Reduction of Sulfonyl Chlorides to Thiols
Reduction of sulfonyl chlorides to thiols can be achieved by the use of lithium aluminum hydride, or zinc or with hydroiodic acid generated in situ from iodine and red phosphorus. However, little is known or reported regarding the catalytic reduction of sulfonyl chlorides to yield the corresponding thiols.
We report here the reduction of aromatic sulfonyl chlorides, such as p-toluenesulfonyl chloride, naphthalenesulfonyl chloride, or p-(chlorosulfonyl)benzoic acid, to yield the aromatic thiols. This reduction was accomplished by use of a palladium catalyst under a moderate pressure of hydrogen. The reduction was carried out in the presence of a mild base to neutralize the strong acid formed during the reduction. When using a basic Amberlite resin to neutralize the acid, disulfide compounds are generated. The disulfides can be reduced to the thiols by use of Raney cobalt catalyst.