A DFT study of permanganate oxidation of toluene and its ortho-nitroderivatives

Abstract

Calculations of alternative oxidation pathways of toluene and its ortho-substituted nitro derivatives by permanganate anion have been performed. The competition between methyl group and ring oxidation has been addressed. Acceptable results have been obtained using IEFPCM/B3LYP/6-31+G(d,p) calculations with zero-point (ZPC) and thermal corrections, as validated by comparison with the experimental data. It has been shown that ring oxidation reactions proceed via relatively early transition states that become quite unsymmetrical for reactions involving ortho-nitrosubstituted derivatives. Transition states for the hydrogen atom abstraction reactions, on the other hand, are late. All favored reactions are characterized by the Gibbs free energy of activation, ΔG≠, of about 25 kcal mol−1. Methyl group oxidations are exothermic by about 20 kcal mol−1 while ring oxidations are around thermoneutrality.FigureOxidation of toluene and its ortho-nitroderivatives

Mechanism of Permanganate-Promoted Dihydroxylation of Complex Diketopiperazines: Critical Roles of Counter-cation and Ion-Pairing

“…monomeric ( M2 ) and dimeric ( D2 ) forms of 2 . (Figure 2) One should emphasize that previous computational studies on the reactivity of the permanganate ion in C–H oxidation 18, 42–43 and other reactions 44–47 typically use N as the model oxidant and do not study the role of ion-pairs.…”

Resolving Discrepancy between Theory and Experiment in 4-Nitrotoluene Oxidation

“…Permanganate oxidation of 4-nitrotoluene can proceed (Figure ), analogically to toluene oxidation, − via two competitive channels: hydrogen abstraction during methyl group oxidation (attack on C m carbon) and aromatic ring oxidation (three regioselective attacks on C 1 –C 2 , C 2 –C 3 , and C 3 –C 4 bonds. , We have excluded mechanisms in which permanganate attacks not adjacent carbon atoms C 2 –C 4 , C 2 –C 5 , and the like, as no bridging transition state structures were found; all such initial structures converged to one of those presented in Figure . These four reaction pathways we have characterized reacting complexes and corresponding transition states while vibrational analysis allowed us to calculate Gibbs free energies of activation, Δ G ‡ and kinetic isotope effects for all atoms.…”

“…19,20,28−30 Similarly, the mechanism of permanganate hydrogen abstraction was also studied experimentally [13][14][15][16][17]19 and theoretically. 18−20 We have contributed to the problem of NACs decomposition in the past by studying isotopic profiles of biotic 31−36 and abiotic 19,20 oxidation of nitrotoluenes in order to get indepth knowledge of the mechanisms of these processes. In the case of abiotic degradation by permanganate the first, and ratedetermining, step (illustrated in Figure 1 for the example of 4nitrotoluene, 4NT) is the attack of permanganate anion on either the aromatic ring (pathways (a) to (c)) or abstraction of hydrogen atom from the methyl group (pathway (d)).…”

“…Among abiotic degradation methods, in situ chemical oxidation (ISCO) is used most commonly . Chemical oxidation of groundwaters contaminants is usually carried out by direct injections of a chemical oxidant − with permanganate being the most popular adjuvant in degradation of organic contaminants, − especially NACs, due to its rapidity, effectiveness, wide pH range, and relatively low cost . The overall mechanism of permanganate oxidation of carbon–carbon double bond was a subject of numerous studies, both experimental − and theoretical. ,,− Similarly, the mechanism of permanganate hydrogen abstraction was also studied experimentally − , and theoretically. − …”

“…Theory Levels That Predict Contribution of Methyl Oxidation (%P m ) Closest to 95%19,20 atoms in the aromatic ring (values collected in the last column of Table2). Overall these values yield ε H of −113.0 ‰.…”