| Abstrakt: |
Studies have been carried out on the hydration of quaternary phosphonium bromides, Bu4−nPhnPBr(n=0–4), in the chloroform phase by means of distribution equilibrium and 1H NMR spectroscopy, in order to clarify the difference between the alkyl- and aryl-substituted ions in ion–water interactions. The hydration constant for these bromides in the chloroform phase increases gradually from Bu4PBr to Bu2Ph2PBr, and then rapidly to BuPh3PBr and to Ph4PBr. The free energy of transfer from water to chloroform was evaluated for the non-hydrated species of the phosphonium bromides in the chloroform phase, the lowest being that for Bu2Ph2PBr. From 1H NMR spectra for water in the chloroform phase, it is concluded that the hydrated water molecule is hydrogen bonded with the anion of the onium salts. In the case of phenyl-rich cations such as BuPh3P+, Ph4P+, and Ph4As+the water molecule occupies a site so close to the central atoms that it undergoes diamagnetic effects of phenyl groups. With phenyl-rich cations such hydration will play a certain role in their aqueous solutions. |
