Acylation of Starch with Vinyl Acetate in Water
| Main Authors: | , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0038-9056 |
| Online Access: | http://www.viks.sk/chk/star_3_4_04_118_121.doc |
| Abstract: | Conclusions. Acetylation of starch with vinyl acetate using sodium carbonate as catalyst in an aqueous medium has been investigated. Degree of acylation was between 1.0 and 1.1, whereas a DS of only 0.02 was achieved for vinyl laurate (dodecanoate) under otherwise identical conditions. A reaction time of 5 h is sufficient for acetylation while 48 h were required to achieve DS 0.02 for the laurate. As vinyl esters are not miscible with water, the organic phase acts as a reservoir of the reagent. This prevents loss of vinyl esters by reaction with water so that equimolar amounts are consumed after recuperation of excess vinyl acetate. Summary. Acetylation of different types of starch with vinyl acetate in water in the presence of a base is described. Maximum degree of substitution under these conditions is 1.1. Vinyl esters of higher homologous acids (vinyl laurate) react very slowly giving very low degrees of substitution after long reaction times. The reaction mixture is biphasic, because vinyl esters are not miscible with water. Formation of two layers reduces loss of acylating agent due to reaction with water - which is a major problem encountered for esterification with acid anhydrides or chlorides - to less than 5%. Unlike acylation of starch in DMSO with vinyl esters, the acetates of starch obtained by the method reported do not show regioselective distribution of acetyl groups within the anhydro-glucose units. |
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| ISSN: | ISSN 0038-9056 |
