Oxidative desulfurization of disubstituted thioureas using Pb(II) salts and investigation of pK_a-dependent regioselective N-acylation

Abstract

A highly efficient method for the N-acylation of both symmetrical and unsymmetrical thioureas by the use of lead (II) salts and triethylamine has been achieved. The reaction gives regioselective N-acylated product for unsymmetrical thiourea. For unsymmetrical thiuourea, regioselective N-acylation takes place towards the amine having lower pK _a. A linear correlation between the pK _as of the amines and the regioselective N-acylation is found. Another attractive feature of this transformation is that lead sulfide, which is important to material science, is obtained as a side product (nanocubes of 20 nm).

Keywords:

• thiourea
• desulfurization
• N-acylation
• urea
• regioselective

Acknowledgements

B.K.P. acknowledges the support of this research from DST New Delhi (SR/S1/OC-15/2006 and SR/S5/NM-01/2005) and CSIR 01(1688)/00/EMR-II. H.G. to CSIR for fellowship. Special thanks to CB and KKS for TEM and CIF IIT Guwahati for the NMR and mass spectrometry work.