Etherification of starch

Etherification of starch dialdehyde is possible. The reaction of starch dialdehyde with propylene oxide and other etherification reactions were described.530 Esterification of starch dialdehyde with carboxylic anhydrides stabilizes the viscosity and adhesiveness of starch dialdehyde.531 This adhesive is additionally blended with urea. 

Extended studies on starch etherification with C2 to C5 aliphatic alkylene oxides in alkaline slurries have been performed 944,945 This reaction was subsequently re-examined for hydroxypropylation.946 No significant effects were observed as a result of using added hydrogen peroxide, benzoyl peroxide, azodiisobutyronitrile, or K2S2O8.945 In all instances, including those studied without such additives, led to water- and alcohol-soluble thermoplastic materials. Further improvements involved etherification in either acetone or butanone in the presence of aqueous NaOH. Ethylene oxide was introduced incrementally.947 Etherification of starch... 

Etherification of starch is a relatively inexpensive method of derivatization. Hydroxyalkylstaiehes are the most eommonly produced starch ethers, accounting for over 200 million pounds of production per year (19). Hydroxyalkylstarches are stable and maintain their structure during additional derivatizations and modifications such as... 

Etherification Improved clarity of starch paste. Used in wide range of food... 

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... 

The reaction of starch with propylene oxide in alkali forms 0-(2-hydroxypropyl)starch.892,930-938 A granular derivative can be prepared by impregnating starch with acetic acid prior to its alkali treatment with and reaction propylene oxide.939 Etherification at 0-3 and 0-2 occurs at approximately the same rate, and the reaction at 0-6 is slightly less favorable.933 However, etherification at 0-2 has priority.940... 

Studies performed on the etherification of potato amylose and amylopectin with (diethylamino)ethyl chloride showed that amylose in the starch granule was more reactive than amylopectin.2429 However, the relative reactivity of both starch components could be changed by physical pretreatment of the granules, for instance, by milling, heat-moisture treatment, freeze-thawing, and chemisorption. The physicochemical properties of amino starches depend on the starch variety reacted 2430 Among potato, sweet potato, rice, wheat, and tapioca starch studied, the last reacted most readily. 

Reaction conditions necessary to carry out the modifications described earlier in this section usually result in some decomposition of amylose and amylopectin, even when simple substitution, addition, or crosslinking are involved. As a rule, graft copolymerization produces derivatives of significantly increased molecular weight. Starch grafting usually entails etherification, acetalation, or esterification of starch with vinyl monomers to introduce a reaction site for the further formation of a copolymeric chain. Such a chain would typically consist of either identical or different vinyl monomers (block polymers), or it may be grafted onto another polymer altogether. 

The technology of polymeric carbohydrates is strongly oriented to the most abundant examples, namely starch and cellulose. Tomasik (Cracow) and Schilling (University Center, Michigan), in their wide-ranging article on chemical derivatization of starch, present an extensive compilation of the literature on potentially useful products formed by esterification, etherification, oxidation, and other reactions with starch. Much of the literature cited comes from patent sources, not subject to the conventional refereeing procedures in effect for journal articles, and so the reader needs to judge appropriately the validity of some of the claims made for product structure and practical application. 

Modification of starch molecules is carried out by the addition of various chemical radicals through oxidation, etherification, esterification, and introduction of anionic or cationic groups, generally at 2 and 6 sites. Major chemical reactions involved in the preparation of modified starches are given below. 

Previous articles in this Series dealt with etherifications of cellulose, and an atlas on infrared analysis includes spectral data for various cellulose ethers. The preparation and industrial importance of starch ethers have been reviewed. The degree of substitution of cellulose ethers may be determined by differential thermal analysis. Where an endothermic or exothermic peak that is characteristic of the cellulose derivative occurs in the analysis curve, the peak height and area have been shown to correlate with the degree of substitution. 

In order to adjust the properties of these starch-based materials to the desired application, it is necessary to combine starch with other polymers, as frequently done in the plastic industry. The need for tuneable properties may also require starch modifications, such as esterification or etherification, grafting and reactive or melting extrusion of thermoplastic starch (TPS). The main forms of starch utilization as a polymer are (i) starch grafted with vinyl monomers, (ii) starch as a filler of other polymers and (iii) plasticized starch (PLS), commonly known as TPS. 

Etherification and esterification of hydroxyl groups produce derivatives, some of which are produced commercially. Derivatives may also be obtained by graft polymerization wherein free radicals, initiated on the starch backbone by ceric ion or irradiation, react with monomers such as vinyl or acrylyl derivatives. A number of such copolymers have been prepared and evaluated in extmsion processing (49). A starch—acrylonitrile graft copolymer has been patented (50) which rapidly absorbs many hundred times its weight in water and has potential appHcations in disposable diapers and medical suppHes. 

Etherification. Carbohydrates are involved in ether formation, both intramoleculady and intermoleculady (1,13). The cycHc ether, 1,4-sorbitan, an 1,4-anhydroalditol, has already been mentioned. 3,6-Anhydro-a-D-galactopyranosyl units are principal monomer units of the carrageenans. Methyl, ethyl, carboxymethyl, hydroxyethyl, and hydroxypropyl ethers of cellulose (qv) are all commercial materials. The principal starch ethers are the hydroxyethyl and hydroxypropylethers (see Cellulose ethers Starch). 

Etherification. A mixture of ethylene chlorohydrin ia 30% aqueous NaOH may be added to phenol at 100—110°C to give 2-phenoxyethanol [122-99-6] ia 98% yield (39). A cationic starch ether is made by reaction of a chlorohydfin-quaternary ammonium compound such as... 

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