Hemithioacetal
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In organic chemistry, hemithioacetals (or thiohemiacetals) are organosulfur compounds with the general formula R−CH(−OH)−SR’. They are the sulfur analogues of the acetals, R−CH(−OH)−OR’, with an oxygen atom replaced by sulfur (as implied by the thio- prefix). Because they consist of four differing substituents on a single carbon, hemithioacetals are chiral. A related family of compounds are the dithiohemiacetals, with the formula R−CH(−SH)−SR’.[1] Although they can be important intermediates, hemithioacetals are usually not isolated, since they exist in equilibrium with thiols (−SH) and aldehydes (−CH=O).
Hemithioacetals are formed by the reaction of a thiol (R−SH) and an aldehyde (R−CH=O):
Hemithioacetals usually arise via acid catalysis. They typically are intermediates in the formation of dithioacetals (R−CH(S−R’)2):
![{\displaystyle {\mathrm {R} {-}\mathrm {CH} (\mathrm {OH} )\mathrm {S} {-}\mathrm {R} {\vphantom {A}}^{\prime }{}+{}\mathrm {R} {\vphantom {A}}^{\prime }{-}\mathrm {SH} {}\mathrel {\longrightleftharpoons } {}\mathrm {R} {-}\mathrm {CH} (\mathrm {S} {-}\mathrm {R} {\vphantom {A}}^{\prime }){\vphantom {A}}_{\smash[{t}]{2}}{}+{}\mathrm {H} {\vphantom {A}}_{\smash[{t}]{2}}\mathrm {O} }}](https://wikimedia.org/api/rest_v1/media/math/render/svg/1c49362ba9cc6e5184e08085942a1ecf73623713)
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