Tritium labelling, tritium N.M.R. and tritium tracing: some new applications

Abstract

N.m.r. chemical shifts have been determined for the first time for ring tritons in m-xylene, o-xylene and methoxy benzene. Assignments were made by preparing individual labeled isomers of each compound using a Grignard synthesis. The data gained in this study, was used to show that the tritium labeling of aromatic compounds on a γ-irradiated silica gel catalyst probably occurs via an electrophilic mechanism. A total of 36 substituted benzamides and N-alkyl benzamides have been tritiated in the labile amido position by exchange with tritiated water. Tritium n.m.r. was used to obtain amido triton chemical shifts. These values were combined with proton chemical shift data from an earlier study and correlated against Hammett σ values. Specifically tritiated fatty acids and labeled wax ester were produced at high specific activities and their metabolism by the domestic pig studied in a series of tracer experiments. Compounds prepared for this purpose included α-3H stearic acid, 9, 10-3H stearic acid, methyl 9 10-3H-oleate, methyl 9, 10-3H2-oleate, 9,10-3H-oleyl alcohol and 3H-oleyl oleate. Tritiation was accomplished using acid catalysed exchange with tritiated water, reduction with labeled diimide, and reduction with tritium gas in the presence of Lindlar's catalyst. In all cases the high specificity of labeling was demonstrated using tritium n.m.r. spectroscopy. An on-line reactor system has been developed to study the conversion of methanol to hydrocarbons on the zeolite catalyst ZSM-5. Ring to side-chain exchange on this catalyst has been studied using ring-tritiated xylenes and methyl-labelled toluene. The results of this study have been used to discount partially a theory for the production of ethylene via side-chain methylation of toluene on ZSM-5. Octane decane and tridecane have been labeled on a Raney nickel catalyst for use by a colleague in studies on the air-sea exchange of natural gas condensates. Toluene has been tritiated using a γ-irradiated silica gel catalyst for the same purposes.