GB869192A - Amylose derivatives and their production - Google Patents

Abstract

Amylose ethers with a degree of substitution not exceeding 0,20 which are completely soluble in water of a temperature below 100 DEG C. are made by etherifying amylose in an alkaline aqueous solution to a degree of substitution not exceeding 0,20, neutralizing the reaction mixture by addition of an acid, adding before, during or after neutralization of the reaction mixture a salt which salts out the amylose ether or an aqueous solution of such a salt, in such an amount that the amylose ether precipitates, separating the precipitated amylose ether from the reaction mixture and washing it with water until it is substantially salt-free. The amylose is preferably dissolved in an aqueous solution having a pH exceeding 13 and treated with an etherifying agent which contains no groups which are ionizable in water, e.g. dialkyl sulphates, alkylene oxides, alkylene chlorohydrins, styrene oxide and halogeno esters of aliphatic and araliphatic alcohols, such as chloromethane. Suitable salts for the salting out step have a multivalent anion, such as sodium or ammonium sulphate or magnesium sulphate. The amylose ether precipitate is preferably kept in an aqueous salt solution for the time required to render it completely insoluble in cold water, whereafter it is washed free of salt. The amylose ether obtained can be rendered soluble in cold water by first dissolving it in hot water and then recovering it from the hot solution, for example by evaporation of the water. Thus an aqueous dispersion of the amylose ether in cold water may be fed to heated rollers producing sheets of a solid product which is water-soluble. An example describes the preparation of an amylose hydroxyethyl ether from amylose and ethylene oxide in aqueous caustic soda, the product being neutralized with sulphuric acid, salted out with magnesium sulphate and washed with water to remove salts.