Esterification starch acetylation

Esterification Starch acetate - Esterification with acetic anhydride or vinyl acetate Acetylated distarch adipate - Esterification with acetic anhydride and adipic anhydride Starch sodium octenylsuccinate - Esterification by octenylsuccinic anhydride... 

Sulfuric acid is a powerful esterification catalyst. It has been widely applied with mixtures of acetic acid and acetic anhydride to promote acetylations of numerous substances. Use of this catalyzed reaction for starch acetylation, however, has not risen to pre-eminence among starch acetylation methods as it has done among cellulose acetylations, although both reactions were discovered at the same time. The underdevelopment of this reaction in the starch field may be due to the following causes (1) sulfuric acid, a powerful acetylation catalyst, strongly catalyzes the hydrolysis of starch molecules and cannot be used for starch acetylations in the concentrations found most effective for cellulose reactions (2) most investigations of this reaction have been made on whole granules... 

Starch has been acetylated by Barnett s mixture, W hich is composed of acetic acid, acetic anhydride, and a catalyst consisting of equal parts of sulfur dioxide and chlorine. This mixture, originally developed for cellulose esterification," readily acetylates starch at 55 , the acetyl content reaching the theoretical value of 44.8% in about four hours. A critical evaluation of the reaction by Hassid and Dore, and particularly by Higginbotham and Richardson, has shown that the acetates prepared have the viscosity, reducing power, and solubility characteristics indicative of a partially degraded starch. 

The most common reaction of esterification is starch acetylation. The oldest methods of starch acetylation consisted mainly in heating starch with acetic acid anhydride in pyridine or ice-cold acetic add. This method of acetylation was applied by, among others, Twele [22, 61, 73]. Contemporarily, starch acetates are usually produced as a result of reaction run in a water suspension by exposing starch to acetic acid anhydride. All of the hydroxyl groups could react with acetic anhydride. One of the three possible products is shown in Figure 7.1. 

Synonyms Starch acetate, oxidized Starch, acetylated, oxidized Definition Starch treated with sodium hypochlorite followed by esterification with acetic anhydride... 

Starch is an abundant, inexpensive polysaccharide that is readily available from staple crops such as com or maize and is thus is mostly important as food. Industrially, starch is also widely used in papermaking, the production of adhesives or as additives in plastics. For a number of these applications, it is desirable to chemically modify the starch to increase its hydrophobicity. Starch modification can thus prevent retrodegradation improve gel texture, clarity and sheen improve film formation and stabilize emulsions [108], This may, for example, be achieved by partial acetylation, alkyl siliconation or esterification however, these methods typically require environmentally unfriendly stoichiometric reagents and produce waste. Catalytic modification, such as the palladium-catalyzed telomerization (Scheme 18), of starch may provide a green atom-efficient way for creating chemically modified starches. The physicochemical properties of thus modified starches are discussed by Bouquillon et al. [22]. 

Catalysis, enzyme-substrate and intermediate compound theory in homo-and heterogeneous, V, 51 Catalysts, for acetonation, III, 51 for acetylation of starch, I, 284, 286 Bourguel s, II, 109, 110, 113 for esterification of cellulose, I, 312 in oxidation of carbohydrates by halogens, III, 177... 

Esterification of starch dialdehyde with chlorosulfonic acid in formamide gave a sulfate ester that could be transformed into an amide and methyl ester.532-536 The classical method of sulfonation, namely, by the action of sulfur trioxide in pyridine, is also applicable.537,538 Hemiacetals of starch dialdehyde result upon treatment with suitable alcohols in the presence of an acidic catalyst. In acetic media amides condensed with the carbonyl groups. Acetylation of starch dialdehyde with acetic anhydride is an obvious reaction. Esters with hexanedioic (adipic) acid were also prepared.537 Starch dialdehyde undergoes etherification with monochloroacetic acid in an alkaline medium.538... 

It is well known that the nucleophilic displacement reactions at tosylated polysaccharides are limited or at least mainly directed towards the primary positions . Therefore, our interest was focused on 6-0-tosyl starch samples with DStos 1- One suitable synthesis path is the protection of 0-2 and the subsequent tosylation. A useful protecting group may be the acetyl ester function. It was recently found that in contrast to conventional esterification processes of starch with acetic anhydride, which leads to a statistic distribution of the ester groups, an acetylation of starch dissolved in DMSO with acetic acid vinyl ester in the presence of sodium chloride yields 2-0-acetyl starch of varying DSac from 0.1 to 1.0. The functionalisation patterns of these new starch products were unambiguously proved by means of various NMR measurements including two dimensional methods . 

By trans-esterification, the degree of acetylation can be easily controlled allowing polymers to form with a wide range of hydrophobicity. Starch acetate can be prepared by the acetylation of starch with pyridine acetic anhydride mixtures and cast into films from 90% solutions of formic acid. The wet strength of the film is maintained in the aqueous solution with sufficient acetyl content when exposed to buffered amylase solution. But the acetyl content permits degradation by a mixture of a- and /5-amylase in 1 h. These films can be useful as membranes for bioreactors, which are degraded by enzyme addition. 

To compensate for the inconvenience of plastics made with pure starch, it can be chemically treated to improve its resistance to humidity. One treatment consists of the acetylation or of the esterification of the free hydroxide groups present in the chain by an anhydrous propionic acid. Another possibility is to add to the formulation of the polymer hydrophobic substances such as natural wax or biodegradable plastics which are not sensitive to humidity, however, all these treatments increase the production costs. Novon (Novon International, USA) was originally developed by Warner Lambert for the fabrication of pharmaceutical capsules, includes up to 80-90% of starch. Some grades are edible others have been developed for thermoforming, sheet and film extrusion or for injection moulding applications. 

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