The rate of reaction of some substituted anilines with phenyl isothiocyanate, and the correlation with amino-proton chemical shifts

Abstract

The rates of reaction of seven meta- and para-, and five ortho-substituted anilines with phenyl isothiocyanate and 4-fluorophenyl isothiocyanate in carbon tetrachloride at 20° have been measured by infrared spectrometry and correlated with the amino-proton chemical shifts of the substituted anilines measured in the same solvent. The reactivity of the amino-group of meta- and para-substituted anilines is linearly dependent on the electron density on the nitrogen atom of the amino-group, but ortho-substituted anilines deviate greatly from the linear correlation. Although this deviation is interpreted in terms of hydrogen-bonding of the amino-proton to the ortho-substituents, the reactivity is mostly governed by steric strain of the amino-group in reaction with phenyl isothiocyanate.