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

Abstract

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 °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−, SO42−, and PO43− 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 °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.