ISOTOPIC COMPOSITION OF RADIOLYTIC HYDROGEN EVOLVED FROM MIXTURES OF BENZENE AND CYCLOHEXANE WITH THEIR DEUTERATED ANALOGUES

Abstract

We have measured the isotopic composition of radiolytic hydrogen evolved from mixtures of benzene and cyclohexane with their deuterated analogues. The data are interpreted in terms of first-order processes of the kinetic form (for C₆D₁₂) C₆D₁₂ → C₆D₁₀ + D₂ and second-order processes C₆D_I2 → X_D + R, X_D + C₆H₁₂ → HD + R.A complete kinetic analysis for the system C₆D₆–C₆H₆ has been made from measurements at the two ends of the concentration range. This gives a satisfactory prediction of the isotopic composition of hydrogen evolved from an equimolar C₆H₆–C₆D₆ mixture. A first-order yield of D₂ is found in solutions of C₆D_I2 in benzene which persists to 'zero' C₆D₁₂ concentration. The mechanisms of the first-order process studied in these experiments, and of the 'unscavengeable'or 'molecular' yields of radiolytic hydrogen, are discussed.