Studies of Tritium-labeled Compounds. VII. The Platinum-catalyzed Exposure Reaction

Abstract

Abstract In order to elucidate the nature of the chemisorption in the platinum-catalyzed exposure reaction with tritium, the effects of the substituents upon the hydrogen-tritium exchange of the aromatic ring and upon the tritium distribution in benzoic acid, salicylic acid and benzoylvaline have been investigated. All the substituents except the hydroxyl group decrease the hydrogen-tritium exchange of the aromatic ring, and the compounds carrying those substituents poison the catalyst for the tritium incorporation of benzene. This retardation effect of the substituents upon the hydrogen-tritium exchange of the aromatic nucleus may perhaps be attributed to the preferential adsorption of the substituents on the catalyst surface. The tritium distribution in benzoic acid and salicylic acid suggests that the hydrogen-tritium exchange in the aromatic ring may follow the substitution rule for electrophilic aromatic exchange. The relative hydrogen-tritium exchange rates of benzoylvaline show that the more readily a hydrogen dissociates, the more rapidly it undergoes the exchange.