Enthalpies of mixing and complex formation of carbon tetrachloride with benzene, toluene, p-xylene, and mesitylene

Abstract

Measurements are presented of the enthalpy of mixing of equimolar mixtures of carbon tetrachloride with benzene, toluene, p-xylene, and mesitylene at temperatures between 281 and 362 K. The results can be understood in terms of a simple theory of complex-formation, but only if it is assumed that while the equilibrium constant for complex-formation at room temperature increases in the sequence benzene < toluene < p-xylene < mesitylene, the magnitude of the (negative) enthalpy of complex-formation decreases in the same sequence. This conclusion prompts us to ask exactly what is meant by a ‘strong’ donor or ‘strong’ complex-formation. Measurements are also presented of the enthalpy of mixing of carbon tetrachloride and toluene over a range of mole fractions at each of five temperatures between 298 and 338 K. At temperatures close to that (313 K) at which the enthalpy of mixing of equimolar mixtures changes sign, a double maximum is predicted by the theory and found by experiment, no previous example of such behaviour being known. The theory is also fairly consistent with the values of the excess Gibbs function where these have been measured.