HETEROGENEOUS PALLADIUM-CATALYZED EXCHANGE LABELING OF REPRESENTATIVEORGANIC-COMPOUNDS WITH TRITIUM GAS

A range of organic substrates was successfully exchanged with tritium gas using NaBH4-reduced palladium oxide or chloride as catalyst. Excha nge conditions involved a reaction temperature of 100 degrees C, a rea ction time of 3 days, and products were analyzed by radio-gas chromato graphy and H-3 NMR spectroscopy. Both aromatic and aliphatic compounds underwent exchange, 18 of the 22 substrates incorporated >35% of the available tritium, and most products showed high radiochemical purity. H-3 NMR analyses showed that both alkanes and the alkyl chains of alk ylbenzenes were rapidly and evenly labelled. Some aromatic compounds s howed general ring exchange while others showed high specificity. Thes e results for bulk palladium catalyst are strikingly different from th ose obtained with bulk platinum and supported palladium catalysts. The results are discussed in terms of currently accepted mechanisms of he terogeneous metal catalyzed hydrogen isotope exchange reactions.