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Prevailing classification of salts based on their effect in solubility and stability of proteins in aqueous solution predicts that tetraalkylammonium salts, guanidinium chloride (GnCl), LiClO 4 act as salting-in (S/I) and LiCl, NaCl act as salting-out (S/O) in aqueous conditions. In the same context the behaviour of GnCl, LiClO 4 and LiCl are contradictory in polar solvents like ethylene glycol and formamide. In these solvents, expected salt effect shows just opposite nature from their usual expectation. However, in the aqueous solution salts like tetraalkylammonium halide (R 4 NX, R = alkyl group, X = Br group) behave like salting-in salts. The physicochemical origin of the salting in effect of R 4 NX type of salts has been discussed elaborately in the present work. The role of cations in terms of substitution of various alkyl groups on R 4 NX has been systematically presented here on the basis of experimental kinetic and thermodynamic studies. The abnormal behaviour of R 4 NX salts in aqueous solution has also been explained by the Setschenov equation (k s ) and Δμ solvation values, which highlights their individual nature out of common properties of R 4 NX.

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Vapor pressures of the system nitrobenzene + tetrabutylammonium picrate, which is continuously miscible from dilute solution to molten salt, are presented at 373 K over the full concentration range. The solvent activities in these systems are analyzed with the Pitzer−Simonson model and a local composition model proposed by Chen. Ion pairing has been considered for both models. The Pitzer−Simonson equations based on a combination of Debye−Huckel and van Laar terms accounting for the long- and short-range interactions, respectively, can accurately reproduce the experimental activity data using ion pairing. The activity data can also be fitted by the local composition model using two parameters.