The aid of calorimetry for the thermochemical and kinetic study of the σ-hole bonding leading to I2 and 4-(dimethylamino) pyridine complexes in solution

The thermochemical and kinetic studies of the formation of iodine (I-2) and 4-(dimethylamino) pyridine (DMAP) complexes in solution were investigated using microcalorimetry at 25 C. First, a theoretical approach of the sigma-hole bonding leading to these complexes based on the calculation of complexation energy values, Vs(min,max), localization of the molecular orbitals and the amount of charge transfer, was developed. The hexane was chosen as a solvent for both DMAP and I-2 solids. The plots of the complexation heats as a function of r(1) = [DMAP]/[I-2] and r(2) = [I-2]/[DMAP] ratios (where [DMAP] and [I-2] are the concentrations of DMAP and I-2, respectively) show that mixing DMAP solution to I-2 ones or vice versa has the same tendency but do not lead to the same enthalpies and is not a reciprocal phenomenon. For particular r(1) and r(2) values, we can suggest complex forms for the reaction between I-2 and DMAP by taking into account the measured and calculated complexation energies. The kinetic mechanisms and theoretical heat flow equations have been proposed for the lowest and highest r(1) and r(2) ratios. Iterating the heat flow equations while considering the deconvoluted curves allows to deduce the kinetic and thermodynamic parameters as: global order, partial order, rate constant, apparent rate constant and complexation enthalpies: for each mechanism, the latter parameter agrees with both the measured and theoretical ones.

Automated summary

This study investigated the thermochemical and kinetic studies of the formation of iodine (I-2) and 4-(dimethylamino) pyridine (DMAP) complexes in solution using microcalorimetry. The complexation heats as a function of the concentration ratios of DMAP and I-2 showed similar tendencies but different enthalpies, indicating a non-reciprocal phenomenon. By considering the measured and calculated complexation energies, complex forms for the reaction between I-2 and DMAP were proposed. The kinetic mechanisms and theoretical heat flow equations were also proposed for different concentration ratios.