Xanthates, hydrolysis

In practice, a degree of substitution of 0.5-0.6 xanthate groups per glucose unit is sufficient to yield a soluble xanthate. Hydrolysis of carbon disulfide by alkali is an unavoidable side reaction which consumes 20-30 per cent of the carbon disulfide charged. 

Next, alcohol 35 was transformed into 36 by reductive dehydroxylation via the nonisolated intermediate xanthate. Hydrolysis of the ester group in 35 to form 30 was followed by decarboxylation to generate 37 by using an improved Barton s method employed with HOTT (5-(l-oxido-2-pyr-idinyl) 1,1,3,3-tetramethylthiouronium hexafluorophos-phate) [35]. Treatment of 37 with TBAF furnished alcohol, which was converted into the proposed structure of paesslerin A by using scandium-catalyzed acetylation. Unfortunately, comparisons of the H- and C-NMR data of the synthetic compound with those reported for the natural product revealed that the substances are not identical. The 2D-NMR data for synthetic 29 are fiiUy consistent with the structure of the target. The result clearly demonstrates that a revision of the structure of natural paesslerin A is required (Scheme 4.17). 

The initial hydrolysis of the xanthate in aqueous solutions at room temperature is characterized by the following reaction involving potassium ethyl xanthate ... 

Further hydrolysis of the carbon disulfide and the trithiocarbonate produces hydrogen sulfide, etc (33). In another study of the decomposition of sodium ethyl xanthate [140-90-9] in flotation solutions, eleven components of breakdown were studied. The dependence of concentration of those components vs time was examined by solving a set of differential equations (34). 

The resultant yellow sodium cellulose xanthate is dispersed in an aqueous caustic soda solution, where some hydrolysis occurs. This process is referred to as ripening and the solution as viscose . When the hydrolysis has proceeded sufficiently the solution it transferred to a hopper from which it emerges through a small slit on to a roller immersed in a tank of 10-15% sulphuric acid and 10-20% sodium sulphate at 35-40°C. The viscose is coagulated and by completion of the hydrolysis the cellulose is regenerated. The foil is subsequently washed, bleached, plasticised with ethylene glycol or glycerol and then dried. 

The described method of preparation of w-nitrophenyl disulfide is essentially that of Foss and co-workers and is a modification of that reported by Ekbom. The disulfide has been prepared by reaction of potassium ethyl xanthate with w-nitrobenzenedi-azonium chloride solution, followed by hydrolysis to yield the mercaptan, which is subsequently oxidized with potassium ferro-cyanide or dilute nitric acid to the disulfide. ... 

The products of hydrolysis and dissociation depend on the pH. In an acid medium, hydrogen sulfide, which has no depressing action, evolves. It is, therefore, necessary to use alkaline circuits in which HS, predominates. These sulfide ions are adsorbed on the copper sulfide mineral surface and react with the surface previously coated with cuprous xanthate. The reaction causes desorption of the collector, and as a result of this desorption the copper sulfide minerals generally become hydrophilic. There is, however, no action of the sulfide ions on molybdenite, and so molybdenite retains its hydrophobic character. 

Chemically dextrans are similar to one another. The activation energy for acid hydrolysis is about 30-35 Kcal/mol (5j. The C-2 hydroxyls appear to be the most reactive in most Lewis base and acid-type reactions. A wide variety of esters and ethers have been described as well as carbonates and xanthates ( 7,8j. In alkaline solution, dextran forms a varying complex with a number of metal ions (9). 

It is synthesized by reaction of the diazonium salt from amine 1 with potassium ethyl xanthate, followed by alkaline hydrolysis to afford thiophenol 2. 

Because of the strong hydrolysis property of antimony salt, it is very difficult to prepare antimony xanthate salt to obtain its IR spectrums. Therefore, the formation of antimony xanthate is difficult to be identified by the UV and FTIR analysis, which has been determined by using XPS. Finally, it can be concluded that the interaction mechanism between ethyl xanthate and jamesonite are attributed to the formation of lead and antimony xanthate on the surface in the light of flotation results, voltammogram measurement, UV and FTIR as well as XPS analyses. 

The important fiber rayon is simply regenerated cellulose from wood pulp that is in a form more easily spun into fibers. Cellophane film is regenerated cellulose made into film. One method of regeneration is formation of xanthate groups from selected hydroxy groups of cellulose, followed by hydrolysis back to hydroxy groups. 

In general, the complexes are prepared by mixing aqueous or alcoholic solutions of the sodium, ammonium or potassium salt of the ligand and CrCl3-6H20, sometimes with Zn dust present.997,998 However, in some cases anhydrous conditions are necessary to prevent the formation of polymeric hydrolysis products,986 and dithiophosphate is much more resistant to temperature and extremes of pH than dithiocarbamate or xanthate. In the preparation of L3, where L is 4-aminophenazonedithiocarbamate, aqueous Cr(N03)3 was added to the reaction mixture from the preparation of the ligand.999... 

Reaction CLV. Action of Potassium Xanthate on Diazonium Compounds with Subsequent Hydrolysis and Oxidation. (E.P., 11865,1892). 

The Leuckart Thiophenol Reaction allows the preparation of thiophenols and corresponding thioethers from anilines or their corresponding diazonium salts. The first step is the reaction of an aryl diazonium salt with a potassium alkyl xanthate to give an aryl xanthate, which affords an aryl mercaptan upon basic hydrolysis or an aryl thioether upon warming. 

Eq. 3.7 shows the cyclization of the xanthate ester (20) formed from homopropargyl alcohol, through 5-exo-dig manner of the formed carbon-centered radical. This reaction is not a deoxygenation reaction of alcohol, but the cyclization of the carbon-centered radical formed from the addition of Bu3Sn to the thiocarbonyl-sulfur atom, onto the side-chained triple bond to form thionolactone, the hydrolysis of which readily creates lactone (21) [21-23]. 

The only practical laboratory procedure for preparing m-thiocresol is by the alkaline hydrolysis of m-tolyl ethyl xanthate, obtained from m-toluenediazonium chloride and potassium ethyl xanthate.3-8 The procedure described is essentially that of Bourgeois.8... 

Cellulose is a linear polymer of anhydroglucopyranose units linked by / -l-4-glucosidic bonds. The number of the units per molecule, the degree of polymerization, can range from 400 in a cellulose xanthate which is to be spun into rayon to 10,000 in a cotton. The glucosidic bond is stable under neutral and alkaline conditions but is hydrolyzed in acid. The rate of hydrolysis increases in proportion to the hydrogen ion concentration. 

In this book, he emphasized the importance of the microscopic and the submicroscopic structure of fibrous high polymers. The reactions of cellulose with water, aqueous alkalis, organic bases, ammonia, and strong salt solutions were all stressed. Special attention was given to various types of cellulose esters, to cellulose xanthate, and to the cellulose ethers. The oxidation of cellulose under a variety of conditions was described, as were the hydrolysis reactions. The latter included discussions on reversion and on the kinetics of acid hydrolysis. It is interesting to note that Heuser, who earlier had criticized the terms hydrocellulose and oxycellulose, and had... 

In their comparative studies, Rogovin and coworkers confirmed the sensitivity of 0-(methoxycarbonyl)celluloses toward aqueous alkali, noted earlier by Heuser and Schneider, but found an 0-[(methylthio)thiocar-bonyl] derivative to possess enhanced stability, similar to that of cellulose acetate. Thus, whereas the action of N sodium hydroxide at 25° causes almost complete de-esterification of O-(methoxycarbonyl) cellulose in 5 minutes, the methyl xanthate suffers only 20 % hydrolysis during 1 hour. No quantitative data of this nature are available for the corresponding mono-thiocarbonate. The product from its iodine oxidation was far more stable than that (see p. 147) derived from cellulose xanthate. The 0-[(methyl-thio)thiocarbonyl] derivative of methyl a-D-glucopyranoside was seemingly more alkali-sensitive than the cellulose analog described above, possibly on account of its higher solubility. 

One of the major factors contributing to reported variations in xanthation is probably the stability of xanthate groups [170-172]. The primary xanthate at C6 was generally shown to be more stable than those at C2 and C3 positions and the latter groups could be hydrolyzed 15-20 times faster under certain conditions. Thus the extent of hydrolysis and the redistribution of xanthate groups varied with the duration of xanthate solution (viscose) in storage (ripening). 

As the product 39 still contains the xanthate group, alternative radical transformations can be performed, which also include its removal with tris(trimethylsilyl)silane. Further manipulations of the dithiane ring comprise desulfurization or hydrolysis, thus confirming the use of such xanthates as the synthetic equivalent of a methyl and formyl radical. Two examples of the use of this chemistry for the extension of alkene-containing sugars were successfully examined, as illustrated in Scheme 27. 

The thiol (SH) group is introduced by reaction with potassium ethyl xanthate followed by acid hydrolysis. The phenylsulfanyl (phenylthio, SPh) group results from reaction with benzenethiolate ion. Sodium disulfide, Na2S2, yields diaryl disulfides. The arsonic acid group is introduced using Bart s reaction, in which a diazonium salt is reacted with sodium arsenite in the presence of a Cu(II) salt (Scheme 8.23). 

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