Reduction of sulfur groups

Reduction is a possible reaction of almost all sulfur-containing organic compounds. According to the conditions used it leads either to thiols or to disulfides. For these purposes importance attaches primarily to reduction of aromatic sulfonyl chlorides and hydrogenating cleavage of disulfides. 

Aromatic sulfonyl chlorides can be converted into thiophenols by many types of reducing agent, but most simply by zinc dust in hydrochloric or sulfuric acid, yields being mostly very good.522 Preparatively the most rewarding process is their reduction in boiling glacial acetic acid by red phosphorus in the presence of catalytic amounts of iodine.523 

Other reducing agents proposed are tin (for the preparation of / -chloro-thiophenol,524 tin(n) chloride (for the preparation of 4,4 -biphenyldithiol),525 iron powder (for the preparation of o- and /7-thiocresol),526 and lithium tetra-hydroaluminate (for the preparation of 1-butanethiol).527 

Sulfonyl chlorides can also be reduced by one hour s heating with a 1.5-fold amount of aluminum amalgam528 in alcoholic-ethereal solution and subsequent gradual dilution with water.529 2,5-Dichlorothiophenol, thio-2- 

Alkali sulfites have proved valuable for reduction of sulfonyl chlorides in the anthraquinone series.530 

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