Catalyseurs D'Oxydation II. Activité Et Configuration Électronique

Abstract

AbstractThe catalytic activities of the enzyme‐like chelates of transition elements, towards the oxidation by molecular oxygen of liquid hydrocarbons (cumene, 100 °C, 1 atm) has been related to the electronic configuration of the complexes. The ligands were salicylaldehyde‐ethylenediimine (C), azoïc pigments (A), formazanic compounds (F), and the salts of naphtenic (N) and stearic acids (S). The theory of catalysis developed by Dowden was applied to the oxidations. The catalytic activity, which results from electron transfer from the hydroperoxide or peroxidic radicals to the catalyst, depends on the energy and entropy of the exchange. From the measurement of magnetic susceptibilities, the number of unpaired electrons (n), and the electronic configuration of the complexes were deduced. A and C induce a high ligand field, which is measured by the high splitting energy of the 3d orbitals of the cation. With these ligands, n is minimum (successively: ligand, cation+2 — but Cr+3, n): C Co, 1; A Co, 1; N Co, 3; C Ni, O; S Ni, 2; C Mn, 1; S Mn, 5; C Cu, l; F Cu, 1; A Cr, 3. The intensity (∫ϵdγ) of absorption of light (14 – 29.103 cm−−1) by the ligands is increased through metallization: by a coefficient of 3.4 to 5.2 for C, and 1.7 for A. This is to be ascribed to charge transfer, i.e. electron transfer from the ligand to the central cation. All these properties explain, in accordance with the theory of catalysis in oxidation, the decrease of the catalytic activity of the transition elements through chelation (energy and entropy factors: vacancy of low energy orbitals and number of them). Results suggest however that means of activation (such as actinic light) can confer high activity to these chelates.