Preparation of starch esters

Abstract

Aqueous slurries or dispersions of starch are reacted with imadazolides of carboxylic or sulfonic acids to yield starch ester derivatives. These starch products can also be prepared in non-aqueous solvents or by a dry reaction process.

I claim: 
     
       1. A process for preparing esters of a starch having free reactive hydroxyl groups comprising the steps of: a. reacting said starch with an .[.imidazolide-acid reaction product.]. .Iadd.imidazolide of carboxylic or sulfonic acid .Iaddend.selected from the .[.group.]. .Iadd.groups .Iaddend.consisting of ##EQU3## and triimidazolides of tricarboxylic acids, wherein R 1  is selected from the group consisting of alkyl, substituted alkyl, unsaturated alkyl, cycloalkyl, aryl, substituted aryl and arylalkyl, R 2  is selected from the group consisting of alkylene, substituted alkylene, bis-alkylene ether, cycloalkylene, arylene and substituted arylene; and R 1  and R 2  each contain from one to 20 carbon atoms; the amount of said imidazolide reagent reacted with said starch being from 0.05 to 100 percent, based on the weight of the dry starch; and     b. isolating the resultant starch derivative.   
     
     
       2. A process according to claim 1 wherein said starch is reacted with said imidazolide in an aqueous medium at a pH of from about 4.0 to about 12.5 and at a temperature of about 35° to 125° F. for a period of from 1 to 24 hours. 
     
     
       3. A process according to claim 1 wherein the reaction is carried out in a non-aqueous liquid medium at a temperature of about 35° to 125° F. for a period of from 1 to 24 hours. 
     
     
       4. A process according to claim 1 wherein the reaction is carried out employing a substantially dry reaction medium at a temperature of about 80° to 160° F. for a period of from 0.5 to 6 hours. 
     
     
       5. A process according to claim 1 wherein said starch is corn starch. 
     
     
       6. A process according to claim 1 wherein said starch is waxy maize. 
     
     
       7. A process according to claim 1 wherein the starch is reacted with 1,1'-carbonyldiimidazole. 
     
     
       8. A process according to claim 1 wherein the starch is reacted with the diimidazolide of succinic acid. 
     
     
       9. A process according to claim 1 wherein the starch is reacted with a diimidazolide of adipic acid.