Transient benzyl radical reactions produced by high-energy radiation

Abstract

Lifctimc mcasurements in solution at 25'C have been made on the beiizyl radical (CbHgCH2') produced by a pulsed beam of electrons from a linear accelerator. The absorption spectrum of the radical has been measured both photographically and pholoelectrically as a function of time and solvent (cyclohexane, ethanol, ethanol+ glycerol, and glycerol). Two distinct kinetic processes were observed : (i) two coincident secondorder reactions with rate constants of 2 x 108 l./mole sec and 4 x l o 7 l./mole sec at a viscosity of 55 cp, and (ii) a first-order reaction which has a rate constant k~ = 19 sec-1 which is indcpcndcnt of solvent and viscosity. The formcr are attributable to the disappearance of benzyl radicals by diffusion-controlled processes. The latter is identified as the decay of a triplet state of stilbene, which is not observed in flash photolysis of the same solutions. Products were analyzed using gas-liquid chromatography, ultra-violet

Direct Observation of the Radicals Formed in the Radiolysis of Liquid Benzyl Alcohol. An Electron Spin Resonance and Spin Trapping Method

“…This, together with the magnitude of the coupling constants, strongly suggests P~~H O H , as in [5] H Saturating the solution with nitrous oxide prior to radiolysis had no effect on the observed e.s.r. spectrum suggesting that [6] does not occur to any appreciable extent.…”

“…spectra while the sample is being irradiated. The transient optical absorption detected in pulse irradiated neat benzyl alcohol (4) and its solution in cyclohexane (5) has been assigned to benzyl radicals. It was suggested that these were formed by the dissociative electron capture reaction [3 1 PhCH20H + e -+ PhCH,.…”

Pulse Radiolysis

“…OH· + CH30H + ·CH20H + H20 (2) with the product ·CH20H, (as well as the electron), being reducing. Sometimes tertiary butanol is used because the radical (CH3)3·COH is often very unreactive and only reduction by the solvated electron then arises.…”

“…Pulse radiolysis was developed as a technique for studying fast processes in solution about 20 years after flash photolysis, [1][2][3][4] The initial consequences of the absorption of ionising radiation is however quite different to that produced by light (250-S00 nm) absorption. This is simply because in the case of light absorption (as in flash photolysis) the energy is absorbed by the solute whereas, at least for dilute solutions, the ionising radiation associated with the pulse radiolysis technique is absorbed by the solvent in a non-specific manner.…”

The Flash Photolysis of 1,3,5‐Cycloheptatriene and Some 7‐Substituted Derivatives

“…Unfortunately, the only data available is for solutions in cyclohexane (11), where the spectrum is displaced to longer wavelengths and is much broader than in the gas phase. Assuming that thef-value of the transition is the same in the two media, we obtain Emax w 8000 1.mole-1 cm-l for the 3050 A band in the gas phase.…”