In organic chemistry, thioacyl chloride is a functional group of the type RC(S)Cl, where R is an organic substituent. Thioacyl chlorides are analogous to acid chlorides, but much rarer and less robust. The best studied is thiobenzoyl chloride, a purple oil first prepared by chlorination of dithiobenzoic acid with a combination of chlorine and thionyl chloride. A more modern preparation employs phosgene as the chlorinating agent, this also generates carbonyl sulfide as a by-product. PhCS2H + COCl2 → PhC(S)Cl + HCl + COSThe compounds are more stable with electron-releasing substituents.