Alkylation of ethylenethiourea with alcohols: a convenient synthesis of S-alkyl-isothioureas without toxic alkylating agents

The alkylation of ethylenethiourea with alcohols and aqueous acids (HCl, HBr, and HI) allows the synthesis of the respective S-alkyl-isothioureas in high yield and purity. Consistently high yields (91–98%) were obtained with 56% HI, the yields for 48% HBr (48–93%) and 37% HCl (36–85%) were lower and varied with the type of alcohol. The method is a convenient low-cost alternative to the use of alkyl iodides and an easy access to the S-tert-butyl isothiourea.