Metal starchates

Other starch varieties chemically bind metal atoms only to the hydroxyl groups, in the same manner as alcoholates. Alkali metal starchates were obtained for the first time by the use of either metal amides in liquid ammonia641 or metals in liquid amines.642 These methods were subsequently used by others.643 Sodium 2-starchate could be prepared by refluxing an alcohol solution of NaOH and dry starch.644 The reaction of dry starch with controlled amount of NaOH in 1-butanol provided either monosodium 2-starchate or disodium 2,3-starchate.645,646 However, complexes of NaOH with starch were also characterized.37,38 Thallation of starch could be performed with thallous hydroxide.647 

If metal halides are sufficiently reactive (this is, readily hydrolyzable), the preparation of relevant metal starchates may be simpler. Aluminum starchate was produced by vigorous stirring of dry anhydrous aluminum chloride and starch654 but the reaction with A1C13 as well as ASCI3 in a benzene suspension was also reported.655 

It was reported that metallation of starch did not change its thermal properties to any significant extent.647,651 655 but also there is report that an increases in thermal resistance of starch can be afforded by derivatizing such starches with metal atoms.666 In every case the reaction products were less susceptible to hydrolysis as compared with unreacted metal salts. 

A separate group of metal starchates comprises metal salts of starches carrying carboxyl, xanthate, sulfate, phosphate, and similar groups. Oxidized, carboxyalkylated, sulfated, xanthated, and phosphorylated starches readily form corresponding salts by methatetical reactions between the sodium salts of the aforementioned derivatives and other water-soluble, metal salts. There are several patents on the formation of these salts for ion exchangers and the removal of 

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The limited solubility of starch and its modified products may affect the reversibility of many reactions. This may explain several, apparently unusual, reactions reported in starch chemistry. There are, for example, reports of starch esterification with sodium hydrogenphosphates, acylation of starch with acyl amides (which is equivalent to the transformation of an amide into an ester), and the formation of alkali-metal starchates upon treatment of starch with alkali (a reaction which fails for simple alcohols). A specific property of starch is its ability to form surface sorption and helical inclusion-complexes with many inorganic and organic guest molecules.4... 

Low density expl contg starchate of alkali metal or ammonia in which the metal is attached through an O atom to a C in the 2 position in the starch mol. Thiochloro, thioammonium or nitro-starches may also be used. E.g NH4 starchate, thiochloro, thioammonium 75 ... 

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