Abstract
The degradation mode of sorbic acid, dehydroacetic acid, methyl- and propyl-p-hydroxybenzoate in aqueous solution respectively was studied, using gas chromatographic assay method. It was noted that sorbic acid both in acidic and alkaline region was the most stable of these preservatives, whereas dehydroacetic acid was rapidly decomposed either in acidic or in strong alkaline and, hydrolysis of p-hydroxybenzoate was observed in alkaline region.
The simultaneous detection of 2, 6-dimethyl-4-pyrone, 2, 6-dimethyl-4-pyrone-3-carboxylic acid, triacetic acid lactone and 2, 6-dihydroxy-2, 5-heptadien-4-one (diacetylacetone) as presumable degradation products of dehydroacetic acid could be readily implemented with direct injection gas chromatography.
The degradation mechanisms of dehydroacetic acid and 2, 6-dimethyl-4-pyrone-3-carboxylic acid, both in acidic solution at 60° respectively, were followed by gas chromatography at a given time interval. As degradation products of dehydroacetic acid and 2, 6-dimethyl-4-pyrone-3-carboxylic acid, 2, 6-dihydroxy-2, 5-heptadien-4-one (diacetylacetone) and 2, 6-dimethyl-4-pyrone were identified with direct injection gas chromatography, and 3-carboxy-2, 6-dihydroxy-2, 5-heptadien-4-one was separable newly as the ester.
According to the degradation products, the degradation pathway of dehydroacetic acid in acidic solution was considered to be the fact that of the lactone ring dehydroacetic acid was first broken to produce 3-carboxy-2, 6-dihydroxy-2, 5-heptadien-4-one, and then its decarboxylation immediately following the reaction yielded 2, 6-dihydroxy-2, 5-heptadien-4-one, which was dehydrated finally to 2, 6-dimethyl-4-pyrone.
