The Vilsmeier reagent derived from N-formylmorpholine produces chlorothioformates from primary and secondary alkyl xanthates. The major side products are the corresponding alkyl chlorides. Secondary alkyl chlorothioformates give lower yields due to their instability. Treating xanthates with other common chlorinating agents (oxalyl chloride, thionyl chloride) gives only dialkyl thiodicarbonates.
The preparation of O-alkyl carbonochloridothioates (2) was improved by performing the reaction of thiophosgene with potassium alkoxides in the corresponding alcohol or in tetrahydrofuran at - 65°C for 1 hour. In all cases, the reaction yielded products 2, O,O-dialkyl carbonothioates (4), and dialkyl carbonates (5) in varying distribution.