Titrations in non-aqueous media. Part VII. Effects of substituents on basicity of aniline

Abstract

The basicities of 22 derivatives of aniline with methyl, amino, hydroxy, chloro, bromo, iodo, nitro and carboxy substituents were determined potentiometrically against a standard in nitrobenzene solvent. Methyl, amino and hydroxy substituents had a basicity-increasing effect and the others a basicity-decreasing effect on aniline. The basicity-increasing effects of each substituent differs depending on whether it is at the ortho, meta or para position. The basicity-increasing order of methyl and amino substituents is p > m > o, whereas that of the hydroxy substituent is p > o > m. Halogens, nitro and carboxy substituents all decrease the basicity of aniline. The basicity-decreasing order of the halogens is o > m > p, and moreover is in the order l > Br > Cl for para derivatives and Br > Cl for ortho and meta derivatives. The basicity-decreasing effect of a nitro substituent is in the order o > p > m, whereas that of a carboxy substituent is p > o > m. Among the isomers of ortho-and para-orienting substituents, para isomers, and among the isomers of meta-orienting substituents meta isomers are the most basic. Of the substituents, the basicity-increasing effects decrease in the order NH₂ > OH > CH₃ and the basicity-decreasing effects in the order NO₂ > COOH > l > Br > Cl.