S-Alkyl-thio:chloroformate deriv. prepn. in high yield - from phosgene and mercaptan using activated carbon catalyst

Continuous prepn. of 5-alkyl thiochloroformates comprises reacting equal amts. of phosgene and a 4-12C alkyl mercaptan counter-currently in two stages. The first stage is carried out at 40-50 degrees C using activated carbon >=2 mm grain size. The mercaptan is charged to the first stage such that it is present in excess and that the mixt. leaving the first stage still has some unreacted mercaptan in it. The second stage is carried out at 40-50 degrees C and with the same type catalyst, but, with the phosgene introduced in excess so that the mixt. from the end of the second stage contains free phosgene, but, no unreacted mercaptan. The final prod. is freed of HCl and any unreacted phosgene by heating in a column and injecting an inert gas. The mixt. of inert gas, phosgene, and HCl is recycled to the first stage, and the final prod. recovered. The prod. is obtd. in improved, quantitative, yield without the need for excessive and expensive safety precautions arising from sepg. excess phosgene from the catalyst.