Hydrogen sulfide, free-radical mechanisms

Hydrogen sulfide (H2S) and thiols add to alkenes to give alkyl thiols or sulfides by electrophilic, nucleophilic, or free-radical mechanisms.In the absence of initiators, the addition to simple alkenes is by an electrophilic mechanism, similar to that in 15-5, and Markovnikov s rule is followed. However, this reaction is usually very slow and often cannot be done or requires very severe conditions unless a proton or Lewis acid catalyst is used. For example, the reaction can be performed in... 

In the past 10 years other reductants of the C— Hg bond have been used, mainly thiols and sodium amalgam. Reduction with hydrogen sulfide, sodium dithionite, metals,alcohols, alkaline aqueous bases, aromatic amines, Wilkinson s catalyst and electrochemical reductions have also been described. Organomercurials react with thiols by free radical substitutions with an 5h2 mechanism (Scheme 34). The reaction between PhSH and A -hexenylmercury chloride initiated by light or AIBN gives a mixture of 1-hexene and methylcyclopentane. ... 

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