| 摘要 |
An accelerated process for preparing a methyl ester having formula (III)said process comprising reacting a carboxylic acid or salt thereof having formula (I)with dimethyl carbonate having formula (II)in the presence of a catalyst selected from the group consisting of 1,8-diazabicyclo[5.4.0]undec-7-ene; 1,4-diazabicyclo[2.2.2]octane; 4-dimethylaminopyridine; and combinations thereof, wherein R1 is selected from the group consisting of an alkyl, aryl, alkoxy, alkenyl, cycloalkyl, benzocycloalkyl, cycloalkylalkyl, aralkyl, heterocyclic, heteroaralkyl, alkoxyalkyl, carboxyalkyl, alkylcarbonyl, alkoxycarbonyl, alkoxycarbonylalkyl, and haloalkyl; and M is selected from the group consisting of hydrogen, a monovalent metal, and a monovalent fractional part of a polyvalent metal, wherein said process is conducted under microwave irradiation at a frequency from 300 MHz to 30 GHz, and at a temperature of from about 120° C. to 300° C. for a period of microwave irradiation time from about 1 second to about 300 minutes. The process of the invention is especially advantageous for preparing methyl esters since the process: (1) utilizes an environmentally friendly methylating reagent, dimethylcarbonate; (2) produces a high yield of the methyl ester, generally 95-99% conversion in less than 30 minutes of microwave irradiation; (3) minimizes degradation and/or racemization of optically pure compounds; and (4) minimizes the formation of by-products.
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