Isobutyl 2,4-dinitrophenyl sulphide

Formation of a symmetrical sulphide (a) (e.g. dipropyl sulphide, Expt 5.204), is conveniently effected by boiling an alkyl halide (the source of carbocations) with sodium sulphide in ethanolic solution. Mixed sulphides (b) are prepared by alkylation of a thiolate salt (a mercaptide) with an alkyl halide (cf. Williamson s ether synthesis, Section 5.6.2, p. 583). In the case of an alkyl aryl sulphide (R-S Ar) where the aromatic ring contains activating nitro groups (see Section 6.5.3, p. 900), the aryl halide is used with the alkyl thiolate salt. The alternative alkylation of a substituted thiophenol is described in Section 8.3.4, p. 1160. The former procedure is illustrated by the preparation of isobutyl 2,4-dinitrophenyl sulphide (Expt 5.205) from l-chloro-2,4-dinitrobenzene and 2-methylpropane-1-thiol. 

Dissolve 340 mg of isobutyl 2,4-dinitrophenyl sulphide (Expt 5.205) in 10 ml of acetic acid, warm to about 50 °C and add dropwise 8 ml of 3 per cent aqueous potassium permanganate solution. Maintain the solution at about 50 °C for 20 minutes, and then pass through the solution a stream of sulphur dioxide to decompose excess potassium permanganate. Add crushed ice to the yellow solution to precipitate the crude sulphone. Filter the precipitate, dry and recrystallise from rectified spirit to give the yellow crystalline product, m.p. 105-106 °C the yield is 190 mg (50%). 

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