Thiophenols from aryl halides

Very few transition-metal catalyzed electroreductive carbon-heteroatom bond formations have been described. The electrochemical silylation of allylic acetates was carried out in the presence of Pd-PPha [131]. The electrosynthesis of arylthioethers from thiophenol and aryl halides [132] and the coupling of bromobenzene with dichlorophenylphosphine [133] were performed with Ni-bpy as catalyst. 

Although not directly analogous to the coupling of thiols with aryl halides, the reaction of thiourea with an aryl halide in the presence of palladium catalyst, nevertheless, can be used to generate a thiophenol from an aryl halide after hydrolysis (Equation (39)).129 This process occurred in greater than 90% yield with a variety of simple aryl halides ... 

Halide displacement by thioanions such as thioalkoxides, thiocyanate and sulfite, can be readily carried out under PTC conditions in activated arenes. The reaction of nitro- and dinitro-aryl halides with thiophenol and NaOH in the presence of an ammonium or phosphonium salt catalyst proceeds readily in toluene at room temperature to give the phenyl aryl sulfides in nearly quantitative yield.189 Excellent yields of thiocyanoarenes were obtained from the reaction of the 2,4-dinitrohalobenzenes with KSCN in toluene at 90 C with a tetraalkyl onium salt PTC catalyst.190... 

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. 

Aryl radicals electrochemically generated from the cleavage of aryl halide radical anions have been observed to react with nucleophiles other than iodide (Pinson and Saveant, 1974, 1978 Saveant, 1980), a reaction known as the SrjjI reaction (Bunnett, 1978). The most commonly used nucleophiles are thiophenolate, mercaptides, and cyanide ion. The reactions observed are... 

A method of preparing alkanethiols and thiophenols by means of thio-carboxylic acids consists of converting, preferably, thioacetic or thiobenzoic acid by an alkyl (or aryl) halide into an 5-alkyl (or 5-aryl) thiocarboxylate and hydrolysing this by acid or alkali this method, and that described in the following paragraphs, have the advantage that the thiols can be obtained free from sulfide.268... 

The procedure outlined above also offers a general method for the synthesis of alkyl and. aryl thiols starting from the appropriate halides. Thus thiophenol may be obtained in 62% yield by lithiation and sulfurization of bromobenzene.8... 

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