THE REACTIVITY OF AROMATIC AND HETEROCYCLIC DERIVATIVES OF HYDRAZINE. VІІ. THE ACID-BASE PROPERTIES OF SUBSTITUTED 5,7-DICHLORO-9-HYDRAZINE ACRIDINE
The reactivity of substituted 5,7-dichloro-9-hydrazine acridine that exhibit various pharmacological ac- tivity by studying acid-base equilibria in the ethanol-water binary solvent (50 Mol % ethanol) at 25°С using the method of potentiometric titration has been investigated. The values рК of the corresponding conjugate acids obtained for 7 compounds indicate that these compounds are very weak bases. Ana- lysis of the impact of the nature and position of substituents in the heterocycle on the strength of the corresponding conjugate acids has shown that the acceptor substituents weaken basicity of 5,7-di- chloro-9-hydrazine acridine, and donor substituents cause the opposite effect. The quantitative asses- sment of the influence of substituents in the molecule by the Hammett equation within the principle of linearity of free energies with convincing statistical parameters has shown a low sensitivity of the reaction centre to structural changes in the molecule of 5,7-dichloro-9-hydrazine acridine. Using the correlation equation and the value рКВН+ experimentally obtained for 1-СН3 substituent the σ-constant of this substituent: σ(1-СН3) = 0.056 has been determined. The Hammett correlation equation is used to predict the acid-base properties of substituted 5,7-dichloro-9-hydrazine acridines and the molecular design of more active pharmacophores.