Validity of a linear Hammett plot for the stability of some carcinogenic 1-aryl-3,3-dimethyltriazenes in an aqueous system.

The stability of fourteen carcinogenic 1-aryl-3,3-dimethyltriazenes to hydrolysis in 0.15 ᴍ phosphate buffer, pH 7.0, at 37° was determined spectroscopically. The data gave an unexpectedly wide span of half-lives resulting in a linear Hammett plot with a reaction constant, ρ= -4.7. These results are in complete agreement with the currently accepted mechanisms of carcinogenic activity associated with this class of compounds. The rapid liberation of a diazonium cation from the labile triazenes (t½, less than 2 × 102 min) seems to be responsible for the induction of local tumours; however, an enzymic activation is necessary for the systemic carcinogenic activity of the compounds stable to hydrolysis (t½, more than 2 × 102 min). Convincing experimental evidence is thus provided for two different mechanisms of activity which are operative within a single class of chemical carcinogens.