Tritium labelling of alkanes using organoaluminium dihalide catalysts

The results of a study of the tritiation of a variety of alkanes using ethylaluminium chloride are reported which show that the technique is applicable to many alkanes, in particular those containing tertiary carbon atoms. This rapid and simple method has already been described in detail for labelling various types of aromatic and olefinic compounds (Long, Garnett and Vining. J.C.S. Perkin; 11:1298 (1975)). Labelling of both cyclic and non-cyclic alkanes was observed in every case where the molecule contained at least one hydrogen atom attached to a tertiary carbon atom. In general the degree of tritium incorporation was considerably enhanced by elevation of the reaction temperature to 960. In contrast, of the alkanes studied, not one possessing only primary and secondary hydrogen atoms showed any significant tritiation at either room temperature or 960. In most instances when labelling of the alkane occurred, some skeletal isomerisation to yield labelled byproduct was also observed. The study shows that the simple tritiation technique described is applicable beyond the aromatic and unsaturated systems previously studied, although reaction times greater than the few minutes required for aromatics are necessary. (U.K.)