SUMMARY
The reactivity of substituted 5,7-dichloro-9-hydrazine acridine that exhibit various pharmacological activity by studying acid-base equilibria in the ethanol-water binary solvent (50 mol % ethanol) at 250? using the method of potentiometric titration has been investigated. The values pK of the corresponding conjugate acids obtained for 7 compounds indicate that these compounds are very weak bases. Analysis 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-dichloro-9-hydrazine acridine, and donor substituents cause the opposite effect. The quantitative assessment of the influence of substituents in the molecule by 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 pKBH+ experimentally obtained for 1-CH3 substituent the s-constant of this substituent: s(1-CH3) = 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 molecular design of more active pharmacophores.