Radiation chemistry of organic amides. Part 3.—Yield and mechanism of formation of molecular hydrogen in N-methylpyrrolidin-2-one
Abstract
The radiolytic formation of molecular hydrogen has been studied in solutions of methyl bromide, sulfuric acid and iodine in N-methylpyrrolidin-2-one (NMP) and also in acidic aqueous solution of NMP using gas chromatography and vacuum techniques. The yield of H2 in NMP was measured to be G(H2)= 107 ± 7 nmol J–1, which is rather low relative to other organic solvents. 61.6% of the H2 formed comes from molecular processes and 38.4% from H˙ abstraction from NMP. The low yield is attributed to the fact that the natural decay of e–s does not lead to the formation of H2. Experiments in acidic aqueous solution show that H-atom abstraction from NMP by H·, rather than addition to the carbonyl group, is the kinetically favoured reaction. The rate constant for the abstraction is 2.1 × 107 dm3 mol–1 s–1, which is estimated to be ca. 200 times faster than the addition reaction. A reaction scheme is proposed for the behaviour of e–s and the formation of H2.