PPh3

Ind. Eng. Chem. Res. 2008, 47, 969-972

969

Regioselective Hydroformylation of Allylic Alcohols Using Rh/PPh3 Supported Ionic Liquid-Phase Catalyst, Followed by Hydrogenation to 1,4-Butanediol Using Ru/PPh3 Supported Ionic Liquid-Phase Catalyst Anil G. Panda, Sachin R. Jagtap, Nitin S. Nandurkar, and Bhalchandra M. Bhanage* Department of Chemistry, Institute of Chemical Technology, UniVersity of Mumbai, N. Parekh Marg, Matunga, Mumbai 400 019, India

The regioselective hydroformylation of allyl alcohol was performed using conventional Rh/PPh3 catalyst in an ionic liquid film supported on silica (Rh/PPh3/SILPC), with water as a reaction medium. Subsequently, the hydroformylation products were hydrogenated using a Ru/PPh3/SILP catalyst to give 1,4-butanediol. The effects of various reaction parameters such as the P/Rh ratio, the substrate/Rh ratio, the temperature, the pressure, and various immobilizing agents on the chemoselectivity and regioselectivity for hydroformylation of allyl alcohol were studied. Extension of this methodology to the hydroformylation of various methylsubstituted allylic alcohols was also studied. Very high conversion and selectivity toward n-aldehyde can be achieved using the present heterogenized homogeneous catalyst system. 1. Introduction Hydroformylation of allyl alcohol, followed by hydrogenation, is one of the most important routes to the synthesis of 1,4-butanediol.1,2 1,4-Butanediol is an important large-scale chemical, and it has extensive application as a polymer feedstock (i.e., in the production of polyurethanes and polybutylene terephthalate (PBT)) and among other products such as tetrahydrofuran (THF), γ-butyrolactone, etc.3,4 The hydroformylation of unsaturated alcohols (e.g., allyl alcohol) is a challenging task, because of side reactions such as isomerization, hydrogenation, dehydration, and condensation, which gives acetals, hemiacetals, etc. under hydroformylation conditions.5,6 Rh-phosphine complexes are active catalysts for this reaction, providing good chemoselectivity toward hydroformylation products, and several methods for the recycling of these catalysts have been reported.7-10 Conventional triphenylphosphine ligands do not offer the required regioselectivity towards n-aldehyde product. Higher regioselectivity (denoted as the n/i ratio, where n is the amount of normal aldehyde and i is the amount of branched aldehyde) can be achieved by specialized bidentate phosphine ligands (BISBI, Xantphos, etc.).11-13 Biphasic hydroformylation that involves organic-water or ionic liquid-water systems has been successfully reported by many research groups and is advantageous, as far as catalyst recyclability is concerned.14,15 Its application is limited by lower reaction rates, in comparison to homogeneous analogues, mainly because of the low substrate solubility with the active catalyst phase where the reaction occurs. The use of biphasic methodology that involves an ionic liquid-water system has disadvantages, such as requiring a large amount of expensive ionic liquid. Because of the high viscocity of ionic liquids, agitational problems arise and the high viscosity also limits the solubility of gases (compared to organic solvents) required for gasliquid-liquid mass-tranfer reactions such as hydroformylation. Supported ionic liquid phase (SILP) rhodium-based (SILP Rh) catalyst systems have been described for olefin hydroformylation,14 hydrogenation,15 hydroamination,16 the Heck * To whom correspondence should be addressed. Tel.: +91 22 24145616. Fax: +91 22 24145614. E-mail addresses: [email protected], [email protected].

reaction,17 etc. The SILP Rh catalyst system is comprised of Rh metal complex dissolved in a thin film of ionic liquid, supported on a high-surface-area porous silica by physisorption. The SILP catalyst results in a very efficient use of the ionic liquids, because of the increased liquid-liquid interfacial area and relatively very short diffusion distances for the reactants, in comparison to those in conventional two-phase systems. In addition, the negligible vapor pressure, the large liquid range, and the thermal stability of ionic liquids ensures that the solvent is retained on the support in its fluid state, even at elevated temperature, which results in a highly stable catalyst system.18 In this paper, we report the regioselective hydroformylation of allyl alcohol using a Rh/PPh3/SILP catalyst, in water (as a reaction medium), and its subsequent hydrogenation to give 1,4butanediol using a Ru/PPh3/SILP catalyst. 2. Experimental Section 2.1. Materials. Ionic liquids,19 HRhCO(PPh3)3 catalyst,20 and RuCl2(PPh3)321 catalyst were prepared according to reported methods and characterized by nuclear magnetic resonance (NMR) spectroscopy (Varian 400-MHz) and Fourier transform infrared (FT-IR) spectroscopy (Perkin-Elmer 100 Spectrochem Series). Silica gel was procured from Sigma-Aldrich (Merck grade, with a BET surface area of 675 m2/g, a particle size of 35-70 mesh (200-500 µm), a mean pore size of 40 Å, and a pore volume of 68 cm3/g), and allylic alcohols were purchased from Lancaster. Synthesis gas (H2 and CO, in a 1:1 ratio) with a purity of 99.9% was obtained from Alchemie Gases Ltd., India. Other reagents used were of analytical grade and used without further purification. Sample analyses were performed using a gas chromatography (GC) system (Chemito GC-1000) that was equipped with a BP10 capillary column (30 m in length and 0.32 mm in diameter) and a flame ionization detection (FID) device, using an external standard method. The products were identified using a gas chromatography coupled with mass spectroscopy (GCMS) system (Shimadzu, Model GCMSQP2010) that was equipped with an Rtx wax capillary column (30 m in length and 0.25 mm in diameter). 2.2. Catalyst Preparation. The supported ionic liquid catalysts were prepared via impregnation of the HRhCO(PPh3)3

10.1021/ie0706865 CCC: $40.75 © 2008 American Chemical Society Published on Web 01/11/2008

970

Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008

Scheme 1: Hydroformylation of Allyl Alcohol

Table 1. Hydroformylation of Allyl Alcohol with the SILP Rh/PPh3 Catalyst Systema entry

P/Rh mole ratio

Sub/Rh mole ratio

temperature (°C)

pressure (MPa)

conversion (%)

[2] (%)

n/ib (2a/2b) ratio

[3] (%)

[4] (%)

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

3 10 20 10 10 10 10 10 10 10 10 10

700 700 700 800 600 600 600 600 600 600 600 600

70 70 70 70 70 80 100 80 80 80 80 80

5 5 5 5 5 5 5 3 4 6 4 4

30 88 78 82 95 100 100 86 99 100 97 96

89 91 89 89 90 87 78 88 90 80 88 87

8 11 14 9 14 16 31 13 20 22 18 16

2 1 2 2 2 3 5 1 2 4 2 2

8 7 8 9 8 10 17 10 8 15 9 10

a Reaction conditions: 22 mmol allyl alcohol, 20.5 mL water; silica gel (Merck grade) support, 10 wt % [(Bmim)PF ], 0.2 wt % Rh metal loading; 6 reaction time ) 5 h. b In this ratio, n refers to normal aldehyde, and i refers to branched aldehyde. c [(Omim)PF6] was used as an immobilizing agent. d o-Xylene was used as an immobilizing agent.

complex with additional PPh3 ligand in an ionic liquid film on a silica. In a typical preparation of SILP catalyst, HRhCO(PPh3)3 (33.6 mg, 0.036 mmol) complex and PPh3 (67.5 mg, 0.252 mmol) were dissolved in 30 mL of dried methylene dichloride under an argon atmosphere. To this solution, 0.18 g of an ionic liquid [(Bmim)PF6] was added and stirred for 30 min. Silica (1.8 g) that had been calcinated at 450 °C for 24 h was added, and the solution was stirred for 60 min. The methylene dichloride was removed under vaccum, and the catalyst was stored under argon untill further use. 2.3. Standard Hydroformylation Experiments. Rh/PPh3/ SILP catalyst in 20.5 mL water (as a solvent) and allyl alcohol (1.28 g, 22 mmol) were charged into a 100 mL stainless steel high-pressure autoclave that was equipped with a mechanical agitator. The reactor was flushed with argon, followed by a CO/ H2 (1:1) mixture at room temperature. The reactor then was heated to 80 °C and pressurized up to 4 MPa of CO/H2 (1:1). The reaction mixture was sampled from time to time and analyzed via GC to monitor the progress of the reaction. After 5 h, the reactor was cooled to room temperature and depressurized. The catalyst was separated by filtration, and the reaction mixture was quantitatively analyzed using GC. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis of the filtrate demonstrated that rhodium metal leaching was negligible (in the range of 1-5 ppm). Filtrate was taken up for further hydrogenation studies. 2.4. Standard Hydrogenation Experiments. The SILP Ru/ 10PPh3 system was prepared using the method described in section 2.3. In this case, Cl2Ru(PPh3)3 (42.15 mg ,0.044 mmol) and PPh3 (81 mg, 0.308 mmol) were used as a catalyst. SILP Ru/PPh3 catalyst, prepared as described previously, was added to the filtrate of the hydroformylation step previously described. The reactor was flushed with argon, followed by hydrogen at

room temperature. The reactor then was heated to 100 °C and pressurized up to 5 MPa of hydrogen gas (H2) pressure. After 4 h, the reactor was cooled to room temperature and depressurized. The catalyst was separated by filtration and the reaction mixture was quantitatively analyzed using GC. 3. Results and Discussions The hydroformylation of allyl alcohol using Rh/SILP catalyst was performed using the procedure described in the Experimental Section. Typical reactions are given in Scheme 1. The desired aldehyde products (2) was obtained up to 91% at 70 °C, 5 MPa of CO/H2 (1:1) pressure, and a P/Rh ratio of 10 (see Table 1, entry 2). A typical 2a/2b ratio of 11 is observed in this case, which indicates higher regioselectivity performance of the catalyst. However 1% of propanal (3) and 7% of isobutyraldehyde (4) was also obtained, as a result of side reactions. A lower P/Rh ratio leads to a decrease in conversion and regioselectivity (2a/2b), whereas an increase in the P/Rh ratio enhances regioselectivity; hence, optimization of the P/Rh ratio is essential. Other reaction parameters, such as the substrate/catalyst ratio, the temperature, the CO/H2 pressure, and the effect of the immobilizing agent on the selectivity of hydroformylation of allyl alcohol, were also optimized (see Table 1). The effect of increasing the Rh catalyst loading from 800:1 to 600:1 results in an enhanced reaction rate with marginal improvement in chemoselectivity (2a and 2b) and regioselectivity (2a/2b) (see Table 1, entries 4 and 5). Further increases in the substrate/catalyst ratio to 500:1 did not have any effect on the conversion and selectivity. Temperature and pressure had an important effect on both the chemoselectivity and regioselectivity of the reaction. When the reaction was performed at

Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008 971 Scheme 2: Hydrogenation of 4-Hydroxybutanal to 1,4-Butanediol

Table 2. Hydroformylation of 1-, 2-, and 3-Methyl Substituted Allylic Alcoholsa conversion (%)

[2] (%)

n/i ratio

1

99

90

20

2

8

2b

100

90

36

3

4

3

76

93

100

6

0

4

75

85

5.4

5.5

4

5c,d

94

92

42

0

2

entry

substrate

[3] (%)

[4] (%)

a Reaction conditions: 22 mmol of substrate, [Rh] ) 0.036 mmol, P/[Rh] ) 10, total volume ) 22 mL; 1.8 g support, silica gel (Merck grade), with 10 wt % [(Bmim)PF6], 0.2 wt % Rh metal loading; T ) 80 °C, P ) 4 MPa of H2/CO (1:1); reaction time ) 5 h. b Contains 2% 2b dehydration product. c Contains 3% 2b dehydration product. d Contains 2% hydrogenation product.

70 °C and 5 MPa, it showed 95% conversion with good chemo and regioselectivity (a 2a/2b ratio of 14) (see Table 1, entry 5). At 80 °C, the reaction was determined to be complete, giving excellent chemoselectivity and regioselectivity, providing a 2a/ 2b ratio of 16 (see Table 1, entry 6). However, when the reaction was conducted further at 100 °C, it had a significant positive effect on regioselectivity but the chemoselectivity decreased (see Table 1, entry 7). Hence, the best tradeoff between conversion and high selectivity was achieved at 80 °C and the pressure study was performed at this temperature. The reaction was studied at four different pressures, and the best result was achieved at 4 MPa (see Table 1, entry 9). To determine the role of the immobilizing agent, [(Bmim)PF6], [(Omim)PF6], and o-xylene were screened (see Table 1, entries 9, 11, and 12). With all three immobilizing agents, the conversion and selectivity remained almost unaffected but slipping of the Rh catalyst from the support was observed, when an organic solvent such as o-xylene was used as an immobilizing agent. Thus, the use of an ionic liquid as a supporting liquid phase is important with regard to features such as stability at higher temperatures and resistance to slipping of the catalyst phase from silica support. Furthermore, the catalyst system can be separated from the reaction mixture by filtration and was recycled up to five consecutive runs without any loss in activity and selectivity performance. To determine the compatibility of the catalyst system for a wider range of substrates, the extension of this methodology to the hydroformylation of various methylsubstituted allylic alcohols is described in Table 2. Higher allyl alcohols such as 3-butene-2-ol, which has methyl substitution at the first position, gives almost complete conversion within 3 h, with high chemoselectivty and regioselectivity (see Table 2, entry 2). 2-Methyl-2-propen-1-ol, which has methyl substitution at the second position, showed complete selectivity toward linear aldehyde, with a conversion of 76% (see Table 2, entry 3). 2-Butene-1-ol, which has a methyl substitution at the third position, provided 75% conversion, with decreased regioselectivity, and the chemoselectivity was observed to be unaffected (see Table 2, entry 4). The probable reason for this observation is due to steric hindrance of methyl group, in comparison to

other substrates. Considering the excellent results, the conditions were also applied to 1,1-disubstituted allyl alcohol, providing 94% conversion with excellent chemoselectivity (up to 92%) and regioselectivity (up to a value of 42) (see Table 2, entry 5). The reasons for such a high selectivity observed using conventional ligands such as PPh3 can be attributed to the observations from kinetic analysis of hydroformylation of allylic alcohols.22,23 Kinetic analysis indicates that a high P/Rh ratio, lower substrate/Rh ratio, and higher concentration of catalyst favor high regioselectivity. With supported catalysts such as Rh/SILPC, it is possible to have a very high catalyst concentration, because the catalyst is immobilized in a small volume of ionic liquid that is adsorbed on a silica surface. Such a high catalyst concentration cannot be achieved in a homogeneously catalyzed reaction, because of the dilution of metal complex with large excess of solvent. In addition to catalyst concentration, a higher PPh3/metal ratio also can be taken in a similar manner. After the hydroformylation step was optimized, the Rh/ PPh3/SILPC catalyst was removed by filtration and the Ru/PPh3/ SILPC catalyst was added to the final reaction mixture without purification (Scheme 2). The solution was pressurized to 5 MPa of H2 and stirred for 4 h at 100 °C. GC analysis of the final solution showed an absence of 2a, and it was completely converted to 1,4-butanediol (5). 4. Conclusion In conclusion, the sequential hydroformylation and hydrogenation of allylic alcohols using Rh/PPh3/SILPC and Ru/PPh3/ SILPC, with water as the reaction medium, allows 1,4butanediol to be obtained with high activity and selectivity. The present catalyst system offers several advantages such as the use of inexpensive and commercially available PPh3 ligand, catalyst reusability, high yield of products, simple workup procedure, and mild reaction conditions, making it an important supplement to existing methods. Acknowledgment Financial support by Council of Scientific and Industrial Research (CSIR), India (through Grant No. 01(2127)/07/EMRII), is kindly acknowledged. Literature Cited (1) Pittman, C. U., Jr.; Honnick, W. D. Rhodium Catalyzed Hydroformylation of Allyl Alcohol: A Potential Route to 1,4-Butanediol. J. Org. Chem. 1980, 45, 2132. (2) Weitz, H. M.; Reib, W. Ullmann’s Encyclopaedia of Industrial Chemistry, Sixth Edition, Vol. 5; Wiley-VCH Verlag Gmbh and Co. KgaA: Weinheim, Germany, 2003; p 706. (3) Haas, T.; Jaeger, B.; Weber, R.; Mitchell, S. F.; King, C. F. New diol processes: 1,3-propanediol and 1,4-butanediol. Appl. Catal., A 2005, 280, 83. (4) Brownstein, M. A. 1,4-butanediol and tetrahydrofuran: exemplary small-volume commodities. CHEMTECH 1991, 21, 506. (5) Eilbracht, P.; Barfacker, L.; Buss, C.; Hollman, C.; Kitsos-Rzychon, B. E.; Kranemann, C. L.; Rische, T.; Roggenbuck, R.; Schmidt, A. Tandem reaction sequences under hydroformylation conditions: New synthetic applications of transition metal catalysis. Chem. ReV. 1999, 99, 3329. (6) Botteghi, C.; Ganzerla, R.; Lenarda, M.; Moreti, G. Advances in hydroformylation of olefins containing functional groups. J. Mol. Catal. 1987, 40, 129.

972

Ind. Eng. Chem. Res., Vol. 47, No. 3, 2008

(7) Deshpande, R. M.; Divekar, S. S.; Bhanage, B. M.; Chaudhari, R. V. Activity of HRh(CO)(PPh3)3 catalyst in hydroformylation of allyl alcohol: effect of second immiscible liquid phase. J. Mol. Catal. 1992, 75, L19. (8) Lindner, E.; Schneller, T.; Auer, F.; Mayer, H. A. Chemistry in interphasessA new approach to organometallic syntheses and catalysis. Angew. Chem., Int. Ed. Engl. 1999, 38, 2155. (9) Mehnert, C. P.; Cook, R. A.; Dispenziere, N. C.; Afeworki, M. Supported Ionic Liquid CatalysissA New Concept for Homogeneous Hydroformylation Catalysis. J. Am. Chem. Soc. 2002, 124, 12932. (10) Cole-Hamilton, D. J. Homogeneous catalysissnew approaches to catalyst separation, recovery and recycling. Science 2003, 299, 1702. (11) Freixa, Z.; van Leeuwan, P. W. N. M. Bite angle effects in diphosphine metal catalysis: Steric or electronic? J. Chem. Soc. Dalton Trans. 2003, 1890. (12) Kranenberg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van Leeuwan, P. W. N. M.; Goubitz, K.; Fraanje, J. New Diphosphine Ligands Based on Heterocyclic Aromatics Inducing Very High Regioselectivity in Rhodium-Catalyzed Hydroformylation: Effect of the Bite Angle. Organometallics 1995, 14, 3081. (13) Riisager, A.; Wasserscheid, P.; van Hal, R.; Fehrmann, R. Continuous fixed bed gas-phase hydroformylation using supported ionic liquid phase (SILP) Rh catalysts. J. Catal. 2003, 219, 252. (14) Chaudhari, R. V.; Bhanage, B. M.; Deshpande, R. M.; Delmas, H. Enhancement of interfacial catalysis in a biphasic system using catalystbinding ligands. Nature 1995, 373 (6514), 501. (15) Wasserscheid, P.; Waffenschmidt, H.; Machnitzki, P.; Kottsieper, W. K.; Stelzer, O. Cationic phosphine ligands with phenylguanidinium modified xanthene moietiessa successful concept for highly regioselective, biphasic hydroformylation of oct-1-ene in hexafluorophosphate ionic liquids. Chem. Commun. 2001, 451. (16) Mehnert, C. P.; Mozeleski, E. J.; Cook, R. A. Supported ionic liquid catalysis investigated for hydrogenation reaction. Chem. Commun. 2002, 3010.

(17) Breitenlechner, S.; Fleck, M.; Muller, T. E.; Suppan, A. Solid catalysts on the basis of supported ionic liquids and their use in hydroamination reactions. J. Mol. Catal., A: Chem. 2004, 214 175. (18) Hagivara, H.; Sugawara, Y.; Isobe, K.; Hoshi, T.; Suzuki, T. Immobilization of Pd(OAc)2 in ionic liquid on silica: Application to Mizoroki-Heck reaction. Org. Lett. 2004, 6, 2325. (19) Riisager, A.; Fehrmann, R.; Flicker, S.; van Hall, R.; Haumann, M.; Wasserscheid, P. Very Stable and Highly Regioselective Supported Ionic-Liquid-Phase (SILP) Catalysis: Continuous Flow Fixed-Bed Hydroformylation of Propene. Angew. Chem., Int. Ed. 2005, 44, 815. (20) Carmichael, A. J., Deetlefs, M., Earle, M. J., Frohlich, U., Seddon, K. R., Rogers, R. D., Seddon, K. R., Eds. Ionic Liquids as Green SolVents, Progress and Prospects; ACS Symposium Series 856; American Chemical Society: Washington, DC, 2003. (21) Evans, D.; Yagupsky, G.; Wilkinson, G. The reaction of hydridocarbonyltris(triphenylphosphine)rhodium with carbon monoxide, and of the reaction products, Hydridodicarbonylbis(triphenylphosphine)rhodium and dimeric species, with hydrogen. J. Chem. Soc. A 1968, 2660. (22) Stephenson, T. A.; Wilkinson, G. New complexes of ruthenium (II) and (III) with triphenylphosphine, triphenylarsine, trichlorostannate, pyridine and other ligands. J. Inorg. Nucl. Chem. 1966, 28, 945. (23) Bhatt, K. N.; Halligudi, S. B. Hydroformylation of allyl alcohol catalysed by (Rh(PPh3)3)+/montmorrilonite: A kinetic study. J. Mol. Catal. 1994, 91, 187. (24) Deshpande, R. M.; Chaudhari, R. V. Hydroformylation of allyl alcohol using homogeneous HRhCO(PPh3)3 catalyst: A kinetic study J. Catal. 1989, 115, 326.

ReceiVed for reView May 15, 2007 ReVised manuscript receiVed October 29, 2007 Accepted December 23, 2007 IE0706865