Site of attack in the interaction of hydrated electrons and hydroxy radicals in the pulse radiolysis of arylalkylamines in aqueous solutions

Abstract

The site of attack and the reaction rate constants of e^-_aq with various alkylarylaminesbenzylamine, α-methyl benzylamine, aminodiphenyl methane, N-methylbenzylamine, and N,N-dimethylbenzylamine have been determined by pulse radiolysis at different pH values taking into consideration the ionization constants of the amino group present in these molecules. The k values are influenced by the polar and steric effects brought out by the substituents and decrease with deprotonation of the NH⁺₃ group. Reductive deamination is the major observation when the amino group is protonated while the molecule with unprotonated amino group forms a radical anion by the addition of e^-_aq to the aromatic nucleus. From the characteristic transient absorption spectra and extinction coefficients of the deaminated radicals, the extent of deamination is calculated. The OH radicals do not lead to any oxidative deamination nor abstract α-H atom, but only add to the aromatic ring. The kOH+arylalkylamines are estimated to be in the range 5.2 to 6.9 × 10⁹ M^-1 s^-1. On the other hand, the O^- radicals give rise to substituted benzyl radical by the abstraction of α-H atoms from the aliphatic chain.