Chemical reaction in medium density fluid. Solvent density effects on the dimerization equilibrium of 2-methyl-2-nitrosopropane in carbon dioxide

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Abstract
The dimerization equilibrium of 2‐methyl‐2‐nitrosopropane in carbon dioxide was studied in a wide range of solvent density from 200 to 1100 kg m−3 at 25.0 and 35.0 °C. We found an inversion of the density dependence of the equilibrium constant. The configurational volume change for the dimerization has a large positive value in the medium density region, although it is negative in the high density region as usually observed for the bond formation reactions in the liquid state. This anomaly is reproduced by the cavity distribution function calculated from the integral equation based on the HNC or PY approximation for the Lennard‐Jones fluid model. The large positive value in the medium density region is interpreted in terms of desolvation effect due to the dimerization. The long‐range correlation between molecules due to attractive forces is suggested to play an important role in determining the reaction volume in the medium density region.