New Route for the Synthesis of Propylene Glycols via

Res. , 2005, 44 (25), pp 9601–9608 ... The feasibility of the VAM hydroformylation route has been demonstrated, and a detailed study has been report...
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Ind. Eng. Chem. Res. 2005, 44, 9601-9608

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New Route for the Synthesis of Propylene Glycols via Hydroformylation of Vinyl Acetate Yogesh L. Borole and Raghunath V. Chaudhari* Homogeneous Catalysis Division, National Chemical Laboratory, Pune 411 008, India

Hydroformylation of vinyl acetate (VAM) has been studied as a key step in the alternative route for the synthesis of 1,2-propanediol (1,2-PDO) and 1,3-propanedol (1,3-PDO) using homogeneous rhodium (Rh) and cobalt (Co) complex catalysts. The feasibility of the VAM hydroformylation route has been demonstrated, and a detailed study has been reported on the key hydroformylation step using homogeneous Rh and Co catalysts. The roles of the catalyst precursors, ligands, and solvents in the activity and regioselectivity of the aldehyde products, i.e., 2-acetoxy propanal (2-ACPAL) and 3-acetoxy propanal (3-ACPAL), and the effect of reaction conditions have been investigated. With Rh-phosphine catalysts, 2-ACPAL is obtained with a selectivity of >90%, while with cobalt carbonyl catalyst, 2-ACPAL and 3-ACPAL are formed with comparable selectivities (∼50% each) thus substantially improving the selectivity of the linear aldehyde, a precursor for 1,3-PDO. In halogenated solvents with cobalt carbonyl catalyst, the selectivity to 3-ACPAL was found to increase still further (58%). A possible mechanism to explain the variation in regioselectivity for the Rh and Co catalysts has been discussed. In the presence of pyridine as a ligand in the Co-catalyzed hydroformylation of VAM, the rate of reaction was found to be enhanced 4-fold. The hydrogenation of acetoxypropanal isomers using Raney-Ni catalyst followed by hydrolysis using Amberlite IR-120 resin catalyst gave quantitative conversion to the mixture of 1,2- and 1,3-PDOs (>90% yield). Introduction Propanediols, i.e., 1,2- and 1,3-PDO, are important bulk commodity chemicals with wide-ranging applications in polymers and as a solvent in the chemical industry. 1,2-PDO is used as a heat transfer fluid and antifreeze agent in food and pharmaceuticals, while 1,3PDO finds uses in the polyurethane, adhesive, and resin industry. Polytrimethylene terephthalate (PTT), synthesized from 1,3-PDO, is an excellent fabric fiber combining the best properties of poly(ethylene terephthalate) (PET) and Nylon. 1,2-PDO has been a bulk product for many years (worldwide production capacity ∼1.03 × 106 TPA in 1990);1 however, until the beginning of this century, 1,3-PDO was considered a scarce and expensive specialty chemical due to the nonavailability of a viable technology.2 While commercial synthesis of 1,2-PDO is carried out via propylene oxide (PO) hydration, 1,3-PDO is commercially produced either via acrolein hydration (Degussa process)3 or the ethylene oxide (EO) hydroformylation route (Shell process).4 Recently, Du Pont5 has developed a green route using an enzyme-catalyzed process for 1,3-PDO from carbohydrates, but it is yet to be commercialized. All the known commercial processes for synthesis of propanediols use hazardous starting materials such as EO, PO, and acrolein. Both EO and PO are flammable and toxic to humans; they are termed as carcinogens and pose problems to the central nervous and respiratory systems. Acrolein is also carcinogenic and highly irritating. Thus, a safe and environmentally benign route for propylene glycols is desirable. In this work, we have proposed, for the first time, a VAM hydroformylation * To whom correspondence should be addressed. Tel.: +9120-25-89-31-63. Fax: +91-20-25-89-32-60. E-mail: rvc@ ems.ncl.res.in.

Figure 1. Total synthesis of propanediols from VAM hydroformylation.

route for simultaneous synthesis of propanediols (PDOs) (Figure 1). It involves three steps, namely, hydroformylation, hydrogenation, and hydrolysis with recyclable catalysts for all three steps. Here, a detailed study on the hydroformylation step using homogeneous Rh and Co catalysts is reported. In hydroformylation reactions, regioselectivity, i.e., linear/branched ratio (l/b), is considered to be the most important issue, which is also significant in the present case due to the expected growth in the demand of 1,3PDO as the end product. From the previous reports it is observed that in hydroformylation of VAM with Rhcatalysts the branched aldehyde, i.e., 2-ACPAL, always predominates (l/b < 0.1).6,7 Abatjoglou and Bryant6 have concluded that the chelating effect of the acetate group is the reason behind the poor l/b ratio. Adkins and Krsek8 have reported Co2(CO)8-catalyzed hydroformylation of VAM among various other substrates with 70% selectivity to acetoxy propanals (ACPALs) with regioselectivity of 62% and 32% for 2-ACPAL and 3-ACPAL, respectively, at 398 K and 24.1 MPa of syngas pressure. In contrast to this report, Tinker and Solodar9 and Tinker10 have reported only 2-ACPAL as the product with no 3-ACPAL, with Co2(CO)8 as the catalyst precursor under wide-ranging conditions of temperature and

10.1021/ie050272g CCC: $30.25 © 2005 American Chemical Society Published on Web 08/20/2005

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Table 1. Effect of Catalyst Precursors on Hydroformylation of VAMa run no.

catalyst-precb

run time min

solvent

catalyst × 103 kmol/m3

VAM kmol/m3

conv %

chemoselectivity, % ald EA AA

1 2 3c 4 5e 6f

A B C D E F

60 200 650 101 215 120

cyclohexane cyclohexane hexane ethanol toluene toluene

0.55 1.09 2.02 0.5 9.1 12

1.46 2.36 1.55 1.94 1.4 1.3

100 99 100 100 36.6 98.9

99 94 93 11d 19.4 96.5

1 0.4 1.6 0.6 33.6 0

0 5.6 5.4 7.3 35 3

regioselectivity, % II III 9 0.7 0 0 0 48.5

91 99.3 100 100 100 51.5

TOF hr-1 6565 1229 111 44 60

a Reaction conditions: temperature, 373 K; P -6 m3. b A ) HRh(CO)(PPh ) ; B ) syngas, 4.1 MPa; CO/H2, 1:1; total charge, 25 × 10 3 3 Rh(CO)2(acac); C ) [Rh(COD)Cl]2; D ) [Rh(CO)2Cl]2; E ) RuCl2(CO)2Py2; F ) Co2(CO)8. c Temperature, 383 K. d Aldehydes are converted e f to acetals. Temperature, 423 K; Psyngas, 10.3 Mpa. Temperature, 393 K; Psyngas, 12.4 MPa; 8.5% ac pols were formed; TOF is calculated at 90% conversion level.

syngas pressures. Botteghi et al.11 in their review on hydroformylation of functionalized olefins have reported that only Rh-catalyzed hydroformylation of VAM is practical, as Co-catalysts give very poor yields (25%) of the aldehyde products irrespective of regioselectivity. In this paper, we present an activity-selectivity study on VAM hydroformylation with different catalyst precursors consisting of Rh, Co, and Ru catalysts. The effect of ligands, promoters, and solvents on the activity and selectivity of 2-ACPAL and 3-ACPAL has been studied for Rh and Co catalysts. To demonstrate the feasibility of the VAM hydroformylation route for propanediol synthesis, hydrogenation of the ACPALs and hydrolysis of acetoxy propanols (ACPOLs) were also studied to establish the feasibility of this route for propanediol synthesis. Experimental Section Materials. Co(CH3COO)2‚4H2O, RhCl3‚3H2O, RuCl3(aq) and all the phosphine, diphosphine, pyridine, substituted pyridines, other ligands such as amines, 5% Ru/Al2O3, etc., were procured from Aldrich, U.S.A. and used as such without further purification. Raney-Nickel (Ni) was procured from Kallin Industries, Mumbai, India. Rh(CO)2(acac),12 [Rh(COD)Cl]2, Rh(CO)2Cl2, and HRh(CO)(PPh3)313 were prepared by the procedures described in the literature. Amberlite IR-120 resin and all solvents were procured from Sd Fine Chemicals, Mumbai, India. CO with 99.9% purity (Matheson, U.S.A.) and H2 with 99% purity (Industrial Oxygen Company, Mumbai, India) were used as received, and syngas mixture in the required CO/H2 ratio was prepared in a reservoir. Co2(CO)8 was prepared by a highpressure/high-temperature technique and was stored (moistened with n-hexane) under high pressures of CO. Hydroformylation Experiments. All the hydroformylation reactions were carried out in a 50 mL Parr autoclave made of SS-material. The experimental setup and procedure used were similar to that described elsewhere.14 For experiments with e7MPa pressure, gas was supplied through a constant pressure regulator attached between the syngas reservoir and the reactor, while for high-pressure experiments, the reactor pressure was maintained constant by intermittent filling of syngas from the reservoir, after every drop of ∼0.2 MPa of reactor pressure. In all experiments, concentrationtime profiles were observed for different sets of reaction conditions. Hydrogenation Experiments. Experiments on hydrogenation of ACPALs to ACPOLs were carried out using Raney-Ni and Ru/Al2O3 catalysts. The procedure followed was similar to that for hydroformylation except that hydrogen gas was used. The experiments were

carried out until H2 absorption stopped to ensure complete conversion of the substrates. The analysis was carried out at the end of the reaction to evaluate conversion, selectivity, and material balance. Hydrolysis Experiments. Hydrolysis of acetoxy propanols was carried out in a 100 mL two-necked round-bottom flask in water or organic-aqueous biphasic modes. Desired amounts of ACPALs, water, and hydrolyzing agents (Amberlite IR-120 resin, etc.) were stirred at 353 K for 3 h using a magnetic stirrer. The reactant/product concentrations were analyzed by GC at the end of reaction. Analytical Methods. The products of the reactions were identified using GC-MS analysis on an Agilent GC series 6890N equipped with a 5973N mass selective detector. Liquid samples were analyzed on a HewlettPackard 6890 series GC controlled by the HP-Chemstation software and equipped with an autosampler unit, using an HP-1 capillary column (30 m × 30 µm × 0.25 µm film thickness with a stationary phase of polymethyl siloxane). The oven temperature was programmed between temperatures of 308-498 K. The quantitative analysis was obtained by constructing a calibration curve. Results and Discussion Hydroformylation of VAM was investigated with the objective of developing a new route for the synthesis of 1,2-PDO and 1,3-PDO. For this purpose, experiments were carried out using homogeneous Rh and Co catalysts. In all experiments, concentration-time profiles were observed and the conversion of VAM and selectivity to aldehyde products calculated. Typical results on the concentration-time profile for a Co catalyst are shown in Figure 5. It was observed that only hydroformylation products, 2-ACPAL and 3-ACPAL, were mainly formed with small amount of acetic acid (AA), ethyl acetate (EA), and propanal as side products. The material balance of aldehyde products formed agreed with the VAM and syngas consumption to the extent of 94-95% as per stoichiometry. The TOF was calculated as moles of aldehydes (2-ACPAL and 3-ACPAL) formed per mole of catalyst (metal g-atom) per hour under conditions of 90% conversion of VAM and hence represent average values. Finally, hydrogenation of ACPALs and hydrolysis of the corresponding ACPOLs were studied to establish a new route for the synthesis of PDOs. Effect of Catalyst Precursors. The effect of different catalyst precursors consisting of Rh, Ru, and Co complexes was studied on the activity-selectivity profile of VAM hydroformylation, and the results are presented in Table 1. Among the various Rh-precursors, HRh(CO)-

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Figure 3. Effect of hydride character on hydroformylation of VAM.

Figure 2. Mechanism of VAM chelation with Rh.

(PPh3)3 was found to be the best catalyst with 99% selectivity to ACPALs. All the Rh catalyst precursors showed g91% regioselectivity to the branched aldehyde, 2-ACPAL. The TOF (hr-1) for HRh(CO)(PPh3)3-catalyzed VAM hydroformylation was nearly 5 times higher than that with Rh(CO)2(acac) precursor. Catalysts with chloride-containing ligands were found to be the least active precursors. Except for HRh(CO)(PPh3)3, all the active Rh-precursors produced AA as a side product. The Ru catalyst precursors, RuCl2(CO)2Py2, RuCl2(CO)2(PPh3)2, and RuCl3‚H2O were tested for hydroformylation of VAM in the temperature range of 393-423 K, among which RuCl2(CO)2Py2 (E) (in toluene) was the only precursor found to be active for hydroformylation at 423 K. With complex E (in toluene) 19.4% selectivity to aldehyde was obtained with 100% regioselectivity to 2-ACPAL (run 5). Among the different Co precursors, such as Co(OAc)2, Co(acac)2, and Con(CO)m etc., only Co2(CO)8 was found to be active for hydroformylation of VAM. Surprisingly, compared to the Rh and Ru catalysts, a significantly improved regioselectivity to the linear aldehyde, 3-ACPAL, was observed with the Co2(CO)8 catalyst. Thus, the l/b ratio of the ACPALs was increased by 10 times with Co2(CO)8 (l/b ) 0.94) compared to the highest obtained with the Rh precursor HRh(CO)(PPh3)3 (l/b ) 0.098). With Co2(CO)8, the chemoselectivity to ACPALs was 88%, with 8.5% of ACPOLs (hydrogenated products). Among the other side products, only 3% of AA was observed. However, the TOF observed for the Co2(CO)8 catalyst was very low, i.e., 60 hr-1, compared to that for the HRh(CO)(PPh3)3 catalyst (6565 hr-1). Thus, from the catalyst precursor study on hydroformylation of VAM it can be concluded that Rh catalysts are the most active but are poor in linear aldehyde selectivity and Co2(CO)8 is less active but showed significantly improved linear aldehyde selectivity compared to the other catalysts. Thus, further studies on these two catalysts were thought to be promising for obtaining higher yields of ACPALs, which can be precursors for 1,2-PDO and 1,3-PDO. Reaction Pathways. According to Abatjoglou and Bryant,6 chelation through the acetate group is the most probable reason for the high regioselectivity to the branched aldehyde in Rh-catalyzed hydroformylation of VAM. It has been proposed that the high stability of the metal-containing five-membered ring (VIII) compared to that of the six-membered ring (IX) leads to preferential formation of branched aldehyde (Figure 2). We propose that besides substrate chelation, there can be two more reasons for the widely varying regio-

selectivity with Co and Rh catalyst precursors. Due to the inductive effect of the carbonyl group of acetate functionality in VAM, double-bond polarization occurs, and a partial negative charge is developed on the “R” carbon atom and a partial positive charge is developed on “β” carbon atom (Figure 3). Such an effect of substrate polarity is also elucidated for substrates such as styrene.15 Hydrido-rhodium carbonyl complexes are known to possess hydride character of the hydrogen and so a partial positive charge on Rh. Due to these partially charged species, anti-Markownikoff addition of HRh(CO)n(L)m takes place across the double-bond of VAM, and Rh-alkyl species of the “R” carbon atom are preferentially formed which leads to a branched aldehyde product. With HCo(CO)4 as a catalyst (formed from Co2(CO)8), due to the strong acidic character of the hydrogen, the double-bond polarization of the VAM affects it in an opposite manner, and preferential formation of Co-alkyl species of the “β” carbon atom takes place leading to a linear aldehyde product. Thus, the two effects, double-bond polarization and substrate chelation, must be operating during hydroformylation of VAM. In the case of Rh-catalysts both the effects compliment each other to give 2-ACPAL (branched aldehyde), whereas in the case of Co2(CO)8 the effects contradict each other giving nearly comparable selectivity for both the aldehydes, 2- and 3-ACPALs. Rh-Catalyzed Hydroformylation of VAM. Further studies on the role of P-, N-, and As-containing ligands were carried out for Rh-catalyzed hydroformylation of VAM. The results are presented in Table 2. With almost all the ligands tested, the initial rate of hydroformylation was found to be higher compared to that with unmodified Rh(CO)2(acac) catalyst. With triphenyl phosphine (TPP) and triphenyl arsine (TPAs) as ligands, Rh(CO)2(acac) gave the highest activity and regioselectivity for the branched aldehyde, 2-ACPAL. Phosphine oxides such as trioctyl phosphine oxide (TOPO) and triphenyl phosphine oxide (TPPO) as ligands were found to produce 2-ACPAL selectively, albeit with poor conversions of 59% and 70%, respectively (runs 4 and 5 in Table 2). It was observed that the chelating bidentate Ncontaining ligands such as bipyridine gives lower catalytic activity (initial rate, 1.4 × 10-4 kmol/m3/s, conversion, 34%) compared to that of the monodentate pyridine as a ligand (initial rate, 3 × 10-4 kmol/m3/s, conversion, 99.6%). The reason may be the prohibition in formation of active hydridocarbonyl species due to the strong coordinating nature of N-ligands. All the diphosphine ligands exhibited excellent chemoselectivity (>98%), and all the ligands favored regioselective formation of 2-ACPAL. With a higher diphosphine ligand such as DPPH, the reaction rates were reduced to half of those with lower diphosphine like DPPP. Thus, instead of acting as a chelating diphosphine ligand, DPPH may be behaving more as a diaryl-alkyl phosphine. These results clearly indicate that, in the case of VAM hydro-

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Table 2. Effect of Ligands on Rh-Catalyzed Hydroformylation of VAMa run no.

ligand

run time min

conv %

ald %

1b 2 3 4 5 6 7 8c 9c 10c 11c

TPP TPAs TOPO TPPO pyridine bipyridine DPPE DPPP DPPB DPPH

170 80 95 114 110 125 100 80 85 84 105

96 100 94 59 70 99.6 34 97 94 99 96

98 93 99 100 100 89.4 84 99 98 98 98

regioselectivity, % II III 1.01 6.5 4.5 0 0 1.5 0.96 1 1.01 1.48 1.01

98.99 93.4 95.5 100 100 98.5 99.14 99 98.99 98.52 98.99

initial rate × 103 kmol/m3/s 0.1 0.69 0.38 0.2 0.19 0.3 0.14 0.4 0.61 0.82 0.31

a Reaction conditions: toluene, 22.5 × 10-6 m3; total charge, 25 × 10-6 m3; VAM, 1.3 kmol/m3; Rh(CO) (acac), 1.01 × 10-3 kmol/m3; 2 ligand/Rh, 3; temperature, 353 K; Psyngas, 4.1 MPa; CO/H2, 1:1; agitation, 16.6 Hz. b Temperature, 373 K. c VAM, 1.085 kmol/m3; -3 3 Rh(CO)2(acac), 0.54 × 10 kmol/m ; ligand/Rh, 1; temperature, 373 K.

Figure 4. Hydroformylation of VAM along with side reactions.

formylation, Rh-catalysts always favor regioselective formation of branched aldehyde product (2-ACPAL) irrespective of the ligand used. Co catalyzed Hydroformylation of VAM. Concentration-time profiles were observed for the Co2(CO)8 catalyst as a catalyst precursor at different concentrations and syngas pressures (Figures 5 and 6, parts A and B). The various products expected to be formed6 under these conditions are shown in Figure 4. Despite the high reactivity of VAM, we found that under appropriate conditions EA was the only side product present in the reaction products. At a lower pressure of syngas (4.1 MPa) and substrate/catalyst ratio of 110, only 70% maximum conversion of VAM was observed. At higher catalyst concentration (substrate/catalyst ratio of 55), the conversion was increased to 98%, but the aldehyde selectivity was reduced and EA formation was increased. At higher pressure (9.65 MPa) and higher catalyst concentration (substrate/catalyst ) 55) the initial rate, conversion, and aldehyde selectivity were found to increase, thus showing a strong dependence of catalyst activity on syngas pressure. Regioselectivity to 3-ACPAL was found to increase with both catalyst concentration and syngas pressure. Effect of Reaction Parameters. The effects of temperature (in the range of 353-433 K), catalyst concentration, substrate concentration, and syngas pressure were studied and the results are presented in

Table 3. The reaction was too slow at lower temperatures (e373 K), whereas it was too fast at higher temperatures (g413 K). In fact, at 373 K the reaction continued for 300 min (55% conversion) at slow rates, whereas at 413 and 433 K, the reaction abruptly stopped after 17 min (59.1% conversion) and 4 min (68% conversion), respectively (see Table 3, entries 2-5). Due to long contact times at 373 K, some 3-ACPAL (I) was decomposed to AA and acrolein, leading to lower l/b. AA was formed in the reaction at 373 K and deactivated the catalyst as observed by a pink-colored precipitate of Co(CH3COO)2. At 393 K, 95% conversion with 95.7% selectivity to aldehydes and an l/b ratio of 0.8 were observed with 1-2% of hydrogenated products, 2-ACPOL and 3-ACPOL. On increasing the catalyst concentration from 0.006 kmol/m3 to 0.012 kmol/m3, the rate of reaction was found to increase by more than 1.5 times (Table 3), at the same time augmenting the side reactionshydrogenation (runs 7 and 9 in Table 3) giving 8.7% and 4.8% selectivity to EA and ACPOLs, respectively. Increase in substrate concentration decreased reaction rates, chemoselectivity, and also product linearity (runs 8 and 9). With an increase in the syngas pressure, the product linearity and alcohol formation were increased slightly while the reaction rates were nearly unaffected (runs 9, 10, and 11). Effect of Phosphine Ligands. Selected results with monophosphine ligands are presented in Table 4. In the experiments with TBP and TPP, at a ligand/Co ratio of 9 at 453 K, total conversion of VAM and corresponding syngas absorption were observed (runs 1 and 2). Surprisingly, aldehyde selectivity was very low at ∼5-6% so also the EA and AA formation. Many small peaks of high boilers were observed in the gas chromatogram. From GC-MS, some of them were found to be oligomers of ACPALs. To avoid the aldehyde decomposition, all the other reactions were carried out at the minimum phosphine concentration and lower temperature. At 433 K and 12 × 10-3 kmol/m3 catalyst concentration, the TPP-modified cobalt catalyst worked better with 85% conversion and 70% chemoselectivity (run 5), though the regioselectivity favored branched aldehyde. Pyridine Ligands. The pyridine-modified Co complex was found to catalyze the hydroformylation of VAM at 373 K to give ∼90% conversion in 250 min, as compared to only 58% in 328 min with unmodified Co catalyst (Table 5, runs 1 and 2). Modification of the Co catalyst with pyridine showed a marginal increase in the initial rate with a decrease in product linearity (40-

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Figure 5. Concentration-time profiles for hydroformylation of VAM at low syngas pressures. (A) Low catalyst concentration (Co2(CO)8, 6 × 10-3 kmol/m3). (B) High catalyst concentration (Co2(CO)8, 12 × 10-3 kmol/m3). Reaction conditions: toluene, 22.5 × 10-6 m3; VAM, 1.3 kmol/m3; total charge, 25 × 10-6 m3; temperature, 393 K; CO/H2 ) 1:1; syngas, 4.1 MPa; agitation, 20 Hz.

Figure 6. Concentration-time profiles for hydroformylation of VAM at high pressure. (A) Liquid sample concentration profile. (B) Syngas absorption profile. Reaction conditions: Co2(CO)8, 12 × 10-3 kmol/m3; toluene, 22.5 × 10-6 m3; VAM, 1.3 kmol/m3; total charge, 25 × 10-6 m3; temperature, 393 K; syngas, 9.65 MPa; CO/H2 ) 1:1; agitation, 20 Hz. Table 3. Effect of Reaction Parameters on Cobalt-Catalyzed Hydroformylation of VAMa run no.

run time min

Co2(CO)8 × 103 kmol/m3

VAM concn kmol/m3

temp K

pres Mpa

conv %

ald %

EA %

AA %

l/b ald

initial rate × 103 kmol/m3/s

1 2b 3 4 5 6c 7 8 9 10 11

41 309 154 17 4 10 90 270 90 64 120

6.9 6 6 6 6 12 6 12 12 12 12

0.88 1 1 1.18 1.1 1.3 1.3 2.4 1.3 1.3 1.3

353 373 393 413 433 433 393 393 393 393 393

11 4.1 4.1 4.1 4.1 13.8 4.1 7.6 4.1 9.65 12.7

8 55 95 59.1 68 81.3 72.8 95.6 98 91.2 98.9

92 80 95.7 92.6 77.8 92.4 94.4 94 87.3 88.2 88.5

0.9 9.8 4 9 15.4 5.9 4.8 2.4 8.7 6.5 3

9.2 0 0 0 1.2 0 3.7 0 1 0

0.8 0.64 0.8 0.68 0.66 0.95 0.83 0.82 0.88 0.91 0.94

0.023 0.053 0.44 2.6 6.2 7.97 0.68 0.71 1.1 1.1 0.98

a Reaction conditions: solvent, toluene; total charge, 25 × 10-6 m3; CO/H , 1:1; agitation, 20 Hz. b Acrolein equivalent to the AA amount 2 is formed. c CO/H2, 3.5:1.

31.5%) and chemoselectivity (96.1-88.4%) (runs 1 and 2). Further increase in pyridine concentration showed a substantial increase in the initial rate at the cost of VAM conversion, product linearity, and aldehyde selectivity (run 3). Formation of acrolein and AA at higher pyridine concentration (py/Co ) 9) also indicates the decomposition of 3-ACPAL (Figure 4). Acrolein formed by this decomposition of 3-ACPAL must have been hydrogenated to propanal. It is known in the literature that acrolein under hydroformylation conditions gives propanal and not the hydroformylation product.16 At 393 K, the effect of pyridine modification was very evident, showing an increase in the initial rates (3-fold), VAM conversion with nearly the same chemoselectivity at a py/Co ratio of 3 (Table 3, run 7 and Table 5, run 4). Thus, at 393 K, pyridine modification greatly helped to increase the activity of the cobalt carbonyl catalyst, without affecting the selectivity of the reaction (Figure 7). Increase in VAM concentration from 1.3 kmol/m3 to

2.66 kmol/m3 inversely affected the conversion and augmented the AA formation reducing the chemoselectivity of ACPALs and regioselectivity of 3-ACPAL (run 5). Unlike the unmodified Co catalyst, the py-modified Co catalyst showed a negligible hydrogenation of aldehyde products. Among the various substituted pyridines tested as ligands, 3-phenyl pyridine was found to give the best results. Substitution at the 2-position in pyridine was found to give poor rates and conversions. Effect of Solvents. Co-catalyzed hydroformylation of VAM was studied using various halogenated solvents (Table 6). DCM as a solvent gives 100% conversion with >97% selectivity to the ACPALs. Highest activity (initial rate ) 2.3 × 10-3 kmol/m3/s) was achieved using ODCB as a solvent, while with chlorobenzene as a solvent, high linearity (58.1%) was observed. In general, the haloge-

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Table 4. Effect of Monophosphines as Ligands on Cobalt-Catalyzed Hydroformylation of VAMa chemoselectivity run no.

ligand

run time min

1b 2b 3 4c 5d 6d 7 8 9d 10d 11d 12 13 14

TPP TBP TPP TPP TPP m-TP TBP TBP TBP TBP TMP TPPO TPPi TBPi

30 30 30 60 90 88 60 60 60 120 120 60 60 60

Co2(CO)8 × kmol/m3

103

6 6 6 24 12 6 12 12 12 12 12 12 12 12

regioselectivity

temp K

syngas MPa

conv %

ald %

EA %

AA %

II %

III %

453 453 453 453 433 433 373 410 433 433 433 453 433 433

4.1 4.1 4.1 4.1 9.6 9.6 4.1 4.1 4.1 9.6 9.6 9.6 9.6 9.6

100 100 11.6 0 85.1 74.4 12 40 95 77.6 82 8.17 8 4

6.2 4.1 40.5 0 70.3 33.8 11 10.5 9 15.2 10.2 29.5 90 73

3 7 25 0 23 6.4 26 15 6 4.6 5.6 28.8 8.1 11.7

9 15 31.1 0 7.3 57 62.6 70 81 71 49 18.1 1.9 16.3

0 0 9.91

100 100 90.

17.09 28.57 44.44 41.18 33.33 20 37.50 0 0 0

82.9 71.4 55.6 58.8 66.7 80 62.5 100 100 100

a Reaction conditions: VAM, 1.3 kmol/m3; toluene, 22.5 × 10-6 m3; ligand/Co, 3; Co/H , 1:1; total charge, 25 × 10-6 m3; agitation, 20 Hz. 2 Ligand/Co ) 9. c Co(OAc)2 is used as a precursor; catalyst preformed at 453 K, 4.1, MPa, 1:1 syngas for 45 min. d Aldehyde hydrogenation occurred with ∼5-6% overall selectivity for alcohols; TPP ) triphenyl phosphine; m-TP ) m-tolyl phosphine; TBP ) tributyl phosphine; TMP ) trimethyl phosphine; TPPO ) triphenyl phosphine oxide; TPPi ) triphenyl phosphite; TBPi ) tributyl phosphite.

b

Table 5. Cobalt-Catalyzed Hydroformylation of VAM with Pyridine/Substituted Pyridines as Ligandsa selectivityb

regioselect ivity

run no.

ligand

run time min

conv %

ald %

AA %

EA %

II %

III %

initial rate × 103 kmol/m3/s

1c 2c 3c,d 4 5e 6 7 8f 9 10 11 12 13f

pyridine pyridine pyridine pyridine 3-phenylpyridine 4-acetylpyridine 2-chloropyridine 2-acetylpyridine 2.3-dihydroxypyridine 2-hydroxy,5-nitropyridine 2,6-bis(chloromethyl)pyridine 2,6-dimethyl pyridine

328 249 172 35 66 40 99 58 27 7 45 15 53

58.2 88.8 60.5 91.4 80.2 95.2 89 50 21.9 11.2 14.8 15.9 89.3

96.1 88.4 42.2 93 76.2 93.3 59.3 85 69.2 73.2 66.9 73.9 75.7

0 6.5 40.1 0 20 0 30.4 1.1 12.9

2.1 4.1 4 4.4 3.4 6.7 4.5 4.4 5.3

22.1

4.0 2.0

40 31.5 18.7 47.4 35.9 44.1 10.7 28.1 11.5 37.9 35.9 20.0 32

60 68.5 81.3 52.6 64.1 55.9 89.3 71.9 88.5 62.1 64.1 80.0 68

0.1 0.14 0.43 2.1 2 2.47 0.94 0.92 0.35 0.44 0.07 0.25 1.1

a Reaction conditions: toluene, 22.5 × 10-6 m3; VAM, 1.3 kmol/m3; Co (CO) , 6 × 10-3 kmol/m3; ligand/Co ) 3; temperature, 393 K; 2 8 Psyngas, 4.1 MPa; CO/H2, 1:1; agitation, 20 Hz. b No alcohol formation observed, propanal is observed whenever AA is formed. c Temp 373 K; Co2(CO)8 12 × 10-3 kmol/m3. d Ligand/Co ) 9. e VAM, 2.66 kmol/m3; 3-ac pol. f Co2(CO)8, 12 × 10-3 kmol/m3; Psyngas, 9.65 MPa.

Figure 7. Comparison of syngas absorption profiles of pyridinemodified and -unmodified Co2(CO)8-catalyzed hydroformylation of VAM. Reaction conditions: same as those of Table 3, run 7 and Table 5, run 4.

nated solvents showed a remarkable effect on the activity and regioselectivity in the hydroformylation of VAM. Process for Propanediols. Hydroformylation of VAM. Mixtures of ACPALs were obtained by using the

cobalt carbonyl catalyst in hydroformylation of VAM, while 2-ACPAL alone was obtained by using the HRh(CO)(PPh3)3 catalyst. In both cases, complete conversion of VAM with greater than 95% selectivity for aldehyde products was achieved under optimum conditions with variation of the regioselectivity. The products 2-ACPAL and 3-ACPAL, being water soluble, were effectively separated from the catalyst phase by extracting in the aqueous phase. With the Co2(CO)8 catalyst, the catalyst was recycled effectively for 3 times after extracting the ACPALs in water in the same reactor. The results of this recycle study are presented in Figure 8, where after each hydroformylation run, the products are extracted in the aqueous phase by using 5 × 10-6 m3 of water 3 times under 2 MPa of 1:1 syngas pressure at room temperature. It was found that the catalyst decomposes if the syngas atmosphere is not applied. These products were also separable by distillation from the hydroformylation reaction mixtures to obtain purity in the range of 96-97%, with the impurities such as AA, acrolein, and some oligomers of ACPALs. These aldehydes were further subjected to hydrogenation followed by hydrolysis. Hydrogenation of Acetoxy Propanols. The hydroformylation products 2-ACPAL or mixtures of 2- and 3-ACPALs were hydrogenated using supported transi-

Ind. Eng. Chem. Res., Vol. 44, No. 25, 2005 9607 Table 6. Effect of Halogenated Solvents on Cobalt-Catalyzed Hydroformylation of VAMa selectivity

regioselectivity

run no.

solvent

run time min

conv %

ald %

AA %

EA %

II %

III %

initial rate × 103 kmol/m3/s

1 2 3 4 5 6a

DCM DCE chlorobenzene bromobenzene ODCB chlorobenzene

120 100 100 75 75 80

98.4 100 97.9 97.2 99.8 97.1

97.2 97.9 93.4 93 95 94.7

0 0 0.3 0 3 0

2.5 3.1 3.4 2.4 1.2 4.7

52.2 50.7 51.9 52.4 51.2 58.1

47.8 49.3 48.1 47.6 48.8 41.9

0.67 0.7 0.64 1.4 2.3 1.1

a Reaction conditions: VAM, 1.3 kmol/m3; solvent, 22.5 × 10-6 m3; Co (CO) , 12 × 10-3 kmol/m3; temperature, 393 K; P 2 8 syngas, 12.4 MPa; CO/H2, 1:1; agitation, 20 Hz. No alcohol formation observed. DCM, dichloromethane; DCE, dichloroethane; ODCB, o-dichlorobenzene. b Syngas, 4.1 MPa.

Table 7. Hydrogenation of Acetoxy Propanalsa run no.

catalyst

1 2 3 4 5 6 7d 8d

5% Ru/Al2O3 Raney-Ni Raney-Ni 5% Ru/Al2O3 Raney-Ni Raney-Ni Raney-Ni 5% Ru/Al2O3 recycled

substrate 2-ac pal 2-ac pal 2-ac pal ac palsc ac palsc 2-ac pal Ac palsc Ac palsc

run time min

catalyst weight g

temp K

conv %

selectivity %b

initial rates × 103 kmol/m3/s

200 11 16 200 17 16 17 200

0.2 0.2 0.1 0.2 0.1 0.2 0.2 0.2

323 353 353 323 353 353 353 323

96 97 96 95 96 93 93 93

99 98 98 95 94 97 94 95

0.6 1.8 1.2 0.5 1.2 1.2 1.2 0.5

a Reaction conditions: aldehyde concentration, 1.3 kmol/m3; water, 22.5 × 10-6 m3; P , 6.9 MPa; agitation, 16.6 Hz. b Total selectivity H2 to acetoxy propanols. c Substrate is a mixture of 2- and 3-acetoxy propanals with 57% and 43% ratio, respectively. d Toluene instead of water as a solvent.

Table 8. Hydrolysis of Acetoxy Propanols to Propylene Glycolsa run no. 1 2 3 4 5 6c

Figure 8. Recycle of Co2(CO)8 catalyst after product extraction in the aqueous phase. Reaction conditions: VAM, 12 kmol/m3; Co2(CO)8, 12 kmol/m3; toluene, 22 × 10-6 m3; 120 °C; 1400 psig; 1:1 ) CO/H2; 1200 rpm; 60 min.

tion metal catalysts to the corresponding ACPOLs, and a few selected results are presented in Table 7. Among the tested catalysts, only Ru/Al2O3 and Raney-Ni showed activity for aqueous phase hydrogenation. The 5% Pd/C and Ni/Al2O3 catalysts were found to be inactive. The 5% Ru/Al2O3 catalyst was found to hydrogenate the ACPALs almost selectively to the corresponding ACPOLs with 96% conversion, 95-99% selectivity, and excellent recyclability. Raney-Ni was found to be the most active catalyst with slightly lower selectivity (94-97%) due to formation of high-boiling products in both the aqueous and organic phases. Thus, it was observed that quantitative hydrogenation of ACPALs can be carried out in both aqueous as well as organic solvents, with excellent activity and selectivity. Hydrolysis of Acetoxy Propanols. Hydrolysis of the hydrogenated products, 2-ACPOL and 3-ACPOL, was carried out using Amberlite IR-120 resin as a catalyst at 353 K, and the results are presented in Table 8. Both 2-ACPOL and its mixture with 3-ACPOL were

substrate 2-ac pol 2-ac pol ac pols ac pols 2-ac pol ac pols

solvent

conv %

selectivity %b

water cyclohexane-water water benzene-water toluene-water benzene-water

92 93 92 93 93 91

97 99 97 99 91 99

a Reaction conditions: substrate, 1.3 kmol/m3; solvent, 22 × 10-6 m3; Amberlite IR 120 resin, 0.2 g; run time, 180 min; T, 353 K. For solvent mixture, the ratio is 1:1; Ac pals is a 57:43 mixture of 2- and 3-acetoxy propanals, respectively. b Selectivity to the corresponding propylene glycols, stoichiometric amounts of acetic acid was observed. c Recycled resin of experiment 4 was used as a catalyst.

hydrolyzed in either the aqueous phase (for aqueous phase hydrogenation solutions) or an organic-aqueous two-phase (for organic phase hydrogenation solutions). The reactions were carried out at 353 K for 180 min with 0.2 g of activated IR-120 resin. Conversions in the range of 92-93% were obtained with almost 99% selectivity for propanediols. A mixture of 2-ACPOL and 3-ACPOL (57:43) on hydrolysis gave 1,2-PDO and 1,3PDO with nearly the same linear/branched ratio as that of the substrate. AA in stoichiometric amount was obtained in all the experiments as a coproduct of hydrolysis. In biphasic reactions, the products were obtained in aqueous phases only and the organic phase did not show even traces of PDOs. As shown in run 6, the resin catalyst was also recycled (without purification or activation) without any loss of activity. Thus, in all the three steps, higher yields of products were obtained, and this route is perhaps most appropriate for coproduction of 1,3- and 1,2-PDOs as products. Since ethylene to vinyl acetate is a fairly matured process,17 this route is particularly attractive when ethylene is visualized as a starting material. In effect, it involves ethylene,

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syngas, and water as the raw materials with complete recycle of AA and high atom efficiency due to high selectivity for the two propanediols. Conclusions Hydroformylation of VAM using homogeneous Rh and Co complex catalysts has been studied with the objective of exploring it as a key step in propanediol synthesis. It was observed that the Rh catalysts in most conditions gave a high regioselectivity to the branched isomer 2-ACPAL, while with the Co2(CO)8 catalyst, a significantly improved regioselectivity for the linear isomer was observed. This indicates a potential application of this route for coproduction of 1,2- and 1,3-PDOs by VAM hydroformylation followed by hydrogenation and hydrolysis steps. The feasibility of this route has been shown with an overall yield of >90% for the mixture of propanediols. It was observed that with the Co2(CO)8 catalyst, the nitrogen-containing ligands such as pyridine enhance the rate of the hydroformylation reaction by almost 4 times, whereas halogenated solvents such as chlorobenzene lead to an l/b ratio of 1.38, is the highest observed so far for VAM hydroformylation. HRh(CO)(PPh3)3 showed very high activity and chemoselectivity for hydroformylation of VAM; however, none of the Rh precursors and ligands tested could improve the regioselectivity beyond an l/b ratio of 0.098. Thus, a new route for the synthesis of propanediols via hydroformylation of VAM is demonstrated, which has many advantages over the known routes. Literature Cited (1) Weissermel, K.; Arpe, H. Industrial Organic Chemistry, 2nd ed.; VCH: Verlagsgesellschaft, 1993. (2) Tullo, A. Peter Debye Award in Physical Chemistry. Chem. Eng. News 2004, 82, 41. (3) Arntz, D.; Wiegand, N. (Degussa Aktiengesellschaft). Preparation of 1,3-propandiol by hydration of acrolein over phosphonate or aminophosphonate group containing ion-exchange resins and subsequent catalytic hydration. U.S. Patent 5,015,789, 1991. (4) (a) Powell, J. B.; Slaugh, L. H.; Forschner, T. C.; Weider, P. R. (Shell Oil Company). Cobalt-catalyzed process for preparing 1,3propanediol using a lipophilic bidentate phosphine promotor. U.S. Patent 5,545,766, 1996. (b) Slaugh, L. H.; Arhancet, J. P. (Shell Oil Company). Process for making 3-hydroxypropanal and 1,3propanediol. U.S. Patent 5,304,686, 1994.

(5) (a) Laffend, L. A.; Nagarajan, V.; Nakamura, C. E. (E. I. du Pont de Nemours and Company; Genencor International Inc.). Bioconversion of a fermentable carbon source to 1,3-propanediol by a single microorganism. U.S. Patent 6,025,184, 2000. (b) Haynie, S. L.; Wagner, L. W. (E. I. du Pont de Nemours and Company). U.S. Patent 5,599,689, 1997. (6) Abatjoglou, A. G.; Bryant, D. R. Rhodium-catalyzed lowpressure hydroformylation of vinyl esters: solvent and phosphine effects on catalyst activity, selectivity and stability. J. Mol. Catal. 1983, 18, 381. (7) (a) Deshpande, R. M.; Chaudhari, R. V. Hydroformylation of vinyl acetate using homogeneous HRh(CO)(PPh3)3 catalyst: a kinetic study. J. Mol. Catal. 1989, 57, 177. (b) Deshpande, R. M.; Chaudhari, R. V. New trends in the kinetics of hydroformylation of vinyl acetate using rhodium complex catalysts. J. Mol. Catal. 1991, 64, 143. (8) Adkins, H.; Krsek, G. Hydroformylation of unsaturated compounds with a cobalt carbonyl catalyst. J. Am. Chem. Soc. 1949, 71, 3051. (9) Tinker, H. B.; Solodar, A. J. Asymmetric hydroformylation process. (Monsanto Co.). CA Patent 1,027,141, 1978. (10) Tinker, H. B. Production of Lactic acid. (Monsanto Co.). U.S. Patent 4,072,709, 1978. (11) Botteghi, C.; Ganzerla, R.; Lenarda, M.; Moretti, G. Advances in the hydroformylation of olefins containing functional groups. J. Mol. Catal. 1987, 40, 129. (12) Varshavskii, Y. S.; Cherkasova, T. G. A simple method for preparing acetylacetonatodicarbonylrhodium(I). Russ. J. Inorg. Chem. 1967, 12, 899. (13) Evans, D.; Osborn, J. A.; Wilkinson, G. Hydroformylation of alkenes by use of rhodium complex catalysts. J. Chem. Soc. A 1968, 3133. (14) Nair, V. S.; Mathew, S. P.; Chaudhari, R. V. Kinetics of hydroformylation of styrene using homogeneous Rh complex catalyst. J. Mol. Catal. 1999, 143, 99. (15) Fuchikami, T.; Ojima, I. Remarkable dependency of regioselectivity on the catalyst metal species in the hydroformylation of trifluoropropene and pentafluorostyrene. J. Am. Chem. Soc. 1982, 104, 3527. (16) Goetz, R. W.; Orchin, M. The reaction of cobalt hydrocarbonyl with R,β-unsaturated aldehydes and ketones. J. Am. Chem. Soc. 1963, 85, 2782. (17) Luyben, M. L.; Tyreus, B. D. An industrial design/control study for the vinyl acetate monomer process. Comput. Chem. Eng. 1998, 22, 867.

Received for review February 28, 2005 Revised manuscript received July 19, 2005 Accepted June 9, 2005 IE050272G