Preparation of Tritium-labelled Derivatives of Benzoic Acid

Abstract

ISOTOPE exchange methods have long been employed for the study of the reactions of hydrogen atoms attached to aromatic ring-systems, and also, to a limited extent, for preparative purposes^1,2. Most of the preparations described in the literature were carried out with water of a comparatively low deuterium content. While these methods are not suitable for the preparation of compounds having a high D : H ratio in the labelled groups, they are (apart from questions of economy in the use of tritium), in principle applicable to the preparation of tritium-labelled materials, since the tritium content of the starting material (water) is normally much less than 1 per cent. The present communication describes a simple, rapid and direct method for the labelling of p-nitro benzoic acid at very high specific activity, with considerable economy in the use of radioactive material. It is also suitable for use with deuterium at high abundance. The two isotopes can, with advantage, be combined in the same preparation: analytical procedures (for example, infra-red spectroscopy) are thereby considerably facilitated.