Excitation labeling with tritium. Studies of side reactions with model compounds

Abstract

A series of model compounds such as hexane, 2-heptene, 3-methylhexane, methylcyclohexane, benzene, toluene, styrene, benzoic acid and phenylalanine have been exposed to a stream of excited tritium atoms produced in a microwave-induced plasma. Product analysis by gas-liquid radiochromatography revealed that the yields of labeled parent compound, based on incorporated non-exchangeable tritium label, ranged from less than 1% for n-hexane to 71% for methylcyclohexane. Other labeled products included high-boiling polymers, degradation products, and saturated analogs formed by tritium addition to double bonds or to the phenyl ring. Incorporation of tritium into the molecule appears to be selective, and the presence of a methyne hydrogen favors the labeling. Not only tritium atoms from the plasma but also long-lived radicals containing tritium in the sample caused tritium-labeling. The latter attacks susceptible solvent molecules post-labeling to produce additional labeled contaminants.