Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF BIDENTATE LIGANDS

Abstract

The present invention provides an improved process for the preparation of bidentate ligands of formula 1 as shown in the drawing accompanying this specification wherein R , R1, R2, R3, R4 are selected independently from hydrogen, alkyl, aryl, arylalkyl, cycloaliphatic, COOH, COOR5 wherein R5 = alkyl, or COOM wherein M is metal cation, R may be optionally bridged with Z, wherein Z is a bond, carbon atom or heteroatom, completing ring containing 4 to 20 carbon atoms or a fused system selected independently wherein said ring or fused system may contain one or more hetero atoms such as N,O,S and Y is selected from elements N, P, As, Sb, and Bi from compounds having formula II , wherein R1, R2, R3, R4 have the same meaning as in formula I.

Full Text

This invention relates to the process for the preparation of novel bidentate ligands particularly useful as catalyst for hydrogenation, hydroformylation, carbonylation reactions. More particularly it relates to the preparation of bidentate ligands having general formula 1 in the drawing accompanying this specification wherein R1, R2, R3, R4 are selected independently from hydrogen, alkyl, aryl, arylalkyl, cycloaliphatic, COOH, COOR5 wherein R5= alkyl, or COOM wherein M is metal cation, R may be optionally bridged with Z, wherein Z is a bond, carbon atom or heteroatom completing ring containing 4 to 20 carbon atoms or a fused system selected independently wherein said ring or fused system may contain one or more hetero atoms such as N, O, S and Y may be independently selected from elements N, P, As, Sb, and Bi, from compounds having formula II, wherein R1, R2, R3, R4have same values as in formula I. These ligands are useful for the formation of efficient hydrogenation, hydroformylation, carbonylation catalysts. Bidentate ligands have recently been shown to be very effective for the preparation of organometallic catalysts, such as low pressure hydroformylation, hydrogenation catalysts wherein bidentate ligands are co-ordinated with rhodium. While a variety of bidentate ligands are useful for such chemical conversions as hydrogenation, their synthesis is often difficult, involving numerous reaction steps, one or more of which give low product yields. The net result is that the target bidentate ligands are obtained in low product yields and arc expensive to prepare. Although the bidentate ligands have been reported in the literature, the process for the preparation of these ligands having formula I has been provided for the first time and hence there is no prior art available for synthesizing these ligands. The main object of the present invention is to provide a process for the preparation of bidentate ligands useful for the hydroformylation, hydrogenation and carbonylation of organic compounds. Accordingly, the present invention provides an improved process for the preparation of bidentate ligands of formula 1 as shown in the drawing accompanying this specification wherein R , R1, R2, R3, R4 are selected independently from hydrogen, alkyl, aryl, arylalkyl, cycloaliphatic, COOH, COOR5 wherein R5 = alkyl, or COOM wherein M is metal cation, R may be optionally bridged with Z, wherein Z is a bond, carbon atom or heteroatom, completing ring containing 4 to 20 carbon atoms or a fused system selected independently wherein said ring or fused system may contain one or more hetero atoms such as N,O,S and Y is selected from elements N, P, As, Sb, and Bi, said process comprising the steps of i) halogenating a compound having formula II wherein R1, R2, R3, R4 has the same meaning as above, in an organic solvent and an inert reaction medium such as herein described, at atmospheric pressure and temperature ranging between 0 to 100°C for a period ranging between 2 to 50 hours to obtain a halogenated intermediate having formula III wherein R1, R2, R3, R4 are as defined above and X = halogen , ii) contacting said halogenated intermediate with an anion having formula IV wherein R has the same meaning as above and optionally bridged with Z as defined above and Y is independently selected from elements N,P, As, Sb, and Bi, at ambient pressure and temperature ranging between -20 to 80°C for a period ranging between 2 to 50 hrs., iii) evaporating the solvent of step (ii) to obtain the ester of formula I and saponifying the ester compound, removing the solvent by conventional method such as herein described to obtain the bidendate ligand of formula I. In still another embodiment the organic solvent used may be unreactive solvents such as acetonitrile, halogenated solvents such as dichloromethane, chloroform, carbon tetrachloride, dichloroethane, preferably halogenated solvents. In another embodiment the inert atmosphere may be created by using inert gases like nitrogen, argon preferably nitrogen. Yet another embodiment the optional saponification may be carried out with water or a co-solvent which may be selected from alcohols, ketones containing 1 to 4 carbon atoms or may be done in presence of aqueous medium with alkali or alkaline earth metal hydroxides exemplified by such as sodium hydroxide, lithium hydroxide, calcium hydroxide etc. In still another embodiment the saponification may be carried out with or without an organic solvent depending upon the physical state of the product, such as melting range and solubility in water The process of the present invention is described hereinbelow with reference to examples which are illustrative only and should not be construed to limit the scope of the present invention in any manner. EXAMPLE 1 This example describes synthesis of Brominated carboxylic acid ester To a reaction system comprising a solution of diethyl maleate (50 g.) in chloroform (100 ml), and bromine (15 ml), in chloroform (100 ml), was added over a period of 2 hrs. and the reaction mixture was stirred for 6 hrs. and at the end of reaction, the mixture was washed twice with 100 ml. saturated sodium thiosulphate and then twice with 100ml water. Organic part was passed through 5 g. sodium sulphate and subsequently treated with activated charcoal. Chloroform was stripped off to yield 60 g. of viscous oil of 3,4-(dibromo)diethyl succinate. EXAMPLE 2 This example describes preparation of bidentate phosphine To a 250ml. three necked glass vessel equipped with addition funnel magnetic stirrer and rubber septum argon was filled. To this vessel, finely cut lithium ribbon (500 mg) was added and assembly then, was thoroughly evacuated and refilled with argon. To this, 50 ml THF was added by a gas tight syringe (THF was previously distilled over sodium benzophenone ketyl). Maintaining argon flow, 8.3 ml chloro diphenyl phosphine was placed in the addition runnel, set up was evacuated and refilled with argon. While maintaining temperature below 25°C entire contents of addition funnel were added to the reaction vessel and stirring was continued for 4 hrs. The reaction colour became red after which the agitation was stopped. To another 250 ml vessel equipped with reflux condenser and rubber septum 30 ml. dry THF was placed by a syringe and the set up was evacuated and refilled with argon. To this, 4.52 g. of above brominated product obtained in example 1 was transferred by a syringe followed by 30 ml. of the above mentioned lithium diphenyl phosphide. Contents of the vessel were maintained at 80°C for 12 hrs. To this reaction mixture, 1 ml methanol was added and THF was removed under vacuum. Syrupy orange coloured liquid was then washed thrice with 25ml ether. The contents of the vessel were dissolved in 50 ml. dichloromethane and boiled with little charcoal filtered and 6.8 g. Syrupy oil of compound, 2,3-bis(diphenylphosphino) diethylsuccicnate was recovered. EXAMPLE 3 This example describes saponification of the compound obtained from Example 2 The 1 gm. phosphine derivative obtained in the above said example was transferred to a vessel equipped with magnetic stirrer and reflux condenser. The set up was thoroughly flushed with argon, and 20 ml. 2% sodium hydroxide and 10 mg. tetrabutyl ammonium chloride were added and the contents were refluxed for 4 hrs. The reaction mixture was cooled to 5°C for 2 hrs. and the precipitated white solid was filtered and washed with cold water, 1 g. of white solid 2,3-bis(diphenylphosphino)disodiumsuccicnate was obtained which a melting point of 159 °C Advantages of the present invention 1. Easy method of preparation. 2. Due to the limited solubility in many of the organic solvents, such as ether, hexane, toluene etc., it is easy to recover the catalyst form the product mixture. 3. High overall yield 4. Clean reaction without any side products We Claim: 1. An improved process for the preparation of bidentate ligands of formula 1 as shown in the drawing accompanying this specification wherein R , R1, R2, R3, R4 are selected independently from hydrogen, alkyl, aryl, arylalkyl, cycloaliphatic, COOH, COOR5 wherein R5 = alkyl, or COOM wherein M is metal cation, R may be optionally bridged with Z, wherein Z is a bond, carbon atom or heteroatom completing ring containing 4 to 20 carbon atoms or a fused system selected independently wherein said ring or fused system may contain one or more hetero atoms such as N,O,S and Y is selected from elements N, P, As, Sb, and Bi, said process comprising the steps of i) halogenating a compound having formula II wherein R1, R2, R3, R4 has the same meaning as above, in an organic solvent and an inert reaction medium such as herein described, at atmospheric pressure and temperature ranging between 0 to 100°C for a period ranging between 2 to 50 hours to obtain a halogenated intermediate having formula III wherein R1, R2, R3, R4 are as defined above and X = halogen , ii) contacting said halogenated intermediate with an anion having formula IV wherein R has the same meaning as above and optionally bridged with Z as defined above and Y is independently selected from elements N,P, As, Sb, and Bi, at ambient pressure and temperature ranging between -20 to 80°C for a period ranging between 2 to 50 hrs., iii) evaporating the solvent of step (ii) to obtain the ester of formula I and saponifying the ester compound, removing the solvent by conventional method such as herein described to obtain the bidendate ligand of formula I. 2. An improved process as claimed in claim 1, wherein the organic solvent used is selected from acetonitrile or halogenated solvents selected from dichloromethane, chloroform, carbon tetrachloride, dichloroethane, preferably halogenated solvents. 3. An improved process as claimed in claims 1 - 2, wherein the inert atmosphere used is created by using inert gases selected from nitrogen, argon preferably nitrogen. 4. An improved process as claimed in claims 1-3, wherein saponification is carried out with water or a co-solvent which is selected from alcohols, ketones containing 1 to 4 carbon atoms , in presence of aqueous medium with alkali or alkaline earth metal hydroxides selected from sodium hydroxide, lithium hydroxide, calcium hydroxide. 5. An improved process for the preparation of bidentate ligands substantially as described hereinbefore with reference to examples contained therein.

Documents:

1560-del-1999-abstract.pdf

1560-del-1999-claims.pdf

1560-del-1999-correspondence-others.pdf

1560-del-1999-correspondence-po.pdf

1560-del-1999-description (complete).pdf

1560-del-1999-drawings.pdf

1560-del-1999-form-1.pdf

1560-del-1999-form-19.pdf

1560-del-1999-form-2.pdf

1560-del-1999-form-3.pdf