In general, on the typical laboratory scale, the direct reaction of a haloalkane with sodium hydrosulfide is inefficient owing to the competing formation of sulfides. Instead, alkyl halides are converted to thiols via an S-alkylation of thiourea. This multistep, one-pot process proceeds via the intermediacy of the isothiouronium salt, which is hydrolyzed in a separate step:
: CHCHBr + SC(NH) → [CHCHSC(NH)]Br
: [CHCHSC(NH)]Br + NaOH → CHCHSH + OC(NH) + NaBr
The thiourea route works well with primary halides, especially activated ones. Secondary and tertiary thiols are less easily prepared. Secondary thiols can be prepared from the ketone via the corresponding dithioketals. A related two-step process involves alkylation of thiosulfate to give the thiosulfonate ("Bunte salt"), followed by hydrolysis. The method is illustrated by one synthesis of thioglycolic acid:
:ClCHCOH + NaSO → Na[OSCHCOH] + NaCl
:Na[OSCHCOH] + HO → HSCHCOH + NaHSO
Organolithium compounds and Grignard reagents react with sulfur to give the thiolates, which are readily hydrolyzed:
:RLi + S → RSLi
:RSLi + HCl → RSH + LiCl
Phenols can be converted to the thiophenols via rearrangement of their O-aryl dialkylthiocarbamates.
Thiols are prepared by reductive dealkylation of sulfides, especially benzyl derivatives and thioacetals.
Thiophenols are produced by S-arylation or the replacement of diazonium leaving group with sulfhydryl anion (SH):
: + SH → ArSH + N