Thermochemistry of some alkylammonium halides and polyhalide complex compounds

Abstract

The standard enthalpies of formation of the alkylammoniumpolyhalides have been calculated from measured enthalpies of reaction with aqueous silver nitrate; standard enthalpies of formation of have been determined by an extra-polation procedure. These calculated enthalpies of formation been used to determine the thermochemical radii of and also to obtain the lattice energies of the alkylammonium polyhalide compounds. Standard enthalpies of formation of the gaseous cations have been derived as The standard enthalpies of formation of ethyl-substituted ammonium halides have been obtained from measured enthalpies of reaction with aqueous sodium hydroxide. Results for are in good agreement with values already reported in the literature. These standard enthalpies of formation were linearly related to the number of ethyl groups, n. Standard enthalpies of formation of tetraethylammonium halides (Cl, Br, I) have been obtained by extrapolation. The lattice energies of these salts have been calculated using the thenuochemical radius procedure. From the calculated thermochemical radii of the cations and the lattice energies the standard enthalpies of formation of methyl-and ethyl-substituted ammonium dichloroiodate, dibromoio-date and tri iodate have been estimated. The standard enthalpies of fomation of alkylammonium polyhalides have been used to estimate the standard enthalpies of dissociation of various polyhalides; these results have been used to discuss the thermodynamic stabilities of the polyhalide compounds. The proton affinities of methyl and ethyl substituted amines have been calculated and are in good agreement with reported values derived from different experimental methods. The standard enthalpies of formation of some i (lll) species have been calculated from measured enthalpies of hydrolysis. Values obtained are: AhIC1 (c) = -89.89 - 1.85 kj mol-1 andH(CH COO)3l(c) = -1047.80 - 4.50 kj mol AHIC12A1C1,(c) = -827.56 - 6.20 kj mol-1 The thermal titrations of hydrolysed ICl

and (CH

COO)

Iagainst aqueous silver nitrate have been performed and used as a : basis for a discussion of reaction mechanisms of these compounds.