Addition of hydrogen sulfide and its derivatives

In the absence of radical-forming catalysts addition of hydrogen sulfide and thiols (mercaptans) to a carbon-carbon double bond occurs preferentially in accord with the Markovnikov rule  

However, the addition occurs contrary to the Markovnikov rule under irradiation by ultraviolet light or in the presence of peroxides 1 for instance, allyl-amine hydrochloride or a derivative thereof in alcoholic solution is thiolated by an excess of hydrogen sulfide under UV-irradiation, exclusively (yields up to 57%), to give 3-aminoalkanethiols.2 Addition of hydrogen sulfide is of use in the laboratory only when the reaction can be carried out in the liquid phase and is then preferably effected under the influence of a basic catalyst Dahl-bom,3 for instance, obtained 3-mefcapto-butyric acid from crotonic acid hydrogen sulfide in the presence of diethylamine in a closed vessel at 70° and 4-mercapto-4-methyl-2-pentanone is obtained in 80% yield from mesityl oxide and hydrogen sulfide with triethylamine as catalyst.4 

The first step in the addition of hydrogen sulfide to unsaturated compounds is the formation of thiols, but further reaction can occur, yielding sulfides (thioethers), the latter being favored by using an excess of the olefin.5 

3/-Thiodipropionic acid 6 A solution of sodium hydroxide (40 parts) in water (100 parts) is saturated with hydrogen sulfide and then treated with a solution of sodium acrylate (94 parts) in water (130 parts). A little (0.1 part) of hydroquinone is added and the mixture is heated at 100° for 20 hours. Acidification then affords S -thiodipropicnic acid. 

Dimethyl 3,3 -thiodipropionate (yield 71-81%)7 and bis-(2-cyanoethyl) sulfide (yield 86-93%)8 are respectively obtained analogously by adding hydrogen sulfide to methyl acrylate in the presence of sodium acetate and to acrylonitrile with catalysis by Triton B (benzyltrimethylammonium hydroxide). 

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