Title of Invention

A PROCESS FOR THE PREPARATION OF AN IMPROVED RHODIUM CATALYST.

Abstract

This invention relates to a process for the preparation of an improved rhodium catalyst. The invention relates to the preparation of the said chiral, water-soluble, phosphorous free catalyst having the structural formula Rh2[C6H5) C(CF3) (OCH3)(CO2)]4 from rhodium acetate Rh2(OAc)4 and -methoxy-a-trifluoromethylphenyl acetic acid [C6H5) C(CF3) (OCH3)(CO2H)]. The process steps comprises; reacting rhodium source with a legend corresponding to an optically active substituted phenyl acetic acid such as herein described in the presence of an organic solvent such as aromatic hydrocarbon at a temperature in the range of 100°C to 150°C for a period ranging between 6-8 hrs, bringing the reaction mixture in contact with a mild base to remove the acetic acid formed during the reaction, cooling the reaction mixture to room temperature, removing the solvent by conventional methods and isolating the catalyst by standard methods.

Full Text

This invention relates to a process for the preparation of an improved rhodium catalyst. More particularly, this invention relates to the preparation of the said chiral, water-soluble, phosphorous free catalyst having the structural formula Rh2[(C6H5)C(CF3)(OCH3)(CO2)]4 from rhodium acetate Rh2(OAc)4 and -methoxy--trifluoromethylphenyl acetic acid [(C6H5)C(CF3)(OCH3)(CO2H)]. Rhodium complexes are chiefly used as catalysts in organic reactions and in industry, there are quite a few practical applications of rhodium complexes. Rhodium (II) carboxylates are used in chemotherapy and though they are less effective than Platinum (II) complexes, unwelcome side effects are fewer with Rh (II) carboxylates. Additionally, rhodium complexes are reported to have been used as radiation sensitisers. In the prior art, water-soluble rhodium catalysts bearing chiefly ligands containing phosphorous are known to be prepared by a number of methods. For example, the famous Wilkinson's catalyst which has rhodium compounds containing organophophines, is prepared by methods well documented in literature. This catalyst is used for several industrially useful processes like conversion of alkenes to aldehydes with high selectivity to linear aldehydes and in several related hydroformylation reactions. The catalysts are generally tested in either two-phase systems or in single phase system. Sometimes they are applied in the form of supported aqueous phase catalysts. Recently, some new water-soluble catalysts containing 2,2'-bis(diphenyIphosphino)-1, 1'-binaphthyl (BINAP) type phosphine and 2,2'-bis(di-p-(3-phenylpropyl)phenyl) phosphinomethyl)-l,1'-biphenyl (BSIBI) type phosphine as applied in the hydroformylation reaction with insitu rhodium catalyst are described [Ding, Hao et.al. J.Mol.Catal.A: Chem, 124 (1), 21-28 (English), 1997]. Water-soluble chiral sulphonated BINAP catalysts for asymmetric synthesis of optically active compounds have also been reported [Davies, Mark.E., Wankam, T, PCT Int. Appl. WO 9522405 Al 24 Aug, 1995]. For biphasic chiral reductions, a novel chiral water-soluble phosphine ligand based on a water soluble acrylic salt is recently reported (Malmstroem, Torsten; Andersson Carlaxel; Chem. Commun., 1996, 1135-1136]. Most of the above mentioned methods suffer from the following drawbacks. 1. Most or all the catalysts possess phosphorous ligands in the form of organo phosphorous compounds, sometimes sulphonated to enable better solubility. These ligands are efficient at ambient temperature and pressure only. 2. At higher temperatures and pressures, the catalysts do not perform efficiently, as they tend to dissociate or gel converted to other unstable materials. 3. Organophosphorous based legends in the catalysts are air sensitive moisture sensitive etc., and tend to degrade to triphenylphosphine oxide which is difficult to get rid off. It is therefore desirable to provide a process for the preparation of an improved rhodium catalyst which is free from phosphorous and having hydrophilic nature etc. The object of the present invention is to provide a process fro the preparation of an improved rhodium catalyst which is water-soluble and free from phosphorous legends. Accordingly, the present invention provides a process for the preparation of an improved rhodium catalyst which comprises; reacting rhodium source selected from rhodium acetate or rhodium octanoate with a ligand which is optically active (R) or (S) isomer of a-methoxy-a-trifluoromethylphenyl acetic acid in the presence of an organic solvent such as aromatic hydrocarbon at a temperature in the range of 100°C to 150°C for a period ranging between 6-8 hrs, bringing the reaction mixture in contact with a mild base to remove the acetic acid formed during the reaction, cooling the reaction mixture to room temperature, removing the solvent by conventional methods and isolating the catalyst by standard methods. 3. Organophosphorous based legends in the catalysts are air sensitive moisture sensitive etc., and tend to degrade to triphenylphosphine oxide which is difficult to get rid off. It is therefore desirable to provide a process for the preparation of an improved rhodium catalyst which is free from phosphorous and having hydrophilic nature etc. The object of the present invention is to provide a process the preparation of an improved rhodium catalyst which is water-soluble and free from phosphorous legends. Accordingly, the present invention provides a process for the preparation of an improved rhodium catalyst which comprises; reacting rhodium source selected from rhodium acetate or rhodium octanoate with a ligand which is optically active (R) or (S) isomer of -methoxy--trifluoromethylphenyl acetic acid in the presence of an organic solvent such as aromatic hydrocarbon at a temperature in the range of 100°C to 150°C for a period ranging between 6-8 hrs, bringing the reaction mixture in contact with a mild base to remove the acetic acid formed during the reaction, cooling the reaction mixture to room temperature, removing the solvent by conventional methods and isolating the catalyst by standard methods. In one of the embodiments of the present invention, the rhodium source used may be rhodium acetate or rhodium octanoate preferably rhodium acetate. In another embodiment the ligand used may be optically active R or S -methoxy--trifluoromethylphenyl acetic acid (Mosher acid) which is commercially available, preferably the R isomer. In yet another embodiment the solvent used in the reaction may be selected from chlorobenzene, xylenes etc, preferably chlorobenzene. In another embodiment acetic acid formed during the reaction is absorbed in a mixture of mild bases like NaHCO3, K2CO3 or Na2CO3 and sand, preferably Na2CO3 and sand. The process of the present invention is further described herein below with reference to examples which are illustrative only and should not be construed to as limit of the scope of the present invention in any manner. Example 1 These examples illustrate a method for the preparation of the catalyst A mixture containing the ligand (R) -methoxy--trifluoromethylphenyl acetic acid (94 mg, 4.0 mmol) and rhodium acetate dimer (44 mg, 1.0 mmol) in chlorobenzene (25 ml) containing Na2CO3 and sand (1:4 ratio, 4 gm) was refluxed using a soxhlet-extractor for 6hrs. After 20 runs with the soxhlet-extractor the whole operation was repeated thrice. The solvent was removed under reduced pressure (450 mm, bath temperature 85 %) isolated yield. Example 2 A mixture containing the ligand (R) -methoxy--trifluoromethylphenyl acetic acid (94 mg, 4.0 mmol) and rhodium acetate dimer (44 mg, 1.0 mmol) in xylene (25 ml) containing Na2CO3 and sand (1:4 ratio, 4 gm) was refluxed using a soxhlet-extractor for 6hrs. After 20 runs with the soxhlet-extractor the whole operation was repeated thrice. The solvent was removed under reduced pressure (450 mm, bath temperature 81 %) isolated yield. Example 3 A mixture containing the ligand (R) -methoxy--trifluoromethylphenyl acetic acid (94 mg, 4.0 mmol) and rhodium octanoate dimer (78 mg, 1.0 mmol) in chlorobenzene (25 ml) containing Na2CO3 and sand (1:4 ratio, 4 gm) was refluxed using a soxhlet-extractor for 6hrs. After 20 runs with the soxhlet-extractor the whole operation was repeated thrice. The solvent was removed under reduced pressure (450 mm, bath temperature 81 %) isolated yield. Example 4 A mixture containing the ligand (S) a-methoxy--trifluoromethylphenyl acetic acid (94 mg, 4.0 mmol] and rhodium acetate dimer (44 mg, 1.0 mmol) in chlorobenzene (25 ml) containing Na2CO3 and sand (1:4 ratio, 4 gm) was refluxed using a soxhlet-extractor for 6hrs. After 20 runs with the soxhlet-extractor the whole operation was repeated thrice. The solvent was removed under reduced pressure (450 mm, bath temperature 70 %) isolated yield. Example 5 A mixture containing the ligand (R) -methoxy--trifluoromethylphenyl acetic acid (94 mg, 4.0 mmol) and rhodium acetate dimer (44 mg, 1.0 mmol) in chlorobenzene (25 ml) containing NaHCO3 and sand (1:4 ratio, 4 gm) was refluxed using a soxhlet-extractor for 6hrs. After 20 runs with the soxhlet-extractor the whole operation was repeated thrice. The solvent was removed under reduced pressure (450 mm, bath temperature 80 %) isolated yield. Example 6 A mixture containing the ligand (R) -methoxy--trifluoromethylphenyl acetic acid (94 mg, 4.0 mmol) and rhodium acetate dimer (44 mg, 1.0 mmol) in chlorobenzene (25 ml) containing K2CO3 and sand (1:4 ratio, 4 gm) was refluxed using a soxhlet-extractor for 6hrs. After 20 runs with the soxhlet-extractor the whole operation was repeated thrice. The solvent was removed under reduced pressure (450 mm, bath temperature 75 %) isolated yield. We Claim: 1. A process for the preparation of an improved rhodium catalyst which comprises; steps of characterized in that reacting rhodium source selected from rhodium acetate or rhodium octanoate with a ligand which is optically active (R) or (S) isomer of -methoxy--trifluoromethylphenyl acetic acid in the presence of an organic solvent such as aromatic hydrocarbon at a temperature in the range of 100°C to 150°C for a period ranging between 6-8 hrs, bringing the reaction mixture in contact with a mild base to remove the acetic acid formed during the reaction, cooling the reaction mixture to room temperature, removing the solvent by conventional methods and isolating the catalyst by standard methods. 2. A process as claimed in claim 1 wherein, the rhodium source is preferably rhodium acetate. 3. A process as claimed in claims 1 and 2 wherein, the ligand used is preferably the R isomer. 4. A process as claimed in claims 1-3 wherein, the solvent used in the reaction is selected from chlorobenzene, xylenes, preferably chlorobenzene. 5. A process as claimed in claims 1-4 wherein, the acetic acid formed during the reaction is absorbed in a mixture of mild bases like NaHCO3, K2CO3 or Na2CO3 and sand preferably Na2CO3 and sand. 6. A process for the preparation of improved rhodium catalyst as fully described herein before with reference to examples.

Documents:

262-del-2000-abstract.pdf

262-del-2000-claims.pdf

262-del-2000-correspondence-others.pdf

262-del-2000-correspondence-po.pdf

262-del-2000-description (complete).pdf

262-del-2000-form-1.pdf

262-del-2000-form-19.pdf

262-del-2000-form-2.pdf