Halogenation of thiodiglicolic acid and thiodilgycolic diethylester was obtained by a variety of methods. Selective halogen introduction at the &alpha,&alpha-positions or at the a,a'-positions was accomplished using either a radical or a polar process. Phase-transfer ring-closure of the a,a'-dibromo diethylester with Na₂S₂ produced the five-membered ring 1,4-dimethyl-1,2,5-trithiapentane diethylester.