Sulphenes dimers

The dimer of hexafluorothioacetone may also be obtained from hexafluoropropene [259] and the former has now been used in a route to a sulphene [260] (Figure 8.98). 

Calculations227 indicate thatthese intermediates have very similar HOMO and LUMO energies and that their LUMO coefficients are very similar to each other so we cannot look to these features to explain the striking difference in the reactivity of these two species. The former (252) cannot be isolated when sulphonyl chlorides are treated with base instead the intermediate sulphene (e.g. 254) rapidly dimerizes.228 By contrast, sulphines (e.g. 255 and 256) are an easily isolated class of compound.226,229 The same... 

If no nucleophilic species are present when the sulphene is produced, then it undergoes reaction with itself to form a dimer and a tetramer, which yield sulphonic acids on work-up311, as shown in equation 64. 

Sulphenyl Halides.—Sulphenyl chlorides are readily available by chlorinolysis of disulphides, and this remains the most commonly used method of synthesis. Chlorinolysis of penicillin esters gives the sulphenyl chloride, and a route to an azetidinone sulphenyl chloride has been devised in which the relatively unstable sulphenic acid produced by penicillin sulphoxide pyrolysis is treated with SOCh in CCl, to give [43 R =C1, R =CH(C02Me)CMe=CH2]. Sulphenyl iodides may be important intermediates in reactions at disulphide bridges in peptides and proteins, and a report of the preparation of a stable sulphenyl iodide is notable. The observation that methanesulphenyl chloride dimerizes (in SO2 in the presence of a Lewis acid) to give MeSSMeCl Cl MeS=SMeCl Cl may be useful in explaining the course of certain electrophilic reactions of sulphenyl chlorides, and should stimulate a search for new reactions of aliphatic compounds of this series. 

The sulphenic acids produced on thermal rearrangement of penicillin sulphoxides have been trapped by a variety of reagents, including thiols and acetylene and olefin derivatives such as norbomadiene, keten dimer, vinyl ethers, keten acetals, and acetylenedicarboxylates. Removal of the nitrogen substituent of the resulting 2-azetidinones, e.g. (98 c,v), was achieved by addition of diazomethane to the olefin followed by base treatment or reduction of the intermediate pyrazoline (99). ... 

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