Heat Capacity Changes of Alkyl-substituted Ammonium Chlorides in Aqueous Solutions

概要

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The changes in the heat capacity for the dissolution in water, ΔCP°, of n-alkylammonium chlorides (methyl to hexyl), di-n-alkylammonium chlorides (methyl to butyl), and tri-n-alkylammonium chlorides (methyl to propyl) at the room temperature were determined from measurements of the relation between the heats of solution of these salts in water and the temperature, and the results were compared with the ΔCP° values for tetraalkylammo-nium salts in the literature. It was found that the effect of the coordination of the charge-bearing nitrogen atom by alkyl groups was definitely reflected in the ΔCP° values. In the cases of MeNH3Cl, EtNH3Cl, Me2NH2Cl, and Me3NHCl, the ΔCP° values are negative, while in the cases of other higher homologues, the ΔCP° values are positive; the increments in the ΔCP° values per methylene group are discussed in terms of the hydrophobic hydra-tion and the steric effect of alkyl chains.
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