Dialkyl Sulphones

The two principal categories of compounds studied have been diaryl or aryl alkyl sulphones (not dialkyl sulphones, which are polarographically not reducible) and S-dioxides of certain heterocyclic compounds, such as thiophene (also benzo- and dibenzothiophenes) and phenothiazines. The first named have half-wave potentials in the region of — 2.0 V, the thiophene dioxides near — 1.0 V. Some examples of each category may be given. 

Truce also examined a few examples of the cleavage of sulphones with sodium in liquid ammonia97 and found essentially similar results except that diaryl sulphones were reduced to sulphinate salts instead of to arylthiolates as with the lithium reductions. Dialkyl sulphones were unreactive towards sodium in liquid ammonia. 

Dialkyl sulphones may be converted to sulphonic acids by reaction with carbon tetrachloride and base at 80 °C209. This reaction proceeds by initial formation of a-chloro sulphones which are then converted to a thiiren intermediate which decomposes to give a sulphonic acid (equation 92). 

An alternative route to sulphones utilizes the reaction of the appropriate activated halide with sodium dithionite or sodium hydroxymethanesulphinite [6], This procedure is limited to the preparation of symmetrical dialkyl sulphones and, although as a one-step reaction from the alkyl halide it is superior to the two-step oxidative route from the dialkyl sulphides, the overall yields tend to be moderately low (the best yield of 62% for dibenzyl sulphoxide using sodium dithionite is obtained after 20 hours at 120°C). The mechanism proposed for the reaction of sodium hydroxymethanesulphinite is shown in Scheme 4.20. The reaction is promoted by the addition of base and the best yield is obtained using Aliquat in the presence of potassium carbonate. It is noteworthy, however, that a comparable yield can be obtained in the absence of the catalyst. The reaction of phenacyl halides with sodium hydroxy-methane sulphinite leads to reductive dehalogenation [7]. 

Dialkyl sulphones are not reducible at a mercury cathode. Aryl alkyl and diaryl sulphones are however reduced with cleavage of a carbon-sulphur bond. Polaro-graphic half-wave potentials for this process are given in Table 5.6. One-electron addition in aprotic media to phenyl methyl sulphone [66] and to diphenyl sulphone [67] leads in both cases to a delocalised radical-anion in which the sulphone grorqj can be described as contributing a vacant symmetrical dx-orbital to the conjugated system. Phenyl methyl sulphone radical-anion is prepared and characterised in liq-... 

S) = —155cr — 133 corr. coeff. = 0.967 symmetric dialkyl sulphones <5(33S) = 8.78cr — 18.0 corr. coeff. = 0.991 monosubstituted dimethyl sulphones... 

There are many examples of the photochemical behaviour of these classes of compounds. The photochemistry is dominated by the fission of a C—S bond affording a carbon radical and a sulphonyl radical. The UY absorptions of these compounds are dependent upon the type of substituent attached to the sulphonyl group. Thus a dialkyl sulphone (19) shows an... 

Dialkyl sulphones 1330-1295 7.52-7.72 vs w "1 Straight-chain alkyl sulphones absorb at slightly higher... 

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