Preparation and Antioxidant Activities of Phenolic Esters and Ethers of L-Ascorbic Acid

Abstract

Esterification of L-ascorbic acid in concentrated sulfuric acid with 0.33 moles of gallic acid gave a 90% yield of a 2:5 mixture of L-ascorbyl 5- and 6-gallate esters. The 6-gallate ester (1) was purified from the 5-gallate ester (2) by fractional crystallization in 40% yield. Three other aromatic derivatives of L-ascorbic acid also were prepared. The order of antioxidant activities of the L-ascorbyl derivatives determined by thiobarbituric acid number in methyl linolenate at 37 °C was as follows: 6-gallate (1) > 6-(3′,4′ -dihydroxy)benzoate (3) = 6-(4′ -hydroxy)phenyl ether (4) >6-(4′ methoxy)phenyl ether (5).