Trapped electrons produced by the deposition of alkali-metal atoms on ice and solid alcohols at 77°K. Part II. Chemical reactions during thermal and photolytic bleaching

Abstract

The deposition of alkali-metal atoms on ice and solid aliphatic alcohols at 77°K yields intensely coloured deposits. Electron spin resonance (e.s.r.) spectra of the deposits show that they contain trapped electrons, e_t^–.

When a sample from an alcohol is either warmed slightly or illuminated with visible light, the colour of the sample fades and the e.s.r. spectrum changes to that of the corresponding α-hydroxyalkyl radical, R¹R²ĊOH. The rates of conversion are of the first order with respect to the concentration of the trapped electrons. Activation energies of 4–5 kcal./mole and pre-exponential factors of the order of 10⁴–10⁷ sec.^–1 are obtained for the various alcohols.

It is postulated that the rearrangement of the electron trap occurs to give a single-step reaction which can be represented formally as e_t^–+ 2R¹R²CH·OH → R¹R²ĊOH + R¹R²CHO^–+ H₂