This is the published version. Copyright © Royal Society of Chemistry 1999A catalyst system consisting of supported palladium in the presence of phosphine ligands, TsOH and LiCl catalyses the carbonylation of 1-arylethanols to 2-arylpropionic acids with significantly improved activity and regioselectivity; the catalyst can be recycled with no loss in activity and selecivity

Chaudhari, Raghunath Vitthal

Jayasree, S.

Seayad, A.

English

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OHR R ClRCO2HRCO2HRMeOPd-Support/PPh3 CO/H2O+4321H+/Cl––H2OH+5c  R =b  R = Pha  R = BuiHighly active supported palladium catalyst for the regioselective synthesis of2-arylpropionic acids by carbonylation S. Jayasree, A. Seayad and R. V. Chaudhari*Homogeneous Catalysis Division, National Chemical Laboratory, Pune- 411 008, India. E-mail: rvc@ems.ncl.res.inReceived (in Cambridge, UK) 30th March 1999, Accepted 5th May 1999A catalyst system consisting of supported palladium in thepresence of phosphine ligands, TsOH and LiCl catalyses thecarbonylation of 1-arylethanols to 2-arylpropionic acidswith significantly improved activity and regioselectivity; thecatalyst can be recycled with no loss in activity andselecivity.Carbonylation of 1-arylethanols is of great interest since itprovides an environmentally benign route1 for the synthesis ofanti-inflammatory drugs such as Ibuprofen, Naproxen etc. Theimportance of this route can be clearly demonstrated from thecommercialisation of an Ibuprofen process at Texas in 1992 byHoechst Celanese Corporation based on the carbonylation of1-(4-isobutylphenyl)ethanol using a palladium complex cata-lyst.2 The desired high selectivity ( > 98%) for Ibuprofen wasachieved only at very high pressures3 (16–34 MPa). Thishomogeneous palladium catalyst system gave lower TOF†(50–100 h21) and selectivity ( < 68%) at lower pressures ( ~ 6.8MPa).4 Additives such as CuCl2 were reported to improve theselectivity under similar conditions.5 In another study, abiphasic catalyst with a water soluble palladium complex6 hasbeen reported but in this case also, very low reaction rates (TOF= 2.3 h21) and lower Ibuprofen selectivity (70%) wereobserved.Here we report, for the first time, highly active and selectivesupported palladium and platinum catalyst systems for thesynthesis of 2-arylpropionic acids from the corresponding1-arylethanols. Supported palladium combined with PPh3, LiCland TsOH provides very high TOF (3375 h21) and moreimportantly high selectivity (99.5%) for 2-arylpropionic acidsat lower pressures (5.4 MPa). The activity as well as theselectivity was substantially higher compared to previousreports under identical conditions. The catalyst was recycledfour times with no loss in activity and selectivity, attaining atotal TON of 55,000. These results indicate that this newcatalyst system (Pd-C/PPh3/TsOH/LiCl) is highly efficient andprovides significant improvement over the current state of theart for the synthesis of 2-arylpropionic acids.In a typical experiment, the supported catalyst,‡ the substrate,the phosphine ligand, LiCl, TsOH, H2O and the solvent (methylethyl ketone) were charged into a stirred pressure reactor andthe reaction was carried out at 5.4 MPa of CO partial pressureat 115 ºC under 1100 rpm for a specified time. The reactionmixture was analysed by gas chromatography§ and the productswere further characterized by GC-MS and NMR.Typical results for the carbonylation of 1-(4-isobutylphenyl)-ethanol (p-IBPE) using different catalysts, supports, promotersand ligands are presented in Table 1. Pt/C provided compar-atively lower activity than Pd/C. Other supports such as g-alumina and H-ZSM-5 were also useful. Different acid andhalide sources were checked and were found to not significantlyeffect the catalytic activity. The nature of the phosphine ligandhas a strong influence on the catalytic activity, as evidencedfrom Table 1. No reaction was observed with diphos ligandssuch as dppb, unlike the catalyst system reported by Ali et al. forthe carbonylation of olefins.7It was important to understand whether the reaction occursheterogeneously or homogeneously (by soluble complexes ofPd formed in situ). For this purpose, liquid phase reactionsamples were withdrawn during reaction and also after the endof the reaction (on cooling of the contents). The analysis of theliquid phase, after the reaction, for Pd content by atomicabsorption spectroscopy showed < 0.1 ppm of Pd in solution,but the sample withdrawn under the reaction conditions showedsignificant leaching of Pd (1.5 ppm Pd). This indicates that thereaction is more likely to be homogeneously catalysed and theenhanced activity and selectivity is due to the combination of Pdwith PPh3 and promoters like TsOH, and LiCl. At the sametime, readsorption of Pd onto the support after the reactionfacilitates repeated recycling. Thus, the proposed catalystsystem offers significant advantages, not only with respect toactivity and selectivity, but also to catalyst recycling.Intermediate sampling for the carbonylation of p-IBPEshowed that the reaction proceeds through the formation of4-isobutylstyrene and 1-(4-isobutylphenyl)ethyl chloride as theintermediates. Here the question was, which intermediate isundergoing carbonylation? To make this point clear, thecarbonylation of 4-isobutylstyrene was performed in theabsence of LiCl. The reaction was found to be very slow (TOF= 300 h21) with very poor Ibuprofen selectivity (65%). But inTable 1 Carbonylation of 1-(4-isobutylphenyl)ethanol (p-IBPE) to giveIbuprofen using supported palladium and platinum catalystsaConver- Selec-Catalyst Ligand t/h sion (%) tivity (%) TOF/h211% Pd/C PPh3 4.2 96 99.2 33751% Pd/g-alumina PPh3 5.5 92 99.5 24751% Pd/H-ZSM-5 PPh3 5.8 90 99.0 22851% Pt/C PPh3 24 90 99.2 550Pd metalb PPh3 8 97 99.3 901% Pd/C P(p-Tol)3 4.5 94 98.5 30621% Pd/C P(p-FPh)3 5.9 95 99.5 23841% Pd/C P(Cy)3 24 50 99.5 3081% Pd/Cc PPh3 8 91 99.0 16761% Pd/Cd PPh3 6 93 98.5 2272a Conditions: p-IBPE (14.04 mmol), catalyst (10 mg), phosphine (0.1908mmol), TsOH (5.6052 mmol), LiCl (5.6052 mmol), H2O (67 mmol), methylethyl ketone (21 ml), PCO =  5.4 MPa, T = 115 ºC. b Pd metal (2 mg). c HCl(5.6052 mmol) instead of TsOH and LiCl. d Bu4NCl instead of LiCl. Scheme 1Chem. Commun., 1999, 1067–1068 1067Published on 01 January 1999. Downloaded on 13/11/2015 16:59:06. View Article Online / Journal Homepage / Table of Contents for this issuethe presence of LiCl the catalytic activity and Ibuprofenselectivity were the same as that of p-IBPE carbonylation.Under similar conditions, 1-(4-isobutylphenyl)ethyl chloridealso showed the same catalytic activity and selectivity behav-iour. This indicates that in the presence of LiCl, the majorreaction pathway is the carbonylation of the chloro derivative,as shown in Scheme 1.The catalyst system was also applicable for the carbonylationof various 1-arylethanols and their corresponding olefin andchloro analogues, as demonstrated in Table 2. In all cases, highTOF and 2-arylpropionic acid selectivity were achieved.In summary, in the presence of phosphines, TsOH and LiCl,with supported palladium and platinum as the catalyst systems,the carbonylation of 1-arylethanols to 2-arylpropionic acidsoccurs with high activity and regioselectivity with efficientrecycling of the catalyst.S. J. and A. S. thank the Council of Scientific and IndustrialResearch, India, for a research fellowship. Notes and references† TOF = Turn over frequency = number of moles of Ibuprofen producedper mole of metal per hour.‡ The catalysts were prepared by wet impregnation of the chloride salts ofthe metals followed by reduction using formaldehyde (for carbon) orsodium formate (for alumina and H-ZSM-5).§ Analysis of the components was by GC (FFAP capillary column 25 m 30.2 mm, FID)1 R. A. Sheldon, Chem. Ind., 1992, 903; C. B. Dartt and M. E. Davis, Ind.Eng. Chem. Res., 1994, 33, 2887.2 J. N. Armor, Appl. Catal., 1991, 78,141.3 V. Elango, D. G. Kenneth, M. M. Alan, M. N. Graham, Z. G. Edward andS. B. Lee, EP 400 892, 1990.4 A. Seayad, A. A. Kelkar and R. V. Chaudhari, Stud. Surf. Sci. Catal.,1998, 113, 883.5 E. J. Jang, K. H. Lee, J. S. Lee and Y. G. Kim, J. Mol. Catal. A: Chem.,1999, 138, 25.6 G. Papadogianakis, L. Maat and R. A. Sheldon, J. Chem. Technol.Biotechnol., 1997, 70, 83; G. Papadogianakis, G. Verspui, L. Maat andR. A. Sheldon, Catal. Lett., 1997, 47, 43.7 B. E. Ali, G. Vasapollo and H. Alper, J. Org. Chem., 1993, 58, 4739.Communication 9/02541CTable 2 Synthesis of 2-arylpropionic acids by carbonylationaSubstrate t/h Conversion (%) Selectivity (%) TOF/h211a 4.2 96 99.2 33752a 4 92 99.1 34003a 4 90 99.3 33001b 13 90 98 10102b 4.6 92 98 29001c 24 90 99 552a Conditions: Substrate (14.04 mmol), catalyst (10 mg), phosphine (0.1908mmol), TsOH (5.6052 mmol), LiCl (5.6052 mmol), H2O (67 mmol), methylethyl ketone (21 ml ), PCO =  5.4 MPa, T = 115 ºC.1068 Chem. Commun., 1999, 1067–1068Published on 01 January 1999. Downloaded on 13/11/2015 16:59:06. View Article Online

Highly active supported palladium catalyst for the regioselective synthesis of 2-arylpropionic acids by carbonylation

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Highly active supported palladium catalyst for the regioselective synthesis of 2-arylpropionic acids by carbonylation

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