Solvent effect on the dissociation of o-nitroanilinium ion in methanol-propylene glycol media at 25°C

✍ Scribed by A.L. De

• Publisher: Elsevier Science
• Year: 1984
• Tongue: English
• Weight: 405 KB
• Volume: 29
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(84)87096-6

✦ Synopsis

The dissociation constants (K,) of o-nitroanilinium ion have been determinedat 25" in methanol, propylene glycol and mixtures of the two components containing 10,30,50,70 and 90 wt. % propylene glycol by spectrophotometric measurements. Standard free energies of transfer, AG;(B) of o-nitroaniline from methanol to the other solvents have been evaluated from themeasurement of solubilities at 2S"C.The solvent effect on the proton transfer process of this acid: AGp[BH+-B], I = 2.303RT[p(K,)-p(K,)) has been discussed in terms of the free energies of transfer AGp from methano r' to other solvents, of the uncharged base B, of the hydrochloride of the base (BHCI) computed from the corresponding values for HCl and also of the individual ions assessed from the previous knowledge of' AG,"(Cl-). The corresponding data for the proton&xl tris(hydroxymethyl)methyl amine [TrisH+] and p-nitroanilinium ion in the same solvent system obtained from the literature are also compared. AGP[BH+-B],,, values for the dissociation of onitroanilinium ion have been found to increase less readily with wk"A propylene glycol compared to pnitroanilinium ion and are in contrast with the decreasing nature of thecorresponding values for the TrisH* ion of different chemical nature. Electrostatic effect being negligible in this solvent system, the overall behaviour of these acids is found to be dictated by specitic chemical nature of solute-solvent interactions besides the effect of relative solvent basicities.