weight PC. Two-step oxidative carbonylation, where DH-type oligomers having a weightaverage molecular weight (Mw) of 3600 obtained in the first step was used as a starting material in the second step, led to the synthesis of polymers with Mw of 33 000.77 Under the usual polymerization conditions, however, the obtained hydroxy-ended oligomers are not amenable to polycondensation. Because of their endgroup functionalities, the dihydroxy-ended prepolymer [DH(n)] should require a multistep processing of pressurized carbonylation77 in order to obtain high molecular weight PC or additional functionalization of the DHs with DPC into phenyl carbonate ended PC precursors80 prior to the polycondensation step. A more recent work80 disclosed a method for preparing high molecular weight PC by first preparing the oligomers DH(n) by oxidative carbonylation of BPA, then converting those DH(n) into PC precursors MpC(n) by melt transesterification with additional DPC, and finally polymerizing the precursors into a high molecular weight PC via melt or solid-state processes. Additional functionalization of DHs was required because oligomers prepared by the reaction (in Scheme 13) were generally not suitable for the solid-state polymerization because of the presence of hydroxy end groups and a too low molecular weight.80 A summary of oxidative carbonylation of BPA is given in Table 8. We investigated the direct oxidative carbonylation of BPA with CO/O2 as shown in Table 9. We employed the same catalyst system of Goyal et al.,76 as shown in run 1. BPA conversion of 67% was obtained even without a dehydrating agent of molecular sieve. The main products were PC oligomers of the DH(n) type (n ) 1-3), but large amounts of byproducts were also produced. The byproducts consisted of ortho and para isomers of BPA and acetate, salicylic acid, and o-PC-type ended derivatives of bisphenols. As discussed, DH(n)-type oligomers are not suitable to obtain high molecular weight PCs in the subsequent polycondensation step. We discovered that the addition of phenol into the reaction system of BPA carbonylation resulted in a successful one-step synthesis of MpCs from CO as shown in Scheme 16.81 This reaction has a great practical implication in COCl2-free syntheses of PC. This coupled carbonylation of BPA and phenol involves two nucleophiles of phenoxy and bisphenoxy anions, and therefore it requires more controlled reaction conditions than the individual carbonylation of phenol or BPA. When phenol was introduced into the reaction system of BPA carbonylation (runs 2 and 4), the BPA conversion was not significantly changed but the byproducts were reduced dramatically. More importantly, MpC(n) was produced in an amount of a half of the weight selectivity

a molecular sieve was used as a desiccating agent; o-PC and salicylic acid type byproducts could be eliminated by use of Ce and phosphine base


1910 Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 Scheme 15. Oxidative Carbonylation of BPA to PC

Scheme 16. Proposed Reaction of Oxidative Carbonylation of BPA to PC with the Addition of Phenol81

Table 9. Direct Oxidative Carbonylation of BPA with and without Phenol45,a product distribution (wt %) run

system

BPA conv (%)

MpC(1)

MpC(2)

DH(1)

DH(2)

ng3

byproductsb

MpC/DHc

1 2 3 4

Pd-Cu w/o phenol Pd-Cu with phenol Pd-Ce w/o phenol Pd-Ce with phenol

67.0 59.2 39.6 38.3

0 19.4 0 21.2

0 4.6 0 tr

34.8 33.8 53.2 47.0

10.1 6.9 5.1 2.8

3.3 1.2 tr 0

51.8 34.1 41.7 29.0

0 1.13 0 0.87

a PdCl (runs 1 and 2) or Pd(OAc) (runs 3 and 4), 0.06 mmol; CuCl or Ce(OAc) , 0.30 mmol; HQ (runs 1 and 2) or BQ (runs 3 and 4), 2 2 2 3 1.50 mmol; Bu4NBr, 1.50 mmol; dichloromethane, 30 mL; BPA, 30 mmol; phenol, 30 mmol; CO pressure, 5 MPa; O2 pressure, 0.5 MPa; temperature, 373 K; time, 4 h. b Major byproducts are phenyl salicylate and o-PC-ended BPA. c The ratio of total MpC moles to total DH moles.

Figure 6. Typical reaction profile with time of the coupled oxidative carbonylation of BPA and phenol:81 Pd(OAc)2, 0.06 mmol; Ce(OAc)3, 0.3 mmol; Bu4NBr, 1.5 mmol; 1,4-BQ, 1.5 mmol; BPA, 30 mmol; phenol, 30 mmol; tetrahydrofuran, 30 mL; CO pressure, 5 MPa; temperature, 373 K.

of DH(n) but a similar amount in moles as indicated from the ratio of MpC/DH. As shown in Figure 6 of a typical reaction profile of the coupled carbonylation, the conversions of reactants and concentrations of products ceased to change within 4 h. However, the conversions could be increased to 65% for BPA and to 25% for phenol when coproduced water was removed by adding dehydrated molecular sieve 3A.36 Although DHs were produced dominantly in the present batch condition, DHs could be regarded as a potential reactant to be converted into the reactive precursor MpC(n) by further coupled carbonylation with CO and phenol in the system. As the equilibrium was shifted to the forward reaction by adding dehydrating agents, the mole ratio of MpC/DH was increased and the absolute amount of DH(1) decreased, resulting in increases of MpC and oligomers of n g 2.82 The reactant molar ratio of phenol to BPA (PhOH/BPA) was a critical variable in controlling the

selective formation of MpCs. As shown in Figure 7, conversion of BPA increased with PhOH/BPA values of up to 1.0 and then decreased for higher ratios. The decrease might be caused by competition of phenol with BPA for the fixed amount of catalyst sites in the system. However, note that the value of MpC/DH increased almost linearly up to 1.8 as PhOH/BPA increased. Thus, as more phenol is introduced, formation of MpCs is more favored over formation of DHs and byproducts. Oxidative carbonylation of phenol should be more difficult than that of BPA in terms of their equilibrium conversions. Therefore, an excess amount of phenol might be essential to obtain the desired MpCs selectively with least formation of DHs under oxidative carbonylation conditions. However, in the reaction stoichiometry of the reaction in Scheme 14, only 1 mol of phenol would be sufficient for n mol of initial BPA, with n being the repeating unit of MpC-type oligomers, if


Figure 7. Effects of the amount of phenol on the coupled oxidative carbonylation of BPA and phenol:82 Pd(OAc)2, 0.06 mmol; Ce(OAc)3, 0.3 mmol; Bu4NBr, 1.5 mmol; 1,4-BQ, 1.5 mmol; BPA, 30 mmol; tetrahydrofuran, 30 mL; 3A molecular sieve, 4 g; CO pressure, 5 MPa; O2 pressure, 0.5 MPa; temperature, 373 K; time, 4 h. Table 10. Qualitative Comparison of the Catalytic Syntheses of PC Precursors or Intermediates by COCl2-Free Methods catalyst system reaction conditions

process aspects

metal compoundsa concentrationb systemc temperature time pressure solvent limitationsd reactivitye cost of monomersf industrial interestsg economical impacth

DPC + BPA

DMC + BPA/DMC + PhOH

CO + BPA/CO + PhOH

alkali 10-6 - 10-4 simple high short low needless none high expensive large small

transition metal 10-4 - 10-2 moderate moderate moderate low to moderate needless thermodynamic moderate moderate small/large moderate

noble metal 10-3 - 10-2 complicated low long high needed thermodynamic and kinetic moderate cheap small large

a Main component of the catalyst. b Mole ratio of the main catalyst to phenolic compounds. c Degree of complexity of the catalytic system. Constraints on the chemical equilibrium state and reaction rate. e Reactivity between reactants. f Cost of carbonate sources, which were synthesized also in a COCl2-free manner. g Based on the number of currently open patents for the syntheses of PC precursors. h Expected effect when the process is successfully commercialized.

d

complete conversion of BPA is achieved. Also, phenol can be recycled after polycondensation. Oxidative carbonylation of BPA would be the most promising method of COCl2-free PC synthesis because it involves the least number of reaction steps from CO and BPA to PC oligomers as prepolymers if it could produce reactive PC precursors that are amenable to the subsequent polycondensation step of the currently commercialized COCl2-free process. The coupled carbonylation of BPA and phenol with CO increased the reactivity of the oligomers relative to those synthesized from the carbonylation of BPA alone by producing phenyl carbonate ended precursors directly. 4. Comparative Considerations of Various Routes In Table 10, we compare in a highly qualitative manner each reaction step and route (in Figure 1) that was reviewed throughout this work in light of some practical aspects. These considerations were based on our experimental results covering various catalytic reactions to synthesize PC precursors or carbonate intermediates without using COCl2. In the case of the DPC-using process (DPC + BPA route), the main concern is how economically the ef-

ficient monomer DPC could be obtained without using COCl2. In transesterification of DMC and phenol, it is required to overcome the serious chemical equilibrium constraint via, for example, the design of a highly efficient catalytic distillation. For oxidative carbonylation of phenol to synthesize DPC directly, it is desired to develop a simpler and completely reusable catalytic system with high activity as well as selectivity. For the DMC-using process (DMC + BPA route), the main concerns should be in the efficient separation and recycle of the reactant DMC from the reaction mixture of DMC/methanol adducts while loss of DMC should be minimized. Further, production of reactive PC precursors, DMC-ended BPA (DmC’s), should be maximized via a process of catalytic distillation. For the direct synthesis of PC precursors from BPA carbonylation in which the least number of reaction steps is involved, attention should be concentrated on the development of a highly effective catalyst system to obtain the reactive PC precursors with the highest yield and selectivity. An efficient recycle scheme for the catalyst system or a possible substitute for the expensive noble metal catalyst (Pd compound) should be achieved. Further continuous removal of coproduced water should be considered to increase the yield of products.


5. Summary In the synthesis of DPC, transesterification of DMC and phenol showed a fast reaction rate but a very low chemical equilibrium yield of the intermediate MPC in the liquid-phase reaction. Thus, the yield of MPC could be increased significantly by process design to continuously remove the byproduct methanol, while the development of new catalysts would not give an effective improvement. The gas-phase reaction at high temperatures using appropriate solid catalysts such as titania supported on silica or carbon could improve the MPC yield of this endothermic reaction. For the disproportionation of MPC to DPC, the some solid catalysts showed good performance in the liquid-phase reaction without a significant equilibrium limitation. This twostep process of gas-phase transesterification followed by liquid-phase disproportionation could alleviate the severe equilibrium constraints that prevail in the synthesis of DPC from DMC and phenol. The direct synthesis of DPC from oxidative carbonylation of phenol required a complicated multicomponent catalyst system, yet it involved low catalytic activity, production of various side reactions, and difficulties in the separation of products and regeneration of catalysts. Melt transesterification of BPA and DPC occurred readily to form reactive PC precursors without a serious equilibrium constraint. Alkali-metal carbonates were efficient at a relatively low temperature. However, transesterification of BPA and DMC was subject to a severe chemical equilibrium limitation in the liquidphase reaction. A recycle scheme involving fractionation of DMC and byproduct methanol should be necessary to increase the yield of PC precursors, although it appears to be difficult because of their close boiling points. Oxidative carbonylation of BPA was theoretically the most promising method because it could synthesize PC precursors in one step from CO and BPA. The low reactivity of the precursors synthesized from this reaction could be improved by the reaction scheme of the coupled oxidative carbonylation of BPA and phenol or functionalization of the oligomer’s end group by DPC, in which the reactive precursors are produced amenable to the subsequent polycondensation step of the current commercialized COCl2-free PC process. Nevertheless, this scheme still has various problems to be resolved like the direct oxidative carbonylation of phenol to produce DPC. Acknowledgment This work has been supported by The Research Center for Catalytic Technology of Pohang University of Science and Technology. We appreciate the support of the Korean Ministry of Education and Human Resources Development through the BK 21 program. Literature Cited (1) Komiya, K.; Fukuoka, S.; Aminaka, M.; Hasegawa, K.; Hachiya, H.; Okamoto, H.; Watanabe, T.; Yoneda, H.; Fukawa, I.; Dozono, T. In Green Chemistry: Designing Chemistry for the Environment; Anastas, P. T., Williamson, T. C., Eds.; American Chemical Society: Washington, DC, 1996; p 20. (2) Rivetti, F.; Romano, U. Alcohol carbonylation with palladium(II) complexes, effects of ligands, carbon monoxide, pressure and added bases. J. Organomet. Chem. 1979, 174, 221. (3) Rivetti, F.; Romano, U. Alkoxy carbonyl complexes of palladium and their role in alcohol carbonylation. J. Organomet. Chem. 1978, 154, 323.

(4) Delledonne, D.; Rivetti, F.; Romano, U. Process and catalyst for preparing organic carbonates. U.S. Patent 5,395,949, 1995. (5) Rivetti, F.; Romano, U.; Delledonne, D. In Green Chemistry: Designing Chemistry for the Environment; Anastas, P. T., Williamson, T. C., Eds.; American Chemical Society: Washington, DC, 1996; p 70. (6) Sato, Y.; Kagotani, M.; Yamamoto, T.; Souma, Y. Novel effective poly(2,2′-bipyridine-5,5′-diyl)-CuCl2 catalyst for synthesis of dimethylcarbonate (DMC) by oxidative carbonylation of methanol. Appl. Catal. A 1999, 185, 219. (7) Yanji, W.; Xinqiang, Z.; Baoguo, Y.; Bingchang, Z.; Jinsheng, C. Synthesis of dimethyl carbonate by gas-phase oxidative carbonaylation of methanol on the supported solid catalyst. I. Catalyst preparation and catalytic properties. Appl. Catal. A 1998, 171, 255. (8) Tomishige, K.; Sakaihori, T.; Sakai, S.; Fujimoto, K. Dimethyl carbonate synthesis by oxidative carbonylation on activated carbon supported CuCl2 catalysts: catalytic properties and structural change. Appl. Catal. A 1999, 181, 95. (9) Tomishige, K.; Sakaihori, T.; Ikeda, Y.; Fujimoto, K. A novel method of direct synthesis of dimethyl carbonate from methanol and carbon dioxide catalyzed by zirconia. Catal. Lett. 1999, 58, 225. (10) Tomishige, K.; Ikeda, Y.; Sakaihori, T.; Fujimoto, K. Catalytic properties and structure of zirconia catalysts for direct synthesis of dimethyl carbonate from methanol and carbon dioxide. J. Catal. 2000, 192, 355. (11) Nakamura, A.; Matsuzaki, T. A new oxidation system using nitrite oxidants. Res. Chem. Intermed. 1998, 24, 213. (12) Cavinato, G.; Toniolo, L. New aspects of the synthesis of dimethyl carbonate via carbonylation of methyl alcohol promoted by methoxycarbonyl complexes of palladium(II). J. Organomet. Chem. 1993, 444, C65-C66. (13) Delledonne, D.; Rivetti, F.; Romano, U. Process for preparing organic carbonates. U.S. Patent 5,118,818, 1992. (14) Haggin, J. Dow develops synthesis for Dimethyl carbonate. Chem. Eng. News 1987, 65 (39), 26. (15) Pacheco, M. A.; Marshall, C. L. Review of dimethyl carbonate (DMC) manufacture and its characteristics as a fuel additive. Energy Fuels 1997, 11, 2. (16) Nishihira, K.; Mizutare, K.; Tanaka, S. Process for preparing diester of carbonic acid. EP Patent 425197, 1991. (17) Aresta, M.; Quaranta, E. Carbon dioxide: A substitute for phosgene. CHEMTECH 1997, Mar. (18) Williams, J. L.; Reynolds, D. D.; Dunham, K. R.; Tinker, J. F. Disproportionation of unsymmetrical carbonates. J. Org. Chem. 1959, 24, 64. (19) Tundo, P.; Trotta, F.; Moraglio, G.; Ligorati, F. Continuousflow processes under gas-liquid-phase transfer catalysis (GL-PTC) conditions: The reaction of dialkyl carbonates with phenols, alcohols, and mercaptans. Ind. Eng. Chem. Res. 1988, 27, 1565. (20) Shaikh, A. G.; Sivaram, S. Dialkyl and diaryl carbonates by carbonate interchange reaction with dimethyl carbonate. Ind. Eng. Chem. Res. 1992, 31, 1167. (21) Fukuoka, S.; Tojo, M.; Kawamura, M. Process for continuously producing an aromatic carbonate. U.S. Patent 5,210,268, 1993. (22) Murata, K.; Kawahashi, K.; Watabiki, M. Continuous production of aromatic carbonates. U.S. Patent 5,380,908, 1995. (23) Harrison, G. E.; Dennis, A. J.; Sharif, M. Continuous production process of diarylcarbonate. U.S. Patent 5,426,207, 1995. (24) Fu, Z.; Ono, Y. Two-step synthesis of diphenyl carbonate from dimethyl carbonate and phenol using MoO3/SiO2. J. Mol. Catal. A 1997, 118, 293. (25) Kim, W. B.; Lee, J. S. A new process for the synthesis of diphenyl carbonate from dimethyl carbonate and phenol over heterogeneous catalysts. Catal. Lett. 1999, 59, 83. (26) Kim, W. B.; Lee, J. S. Gas-phase transesterification of dimethylcarbonate and phenol over supported titanium dioxide. J. Catal. 1999, 185, 307. (27) Kim, W. B.; Kim, Y. G.; Lee, J. S. The role of carbon deposition in the gas-phase transesterification of dimethylcarbonate and phenol over TiO2/SiO2 catalyst. Appl. Catal. A 2000, 194195, 403. (28) Ono, Y. Dimethyl carbonate for environmentally benign reactions. Pure Appl. Chem. 1996, 68, 367. (29) Romano, U.; Tesei, R. Process for the preparation of aromatic carbonates. U.S. Patent 4,045,464, 1977. (30) Hallgren, J. E. Diaryl carbonate process. U.S. Patent 4,410,464, 1983.

Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 1913 (31) Fukuoka, S.; Deguchi, R.; Tojo, M. Process for producing diaryl carbonate. U.S. Patent 5,166,393, 1992. (32) Stratton, J.; Gatlin, B.; Venkatasubban, K. S. Proton inventories of the basic methanolysis of phenyl methyl carbonate and diphenyl carbonate. J. Org. Chem. 1992, 57, 3237. (33) Oh, K. S.; Lee, B. G.; Han, M. S.; Shul, Y. G. Effect of calcination conditions on MoO3/SiO2 catalysts for synthesis of methylphenyl carbonate. React. Kinet. Catal. Lett 2002, 77, 51. (34) Fuming, M.; Guangxing, L.; Jin, N.; Huibi, X. A novel catalyst for transesterification of dimethyl carbonate with phenol to diphenyl carbonate: samarium trifluoromethanesulfonate. J. Mol. Catal. A 2002, 184, 465. (35) Yin, G.; Jia, C.; Kitamura, T.; Yamaji, T.; Fujiwara, Y. A new efficient Pd-catalyzed synthesis of diphenyl carbonate with heteropolyacid as a cocatalyst. J. Organomet. Chem. 2001, 630, 11. (36) Yin, G.; Jia, C.; Kitamura, T.; Yamaji, T.; Fujiwara, Y. A new efficient catalytic system for synthesis of diphenyl carbonate with W-Mo-heteropolyacids as a cocatalyst. Catal. Lett. 2000, 69, 89. (37) Goyal, M.; Novosad, J.; Necas, M.; Ishii, H.; Nagahata, R.; Sugiyama, J.; Asia, M.; Ueda, M.; Takeuchi, K. Novel usage of palladium complexes with P-N-P ligands as catalysts for diphenyl carbonate synthesis. Appl. Organomet. Chem. 2000, 14, 629. (38) Turska, E.; Wrobel, A. M. Kinetics of polycandensation in the melt of 4,4-dihydroxy-diphenyl-2,2-propane with diphenyl carbonate. Polymer 1970, 11, 415. (39) Hersh, S. N.; Choi, K. Y. Melt transesterification of diphenyl carbonate with bisphenol-A in a batch reactor. J. Appl. Polym. Sci. 1990, 41, 1033. (40) Kim, Y.; Choi, K. Y.; Chamberlin, T. A. Kinetics of melt transesterification of diphenyl carbonate and bisphenol-A to polycarbonate with LiOH-H2O catalyst. Ind. Eng. Chem. Res. 1992, 31, 2118. (41) Kim, Y.; Choi, K. Y. Multistage melt polymerization of bisphenol-A and diphenyl carbonate to polycarbonate. J. Appl. Polym. Sci. 1993, 49, 747. (42) Fukawa, I.; Fukuoka, S.; Komiya, K.; Sasaki, Y. Porous, crystallized, aromatic polycarbonate prepolymer, a porous, crystallized aromatic polycarbonate, and production methods. U.S. Patent 5,204,377, 1993. (43) Yamato, T.; Oshino, Y.; Fukuda, Y.; Kanno, T.; Kuwana, T. Process for producing polycarbonate. U.S. Patent 5,432,250, 1995. (44) Varadarajan, G. S.; Sivaram, S.; Idage, B. B.; King, J. A. Method for preparing polycarbonate by solid-state polymerization. U.S. Patent 5,717,056, 1998. (45) Kim, W. B.; Lee, J. S. Comparison of polycarbonate precursors synthesized from catalytic reactions of bisphenol-A with diphenyl carbonate, dimethyl carbonate or carbon monoxide. J. Appl. Polym. Sci. 2002, 86, 937. (46) Shaikh, A. G.; Sivaram, S.; Puglisi, C.; Samperi, F.; Montaudo, G. Poly(arylenecarbonate)s oligomers by carbonate interchange reaction of dimethyl carbonate with bisphenol-A. FABMS evidence for the nature of end groups in the oligomers. Polym. Bull. 1994, 32, 427. (47) Losev, I. P.; Smirnova, O. V.; Smurova, Y. V. Kinetics of polycarbonate synthesis by transesterification between 2,2-(4hydroxyphenyl) propane and diphenyl carbonate. Polym. Sci. USSR 1963, 5, 662. (48) Woo, B. G.; Choi, K. Y.; Song, K. H. Melt polycondensation of bisphenol-A polycarbonate by a forced gas sweeping process. Ind. Eng. Chem. Res. 2001, 40, 1312. (49) Woo, B. G.; Choi, K. Y.; Song, K. H. Melt polycondensation of bisphenol-A polycarbonate by a forced gas sweeping process. II. Continuous rotating disk reactor. Ind. Eng. Chem. Res. 2001, 40, 3459. (50) Woo, B. G.; Choi, K. Y.; Song, K. H.; Lee, S. H. Melt polymerization of bisphenol-A and diphenyl carbonate in a semibatch reactor. J. Appl. Polym. Sci. 2001, 80, 1253. (51) Yamamoto, T.; Oshino, Y.; Fukuda, Y.; Kanno, T.; Kuwana, T. Process for producing polycarbonate. U.S. Patent 5,418,314, 1995. (52) Yokoyama, M.; Takakura, K.; Takano, J. Process for producing aromatic polycarbonate. U.S. Patent 5,391,691, 1995. (53) Yokoyama, M.; Takano, J.; Hasegawa, M.; Tatsukawa, Y. Process for producing aromatic polycarbonate. U.S. Patent 5,578,694, 1996.

(54) Hayashi, K.; Masumoto, M.; Nakajima, M.; Hasaki, T.; Ishikawa, M.; Hirashima, T. Method for preparing polycarbonates by transesterification in a steel reactor. U.S. Patent 5,457,174, 1995. (55) Brunelle, D. J. Transesterification process utilizing as a reactant bis(O-haloaryl)carbonates. U.S. Patent 4,321,356, 1982. (56) Yashiro, T.; Matsushima, K.; Kameyama, A.; Nishikubo, T. A novel synthesis of poly(carbonate)s by the polyaddition of bis(epoxide)s with diphenyl carbonate. Macromolecules 2001, 34, 3205. (57) Fukuoka, S.; Watanabe, T.; Dozono, T. Method for producing a crystallized aromatic polycarbonate, and a crystallized aromatic polycarbonate obtained thereby. U.S. Patent 4,948,871, 1990. (58) Ignatov, V. N.; Tartari, V.; Carraro, C.; Pippa, R.; Nadali, G.; Berti, C.; Fiorini, M. New catalysts for bisphenol-A polycarbonate melt polymerization, 1: Kinetics of melt transesterification of diphenyl carbonate with bisphenol-A. Macromol. Chem. Phys. 2001, 202, 1941. (59) Ignatov, V. N.; Tartari, V.; Carraro, C.; Pippa, R.; Nadali, G.; Berti, C.; Fiorini, M. New catalysts for bisphenol-A polycarbonate melt polymerization, 2: Polymer synthesis and characterization. Macromol. Chem. Phys. 2001, 202, 1946. (60) Gross, S. M.; Roberts, G. W.; Kiserow, D. J.; Desimone, M. J. Synthesis of high molecular weight polycarbonate by solidstate polymerization. Macromolecules 2001, 34, 3916. (61) Shi, C.; Gross, S. M.; Desimone, J. M.; Kiserow, D. J.; Rpberts, G. W. Reaction kinetics of the solid-state polymerization of Poly(bisphenol-A carbonate). Macromolecules 2001, 34, 2060. (62) Gross, M. S.; Bunyard, W. C.; Erford, K.; Roberts, G. W.; Kiserow, D. J.; Desimone, J. M. Determination of the equilibrium constant for the reaction between bisphenol-A and diphenyl carbonate. J. Polym. Sci. A 2002, 40, 171. (63) Shaikh, A. G.; Sivaram, S. Organic carbonates. Chem. Rev. 1996, 96, 951. (64) Mork, C. O.; Priddy, D. B. Facile measurement of phenolic end-groups in bisphenol-A polycarbonate using GPC-UV analysis. J. Appl. Polym. Sci. 1992, 45, 435. (65) Haba, O.; Itakura, I.; Ueda, M.; Kuze, S. Synthesis of polycarbonate from dimethyl carbonate and bisphenol-A through a non-phosgene process. J. Polym. Sci. A 1999, 37, 2087. (66) Yamato, T.; Fukuda, Y. Preparation method of polycarbonate. JP 03-174443, 1991. (67) Sugano, T.; et al. Preparation method of polycarbonate. JP 2,284,916, 1990. (68) Kiso, Y.; Shimamoto, K.; Ishibashi, M. Preperation method of aromatic polycarbonates diols. JP 02-251523, 1990. (69) Kiso, Y.; Shimamoto, K.; Ishibashi, M. Purification method of polycarbonate. JP 02-251525, 1990. (70) Pokharkar, V.; Sivaram, S. Poly(alkyene carbonate)s by the carbonate interchange reaction of aliphatic diols with dimethyl carbonate: synthesis and characterization. Polymer 1995, 36 (25), 4851. (71) Shaikh, A. G.; Sivaram, S. Synthesis and characterization of poly(ester carbonate)s based on bisphenol-A and diacid chlorides: a new synthetic approach. Polymer 1995, 36 (16), 3223. (72) Deshpande, M. M.; Jadhav, A. S.; Gurani, A. A.; Sehra, J. C.; Sivaram, S. Polycarbonate synthesis by the melt phase carbonate-ester interchange reaction of bisphenol-A diacetate with dimethyl carbonate. J. Polym. Sci. A 1995, 33, 701. (73) Bolon, D. A.; Hallgren, J. E. Synthesis of polycarbonate from dialkyl carbonate and bisphenol diester. U.S. Patent 4,452,968, 1984. (74) Hallgren, J. E. Catalytic aromatic carbonate process. U.S. Patent 4,201,721, 1980. (75) Chalk, A. J. Catalytic aromatic carbonate process. U.S. Patent 4,187,242, 1980. (76) Goyal, M.; Nagahata, R.; Sugiyama, J.; Asai, M.; Ueda, M.; Takeuchi, K. Direct synthesis of aromatic polycarbonate from polymerization of bisphenol-A with CO using a Pd-Cu catalyst system. Polymer 1999, 40, 3237. (77) Goyal, M.; Nagahata, R.; Sugiyama, J.; Asai, M.; Ueda, M.; Takeuchi, K. Pd catalyzed polycarbonate synthesis from bisphenol-A and CO: control of polymer chain-end structure. Polymer 2000, 41, 2289. (78) Goyal, M.; Nagahata, R.; Sugiyama, J.; Asai, M.; Ueda, M.; Takeuchi, K. Direct formation of polycarbonates by oxidative carbonylation of bisphenol-A. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 1998, 39 (2), 589.

1914 Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 (79) Ishii, H.; Goyal, M.; Ueda, M.; Takeuchi, K.; Asai, M. Direct synthesis of polycarbonate from carbon monoxide and bisphenol-A using efficient Pd complex catalyst systems. Macromol. Rapid Commun. 2001, 22, 376. (80) Chaudhari, R. V.; Kelkar, A. A.; Gupte, S. P.; Bhanage, B. M.; Qureshi, M. S.; Moasser, B.; Pressman, E. J.; Sivaram, S.; Avadhari, C. V.; Kanagasabapathy, S. Method for preparing polycarbonates by oxidative carbonylation. U.S. Patent 6,222,002, 2001. (81) Kim, W. B.; Lee, J. S. A one-step synthesis of reactive polycarbonate precursors by the coupled oxidative carbonylation of bisphenol-A and phenol with carbon monoxide. Chem. Lett. 2001, 1044. (82) Kim, W. B.; Park, K. H.; Lee, J. S. Coupled oxidative carbonylation of bisphenol-A and phenol into phenylcarbonate ended polycarbonate precursors over a homogeneous Pd-Ce redox catalyst. J. Mol. Catal. A 2002, 184, 39. (83) Kim, W. B.; Park, E. D.; Lee, J. S. Effect of inorganic cocatalysts and initial states of Pd on the oxidative carbonylation of phenols over heterogeneous Pd/C. Appl. Catal. A 2003, 242, 335. (84) Moiseev, I. I.; Vargaftik, M. N.; Chernysheva, T. V.; Stromnova, T. A.; Gekhman, A. E.; Tsirkov, G. A.; Makhlina, A. M. Catalysis with a palladium giant cluster: phenol oxidative carbonylation to diphenyl carbonate conjugated with reductive nitrobenzene conversion. J. Mol. Catal. A 1996, 108, 77. (85) Vavasori, A.; Toniolo, L. Multistep electron-transfer catalytic system for the oxidative carbonylation of phenol to diphenyl carbonate. J. Mol. Catal. A 1999, 139, 109. (86) Goyal, M.; Nagahata, R.; Sugiyama, J.; Asai, M.; Ueda, M.; Takeuchi, K. Effect of inorganic redox cocatalysts on Pdcatalyzed oxidative carbonylation of phenol for direct synthesis of diphenyl carbonate. Catal. Lett. 1998, 54, 29. (87) Goyal, M.; Nagahata, R.; Sugiyama, J.; Asai, M.; Ueda, M.; Takeuchi, K. Direct synthesis of diphenyl carbonate by oxidative carbonylation of phenol using Pd-Cu based redox catalyst system. J. Mol. Catal. A 1999, 137, 147. (88) Song, H. Y.; Park, E. D.; Lee, J. S. Oxidative carbonylation of phenol to diphenyl carbonate over supported palladium catalysts. J. Mol. Catal. A 2000, 154, 243. (89) Kezuka, H.; Okuda, F. Process for producing an organic carbonate. U.S. Patent 5,336,803, 1994. (90) Mizukami, M.; Hayashi, K.; Iura, K.; Kawaki, T. Method for preparing aromatic carbonate. U.S. Patent 5,380,907, 1995. (91) Iwane, H.; Miyagi, H.; Imada, S.; Seo, S.; Yoneyama, T. Method for producing aromatic carbonate. U.S. Patent 5,543,547, 1996. (92) Takagi, M.; Kujira, K.; Yoneyama, T.; Ohgomori, Y. Method of producing aromatic carbonate. U.S. Patent 5,726,340, 1998. (93) Buysch, H.-J.; Hesse, C.; Rechner, J. Process for preparing diaryl carbonates. U.S. Patent 5,663,408, 1997. (94) Pressman, E. J.; Shafer, S. J. Method for preparing diaryl carbonates employing hexaalkylguanidinium halides. U.S. Patent 5,898,079, 1999. (95) Hallgren, J. E.; Lucas, G. M.; Matthews, R. O. The palladium-catalyzed synthesis of diphenyl carbonate from phenol, carbon monoxide, and oxygen. J. Organomet. Chem. 1981, 204, 135. (96) Hallgren, J. E.; Lucas, G. M. The palladium-catalyzed synthesis of diphenyl carbonate from phenol, carbon monoxide, and oxygen. II. Aqueous sodium hydroxide as a base. J. Organomet. Chem. 1981, 212, 135. (97) Hallgren, J. E.; Matthews, R. O. The reaction of carbon monoxide and phenols promoted by palladium complexes. J. Organomet. Chem. 1979, 175, 135. (98) Takagi, M.; Miyagi, H.; Yoneyama, T.; Ohgomori, Y. Palladium-lead catalyzed oxidative carbonylation of phenol. J. Mol. Catal. A 1998, 129, L1. (99) Ishii, H.; Ueda, M.; Takeuchi, K.; Asai, M. Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd dinuclear complex. J. Mol. Catal. A 1999, 144, 477. (100) Ishii, H.; Goyal, M.; Ueda, M.; Takeuchi, K.; Asai, M. Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd dinuclear complex bridged with pyridylphosphine ligand. J. Mol. Catal. A 1999, 148, 289. (101) Ishii, H.; Goyal, M.; Ueda, M.; Takeuchi, K.; Asai, M. Oxidative carbonylation of phenol to diphenyl carbonate catalyzed

by Pd complex with 2,2′-bipyridyl ligands. Appl. Catal. A 2000, 201, 101. (102) Ishii, H.; Goyal, M.; Ueda, M.; Takeuchi, K.; Asai, M. Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd complex with diimine ligands. Catal. Lett. 2000, 65, 57. (103) Ishii, H.; Ueda, M.; Takeuchi, K.; Asai, M. Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd2Sn heterotrinuclear complex along with Mn redox catalyst without any addition of ammonium halide. J. Mol. Catal. A 1999, 144, 369. (104) Ishii, H.; Ueda, M.; Takeuchi, K.; Asai, M. Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by PdSn complexes with redox catalyst. J. Mol. Catal. A 1999, 138, 311. (105) Ishii, H.; Takeuchi, K.; Asai, M.; Ueda, M. Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pdpyridyl complexes tethered on polymer support. Catal. Commun. 2001, 2, 145. (106) Ishii, H.; Ueda, M.; Takeuchi, K.; Asai, M. Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by bis(benzonitrile)dichloropalladium in the presence of polyvinylpyrrolidone. Catal. Commun. 2001, 2, 17. (107) King, J. A. Method for making organic carbonates. U.S. Patent 5,132,447, 1992. (108) King, J. A.; Krafft, T. E.; Faler, G. R. Method for making organic carbonates. U.S. Patent 5,142,086, 1992. (109) King, J. A.; Mackenzie, P. D.; Pressman, E. J. Method for making aromatic organic carbonates. U.S. Patent 5,399,734, 1995. (110) Joyce, R. P.; King, J. A.; Pressman, E. J. Method for making aromatic carbonates. U.S. Patent 5,231,210, 1993. (111) Pressman, E. J.; Shafer, S. J. Method for making aromatic organic carbonates. U.S. Patent 5,312,955, 1994 (112) Pressman, E. J.; Shafer, S. J. Method for preparing diaryl carbonates with improved selectivity. U.S. Patent 5,760,272, 1998. (113) Pressman, E. J.; King, J. A. Method for making aromatic carbonates. U.S. Patent 5,284,964, 1994. (114) Pressman, E. J.; Shafer, S. J. Method for making aromatic organic carbonates. EP 05-83938 A1, 1994. (115) Kezuka, H.; Okuda, F. Process for producing an organic carbonate from an organic hydroxyl compound and carbon monoxide in the presence of a palladium catalyst. U.S. Patent 5,283,351, 1994. (116) Buysch, H.; Hesse, C.; Rechner, J.; Schomacker, R.; Wagner, P.; Kaufmann, D. Process for continuous preparation of diaryl carbonates. U.S. Patent 5,498,742, 1996. (117) Buysch, H.; Dohm, J.; Hesse, C.; Rechner, J.; Kaufmann, D. Process for preparing diarylcarbonates. U.S. Patent 5,502,232, 1996. (118) Yoshisato, E. Catalyst and process for the preparation of aromatic carbonates. U.S. Patent 6,534,670 B2, 2003. (119) Shalyaev, K. V.; Soloveichik, G. L.; Johnson, B. F.; Method and catalyst system for producing aromatic carbonates. U.S. Patent 6,512,134 B2, 2003. (120) Ofori, J. Y.; Pressman, E. J.; Shalyaev, K. V.; Williams, E. D.; Battista, R. A. Process for the production of diaryl carbonates. U.S. Patent 6,521,777 B2, 2003. (121) Barcelo, G.; Grenouillat, D.; Senet, J. P.; Sennyey, G. Pentaalkylguanidines as etherification and esterification catalysts. Tetrahedron 1990, 46, 1839. (122) Kim, W. B.; Choi, S. H.; Lee, J. S. Quantitative Analysis of Ti-O-Si and Ti-O-Ti bonds in Ti-Si binary oxides by the Linear Combination of XANES. J. Phys. Chem. B 2000, 104, 8670. (123) Lee, J. S.; Kim, W. B.; Choi, S. H. Linear combination of XANES for quantitative analysis of Ti-Si binary oxides. J. Synchrotron Radiat. 2001, 8, 163. (124) Joshi, U. A.; Kim, W. B.; Lee, J. S., unpublished results. (125) Kim, W. B.; Park, E. D.; Lee, C. W.; Lee, J. S. Nature and role of active states of Pd and Cu in the oxidative carbonylation of phenols with Pd/C and cuprous oxide. J. Catal. 2003, 218, 334.

Received for review July 16, 2003 Revised manuscript received November 25, 2003 Accepted December 17, 2003 IE034004Z

Making Polycarbonates without Employing Phosgene - American

Recommend Documents