The reactions of recoil tritium with substituted benzoic acids

Recoil tritium atoms react with substituted benzoic acids to form tritiated benzoic acid when the substituent group is -NH2,-NO2,-OH,-COOH,-F,-Cl,-Br,-I. The ratio of the total radioactivity bound as benzoic acid to that as the parent molecule ranges from 0.02 for m-am inobenzoic acid to 0.58 for o-iodobenzoic acid. The ease of replacement increases rapidly as the bond strength of the substituent to the aromatic ring decreases. Intramolecular degradation of the benzoic acids shows that most of the tritium radioactivitv substitutes into the position of the substituent. A smaller amount of the benzoic acid activity is always found in other positions than that formerly occupied by the substituent group. Labeled aniline was also isolated from irradiated aminobenzoic acids. The sensitivity to bond strength implies that chemical bonding is much more important than the physical mass of the bonded atoms or groups in determining the course of recoil tritium reactions. This sensitivity also implies that the energy at the time of reaction, while well in excess of thermal energies, is probably in the range of a few electron volts.