Heat capacity changes and standard partial molal heat capacities of aqueous solutions of some tetra-alkyl ammonium halides at 30°C and the effect on water structure

Abstract

ACi values of tetra-alkylammonium halide salts Me4NBr, Me4NT, Et,NBr, Et4NI, Pr4NBr, Pr4NI and Bu4N13r in aqueous solutions at 30°C have been determined by measuring integral heats of solution at 25 and 35°C AC; values which vary from -16.5 to 179 cal deg.-' mole-' are in the increasing order of Me,NI< Me,NBr< Et4NBr 5 Et,NI< Pr4NBr % Pr4NI< Bu4NBr. Results are discussed in terms of the influence of tetra-allcylammonium halide salts on the water structure. Me4NBr and Me,NI break water structure, while all other tetra-alkylammonium bromide and iodide salts enhance or promote water structure. The influence of %N+ salts in promoting water structure increases greatly with increase in the size of the alkyl group R. The influence of anions (bromide and iodide) does not appear to be significant in modifying the structure of water. Results from this work support the concept of " cation-cation interactions " in explaining the nature of interaction of tetra-alkylammonium halide salts with water.

Solvation Enthalpies of Some Alkali Metal and Tetraalkylammonium Salts in Dioxane-Water Mixtures

“…The increase in the AH: value of Me4NBr in passing from pure water to 44.5% cannot be explained on the basis of normal behavior. The positive ACpO values for the rest of the tetraalkyl ammonium bromide salts in water indicate that these salts increase the structure of water (7,22,23). Since the AH: values become more endothermic in passing from pure water to 64.5% dioxane-water mixtures, a similar conclusion can be drawn for these salts in dioxane-water mixtures.…”

Thermodynamic properties of organic compounds in aqueous solutions. Apparent molal heat capacities of amines and ethers

“…20) ; e calculated from the value reported in ref. (22) for (CH&NBr and @c, of HCI and HBr in ref. (20).…”

“…(20); e calculated from the value reported in ref (22). -APPARENT MOLAL HEAT CAPACITY @cn = f( T ) OF AMINE HYDROCHLORIDES t-40)+ ~( t -40)2 ' The reported uncertainties were calculated as mean standard deviations obtained by a least square method ; b ref.…”

Thermodynamic properties of tetraalkylammonium halides: volumes, heat capacities, and expansibilities in H2O, D2O and urea–water mixtures from 278 to 328 K

“…Expansibilities and compressibilities are also used to calculate heat capacities at constant volume from heat capacities at constant pressure (161, Recently, much data has been accumulated on the partial molal heat capacities of R4WX in water. Ahluwalia and co-workers (17)(18)(19), de Visser and Somsen (20,21), Mastroianni and Criss (22), and Arnett and Campion (23) have measured the standard enthalpies of solution at various temperatures and derived the change in heat capacity of R4NX from the pure solid state to infinite dilution. The standard partial molal heat capacities cpo can then be calculated if the specific heat capacities of the solid electrolytes are known.…”