Hemisulfur mustard, Zchloro-2'-hydroxydiethyl sulfide (I), has been prepared from sodiomercaptoethanol and ethylene chloride, The stability of I is measured by the use of P (p- nitrobenzy1) pyridine (NBP). Direct acylation of I with acid chlorides yields ita corresponding esters. Alternatively, these esters may be prepared by first addition of mercaptoethanol to vinyl esters or direct monoacylation of thiodiglycol, followed by chlorination of the ...