Disulfide hydrolysis

The finished xanthate, colored a strong red-orange by the trithiocarbonate by-product, is dissolved in dilute caustic to.form viscose (ts ically, 6-9 per cent cellulose and 5-8 per cent sodium hydroxide plus by-products of carbon disulfide hydrolysis, of viscosity 30-50 poises at 20°C). Viscose, in turn, yields regenerated cellulose fibers or film when extruded into an acid coagulating and regenerating bath. The instability of the xanthate halfester under acid conditions makes rapid regeneration possible. 

In contrast to the speciation work there have only been a modest number of reports on kinetic and mechanistic details. The formation of Zn" complexes of GSH proceeds by two pH-dependent mechanisms involving coordination at the thiol group, although no thiol involvement is apparent in Ni" complex formation. Different behaviom is found again with MeHg", which binds to GSH by an associative pathway. The Cu"-GSH system is further complicated by the observation that the disulfide hydrolysis in alkaline solution is accelerated by Cu" ions (equations 3-5). 

Alternative means for removal of carbonyl sulfide for gas streams iavolve hydrogenation. For example, the Beavon process for removal of sulfur compounds remaining ia Claus unit tail gases iavolves hydrolysis and hydrogenation over cobalt molybdate catalyst resulting ia the conversion of carbonyl sulfide, carbon disulfide, and other sulfur compounds to hydrogen sulfide (25). 

Commercial-scale processes have been developed for the production of hydrogen sulfide from heavy fuel oils and sulfur as well as from methane, water vapor, and sulfur. The latter process can be carried out in two steps reaction of methane with sulfur to form carbon disulfide and hydrogen sulfide followed by hydrolysis of carbon disulfide (116). 

Many other routes to produce thioglycohc acid have been iavestigated (9). To try to minimise by-products, nucleophilic agents other than alkah sulfhydrates have been claimed, eg, thiosulfates, sodium disulfides, thiourea, xanthogenic acid derivatives, and sodium trithiocarbonates (10). These alternative methods, which require reduction of the disulfides or hydrolysis of carboxymethylthio derivatives, seem less competitive than those usiag alkah sulfhydrates. 

Cysteine [52-90 ] is a thiol-bearing amino acid which is readily isolated from the hydrolysis of protein. There ate only small amounts of cysteine and its disulfide, cystine, in living tissue (7). Glutathione [70-18-8] contains a mercaptomethyl group, HSCH2, and is a commonly found tripeptide in plants and animals. Coenzyme A [85-61-0] is another naturally occurring thiol that plays a central role in the synthesis and degradation of fatty acids. 

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). 

Carbon disulfide is essentially unreactive with water at room temperature, but above about 150°C in the vapor phase some reaction occurs forming carbonyl sulfide (carbon oxysulfide) [463-58-1] and hydrogen sulfide [7783-06-4]. Carbonyl sulfide is an intermediate in the hydrolysis reaction ... 

PhSH, >50° or HSCH2CO2H, 45°, 15 h, quant. The 5-ethyl disulfide is stable to acid-catalyzed hydrolysis (CF3CO2H) of carbamates and to am-monolysis (25% NH3/CH3OH).-... 

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. ... 

In these papers, the carboxylic acid to be protected was a stable, unsubstituted compound. Harsh conditions were acceptable for both formation and cleavage of the amide. Typically, a simple secondary amide is very difficult to cleave. As the pKa of the conjugate acid of an amide decreases, the rate of hydrolysis of amides derived from these amines increases. The dimethylamide of a cephalosporin was prepared as follows using 2,2 -dipyridyl disulfide. ... 

Thiophenols may also be synthesized via the photochemical decomposition route 156). Thus, treatment of arylthallium ditrifluoroacetates with an aqueous solution of potassium Ar,AT-dimethyldithiocarbamate led in quantitative yields to the formation of the corresponding aryl AT,A -dimethyl-dithiocarbamates. Subsequent photolysis in aqueous acetone then led to disulfides which were reduced to the thiophenols. A small amount of aryldithiocarbamate formed as a by-product in the photolysis was converted to the same thiophenol by hydrolysis. The overall reaction sequence is illustrated in Eq. (18). 

The most suitable routine analytical method for the determination of alkylenebis-(dithiocarbamate) residues in fruits and vegetables is hot acid hydrolysis with stannnous chloride and concentrated hydrochloric acid, followed by determination of the evolved carbon disulfide by spectrophotometry or GC. 

Disruption of the native structure of a protein can also contribute to chemical instability by accelerating the rates of a variety of degradation routes, including deamidation, hydrolysis, oxidation, disulfide exchange, /1-elimination, and racemization. 

The genus Thiobacillus, especially the species T. denitrificans catalyzed the oxidation reactions of hydrogen sulfide yielding soluble hydrosulfide compounds, elemental sulfur, and sulfuric acid. Carbonyl sulfide and carbon disulfide are converted to hydrogen sulfide by hydrolysis. Additionally, they are oxidized to SOx and sulfates via microbial action. The reported oxidation reactions of thiosulfate using nitrate as electron acceptor are ... 

Titanium(IV) iodide is extremely hygroscopic. It dissolves in water with decomposition, and it fumes in air owing to hydrolysis. It forms 2 1 adducts with ammonia,7 pyridine,33 and ethyl acetate.34 With excess ammonia it undergoes ammo-nolysis to give ammonobasic titanium(IV) iodides.7 Analogous aminolysis reactions occur when titanium(IV) iodide is treated with an excess of primary or secondary amine.36 Titanium(IV) iodide is sparingly soluble in petroleum ether, moderately soluble in benzene, and even more soluble in chlorinated hydrocarbons and carbon disulfide. At elevated temperatures it... 

Sulfo-LC-SMPT is not as stable as SMPT. The sulfo-NHS ester is more susceptible to hydrolysis in aqueous solutions and the pyridyl disulfide group is more easily reduced to the free sulfhydryl. Stock solutions of sulfo-LC-SMPT may be prepared in water, but should be used immediately to prevent loss of amine coupling ability. 

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