反应详情

Many methods are described in prior art for conversion of lactic acid to alkyl esters. Reaction between lactic acid and alcohols or carboxylic acids catalyzed by lipase from Candida antarctica with hexane as solvent was reported (Biotechnol. Lett. 1997, 19, 315-317). The authors found lactic acid to be a good acyl donor and esters of both primary and secondary alcohols were synthesized. Dimer formation due to lactic acid acting as both nucleophile and acyl donor was not observed. Butyl lactate was synthesized using heterogeneous supported hetero polyacid catalyst, PW12/SiO2 (Huaxue Yu Nianhe, 1996, 3, 128-130). Japanese patents (JP-05, 155,816; JP-05, 140,039) describe preparation of ethyl lactate from lactonitrile with water and sulfuric or phosphoric acid followed by esterification with ethanol. U.S. Pat. No. 5,264,617 report synthesis of butyl lactate by depolymerization of polylactide by heating with butanol in the presence of p-toluene sulfonic acid. European Patent [EP 517,571] describes esterification of ammonium lactate with methanol at reduced pressure. Japanese Patent (JP 07,258,154) describes that autoclaving a mixture of lactamide, Zr oxide and methanol at 200° C. and 34 atm for 2 hr give methyl lactate in 97.8% selectivity at 94.3% conversion. A process for manufacture of ethyl lactate for use in food industry is described in a patent [CN 1,102,180] with a catalyst comprising of H-type acidic resin complex of glycerin or ethylene glycol and boric acid, sodium dihydrogen phosphate in weight ratio of 1:(0.5-1.0):(0.1-0.2). The process comprises reacting 80% lactic acid and ethanol (92-93%) in the presence of the catalyst. A research paper describes the kinetics of liquid phase synthesis and hydrolysis of butyl lactate catalyzed by cation exchange resin [J. Chem. Technol. Biotechnol, (1994) 59, 149-50]. Japanese Patent (JP 07,10,805) describes preparation of hydroxy carboxylic acid ester in a two phase system of aqueous lactic acid and alcohol like butanol in the presence of inorganic salt like sodium chloride and sulfuric acid catalyst at room temperature with vigorous stirring for 2 h to give yield of 70% butyl lactate and the yield was 37% without sodium chloride. n-Butyl lactate was synthesized with solid super strong acid catalyst derived from sulfuric acid and TiO2 (CA, 1995, 122, 190924n). Method of producing lactic acid and lactic acid esters is described in European Patent (EP 614,983). The process involves fermentation of a culture medium with ammonia and adjusting pH of the culture medium with ammonia and to the resulting ammonium lactate solution is added butanol or pentanol and heating the resultant mixture thereby inducing esterification of lactic acid with alcohol and at the same time effecting liberation and recovery of ammonia and adding a mineral acid to promote complete esterification.

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