Preparation of Symmetrical Thioethers

Symmetrical dialkyl sulfides have been prepared in high yield by the reaction of sodium or potassium sulfide with a primary or secondary halide under phase transfer conditions. Both quaternary ions [1] and crown ethers [2] have been successfully utilized in this reaction. It was found that at 70 several different alkyl halides would condense with 0.6 to 1.0 equivalent of sodium sulfide to give generally excellent yields of symmetrical thioethers according to equation 13.1. Even the highly 

Thiolacetic acid has also been used as a source of sulfur in the preparation of symmetrical sulfides [4]. Crotonaldehyde, for example, has been shown to condense with thiolacetic acid, hydrolyze, add to a second molecule of aldehyde, and then undergo 

Alkyl halide % Yield Inorganic sulfide Catalyst Refer- ences 

Quaternary onium salts, crown ethers, and cryptates have all proved effective as catalysts in the synthesis of unsymmetrical thioethers under phase transfer conditions. Both primary and secondary alkyl bromides can be used to alkylate the mercaptan or thiophenol under basic conditions [5—9]. 

A detailed mechanistic study of the reaction of thiophenol with -bromooctane in an alkaline two-phase system has been conducted [5, 6] (see Eq. 13.3) and the essential findings are discussed in Sect. 1.6. The reaction appears to be a true cata- 

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