Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF UNSYMMETRICAL AROMATIC CARBONATES"

Abstract

An improved process for the preparation of unsymmetrical aromatic carbonates. The present invention provides an improved process for the preparation of unsymmetrical carbonates vvhich comprises hydroxyl compound and halo formats reacted in the presence of transition metals or a mixture of metals powder as a condensing agent. Thus the present procedúre avoids the use of organic bases. The use of transition metals povvder enhances the character of arylium ion, vvhich can be attacked by nucleophile and makes the reaction very efficient.

Full Text

This invention relates to an improved process for the preparation of the unsymmetrical carbonates. Particularly the present invention relates to an improved process for the preparation of unsymmetrical carbonates using transition metal poxvder äs a catalyst. The process finds application for the preparation of a variety of aryl, alkyl and heterocyclic carbonates. The mam aim of the invention is to prepare the carbonates by the reaction of readily available chloroformates xvith alcohols in hydrocarbon solvents in the presence of inexpensive metals poxvder. The metals powder used is recoverable and reused again. A novel feature of the invention is that the transition metals poxvder is used as a condensing agent and the yields of the title compounds are good. It also avoids the classical moisture sensitive bases. Reference may be made to (Japan patent 7024966, 1920) wherein dialkyl carbonates have been prepared by the reaction of alcohol xvith carbondioxide and mercury salt. The draxvbacks are the use of toxic metal salt xvhich creates the pollution problem at the source. Moreover, the yields are less (58%). Reference may be made , Huhgarian patent 11211, 1977) xvherein inorganic carbonates via alkylation in chlorobenzene give carbonates at higher temperature. The draxvbacks are, this method is limited to only ethyl are methyl carbonates and the maintenance of temperature at 210 °C is very inconvenient. Reference may be made to (Cherti. Lett, 1981,749) xvherein in the alkylation of potassium carbonate xvith alkyl bromide can be affected in the presence of organostannyl catalyst . The draxvbacks are the use of expensive organostannyl compounds. Reference may be made to (J.Org.Chem. 1984,49, 1122,) xvherein the symmetrical dialkyl carbonates can be generated from metal carbonates and alkyl halides using - methyl pyrrolidine as a solvent and phase transfer catalyst. The draxvbacks are the use of expensive - methyl pyrrolidine and the yields are only moderate. Reference may be made to (J. Org. Chem. 1995 60, 6205,) xvherein mixed or symmetrical carbonates are generated by the reaction of alcohol, carbondioxide and alkyl halides in the presence of base like N-cyclohexyl- N', N', N", N"- tetramethyl guanidine in 1-methylupyrrolidinone. The draxvbacks are, use of expensive base N- cyclohexyl-N',N', N",N"- tetramethyl guanidine. AH these methods have very little feasibility on commercial basis in terms of cost, availability of reagents, recycling of catalyst and minimum waste effluent. Therefore, the existing methods of carbonate formation have the disadvantages: 1. Heavy metal salts are toxic which are difficult to handle and require effluent treatment or pollutes the environment. 2. Some of the methods have limitations to only symmetrical and lower alkyl carbonates. 3. Solvent and bases used are very expensive and are not recoverable. This has negatíve influence on the economy of the process. 4. Some methods require activation by organometallic compounds like stannates which are very difficult to prepare and expensive. 5. Reaction temperature is very high (210°C) and it is very difficult to maintain during the reaction time. The main object of the present invention is to provide an improved process for the preparation of unsymmetrical carbonates, which obviates the drawbacks as detailed above. Another object of the present invention is to recover and reuse the catalyst, which would minimize the waste effluent in large-scale preparation and have the positive influence on the economy of the process. Still another object of the present invention is to replace the moisture sensitive bases. Accordingly, the present invention provides an improved process for the preparation of unsymmetrical aromatic carbonates of formula 1 as shown in the drawing accompanying this specification, wherein R is alkyl, aryl and/or heterocyclic and R1 is ethyl, benzyl and/or isobutyl, which comprises reacting hydroxyl compounds selected from alcohol having C5 - C15 straight or branched chain with haloformate selected from benzyle chloroformate, isobutyl chloroformate in presence of transition metals selected from Zn, Fe, Cd, Cu or mixture of metal powder thereof , in organic solvent such as herein described, for a period in the range of 4 to 6 hrs, recovering the unsymmetrical carbonates of formula 1 by conventional methods, such as herein described. In an embodiment of the present invention the unused metal is recovered from the reaction mixture and after successive washing with ether, benzene, acetone and drying, it may be again reused. In another embodiment of the present invention the alcohols includes C5-C15 straight or branched chain, t-butyl benzylic and heterocyclic. The chloroformates may be benzyl or ethyl. In yet another embodiment of the present invention the transition metal used may be such as Zn, Fe, Cd, Cu or mixture thereof. Still another embodiment of the present invention the hydrocarbon solvent used may be any solvent, which is chemically inert such as benzene, toluene and xylene. In a feature of the invention the metals used in the range of 0.3-1.5% of the reactant. In another feature of the invention, after completion of the reaction the reaction mixture is filtered and washed with diethyl ether, neutralised with sodium bicarbonate (10%). The unused metal powder may be reused. In the drawings accompanying this specification figure (1) represents preparation of unsymmetrical carbonates from readily available chloroformates and alcohols in the presence of transition metals powder. Accordingly the present invention provides an improved process for the preparation of unsymmetrical carbonates which comprises alcohol and chloroformates reacted in the presence of transition metals or a mixture of metals powder as a condensing agent. Thus the present procedure avoids the use of organic bases. The use of transition metals powder enhances the character of arylium ion, which can be attacked by nucleophile and makes the reaction very efficient. The present process further reveals mat the properly activated transition metals powder such as zinc, cadmium, iron, copper or a mixture of metals poxvder used are in the mole ratio iron-zinc (1:3); cadmium-copper (1:2); zincucadmium (3:1), zinc-copper (1:1). The mixture metals powder may be used in the range 0.3 to 1.5 equivalent of the reactants. The variation in the ratio of metals powder is arbitrary. The use of less equivalent of metals poxvder slow downs the rate of the reaction. All the hydrocarbon solvents or the mixture of solvents are suitable for good results preferably the composition of higher boiling solvent and lower boiling solvent (3:1) gives the better yield .The reaction of alcohol and chloroformate carried out at the temperature ranging from 40 °C to the boiling temperature (120 ° C) of the solvent. The lower temperature slows down the reaction. The reaction is accomplished nearly in 8 to 10 hrs. After completion of the reaction, it is filtered and filtrate is washed with dilute alkali solution. Evaporation of the solvent gives high yield of carbonates. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention EXAMPLE-1 Benzyl chloroformate (10 mol) is stirred with metal powder (Fe-Zn,l:3,0.3 mol) in benzene for 15 minutes. To this is added a benzene solution of 1-Dodecanol (10 mol) and then the mixture is refluxwd the unused catalyst is separated by filtration and the filtrate is neutralised with sodiumbicarbonate solution( 10%). After evaporation of the solvent gives benzyl-dodecanoate in 90% yield. EXAMPLE-2 Bjenzyl chloroformate (10 mol) is stirred with metal powder (Fe-Zn,l:3,0.3 mol) in benzene for 15 minutes. To this is added a benzene solution of tert-Butanol(10 mol) and then the mixture is refluxwd .the unused catalyst is separated by filtration and the filtrate is neutralised with sodiumbicarbonate solution(10%).After evaporation/ qf the solvent gives benzyl-tert-butanoate in 92% yield. EXAMPLE-3 ifcobutyl chloroformate (10 mol) is stirred with metal powder (Cd-Zn, 1:3,0.3 mol) in penzene for 15 minutes. To this is added a benzene solution of 3-benzyloxy-2-methyl-propanol(10 mol) and then the mixture is refluxwd fof oifrs.the unused catalyst is separated by filtration and the filtrate is neutralised with sodiumbicarbonate solution( 10%). After evaporation of the solvent gives isobutyl-3-benzyloxy-2-methyl-propanoate in 96% yield. The main advantages of the present invention are: The present invention for carbonates using transition metals powder as a condensing agent has the following distinct advantages over the existing process. l. Moisture sensitive bases are replaced by transition metals powder, which are very convenient to handle. 2. Metals powder used is less than stoichiometric amount and some of it is recoverable and reusable. So the cost of catalyst is reduced and has a positive influence on the economy of the process. 3. As the metals powder is recovered and reused, this aspect minimizes the waste effluent at the source. 4. Yields are very high. We Claim: 1. An improved process for the preparation of unsymmetrical aromatic carbonates of formula 1 as shown in the drawing accompanying this specification, wherein R is alkyl, aryl and/or heterocyclic and R1 is ethyl, benzyl and/or isobutyl, which comprises reacting hydroxyl compounds selected from alcohol having C5 - C15 straight or branched chain with haloformate selected from benzyle chloroformate, isobutyl chloroformate in presence of transition metals selected from Zn, Fe, Cd, Cu or mixture of metal powder thereof , in organic solvent such as herein described, for a period in the range of 4 to 6 hrs, recovering the unsymmetrical carbonates of formula 1 by conventional methods, such as herein described. 2. An improved process as claimed in claims 1 and 2 wherein the organic solvent used is selected from benzéne, toluéne or xyléne. 3. An improved process as claimed in claims 1 to 3 wherein the metals or mixtures of metal powder used as catalyst is in the range of 0.3 - 1.5 mol% of the reactant. 4. An improved process for the preparation of unsymmetrical aromatic carbonates substantially as herein described with reference to the examples and drawings accompanying this specification.

Documents:

1093-del-1999-abstract.pdf

1093-del-1999-claims.pdf

1093-del-1999-correspondence-others.pdf

1093-del-1999-correspondence-po.pdf

1093-del-1999-description (complete).pdf

1093-del-1999-drawings.pdf

1093-del-1999-form-1.pdf

1093-del-1999-form-19.pdf

1093-del-1999-form-2.pdf

1093-del-1999-form-3.pdf