The trifluoroacetic acid solvent system. Part V. Cryoscopic measurements

Measurement of freezing point depressions for the non-electrolytes, CCl4. CH3SO2F, and (CF3CO)2O permit calculation of the cryoscopic constant for trifluoroacetic acid, HOTFA. Water is shown to give freezing point depressions lower than those for non-electrolytes and this is attributed to association. Freezing point depressions for NaOTFA, KOTFA, and CsOTFA have been measured and accounted for in terms of ion-pair dissociation constants previously determined from electrical conductivity measurements. The results cast doubt on the existence of triple ions in this solvent.

Cryoscopy in molten pyridinium chloride

The molal cryoscopic constant in molten pyridinium chloride (m.p. 146.0�) has been found to be 17.4� (subject to confirmation by calorimetry) and the cryoscopic heat of fusion, 2310�40 cal mole-1. In pyridinium chloride as a solvent, iodides appear to dissociate completely while bromides do not yield the expected depression possibly because of solid solution. Tetraalkylammonium and alkyl-pyridinium halides of high molecular weight are ideally dissociated in extremely dilute solution but with increasing concentration apparently form micelles.