Thiosulfinates thiosulfonates

Further oxidation to the sulfone was found to be very slow in comparison to sulfide oxidation, and could be achieved on addition of a further equivalent of hydrogen peroxide. Thioketones have been oxidized in a similar fashion to yield ketones with expulsion of sulfur dioxide. Symmetrical disulfides have been oxidized to the corresponding thiosulfinates, thiosulfonates, and sulfonic acids. 

The oxidation of sulfoxides by aliphatic peroxy acids is first order in both reactants the solvent effects have also been investigated. Thiosulfinates are oxidized by peroxy acids to thiosulfonates and not disulfoxides. It had previously been proposed that the disulfoxides are formed first but homolytically cleave and recombine to give thiosulfonates. A series of ab initio calculations were performed (at the 3-210 and 6-3IG levels) which indicate little difference in the rate of oxidation of S over S(0) in the gas phase but faster S(0) oxidation in a reaction cluster. ... 

The most important flavour compound in raw onions is thiopropanal-S-ox-ide, the lachrymatory factor [145,146]. Other important flavour compounds are 3,4-dimethyl-2,5-dioxo-2,5-dihydrothiophene and alkyl alkane thiosulfonates such as propyl methanethiosulfonate and propyl propanethiosulfonate with a distinct odour of freshly cut onions [35, 36, 147]. Various thiosulfinates that have a sharp and pungent odour may also contribute to the flavour of onions. These compounds, however, are rapidly decomposed to a mixture of alkyl and alkenyl monosulfides, disulfides and trisulfides (Scheme 7.3) of which dipropyl disulfide, methyl ( )-propenyl disulfide, propyl ( )-propenyl disulfide, dipropyl trisulfide and methyl propyl trisulfide are the most important contributors to the aroma of raw and cooked onions (Table 7.5, Fig. 7.6) [148-150]. Recently, 3-mercapto-2-methylpentan-l-ol was identified in raw and cooked onions eliciting intense meat broth, sweaty, onion and leek-like odours [142, 151]. 

The following routes to unsymmetrical disulfides and symmetrical trisulfides use silyl sulfides and thiosulfinates [41.42]. Thiosulfonates react similarly. 

Bass, S.W. and Evans, S.A., Jr., Carbon-13 nuclear magnetic resonance spectral properties of alkyl disulfides, thiosulfinates, and thiosulfonates, J. Org. Chem., 45, 710, 1980. 

Sulfane oxides are compounds of type R2S Om ( > 1, m = 1, 2, 3...) with the oxygen atoms present as sulfoxide or sulfone groups. For the nomenclature of organic sulfur-oxygen compounds see Table 2 for reviews on oxidized sulfur chains and rings, see Steudel. Disulfane 1-oxides, RS(0)-SR, are also known as thiosulfinates and the 1,1-dioxides are usually termed as thiosulfonates. Trisulfane 1-oxides and 1,3-dioxides, as well as tetrasulfane 1-oxides and 1,4-dioxides, have been obtained by stepwise oxidation of the corresponding sulfanes by peroxy acids (equations 151 153) 67,101,123,127,262 26s... 

Lower yields are observed when R is a secondary group, and no thiosulfonate is formed with R = r-Bu. Although thiosulfinates, RSOSR, are intermediate products, they are not oxidized under the electrolysis conditions. It was shown that thiosulfinates are transformed into thiosulfonates in the presence of disulfides being oxidized, presumably involving an intermediate species electrogenerated from the disulfide [38b]. Diaryl disulfides also lead to thiosulfonates in good yields when oxidized under similar conditions [39]. The disulfoxide, RSOSOR, supposedly obtained in the anodic oxidation of dibenzyl disulfide in a HOAc/HCl solution at a Pt anode [40], is probably also a thiosulfonate. 

In laboratory work the oxidation of disulfides has been applied particularly to the preparation of thiosulfinic and thiosulfonic esters ... 

Oxidation to thiosulfinic esters is best effected by an equivalent amount of perbenzoic acid or peracetic acid in chloroform,594 and the preparation of thiosulfonic esters by a slight excess of hydrogen peroxide in acetic acid or by chlorine in the presence of glacial acetic acid with subsequent treatment by water.595-597... 

Synthesis of Sulfinate Ester. 5-Ethyl ethanethiosulfinate can be transformed to the stable sulfinate esters by replacement of the sulfenyl group with catalytic bromine and H2 O2 in the presence of an alcohol such as Isopropanol (eq 11). However, in absence of the alcohol, the thiosulfinate disproportionates rapidly under these conditions and forms a mixture of thiosulfonate and disulfide. 

The mechanism of flavor formation from the alkyl cysteine sulfoxide (alhin) is outlined in Figure 4.13. While the initial steps of this pathway are enzymatic, reactions beyond sulfenic acid are purely chemical in nature. Sulfenic acid is extremely reactive, readily forming the unstable thiosulfinate intermediate by reaction with a second sulfenic acid molecule. This thiosulfinate decomposes to form a relatively stable thiosulfonate and mono, di- and trisulfldes. Considering that several different aUcyl precursors are available in each Allium species, a host of different mono-, di-, and trisulfides can be formed via different sulfenic acid combinations. It is these mono-, di-, and trisulfides that are most important in determining typical Allium flavor. 

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