Preparation of Long-chain Esters of Starch Using Fatty Acid Chlorides in the Absence of an Organic Solvent

Abstract

An efficient method of synthesizing fatty acid esters of starch without organic solvents is described. The octanoate of starch was prepared by gelatinization of native starch with formic acid, followed by treatment with octanoyl chloride. Esterification was readily carried out under a stream of N2 at a stirring rate of 500 min -1 at 25—130°C for a reaction duration of 20—120 min. Formic acid enabled esterification of starch by long-chain acyl chlorides with minimum degradation. The major factors affecting the esterification reaction were optimized. The results indicated that the octanoyl degree of substitution (DS8) was increased with increase in fatty acid chloride concentration (from 3—12 eq. per anhydroglucose unit) and rise in temperature (25°C to 130°C). Higher octanoyl chloride concentrations and temperatures led to a reduction in yield due to acid hydrolysis of starch chains. A maximum DS8 of 1.7 was reached after 40 min of reaction, and high concentrations of formic acid decreased the octanoyl substitution. On the other hand, higher concentration of octanoyl chloride, higher temperatures and longer reaction times increased the substitution of the long acyl chain into starch.