Ethyl orthothioformate

A cloudy mixture of 20 g. (0.32 mole) of ethyl mercaptan and 12 g. (0.16 mole) of ethyl formate is cooled in an ice-salt bath while dry hydrogen chloride is introduced until the mixture becomes saturated. (Hood.) On the introduction of the hydrogen chloride, the mixture becomes clear for a while, after which the water formed in the reaction causes reappearance of a second liquid phase. After several hours the reaction mixture is washed with water and the oily layer is removed by extraction with ether. After drying over calcium chloride, the ether layer is distilled to give 16 g. of ethyl orthothioformate, b.p. 133°/21 mm. The yield is 82% based on ethyl mercaptan. 

---

Preparation of Ethyl Orthoformate from Ethyl Orthothioformate [39]... 

Ethyl orthoacetate, 48 Ethyl orthobenzoate, 54 Ethyl orthobromoacetate, 60 Ethyl orthodibromoacetate, 60 Ethyl orthoformate, 50 Ethyl orthothioformate, 50 Ethyl a-phenylazo-a-methylacetoacetate, 299... 

This interchange reaction is a convenient process for making orthoformates. The equilibrium is shifted to the right by removal of the volatile mercaptan to give high yields of the ortho esters. The reaction is catalysed by Frledel-Crafts type catalysts. The ethyl orthothioformate is available in nearly quantitative yield om ethyl formate and ethyl mercaptan. 

Dithioacetals and related compounds have a number of uses in synthesis, both in Friedel-Crafts-type reactions and in reactions which exploit the high reactivity of carbanions stabilized by two or more sulphur atoms bonded at the carbanion centre. Benzyl orthothioformate, CH(SCH2Ph)3, may be used to introduce a — CH(SCH2Ph)2 group into 2- and 3-positions of an indole, with TiCU as catalyst at - 5 °C in CHQ3, and has been used in this way for 2-substitution of (79), giving (80) and (81), with further elaboration of (80) into 2-methyl-lysergic acid. Studies of ethyl dithio-... 

---