Kinetics and mechanism of hydrolysis of benzhydryl N-arylthiocarbamates and study of their IR spectra

Abstract

The hydrolysis of benzhydryl N-arylthiocarbamates proceeds by the ElcB mechanism. The reaction mechanism of S-benzhydryl N-arylthiocarbamates has been determined by trapping the reactive intermediate phenyl isocyanate (as N-phenyl-N'-mopholinourea) and by following the substitutent effects in benzene ring of the benzhydryl group. The hydrolysis mechanism of O-benzhydryl N-arylthiocarbamates has been confirmed by spectral and kinetic determination of phenyl isothiocyanate. The hydrolysis of the primary formed phenyl isothiocyanate is almost 10 times slower than that of the starting thiocarbamate. With O-benzhydryl N-arylthiocarbamates at pH below 9 there takes place, at first, a rapid rearrangement to S-benzhydryl N-arylthiocarbamates, and benzhydrol is the reaction product. The rearrangement rate is pH independent. At pH above 11.5 the hydrolysis of O-benzhydryl N-arylthiocarbamates is much faster than the rearrangement, and thiobenzhydrol is the reaction product. Using the deuterated derivatives, the IR spectra of carbamates and thiocarbamates have been interpreted with respect to coupled vibrations of carbamic, thiocarbamic, and dithiocarbamic groups.