Resolution of the over-all basicity of carcinogenic and noncarcinogenic derivatives of 4-aminoazobenzene.

The pKa of the over-all basicity of 4-aminoazobenzene and derivatives has been re solved in pKam and pK^, which represent the pKa of the two basic centers, the amino nitrogen and the /3-azo nitrogen. This resolution has made possible for the first time a comparison of the carcinogenic activity of these dyes with a property related to electron density at these centers. It appears that excessive electron density around the amino nitrogen brings about loss of activity. The recent hypothesis of the Pullmans that both basic centers are concerned in the activity of aminoazo dyes is consistent with the results of the present work. There is a fairly good correspondence between our pK&mand pK,¿z data and the electric charges on the amino nitrogen and /3-azonitrogen atoms as theoretically evalu ated by the Pullmans.