Submitted to: Carbohydrate Polymers
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/7/2008
Publication Date: 6/13/2008
Citation: Biswas, A., Shogren, R.L., Selling, G.W., Salch, J., Willett, J.L., Buchanan, C.M. 2008. Rapid and Environmentally Friendly Preparation of Starch Esters. Carbohydrate Polymers. 74:137-141. Interpretive Summary: Starch is a well-known, versatile, and inexpensive agricultural material used for a variety of industrial applications. In addition to being a major food item, it is currently used industrially as coatings and sizing in paper, textiles and carpets, as binders and adhesives, as absorbants, and as encapsulants. Often it is modified to improve its end-use properties, e.g., oxidation, hydrolysis, and substitution with ether and ester such as starch acetate or a quaternary amine. We would like to report a simple microwave-assisted 2 minute solvent-less rapid method to acetylate starch. We have found that acetic anhydride in the presence of a catalytic amount of iodine is an excellent acylating reagent for starch. It is believed that iodine activates the carbonyl group of acetic anhydride, which renders it more reactive. Thus, iodine-activated acetic anhydride is strong enough of an acylating agent to react with starch directly. This reagent works only in the absence of a solvent. Furthermore, when starch was heated with acetic acid and iodine, there was no reaction and starch remained unreacted. This microwave-assisted, rapid solvent-free method that we discovered would help the starch acetate manufacturers to prepare starch acetate in an environmental friendly way. This method reduces the use of solvents and acids.
Technical Abstract: A novel method for the speedy preparation of starch esters by rapid microwave heating is described herein. A two minute method to prepare starch acetate with a 3 deg C of substitution (DS) was developed by fast microwave heating of starch with acetic anhydride in the presence of catalytic amounts (0.16-2.5 mol %) of iodine. Proton NMR, titration and IR were used to determine the DS. In the absence of iodine the reaction did not occur. When the same reactants were heated with a conventional heat source, 10 minutes of heating were required to achieve the same degree of esterification.