Pulse radiolysis of aqueous solutions of sodium tetraphenylborate

Abstract

In previous work on the 60Co γ-radiolysis of aqueous tetraphenylborate (TPB -) solutions carried out in this laboratory, it was found that several organic products, including benzene, phenol and biphenyl, are produced with substantial yield. However, the reaction mechanism was not established. In the present study, reactions initiated by OḢ radicals, N 3 radicals and e - aq in aqueous TPB - solutions were studied by pulse radiolysis using a 600 keV Febetron electron accelerator. The lack of reactivity between TPB - and e - aq was demonstrated by directly monitoring the transient optical absorbance of e - aq. Concerning the reaction with O Ḣ, two schemes were considered: (1) electron transfer from B(C 6H 5) - 4 to O Ḣ; or (2) O Ḣ addition to B(C 6H 5) - 4. Comparison of observed transient absorption spectra with expectations based on two different schemes suggests that O Ḣ addition is the dominant reaction pathway under conditions of N 2O saturation, with an experimentally determined second-order rate constant of 6.2×10 9M -1s -1. A mechanism based on an initial first-order self-decomposition of the O Ḣ adduct, (C 6H 5) 3BC 6H 5OH -· with a measured rate constant of 4×10 4s -1 is proposed. Kinetic modeling on the proposed mechanistic scheme gives good agreement with our experimental results.