Preparation of long-chain esters of starch using fatty acid chlorides in the absence of an organic solvent

An efficient method of synthesizing fatty acid esters of starch without org anic solvents is described. The octanoate of starch was prepared by gelatin ization of native starch with formic acid, followed by treatment with octan oyl chloride. Esterification was readily carried out under a stream of N-2 at a stirring rate of 500 min(-1) at 25-130 degrees C for a reaction durati on of 20-120 min. Formic acid enabled esterification of starch by long-chai n acyl chlorides with minimum degradation. The major factors affecting the esterification reaction were optimized. The results indicated that the octa noyl 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 degrees C to 130 degrees C). Higher octanoyl chloride conc entrations and temperatures led to a reduction in yield due to acid hydroly sis of starch chains. A maximum DS8 of 1.7 was reached after 40 min of reac tion, and high concentrations of formic acid decreased the octanoyl substit ution, On the other hand, higher concentration of octanoyl chloride, higher temperatures and longer reaction times increased the substitution of the l ong acyl chain into starch.