Dimethyl trisulphide

Among the odorants listed in Table 6.33, l-octen-3-ol (no. 4), the character impact aroma compound of mushrooms [62], is also responsible for the characteristic mush-room-like note of camembert, which is intensified by l-octen-3-one (no. 5). Although the concentration of this ketone is much lower than that of the alcohol, it can be aroma-active in cheese because its odour threshold is 100 times lower than that of the alcohol [60], Methanethiol, methional, dimethylsulphide, dimethyl trisulphide and methylene-bis(methylsulphide) generate the sulphurous odour note, whereas phenyle-thyl acetate is responsible for the floral odour note [61 ]. 

Methanethiol Dimethyl sulphide Dimethyl disulphide Dimethyl trisulphide (2,3,4-Trithiapentane)... 

Several polysulphides occur in hop oil. Dimethyl trisulphide (2,3,4-trithiapentane) occurs only in oil prepared from hops which have not been treated with sulphur (dioxide) on the kiln. It is absent from oil prepared by vacuum distillation at 25°C but is formed at lOO C from the precursor 5-methylcysteine sulphoxide (CH3SO-CH2CH(NH2)COOH). This precursor is destroyed by sulphur dioxide when sulphur is burnt in the oast but is slowly regenerated on storage. Dimethyl tetrasulphide and 2,3,5-trithiahexane are... 

Hop oil contains a series of thioesters (Table 13.7) the combined amount of which in steam-distilled hop oil usually exceeds 1000 ppm. The level of thioesters in the oil does not appear to be affected either by treatment of hops with elemental sulphur on the bine or by sulphur dioxide kilning [50]. Thioesters are formed in hops largely by the action of heat, so low levels will be introduced into beer by dry hopping. Few sulphur volatiles survive 60 min of wort boiling but after late addition of hops to the copper most of the sulphur compounds discussed above are present in the wort including the thioesters. During fermentation dimethyl trisulphide and some of the thioesters disappear but some sulphur volatiles survive into the finished beer S-methyl 2-methylbutanethiolate is the principal thioester to survive. This last ester and 5-methyl hexanethiolate, the thioester with the lowest taste threshold, are the major thioesters introduced into beer by dry hopping [50]. 

Some of the dimethyl sulphide in barley and malt is oxidized to dimethyl sulphoxide (CHg-SO-CHa) together with a trace of dimethyl sulphone (CH3 S02 CH3). Malt contains 1 42-3 7 ppm of dimethyl sulphoxide. Yeasts are capable of reducing dimethyl sulphoxide back to DMS and this may be one source of DMS present in finished beer [116]. Late addition of hops during wort boiling also contributes dimethyl sulphide, and dimethyl trisulphide, to wort. 

The only odour-intensive species conclusively identified in the odorous emission of water reclamation works were dimethyl -disulphide, -trisulphide and -tetrasulphide. 

Molecules of the type RS3R that have been studied include 2 2 -diiododiethyl trisulphide, S3(C2H4l)2, dimethyl trisiilphide, and cyanogen triselenide (selenium diselenocyanate). The shape of the first molecule can be appreciated from Fig. 16.7(d). The three shaded circles represent S atoms, and one of the -CH2—CH2—I... 

Kinetic data, activation parameters, and Hammett p values have been reported for the reaction of trico-ordinate phosphorus compounds with diphenyl trisulphide, and the results discussed in terms of a biphilic mechanism.A dithymidyl 3 -S phosphorothioate (33) has been prepared from a thymidin-3 -yl disulphide and a dimethyl 5 -thymidyl phosphite. ... 

Extrusion of sulphur from disulphides " and trisulphides gives sulphides and disulphides, respectively, by treatment with phosphines (a polymeric aminophosphine has been advocated ), phosphites, and MeHgOAc. Ionic pathways continue to be preferred for these reactions, and concurrent electrophilic and nucleophilic mechanisms are in operation, according to interpretations of kinetic data for the reaction with dimethyl disulphide. A new view on nucleophilic attack is advanced in this work, where the encounter involves the o orbital of the S—S bond. Further support is given by c.i.d.n.p. to a radical mechanism that involves PhCHjSe for the reaction of dibenzyl selenide with PhjP. The process PhTeTePh + RN2 Cl - RTeCljPh in the presence of lCu(OAc)2l may be more easily understood on this basis. 

Several papers have appeared describing the cleavage of disulphides and diselenides with phosphines. A two-step mechanism applies to the reduction of a disulphide with Ph3P in aqueous media, and the intermediate Ph3PSAr ArS hydrolyses to ArSH + PhaPO. More complex disulphides containing acetamido-alkyl and o a-di(ethoxycarbonyl)alkyl substituents give oxazole and trisulphide side-products during reduction with PhaP. Conversion of dimethyl diselenide with (R2N)aP into dimethyl selenide, and photochemical deselenation of diethyl diselenide to diethyl selenide with PhaPMe, which involves an EtSe radical chain mechanism, have been described. 

---