Disulphides oxidation

Augusti, K.T. and Mathew, P.T. 1974. Lipid lowering effect of allicin (di allyl disulphide oxide) on long term feeding in normal rats. Experientia 30, 468-470. 

The problem of avoiding molybdenum disulphide oxidation in the production of composites is illustrated by Table 12.9, which shows the melting-points and other important temperatures for various metals which have been used to produce composites. It can be seen that most of them are higher than the oxidation temperature of molybdenum disulphide (350 - ASO C). Even the softening or... 

The really unique reaction of the lipoate centre in ct-keto acid metabolism is the oxidative thioester formation from a thiamine-coordinated active aldehyde . Thiol transacetylase and dithiol-disulphide oxidation reduction roles are well-known attributes of other biological thiols. Unfortunately mechanistic studies on this reductive acylation of a cyclic disulphide have so far received little attention. Proposals that a lipoic acid-thiamine pyrophosphate compound was the functional entity in a-keto acid oxidation have been completely abandoned, but data supporting this concept remain unexplained. Investigations in this area might have some relevance for the reductive acylation process. 

Cubic autocatalysis is less common than quadratic. It was first invoked to interpret hydrocarbon oxidation and carbon disulphide oxidation [5]. Both these are gas-phase examples. Iti aqueous solution, it has been used very successfully to interpret the iodate-arsenous acid oxidation [8, 9]. 

Mathew, P.T. and August , K.T. 1973. Studies on the effect of allicin (diallyl disulphide-oxide) on alloxan diabetes. I. Hypoglycemic action and enhancement of serum insulin effect and glycogen synthesis. Indian JBiochem Biophys 20(3) 209-212. 

Studies of addition of thiolates to flavans showing that addition to a 4a- or S-position of an isoalloxazine ring may be implicated in flavin catalysis of thiol-disulphide oxidation, are sufficiently broad to include dithiols and arenesulphinic acids. ... 

Thiolsulphonates.—Reference is also made in the preceding and following sections to these, the most easily prepared and commonly encountered disulphide oxides. 

Cyclic Disulphides.—A number of papers dealing with the properties of lipoic acid (73) have appeared. When irradiated in an aldehyde solvent (e.g. acetaldehyde, propionaldehyde), the monoacetylated products (74) of S—S bond fission were obtained in 70—80% yield. The reaction was successfully extended to a series of 3,3-dialkyl-l,2-dithiolans, 1,2-dithians, and acyclic disulphides. Oxidation of (73) with a variety of reagents, including singlet oxygen, t-butyl... 

Crystalline solid m.p. 35-36 "C, b.p. 154--156 C, prepared by oxidizing A,A -dicycIo-hexylthiourea with HgO in carbon disulphide solution, also obtained from cyclohexylamine and phosgene at elevated temperatures. Used as a mild dehydrating agent, especially in the synthesis of p>eptides from amino-acids. Potent skin irritant. 

The base lubricant is usually a petroleum oil while the thickener usually consists of a soap or soap mixture. In addition they may contain small amounts of free alkali, free fatty acid, glycerine, anti-oxidant, extreme-pressure agent, graphite or molybdenum disulphide. 

Crystalline powder, m.p. 174-179 C. Prepared by treatment of thiocarbanilide with sulphur, or by heating aniline, carbon disulphide and nitrobenzene. It is an important rubber accelerator, and on oxidation gives dibenzthiazyl disulphide, also a rubber accelerator. 

A pletliora of different SA systems have been reported in tire literature. Examples include organosilanes on hydroxylated surfaces, alkanetliiols on gold, silver, copper and platinum, dialkyl disulphides on gold, alcohols and amines on platinum and carboxyl acids on aluminium oxide and silver. Some examples and references can be found in [123]. More recently also phosphonic and phosphoric esters on aluminium oxides have been reported [124, 125]. Only a small selection out of tliis number of SA systems can be presented here and properties such as kinetics, tliennal, chemical and mechanical stability are briefly presented for alkanetliiols on gold as an example. 

Phosphorus(III) oxide dissolves in several organic solvents, for example benzene, carbon disulphide the molecular weight in these solvents corresponds to the formula P40(, as does the density of the vapour, and the structure is ... 

When sulphur is melted viscosity changes occur as the temperature is raised. These changes are due to the formation of long-chain polymers (in very pure sulphur, chains containing about 100 (X)0 atoms may be formed). The polymeric nature of molten sulphur can be recognised if molten sulphur is poured in a thin stream into cold water, when a plastic rubbery mass known as plastic sulphur is obtained. This is only slightly soluble in carbon disulphide, but on standing it loses its plasticity and reverts to the soluble rhombic form. If certain substances, for example iodine or oxides of arsenic, are incorporated into the plastic sulphur, the rubbery character can be preserved. 

The dialkyl disulphides may be prepared by the oxidation of an alkaline solution of a mercaptan with iodine, for example ... 

Oxidation product has been isolated out of chloroform solution. Based on IR spectra and literacy data assumption has been made that oxidation of EMT leads to transformation of thionic group into disulphide tetraethylamino-thiobaenzophenone. 

The first step in the manufacture of the foil involves the production of alkali cellulose. This is then shredded and allowed to age in order that oxidation will degrade the polymer to the desired extent. The alkali cellulose is then treated with carbon disulphide in xanthating chums at 20-28°C for about three hours. 

During World War II, polychloroprene was chosen as a replacement for natural rubber because of its availability. Two copolymers of chloroprene and sulphur which contain thiuram disulphide were available (Neoprene GN and CG). One of the first successful applications of these polychloroprene adhesives was for temporary and permanent sole attachment in the shoe industry. However, these polychloroprene cements show a decrease in viscosity on ageing and a black discolouration appears during storage in steel drums. Discolouration was produced by trace amounts of hydrochloric acid produced by oxidation of polychloroprene... 

Formulation 100 phr Hycar OR-25EP different amounts of phenolic resin 5 phr zinc oxide 1.5 phr sulphur 1.5 phr benzothiazol disulphide 1.5 phr stearic acid [68]. 

The selective oxidation of the sulphide grouping in the presence of the disulphide bond was observed when a methanolic solution of amide 46 was treated with an aqueous solution of sodium metaperiodate77 (equation 20). 

The oxidation of disulphide species with at least one sulphur atom at the sulphoxide oxidation level will also be covered briefly. 

Thiosulphinates are derivatives of disulphides with one of the sulphur atoms at the sulphoxide oxidation level. In theory, oxidation of a thiosulphinate could produce two products, a disulphoxide and a thiosulphonate (equation 79). Discussions of this topic have been very polarised over the years but now it is fairly well established that the thiosulphonate is the major product formed in most cases, although the intermediacy of a a-disulphoxides is indicated from some data. 

Unsymmetrical thiosulphinates and thiosulphonates are both oxidized by potassium superoxide in pyridine in the presence of 18-crown-6 ether to produce sulphinic and sulphonic acids and a disulphide, under mild conditions (equation 84)200,201. Sulphinic and sulphonic acids were produced from both the R and R substituents whilst the disulphide was derived only from the sulphenyl side of the reactant. Thus, the reaction mixture contained five products, making the reaction not synthetically useful. Pyrolysis of thiosulphinates also produces mixtures of products, one being the thiosulphonate again this is not a synthetically useful reaction202. 

Levitt (1962) has of course proposed a theory of frost injury based on the oxidation of sulphydryl groups and the formation of intermolecular disulphide bonds and he has subsequently extended this concept to dehydration injury (see Levitt, 1972). Although popular in the 1960s and 1970s this theory appears to have lost favour in recent years. 

Allyl propyl disulphide a-Alumina, see Aluminium oxide Aluminium as Al Metal dust Pyro powders Welding (umes Soluble salts Alkyls (NOC)... 

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