Disulphide mixed

Cysteine Cys-disulphides mixed-disulphides Sulphenic acid, sulphinic acid, Sulphonic acid (via alkyl thioradicals)... 

E. Demar ay passed carbon tetrachloride vapour over chromic oxide to obtain chromic chloride—-P. CambouUves recommended a temp, of 580°. G. Ranter observed that when chromium trioxide or a chromate is heated in the vapour of silicon tetrachloride, chromic chloride is formed and A. Michaelis found that it is formed by the action of phosphorus trichloride on chromyl chloride. H. Quantin prepared chromic chloride by heating chromyl chloride in a current of carbon monoxide, or of carbon tetrachloride and M. Prud homme worked with the materials in a sealed tube at 200°. F. P. Venable and D. H. Jackson found that the chlorination of chromic oxide with a mixture of chlorine and carbon monoxide starts at 625°. P. Curie passed the vapour of carbon disulphide mixed with hydrogen chloride over heated chromic oxide and J. J. Berzelius, C. E. Ufer,... 

This reagent is prepared from 3.0 mL of diethylamine in chloroform and 1 mL of carbon disulphide in 9 mL of chloroform. Mix carefully and store in a dark bottle in a refrigerator. 

Few racemic alkyl p-tolyl sulphoxides were prepared in rather low yields (16—40%) by the reaction of Grignard reagents with mixed anhydrides 108, 109 and compound HO formed in situ from p-toluenesulphinic acid and 3-phthalimidoxy-l,2-benzoisothiazole 1, 1-dioxide167 (equation 59). The mixed anhydrides 109 or 110 when reacted with cyclopen-tene and cyclohexene enamines 111 gave the corresponding a-ketocycloalkyl sulphoxides 112 in low yields (10-41%) along with small amounts of several by-products such as disulphides and thiosulphonates167 (equation 60). 

The anaerobic oxidation of phosphines to their oxides by hydroxide ion has been shown to involve the liberation of hydrogen, possibly from the intermediate (21). These oxidations were studied with water-soluble phosphines, since solubility was found to be the main factor controlling the rate of oxidation. The preparation, and detailed n.m.r. spectrum, of PP-dimethyl-P P -diphenyldiphosphine disulphide (22) is a relatively rare example of a study of a mixed disulphide. Many examples of routine oxidation of phosphines to their oxides have appeared. These include the preparation of polyhalogenoarylphosphine oxides using dichromate... 

Figure 4.14 Diagrammatic representation of (a) oxy-radical>mediated S-thioiation and (b) thiol/disulphide-initiated S-thiolation of protein suiphydryl groups. Under both circumstances mixed disuiphides are formed between glutathione and protein thiois iocated on the ion-translocator protein resulting in an alteration of protein structure and function. Both of these mechanisms are completely reversible by the addition of a suitabie reducing agent, such as reduced glutathione, returning the protein to its native form.

Brigelius, R. (1985). Mixed disulphides biological functions and increase in oxidative stress. In Oxidative Stress (ed. H. Sier) pp. 243-272, Academic Press, London. 

The use of the triphenylphosphine-di(2-pyridyl) disulphide reagent for effecting condensation reactions has been reviewed.84 Combination of triphenylphosphine with bis(O-thiocarbonyl) disulphide gives a superior reagent compared to that mentioned above for the preparation of mixed diesters of phosphoric acid from monophosphate esters.86... 

Dithio-bis(inosinylimidodiphosphate) (66) forms mixed disulphides between the 6-thiol group of the purine and cysteine residues on myosin on binding four... 

The mixed-potential model demonstrated the importance of electrode potential in flotation systems. The mixed potential or rest potential of an electrode provides information to determine the identity of the reactions that take place at the mineral surface and the rates of these processes. One approach is to compare the measured rest potential with equilibrium potential for various processes derived from thermodynamic data. Allison et al. (1971,1972) considered that a necessary condition for the electrochemical formation of dithiolate at the mineral surface is that the measmed mixed potential arising from the reduction of oxygen and the oxidation of this collector at the surface must be anodic to the equilibrium potential for the thio ion/dithiolate couple. They correlated the rest potential of a range of sulphide minerals in different thio-collector solutions with the products extracted from the surface as shown in Table 1.2 and 1.3. It can be seen from these Tables that only those minerals exhibiting rest potential in excess of the thio ion/disulphide couple formed dithiolate as a major reaction product. Those minerals which had a rest potential below this value formed the metal collector compoimds, except covellite on which dixanthogen was formed even though the measured rest potential was below the reversible potential. Allison et al. (1972) attributed the behavior to the decomposition of cupric xanthate. 

Table 4.1 shows the measured rest potential of sulphide electrode in thio collector solutions at pH = 6.86 and the equilibrium potential calculated for possible processes. In terms of the mixed potential model, the reaction products should be metal collector salts between four thio collectors and galena and jamesonite and should be disulphide between four thio collectors and pyrite and... 

Bis[dimethylthienol]l,4,6,8-tetratellurafulvalene. 3,4-Dibromo-2,5 dimethylthiophene in tetrahydrofuran is treated at -78°C with 2 equiv of ferf-butyllithium. After 2 h, 1 equiv of tellurium powder is added. The mixture is slowly warmed to 0°C and kept at 0°C until all the tellurium has dissolved. The mixture is cooled again to -78°C, treated with tert-butyllithium and then with tellurium at 0°C. The ditellurolate solution is cooled to -78°C, mixed with 0.5 equiv of tetrachloroethene, stirred for 18 h and allowed to warm to 20°C. The brown solid is isolated by filtration and extracted with carbon disulphide. The extract is evaporated and the residue recrystallized from 1,1,2-trichloroethane to give bronze-coloured crystals. Yield 75% m.p. 295-298°C. 

A number of furans with thiol, sulphide or disulphide substitution have been reported as aroma volatiles, and these are particularly important in meat and coffee. In the early 1970s, it was shown that furans and thiophenes with a thiol group in the 3-position possess strong meat-like aromas and exceptionally low odour threshold values [50] however, it was over 15 years before such compounds were reported in meat itself In 1986,2-methyl-3-(methylthio)furan was identified in cooked beef and it was reported to have a low odour threshold value (0.05 pg/kg) and a meaty aroma at levels below 1 pg/kg [51]. Gasser and Grosch [52] identified 2-methyl-3-furanthiol and the corresponding disulphide, bis(2-methyl-3-furanyl) disulphide, as major contributors to the meaty aroma of cooked beef. The odour threshold value of this disulphide has been reported as 0.02 ng/kg, one of the lowest known threshold values [53]. Other thiols which may contribute to meaty aromas include mercaptoketones, such as 2-mercapto-pentan-3-one. 2-Furylmethanethiol (2-furfurylmercaptan) has also been found in meat, but is more likely to contribute to roasted rather than meaty aromas. Disulphides have also been found, either as symmetrical disulphides derived from two molecules of the same thiol or as mixed disulphides from two different thiols [54]. 

Hey is a sulphydryl amino acid of molecular weight 135.2. It oxides readily to its disulphide form homocystine, and can be converted to the thiolactone form in acid solution. In normal plasma, Hey exists in various forms the sulphydryl form (approximately 1%), bound to the cysteine residues of proteins (approximately 70%), and bound to free cysteine as cysteine-Hcy mixed disulphide (approximately 30%). When levels are elevated, the disulphide form homocystine is formed. All of these forms can be converted to Hey by chemical reduction and then measured as tHcy. 

Thiols exist in biological systems in various oxidised and reduced forms. Very little Hey in the free sulphydryl form is found in plasma and it exists mainly as cysteine-Hcy mixed disulphide, bound to cysteine residues of plasma proteins, or as its disulphide homocystine, but the latter only when levels are high. Routinely measured tHcy constitutes all of these forms together and is produced by chemical reduction. 

Mixtures of chlorates with such materials must not be ground together with a postle and mortar. The materials should be ground separately, and then carefully mixed on paper with a feather. Phosphorus in contact with a chlorate may explode spontaneously. Thus if a drop of soln. of phosphorus in carbon disulphide be allowed to fall on a little potassium chlorate, a loud explosion occurs as soon as the carbon disulphide has evaporated. The red phosphorus in the mixture on the side of a box of safety matches gives a series of sparks when a crystal of potassium chlorate is rubbed thereon, and serious accidents have occurred as a result of the accidental rubbing of tabloids of potassium chlorate against the sides of a match-box in the pocket. 

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