Symmetrical disulphide

Aliphatic and aromatic sulphonic acids have been reduced to symmetrical disulphides in almost quantitative yields using potassium iodide and ethyl polyphosphate... 

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]. 

Dialkyl disulphides, of which (S)-cystine above is an example, may be prepared from thiols by mild oxidation, usually with iodine in the presence of alkali. A convenient synthesis of unsymmetrical analogues results when a symmetrical disulphide is heated with thiol to establish an equilibrium mixture. By careful choice of the reactants, fractional distillation then removes the more volatile thiol leaving the mixed disulphide as a residue.240... 

The introduction of redox-sensitive linkages, such as the disulphide group, has been used to prepare liposomes that are susceptible to the lower intracellular redox potential relative to the extracellular environment. Symmetrical disulphides are synthesised by oxidation of thiol-containing structures [64, 130, 131] (see Fig. 7),... 

Diphosphine disulphides can also be made by heating secondary phosphine sulphides with phos-phinothionic chloride (9.595), and if diphosphine disulphides are heated with diphosphines, R 2P-PR 2, under appropriate conditions unsymmetrical monosulphides R 2P-P(S)R2 result. Symmetrical disulphides are obtainable by the SO2 oxidation of secondary phosphines (6.268). 

The thiol-substituted amines such as sulphenamides and tris-(alkanesulphenyl) amines are often prepared from sulphenyl chlorides and ammonia and never from nitrogen trichloride and a thiolate anion or a thiol. Chloramines react with thiols to produce symmetrical disulphides . 

Symmetrical disulphides are formed in the reaction of a thiol with an azide in the presence of copper(i). The reaction probably proceeds through the formation of a sulphenamide which is decomposed by the thiol. ... 

The cleavage of the N—S bond in N(thiosulphenyl)phthalimide with thiols yields an unsymmetrical trisulphide >. Unsymmetrical disulphides are also formed in the thiolate anion fracture of the C—S bond in ethyl thiocyanate in DMF small amounts, less than 10%, of the symmetrical disulphides are formed. ... 

Unsymmetrical disulphides are prepared by the reaction of thiols with sulphenyl compounds, a new synthesis of this type involving first the conversion of a thiol R SH into R SSC02R by its reaction with CISCO2R in MeOH at 0 °C, followed by room-temperature reaction of the intermediate with a second thiol R SH to give R SSR and HO CS -OR . Acetyl sulphenyl chlorides AcSCl similarly yield AcSSR with RSH, - though the product is susceptible to attack by the thiol, resulting in the formation of symmetrical disulphides. Acyl alkyl... 

D. C. Scott and J. P. McCullough, The Chemical Thermodynamic Properties of Hydrocarbons and Related Substances. Properties of 100 Linear Alkane Thiols, Sulphides, and Symmetrical Disulphides in the Ideal Gas State from 0 to 1000 K , U.S. Bureau of Mines, Bulletin 395, 1961. 

In contrast to the iodine-methanol procedure, the sulphenyl-thiocyanate method does not provide statistical mixtures of symmetrical and unsymmetrical disulphides. Thus the reaction of thiols or S-trityl thioethers with sulphenyl thiocyanates appears to be relatively specific and rapid (e.g., (31) from the S-trityl thioether). In situations when the reaction is slow (e.g., (31) from S-benzhydryl thioether with no acid catalysis) disproportionation of the sulphenyl thiocyanate seems to occur (as with the sulphenyl iodides) and symmetrical disulphide can be isolated. Thus as pointed out by Kamber [92] the iodine oxidation of thioethers appears useful in situations where the... 

Despite these successes serious side reactions can result from the action of alkali on cysteine or cystine-containing peptides. Open-chain unsymmetrical cystine derivatives [92, 103, 166] and some cyclic molecules including oxytocin [153] and calcitonin [24, 25] are known to undergo rapid base-catalyzed disulphide interchange yielding symmetrical disulphides or mixtures of polymer and parallel and antiparallel dimers [107, 153]. Furthermore the possibility of /3-elimination of trityl, benzhydryl, and benzyl mercaptide ion from the corresponding peptide bound cysteine residue is known [154] the extent of... 

Trialkylboranes react with elemental sulphur to give good yields of symmetrical disulphides oxygen-induced free-radical chain reaction with organic disulphides gives sulphides/ as shown in Scheme 146. 

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