A Column-Free and Aqueous Waste-Free Process for Thioamide Preparation with Lawesson’s reagent

After completing thio-substitution with the Lawesson’s reagent, ethanol was found to be able to efficiently decompose the inherent stoichiometric six-membered-ring by-product from the Lawesson’s reagent to a highly polarized diethyl thiophosphate. This treatment could significantly simplify the following column purification of the desired thioamide in a small scale preparation. As scaling up the preparation of two pincer-type thioamides, we have successfully developed a convenient process with ethylene glycol to replace ethanol during the workup, including traditional phase-cut, extraction, and re-crystallization. The newly developed column-free procedure did not generate P-contained aqueous waste, and only organic effluents were discharged. It was believed that the optimized procedure can greatly provide opportunity of the application of the Lawesson’s reagent for various thio-substituted reacions in scaling up preparation.