Synthesis of Hydrophobic Starch Esters by Reaction of Starch with Various Carboxylic Acid Imidazolides

A novel efficient method of preparing hydrophobic starch esters with a DS = 1.55—2.0 using amylose enriched starch (amylomaize starch) or potato starch and a fatty acid imidazolide in DMSO as solvent is described. The fatty acid imidazolides can be easily prepared by conversion of the corresponding acyl chloride with imidazole in toluene according to a synthesis route developed by Staab et al. [1—4]. The by-product imidazole hydrochloride could be converted to imidazole by alkaline work up with Na2 CO3. As compared with the direct esterification of starch in presence of a fatty acid chloride the presented synthesis method does not need toxic amines like pyridine as catalyst. Only a catalytic amount of a methanolic KOCH3 solution is required. Furthermore no hydrolytic degradation of starch could be observed in contrast to the direct esterification reaction with a fatty acid chloride.