Starch esters reactions

Starch esters have been obtained by reactions of starch and carboxylic or sulfonic acid imidazolides in aqueous NaOH or nonaqueous solutions, as described in reference [226]. The esterification of dextran with butyric or palmitic acid using CDI in DMSO or formamide is discussed in reference [174]. 

Much helpful information on starch esterification methods and on the probable properties of starch esters may be obtained by examining similar reactions and esters in the cellulose field. This is because both starch and cellulose consist of polymerized glucose units capable of esterification to the triester stage, and because the superior ability of the cellulose esters to form plastics, films, fibers, and lacquers has promoted an accumulation of information on cellulose esters which far exceeds the present knowledge of starch esters. 

Starches have been chemically modified to improve their solution and gelling characteristics for food applications. Common modifications involve the cross linking of the starch chains, formation of esters and ethers, and partial depolymerization. Chemical modifications that have been approved in the United States for food use, involve esterification with acetic anhydride, succinic anhydride, mixed acid anhydrides of acetic and adipic acids, and 1-octenylsuccinic anhydride to give low degrees of substitution (d.s.), such as 0.09 [31]. Phosphate starch esters have been prepared by reaction with phosphorus oxychloride, sodium trimetaphosphate, and sodium tripolyphosphate the maximum phosphate d.s. permitted in the US is 0.002. Starch ethers, approved for food use, have been prepared by reaction with propylene oxide to give hydroxypropyl derivatives [31]. 

In other reactions of starch esters, for example, 2,3-di-O-acetylamylose reacted with A-iodosuccinimide in the presence of triphenylphosphine to give 2,3-di-0-acetyl-6-deoxy-6-iodoamylose.2019 The ester bonds are fairly stable to acid-catalyzed hydrolysis. Starch esterified with acetylsalicylic acid administered to dogs did not increase the acetylsalicylic acid level to any significant extent in the animal s blood serum.2020 The slow release of herbicides from their esters with starch was analyzed.2021,2022 Alkaline hydrolysis of starch esters is easier than acid hydrolysis.2023 The enthalpy of starch acetate formation was 143.5kJ/mole, and acetylation decreased the susceptibility of the starch backbone to enzymatic hydrolysis and iodine uptake.2024 The hydrolysis of starch and starch acetate in alkaline solutions obeys second-order kinetics.1988... 

Chemical modifications may also include the derivatization of starch by reaction of its hydroxyl groups with alkylene oxides. Other suitable substances are such that form ether linkages, ester linkages, urethane linkages, carbamate linkages, or isocyanate linkages. The degree of substitution of the chemically modified starch varies from 0.05 to 0.2. 

Starch esters are synthesized by reaction of a carboxylic acid or an acyl chloride or an acid anhydride with the hydroxyl groups of amylose or amylopectin chains. As in the case of cellulose derivatives, there are organic and inorganic esters depending on the origin of the substituent. 

Properties of starch esters depend on the type of an esterifying agent applied, conditions of the reaction, and a DS. The esterified starches have found applications in the food industry, papermaking industry, in pharmacy, and have been used for the production of thickening agents and for permanent finishing of fabrics [57],... 

Starch esters represent an important class of starch derivates and have been recently reviewed by Tessler and Billmers [63]. Starch esters can be produced by an aqueous process, at low alkalinity, under controlled pH, and low temperature reactions usually reaching a fairly low degree of substitution (DS<0,2) [64]. Starch acetates with a DS of 2.4 or higher are not biodegradable, like cellulose, while intermediate DS acetate would be easily biodegradable [63,31,32]. Most commercially used starch derivates have a DS less than 0.2 [60]. Pure amylose starch is considered the most desirable precursor for starch-ester based thermoplastics since amylopectin has an adverse impact on mechanical and physical properties of these derivatives [64]. 

Starch can react with organic anhydride in water to yield starch esters, such as starch acetate that have been produced commercially by this process. Esters have also been prepared by aqueous reaction with vinyl esters, the byproduct acetaldehyde can be used to cross-link the starch by lowering the pH once esterification has been completed. 

Mixed carbonic anhydrides, acyl guanidine, N-acylimidazoles, N-acyl-N -methylimidazolium chloride and acyl phosphates are other agents that have been used to esterify starch in water [65-76]. Starch esters containing carboxylic acid group have been prepared by reaction with cyclic dibasic anhydrides [65]. 

Xie WL, Wang YB (2011) Synthesis of high fatty acid starch esters with l-butyl-3-methylimidazolium chloride as a reaction medium. Starch-Starke 63 (4) 190-197. doi 10.1002/star.201000126... 

If water is eliminated from the reaction mixture, the equilibrium tends to the right side, and almost all acid or alcohol is transferred to the ester. In context with RR, the following esters should be mentioned - Cellulose esters, - starch esters, - sucrose fatty acid esters, - soibitan esters of fatty acids, - sulfosuccinates, - fatty acid esters, - waxes, fats and oils and all other glycerides, alkyd resins, esters of inorganic acids with fatty alcohols, e.g., fatty alcohol sulfates, fatty alcohol ether sulfates, fatty alcohol phosphates, phtalates, azelates and sebacates (aplastic additives), as well as the esters of - citric acid, - tartaric acid and - lactic acid. 

Granular starch is contacted with solutions or suspensions of reactants, inhibitors or catalysts by soaking or spraying. After predrying, the reaction is carried out at elevated temperatures to yield - dextrins, - starch esters - cationic starches. Successful attempts have been made to react semi-dry systems yielding - extrusion cooked starches. Sometimes, excess reactants or by-products must be removed by subsequent extraction. 

Starches can be esterified by modifications with an acid. An ester is the result of reacting an alcohol with an acid. The starch loses a hydroxyl group, and the acid loses a hydrogen. These combine to form water as the other product of the reaction. 

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