A Computational Study of the Ozonolysis of Phenanthrene

M.H. Almatarneh, E. Al-Shamaileh, Z.M. Ahmad, A.A.-A.A. Abu-Saleh and I.A. Elayan The University of Jordan, Department of Chemistry, Amman, 11942, Jordan

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A computational study of the ozonolysis of phenanthrene has been carried out using DFT methods (B3LYP and M06-2X). The reaction mechanism for the ozonolysis was studied in both gas phase and in solution, using the polarizable continuum solvation model. The structures for all proposed reaction mechanisms were optimized using M06-2X and B3LYP methods with 6-31G(d), 6-31+G(d), and 6-31G(2df,p) basis sets. In solution, all structures were optimized using B3LYP/6-31+G(d,p) and polarizable continuum solvation model. Six different mechanistic pathways were explored for the ozonolysis of phenanthrene that forms aldehyde compounds. The activation energy of the formation of the primary ozonide intermediate in pathway A is 13 kJ mol-1 in the polarizable continuum model with the B3LYP/6-31+G(d,p) method. This reaction is followed by a dissociation into a zwitterionic Criegee intermediate with an activation energy of 76 kJ mol-1 in polarizable continuum model with B3LYP/6-31+G(d,p). Furthermore, the nucleophilic addition reactions of methanol to the Criegee intermediate have been studied along two pathways, B1 and B2. The water-mediated mechanism for pathways B2 and C2, where the water molecule acts as a mediator through a 1,5-proton shift, dropped the activation barriers by 18 and 26 kJ mol-1, respectively, based on B3LYP/6-31G(2df,p) method. The solvation model (polarizable continuum) reduces the energy barriers for all pathways except for the reaction of methanol with the Criegee intermediate. This study provides an insight into understanding the mechanism of transformation of this pollutant into non-toxic compounds.

DOI: 10.12693/APhysPolA.132.1149 topics: Ozonolysis of Phenanthrene, Primary Ozonide, Criegee Intermediate