The Dimerization Constant of Nitrobenzene in Benzene: A Critique of Partition as a Thermodynamic Method

Abstract

The dimerization constant (K) of nitrobenzene in benzene was determined at 5.5 and 25 °C by means of partition (solvent extraction). A hydration study was performed at these temperatures to determine the extent of hydration of nitrobenzene in the benzene phase. Published freezing point depression data for the anhydrous benzene–nitrobenzene system were used to obtain a value of K at 5.5 °C. The heats of solution of nitrobenzene in benzene (anhydrous) were determined at 25 °C. The heat of solution and freezing point depression data were combined to obtain a value of K for the anhydrous system at 25 °C. At each of 5.5 and 25 °C the value of K determined by partition was significantly smaller than the corresponding value of K for the anhydrous system, and the discrepancy was larger at 25 than at 5.5 °C. It was found that by fitting a simple electrostatic model to the difference in the values of K found at 5.5 °C, the difference at 25 °C could be predicted.