Pulse radiolysis of benzyl chloride and -bromide; The UV-visible absorption spectrum of the benzyl cation

Abstract

Pulse radiolysis study of liquid benzyl chloride has been carried out at room temperature. In order to identify transient species that absorb in the UV-vis region, various scavengers were used including oxygen, ethanol, pyrrole, biphenyl, and mesitylene (1,3,5-trimethylbenzene). The spectrum of the benzyl cation was obtained by subtracting the transient spectrum for the 0.6 M solutions of ethanol in O2-saturated benzyl chloride from that for O2-saturated benzyl chloride. The difference spectrum obtained has a strong absorption band at 303±2 nm and a weak broad band near 500 nm. The analyses of end products formed in the γ radiolysis of benzyl chloride were done in the presence and absence of scavengers. The formation of benzyl ethyl ether with a G value of 0.9 from a 0.6 M solution of ethanol in O2-saturated benzyl chloride was taken as evidence that added ethanol reacts with benzyl cations to give benzyl ethyl ether. Some pulse radiolysis experiments were performed with benzyl bromide. Transient spectra observed in benzyl bromide are similar to those observed in benzyl chloride. It is, however, inferred from the product analysis that the radiolytic mechanisms of benzyl bromide appreciably differ from those of benzyl chloride.