Preparation of thiols and disulfides

For such reactions to succeed with aryl halides the halogen must be particularly reactive. For example, o-halobenzoic acids give o-mercaptobenzoic acid when heated with an alkali hydrogen sulfide in the presence of copper powder under pressure 265 and / -chloronitrobenzene gives / -aminothiophenol when heated with an excess of sodium sulfide in aqueous solution, the nitro group being simultaneously reduced.266 

Mercaptoacetic acid 267 This is formed very smoothly, even in aqueous solution, as follows. A solution of chloroacetic acid (100 g) is added gradually to a stirred solution (ca. 15%) of potassium hydrogen sulfide (2 moles) in water (500 ml). The mixture is heated for 15 min on a water-bath,then treated with a concentrated solution of barium chloride, followed by 25% ammonia solution (ca. 1.25 mole). The barium salt is caused to separate by scratching and shaking and is collected and treated with a three-fold amount of 12% hydrochloric acid. The acid liberated is taken up in ether and purified by distillation (b.p. 107-108°/16 mm). 

A method of preparing alkanethiols and thiophenols by means of thio-carboxylic acids consists of converting, preferably, thioacetic or thiobenzoic acid by an alkyl (or aryl) halide into an 5-alkyl (or 5-aryl) thiocarboxylate and hydrolysing this by acid or alkali this method, and that described in the following paragraphs, have the advantage that the thiols can be obtained free from sulfide.268 

1-Mercapto-l-phenylacetone The above acetylthio derivative (14.5 g) is shaken vigorously with 5% sodium hydroxide solution (180 ml) until after about 0.75 h it has all dissolved. The solution is then rapidly extracted with ether, and the thiol is precipitated by acidification. This product is taken up in ether and dried over sodium sulfate, and the ether is distilled off, leaving an oil that slowly crystallizes. Recrystallization from aqueous ethanol gives the thiol as pale yellow crystals, m.p. 108-110°, in 80% yield (10-11 g). 

Replacement of halogen leads to formation of a C-S bond in many cases when alkyl or aryl halides are allowed to react with thiocarbonic acid derivatives such-as thiocarbamates, thiourea, dithiocarbamates, or xanthates. The importance of this method is due to the fact that the intermediates are readily converted into thiols by hydrolysis  

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Sulfides (thioethers) can be obtained by replacing the halogen of alkyl and suitable aryl halides in a reaction with sodium sulfide, this being analogous to the preparation of thiols and disulfides. The reaction is usually carried out... 

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