Starch xanthates reactions

It is remarkable that neither of these workers appears to have investigated aqueous preparative methods, despite the fact that Cross and Bevan and their colleagues, from 1892 onward, had been developing the Viscose process for cellulose, and had, in 1907, applied similar reaction-conditions to starch. The formation of a starch viscose imder aqueous conditions was confirmed later by Ost and coworkers, who found that the solution decreased in viscosity on storage ( ripened ), like cellulose Viscose, but with no accompanying separation of starch. Various industrial uses for starch xanthate have since been suggested for example, as a frothing... 

Starch xanthate can be methylated as well as acetylated.45 The first reaction is base-catalyzed and the second acid-catalyzed. Neither procedure decreases the DS of the modified xanthate. Cationization of starch xanthate occurs on reaction with the water-soluble poly(vinylbenzyltrimethylammonium) chloride.2157 Xanthates have been cyanoethylated to produce rubber mixes.2158 2159 Sulfonated products were made by reaction with sultones.2160... 

Starch thiols can have the SH group directly on the pyranose ring or in a side chain. There are several methods of synthesizing starch thiols of the first type. One of them is based on the pyrolysis of starch xanthates (32), but the reaction proceeds in two parallel routes one producing thionates (35) and the other producing thiols (37).2675,2677 Reduction of starch xanthates with NaBPU in alkali is another approach to thiols. Thiols prepared in this manner were subjected to graft polymerization with vinyl polymers. Nucleophilic substitution of the chlorine... 

The modification of cellulose with alkaline carbon disulfide to introduce xanthate groups has been extensively exploited in the industrial production of viscose. Early work on the preparation and properties of starch xanthate has been discussed. Xanthate derivatives of cellulose and starch have been discussed with respect to general xanthate chemistry, and the xanthation of cellulose in homogeneous medium is known to be a second-order reaction. Cellulose xanthate shows some potential as a matrix for enzyme insolubilization, " and stable derivatives of this xanthate may be prepared by transesterification. Thermal decomposition of cellulose allyl- and benzyl-xanthates gives 5,6-cellulosene. Some thiocarbonyl derivatives of polysaccharides have been prepared. "... 

Starch xanthate and alkyl diepoxides formed gels in concentrated (6—8%) solutions or in turbid suspensions in dilute (0.1—1.0%) solutions, the degree of gelling varying with the nature of the epoxide. When wood pulp was added to dispersions or suspensions of the gel, the paper produced therefrom possessed improved strength. These improvements were unrelated to the degree of xanthation, but depended on the reaction times and on the order in which the diepoxide and xanthate were added. 

Limitations in possibility of chemical modifications of starch result from steric hindrance of reaction sites, solubility, viscosity of reaction medium, and susceptibility to side reactions among them, depolymerization almost always accompanies intended modification. As a rule, polysaccharides are soluble, although frequently only sparingly, in water and dimethyl sulfoxide. Polysaccharides solubilize on xanthation, i.e., on reaction with CS2 in alkaline medium, to form syrups of xanthates. On acidification polysaccharides could be recovered. Such procedure was utilized for several decades for production of artificial silk from cellulose. 

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... 

Artificial silk (viscose rayon) is spun from a viscous medium that is produced by reacting cellulose with carbon disulfide in alkali. The unusual success of this reaction prompted scientists to analyze similar reactions with starch, and indeed, starch viscose can be obtained.2134,2135 The properties of xanthates (32), mainly the degree of substitution, depend on such reaction conditions as the proportions and concentrations of reagents, and the duration and temperature of the process. Xanthation of starch using 2-3 moles of sodium hydroxide in 5-20% aqueous solutions per mole of starch and 20-25 mL of carbon disulfide per 10 g of starch is complete within 24 h of shaking at room temperature. Further studies suggested a 3-molar NaOH solution as the most suitable.2136 The temperature is a critical parameter and... 

This includes reactions of the polymer groups with metallic sites on the particle surface that may result in the formation of stable or insoluble compounds through covalent, ionic or coordination bonding. Carboxyl flocculants such as polyacrylic acid and carboxyl-methyl cellulose can chemisorb on the surface of calcite and sphalerite which have calcium or zinc sites on them. Certain flocculants, such as cellulose and starch with xanthate and polyacrylamide with dithiocarbamate with high chemically active groups, have been found to exhibit selective reaction with sulfide minerals. Such complexing polymers have been investigated for their use in selective flocculation processes. 

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