Hydrates of Organic Compounds. VII. The Effect of Anions on the Formation of Clathrate Hydrates of Tetrabutylammonium Salts

Article abstract of DOI:10.1246/bcsj.56.877

Phase diagrams of the binary mixtures of tetrabutylammonium salt <(n-C4H9)4N>nX (X = NO2, NO3, BrO3, ClO3, IO3, ClO4, MnO4, and NCS for n = 1; X = CO3, SO4, WO4, and CrO4 for n = 2; and X = PO4 for n = 3) with water were determined over the temperature range between -10 and +50 deg C.From these diagrams the following results were obtained: (1) the formation of a clathrate-like hydrate for salts having such anions as NO2^-, NO3^-, BrO3^-, ClO3^-, IO3^-, SO4^2- and PO4^3- was newly confirmed; (2) the melting point of the clathrate hydrate of the salt with monovalent anion was appreciably influenced by the kind of anion; (3) in the hydrates of the salt having either di- or trivalent anions, the melting points were relatively high and were only slightly affected by the kind of anion; (4) the crystal structure of these hydrates was essentially the same as that of the tetrabutylammonium fluoride hydrate, judging from the hydration numbers; (5) the solubilities in water of both permanganate and perchlorate were markedly lower than that of the iodide; and (6) in the thiocyanate system a phase separation into two liquid phases was observed at temperatures higher than +3.5 deg C.The effect of a monovalent anion on the stability of the clathrate hydrate was discussed in connection with the conventional partial molal volume of the anion.