High-Yield Syntheses of N-Mono- And N,n-Di-Substituted Ureas and Thioureas From Silicon Pseudohalides

This study demonstrates that N-mono- and N,N-di-substituted ureas and thioureas may expediently be synthesized, in essentially theoretical yield, by reacting primary or secondary aliphatic, alicyclic, aralkyl, aromatic, and heterocyclic amines with silicon tetraisocyanate or tetraisothiocyanate, or the corresponding methyl-substituted analogues. The method fails with aromatic amines possessing bulky (e.g. phenyl, bromo), or strongly electronegative (e.g. trifluoromethyl), substituents in the 2-, or 2,6-positions of the aromatic nucleus. Data on several new substituted ureas and thioureas are reported, and improved preparative procedures for the silicon pseudohalides are described.