Reaction of carboxylic acid derivatives with sulfur compounds

Reaction of carboxylic acid derivatives with sulfur compounds 

Thiocarboxylic acids are obtained by acylation of hydrogen sulfide (cf. page 642). For example, thiobenzoic acid is formed (61-76% yield) from benzoyl chloride and potassium hydrogen sulfide,426 and thioacetic acid (74% yield) when hydrogen sulfide is passed into acetic anhydride.427,428 This method can also be applied to other anhydrides.429 

5-Esters of thiocarboxylic acids are formed on acylation of thiols by acid anhydrides. For the preparation of the lower 5-esters the following Schotten-Baumann procedure is used 430,431 

A mixture of sodium hydroxide (40 g), water (75 ml), and thiol (1.2 moles) is poured on crushed ice (500 g), and the whole is stirred vigorously while acetic anhydride (1.25 moles) is added. After a further 5 minutes stirring, the ester is separated, washed, dried, and distilled. 

The C4 to C8 5-alkyl thioacetates are prepared431 by heating the thiol (1 mole), acetic anhydride (1.2 moles), and anhydrous sodium acetate (one-fifth of the weight of the anhydride) under reflux for 1 h in an oil-bath whose temperature is raised from an initial 130° to 150° the reaction is usually so violent that the flask must be removed from the heating-bath for a short time. After cooling, the mixture is poured into water, and the ester is isolated as above. 

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