Subcritical Solvent Effects on a Parallel Diels−Alder Reaction Network

The effect of pressure on the measured bimolecular rate constants of a parallel Diels−Alder reaction network in subcritical propane at 80 °C is determined. The network consists of maleic anhydride reacting simultaneously with isoprene and 1,3-cyclohexadiene. A phase behavior observation is made for each reaction to ensure the homogeneity of the system. Ratios of the bimolecular rate constants measured simultaneously in the parallel reaction network are compared to the ratios obtained when the two reactions are carried out independently. Also, a comparison of the experimental pressure effect for each independent reaction and the reaction network to predictions of the thermodynamic pressure effect using transition-state theory and the Peng−Robinson equation of state is made. Furthermore, an attempt is made to correlate the normalized rate constants of the individual reactions with the density of the solution. The results of the investigations are interpreted in the context of local reactant concentrations about the maleic anhydride and solvent−solute/cosolvent−solute interactions.