The desulphurisation of thiocarbonyl compounds

The desulphurisation of thioesters by mercury (II) carboxylate salts was shown to give aliphatic acid anhydrides in high yield. The reaction is rapid at room temperature, giving a mixture of mercuric sulphide, ester and anhydride. The mercuric sulphide is removed by filtration and the ester by distillation. An intramolecular mechanism involving two cyclic transition states was proposed for this desulphurisation reaction, and attempts were made to gather evidence for this mechanism. The desulphurisation of thioesters by active W-2 Raney nickel was shown to give saturated ethers in good yields. Thiobenzoates gave alcohols, due to hydrogenolysis of the intermediate benzyl ether. The desulphurisation of thiopheny1 acetates by deactivated W-2 Raney nickel gave enol ethers in moderate yields. The enol ethers were identified by their mass spectra, and by their methanolysis in the presence of an acid catalyst. Thioesters other than thiophenylacetates gave a mixture of products.