Synthesis of starch vernolate in 1‐butyl‐3‐methylimidazolium chloride ionic liquid

Abstract

A new method for the preparation of epoxy fatty acid esters of cassava starch (starch vernolates) is presented based on the reaction of cassava starch with vernonia oil methyl ester (epoxy ester) using only 1-butyl-3-methylimidazolium chloride, [C4C1im]Cl, ionic liquid as a reaction medium and a cheap inexpensive base such as pyridine as a catalyst. Under the reported reaction conditions, a high degree of substitution of 1.03 was achieved, at a reaction temperature of 110°C and 24 h reaction time. The new starch vernolates were characterized by infrared spectroscopy (FTIR) and solid state NMR (CP/MAS 13C NMR). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that the new product is an amorphous material with a continuous and shapeless morphology. The melting point measured by differential scanning calorimetry (DSC) is 111.4°C. The new synthetic method makes the synthesis of starch vernolates less time consuming and more inexpensive. The differences in melting point and degree of substitution with previously synthesized starch vernolates using enzymatic catalysis suggest a difference in reaction selectivity via this new reaction path.