Ultrasonic Velocity and Compressibility Studies of Tetraalkylammonium Salts in Acetonitrile plus Methanol Binary Mixtures at 298.15 K

摘要

The ultrasonic velocities (u) and densities (rho) of tetraalkylammonium perchlorates (R4NClO4, where R = Methyl, Ethyl, Propyl or Butyl) and tetrabutylammonium tetraphenylborate (Bu-4 NPh4B) solutions have beenmeasured at different salt concentrations in the range (30-500) x10(-4) mol kg(-1) in binary mixtures of acetonitrile (AN) with methanol (MeOH) containing 0, 20, 40, 60, 80 and 100 mol% methanol at 298.15 K. The isentropic compressibilities (K-s) and apparent molal isentropic compressibilities (K-s,K-phi) of different salts in the solvent mixtures have been calculated. Limiting apparent molal isentropic compressibilities (K-s,phi(0)) for various salts have been evaluated and split into contributions of individual ions i.e., into (K-s,phi(0))(+) values. The variation of (K-s,phi(0))(+) values with solvent composition shows that Bu4N+ and Ph4B+ have very large positive (K-s,phi(0))(+/-) values which show strong solvophobic interactions in AN and in AN + MeOH mixtures over the entire solvent composition range. These positive values indicate some special type of interactions with the solvent molecules, which increase with the increase of MeOH composition. ClO4-shows much weaker solvation in AN + MeOH mixtures by having some interaction withANin the AN rich region of the mixtures. The negative values of Me4N+ and Et4N+ ions show strong structural effects which arise due to solute-solvent interactions in MeOH rich region of mixtures.