Starch acetals reactions

Low DS starch acetates ate manufactured by treatment of native starch with acetic acid or acetic anhydride, either alone or in pyridine or aqueous alkaline solution. Dimethyl sulfoxide may be used as a cosolvent with acetic anhydride to make low DS starch acetates ketene or vinyl acetate have also been employed. Commercially, acetic anhydride-aqueous alkaU is employed at pH 7—11 and room temperature to give a DS of 0.5. High DS starch acetates ate prepared by the methods previously detailed for low DS acetates, but with longer reaction time. 

Starch acetates [9045-28-7] are made by reaction of starch with acetic anhydride. Starch acetates are used in foods to provide paste clarity and viscosity stabiHty at low temperatures. A waxy maize starch acetate is most commonly used. Waxy maize starch acetates for food use are often cross-linked. Acetylated starches are also widely used in warp sizing of textiles. 

The preparation of the first starch acetate, as well as the first cellulose acetate, was announced by SchUtzenberger in 1865. These acetates were prepared by heating the carbohydrates in acetic anhydride to about 140-160 . Further examination of this reaction has been made by Traquair who found that on heating starch to 90° with acetic anhydride a derivative of low acetyl content (1-4%) is obtained which is capable of forming clear, somewhat elastic films. This starch acetate, termed Feculose, was produced commercially for a time, being sold for use as a thickening agent and as a size for textiles and paper. 

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... 

Acylated starch can be copolymerized to yield materials for films, lacquers, and fibers.2111 Starch acetate copolymerized with epichlorohydrin was extruded to give cold-water swelling products with a high degree of friability.2112 Epichlorohydrin-crosslinked starch has been acylated with 2,3-di-O-benzoyl-L-threaric anhydride.2113 The reaction proceeded either in /V,/V-dimethy 11 ormam ide or in toluene, and the non-crosslinked product has also been reported.2114... 

Halogen molecules can be added to double bonds in starch derivatives, as demonstrated487 by the addition of bromine to the 2,3-double bond of 2,3-dideoxy-2,3-didehydro-6-0-trityl-starch. The reaction proceeded in methanol in the presence of silver acetate 487... 

Starch Acetals. Acid Sensitivity and Preferred Site of Reaction, M. L. Wolfrom and S. S. Bhattachaijee, Die Starke, 21, 116-118 (1969). 

The reaction of polysaccharides ivith aldehydes to give cross-linked products has been known and exploited industrially for some time. Starch acetals may also be prepared by a method that does not give rise to cross-links and involves treatment of starch with a cyclic vinyl ether, 3,4-dihydro-2H-pyran, to give a tetrahydropyran-2-yl derivative (16). At low levels of substitution, the acetals are water-soluble, at... 

Methyl-, hydroxyethyl-, hydroxypropyl-, and carboxymethyl starches, starch acetates, succinates, alkenyl succinates (Fig. 2), adipates, and phosphates, are all well-known products. Furthermore, special derivatives have also been prepared, such as vinyl-, silyl-, ° or propargyl starches, as reactive intermediates for fiirther fime-tionalization. Unusual substitution patterns can also be established by highly selective deacetylation with alkyldiamines and subsequent introduction of such functional groups as sulfates. From die analytical point of view, the most important aspects are stability under alkaline (mediylation) and acidic or Lewis-acidic (depolymerization) conditions, reactivity (such as migration, rearrangement, further substitution or addition reactions, or any intramolecular reaction), and polarity (lipophilic/hydrophilic, ionic/nonionic, acidic/basic). These properties mainly determine the analytical... 

Reaction of tosyl starch and tosyl starch acetate viith iodine... 

Starch acetates are one of the more common derivatives of starch and are made from starches with a variety of different amylose to amylopectin ratios. The reaction differs from other substituted starches in that it is begun with a neutral water starch slimy (pH 7 to 8), which is then blended with acetic anhydride [Figure 14] (34), acetic acid (35), vinyl acetate (36), or a number of other acetyl donating reagents (37,38,39). 

Of the esters, starch phosphate is produced by reaction with phosphorus oxychloride, polyphosphates, or metaphosphates a cross-bonded product results. Total degree of substitution is determined by measuring the phosphorus content, and the mono- to disubstitution ratio can be calculated by potentio-metric titration. Allowance is made for the natural phosphorus content of the starch. Treatment of starch with acetic anhydride produces starch acetate, which has improved paste stability over native starch. The acetyl group is very labile, and hydrolyses readily under mild alkaline conditions. When a known amount of alkali is used, the excess can be titrated and the ester function measured. This is not specific, however, and a method based on an enzymatic measurement of the acetate has been developed in an ISO work group. The modified starch is hydrolyzed under acidic conditions, which releases acetic acid and permits filtration of the resulting solution. Acetic acid is then measured by a commercially available enzyme test kit. Both bound and free acetyl groups can be measured, and the method is applicable... 

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. 

Figure 5 gives the results obtained in the following reaction conditions starch 12g, butadiene ca 40g, catalyst Pd(OAc)2/TPPTS 1/3, aqueous NaOH (O.IM) 50ml/iPrOH 10ml, 3h. At 90°C, with 0.5 wt.% of Pd(OAc)2, the DS reached almost 0.6 while less than 0.3 was achieved with 0.12 wt% catalyst. At 50°C, the DS was lower but much less affected by the catalyst/starch ratio, thus the DS decreased from 0.15 to 0.08 as the amount of catalyst decreased from 0.5% to 0.05%. This is because at 90°C Pd/TPPTS complex is unstable and decomposes progressively into palladium metal whereas at 50°C the catalyst is stable enough. When the reaction was performed in the presence of 0.25% palladium acetate, 0.08 wt% residual palladium was detected by chemical analysis of modified starch after reaction at 50°C. In contrast, no palladium was detected in the modified polymer when the reaction was conducted in the presence of 0.05% palladium. An optimum DS of 0.06 suitable for application in latex preparation for decorative paints was obtained with 0.03% palladium at 50X. 

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