Methyl esterification of non-volatile organic acids with HCl-methanol

IWASE Hiroshi, KIMURA Toshiko, SUGIYAMA Taeko

doi:10.2116/bunsekikagaku.24.272

The column conditions and the reaction conditions for the separation of non-volatile organic acids were studied by gas chromatography. Non-volatile organic acids was first converted into suitable volatile derivatives prior to gas chromatography. Two different methods for esterification were investigated following; (1) acid mixture containing(56) mg of each acid were heated with 2 ml of 5% HCl-methanol for 4 hours at 55°C on a water bath, (2) acid mixture containing (56)mg of each acid were refluxed with 2 ml of 5%HCl-methanol for 4 hours. The former method gave better recoveries of the organic acid esters than the latter. One milliliter of deionized water was added to the esterified solution, then this solution was shaken 4 times with 2 ml of chloroform for 3 minutes in a 10 ml separatory funnel. The extracts were dried over anhydrous sodium sulfate, filtered and diluted to 10 ml with chloroform. When maleic acid was esterified, two peaks were detected. The retention time of one peak corresponded to that of the authentic dimethyl maleate, while the retention time of the other corresponded to that of dimethyl fumarate. This may be caused by cis-trans isomerism. Two peaks were also detected in keto acids such as pyruvic acid and α-ketoglutaric acid, probably owing to tautomerism. Various stationary phases were tested for the separation of organic acids. The organic acid methyl esters investigated here could be separated on both NPGS and FFAP column. Column temperature was programmed to rise from 100 to 220°C at a rate of 7.5°C/min.

Methyl esterification of non-volatile organic acids with HCl-methanol

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