Xanthates polysaccharides

A general lack of effectiveness has been noted for several MCAs in the suppression of GI-uptake of cadmium in mice. In this study the MCAs, the metal-binding capacity was 2-6.8 mM g 1, ranged from DTPA immobilized via amide bond formation to finely divided aminopropyl-silica, xanthates of polyvinylalcohol and various polysaccharides, and a dextran bearing ethylthiol moieties produced by action of ethylenesulphide on dextran209. ... 

In the third paper of the series, concerned with the formation of -(copper thiolthiocarbonyl) derivatives of polysaccharides, Lieser and Hackl reviewed the few earlier studies on polysaccharides other than cellulose. They claimed that the starch xanthates obtained by Cross, Sevan, and Briggs and by Ost and his colleagues had been given incorrect formulas,... 

The kinetics of the xanthation of sucrose were studied in the same year by Cherkasskaya, Pakshver, and Kargin, who determined potentiometric-ally the concentrations of the dithiocarbonate derivative and also of inorganic sulfide and trithiocarbonate. The rate of formation of 0-(sodium thiol-thiocarbonyl)sucrose was found to pass through a maximum with increasing alkali concentration, presumably due to a shift of the equilibrium in favor of side reactions in strongly alkaline solution. This result appears to parallel the qualitative findings of Lieser and Hackl for polysaccharides. 

Cellulose is the most abundant naturally oeeurring polysaccharide formed out of glucose-based repeat imits, connected by 1,4-beta-glucosidic linkages. Cellulose and its derivatives are widely used as tough versatile materials. Cellulose nitrate, cellulose acetate (CA) and cellulose xanthate (rayon) can be easily molded or drawn into fibers for textile applications, for designing composite materials (safety glass), as thermoplastics etc [80]. 

The latter method has the advantage of recycling the natural or waste product. Significant examples are cotton modified with amines [3, 4], starch utilized in xanthate form [5, 6, 7], thiol type keratine gel prepared from the wool [8, 9,10], wool simply reduced [11] or modified with amine groups [12, 13, 14] and finally polysaccharides such as cellulose [15, 16, 17], glucose [18] or polyosides [19] modified with thiol or amine groups. 

Starch xanthate. A water-insoluble synthetic polysaccharide made by reacting starch with sodium hydroxide and carbon disulfide biodegradable. 

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. 

The importance of polysaccharide derivatives to industry and society is frequently overlooked by, or even unknown to, many chemists. However, those who have an interest in the subject will know of the great economic investment involved in the industrial production of polysaccharide derivatives for inclusion in a wide variety of commodities, such as explosives, synthetic fibers and fabrics, foodstuffs, paints, and plastics. Indeed, several polysaccharide derivatives have been known and commercially exploited for a long time (for example, cellulose xanthate for rayon, and cellulose nitrate for explosives), and, just a few years ago, it might have been claimed that the use of polysaccharide derivatives had reached a peak. 

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. "... 

Polysaccharides react with carbon disulfide and sodium hydroxide to give dithiocarbonic acid esters known as xanthates ... 

The xanthate group appears to become preferentially attached to C-2 of D-glucose units in cellulose. Diazomethane replaces the xanthate groups with methyl groups so that subsequent hydrolysis yields 2-0-methyl-D-glucose (140). A high degree of xanthation is obtained when the polysaccharide is dispersed and esterified with carbon disulfide in tetraalkylam-monium hydroxide (I40). 

Polysaccharide xanthates, the product of a weak acid and strong base, decompose spontaneously owing to the formation of free polysaccharide xanthic acid. The decomposition is greatly accelerated by the addition of mineral acid. 

Polysaccharides can be oxidized even by such a mild oxidant as atmospheric oxygen. The rate of oxidation is greatly enhanced by alkalies and by various heavy metal ions. Mild oxidations are beneficial when properly employed for producing new and useful properties in polysaccharides. As an example, starch is mildly oxidized by small amounts of bleaching powder to produce improved textile sizes. Atmospheric oxidation of alkali-treated cellulose reduces the chain length of commercial cellulose to the point where its xanthate can be dissolved in a strong alkaline solution and can be used... 

The influence of intrinsic and extrinsic Cotton effects on the o.r.d. and c.d. spectra of acetate and xanthate derivatives of polysaccharides has been studied. "... 

An example is the preparation of a starch xanthate sludge polymer with herbicides, such as thiocarbamates. The starch xanthate was formed by using oxidatively crosslinked aqueous starch xanthate in the presence of active agents to produce a granular matrix that entraps the agent. The sludge is formed by a heterogeneous mix of polysaccharides, crosslinked... 

Meadows, G.W., Process for Conditioning Soil with Polysaccharide Xanthates. U.S. Pat. 2761247. 

Polysaccharides react with carbon disulfide and sodium hydroxide to give dithiocarbonic acid esters called xanthates. The polysaccharide, such as cellulose, is first treated with 18% sodium hydroxide to give alkaline cellulose (reaction 7.4). The alkaline cellulose is usually aged several hours to achieve lower d.p. values. It is then reacted with carbon disulfide for 1-3 hr at 20-30°C (reaction 7.4). 

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