Theoretical and Experimental Studies on Selective Oxidation of Aromatic Ketone by Performic Acid

Abstract

The Baeyer-Villiger (B-V) reactions of 3,4-dimethoxy acetophenone (DMOAP), 4-methyl acetophenone (MAP), and acetophenone (AP) with performic acid (PFA) in formic acid (FA) solvent have been studied by density functional theory (DFT) method. The noncatalyzed and the formic acid-catalyzed reaction paths have been calculated at the MPWB1K/6-311++G(d,p)-IEF-PCM// MPWB1K/6-311G(d,p) level of theory. On the basis of the calculations, the attack of peracid to the carbonyl carbon is rate-determining in both the noncatalyzed and acid-catalyzed paths. The selective oxidation of 3,4-dimethoxy acetophenone and 4-methyl acetophenone by performic acid into aromatic esters have been experimentally investigated. The kinetic rate constants were obtained in the temperature range of 303 to 323 K. The selectivity of product was also explained by the NBO electric charge analysis. The calculated activation energy barriers of the B-V reaction of DMOAP and MAP were in good agreement with those of experiment.

Reinvestigation of Acetophenones Oxidation by Performic Acid in Formic Acid

“…In addition, our calculations showed that migration continued to be the RDS as solvent polarity increased. Some years ago, Liu and colaborators 29 performed a theoretical and experimental study of the BV reactions of acetophenone, 4-methylacetophenone, and 3,4-dimethoxyacetophenone, with PFA in FA acting both as catalyst and solvent. The authors claim that, according to their results, the addition step is the RDS for the three aromatic ketones.…”

“…The energy data were refined by single-point calculations with the same functional and the 6-311++G­(d,p) basis set, with inclusion of the IEF-PCM continuum model using FA as solvent and the UFF radii. In our preceding studies, this functional was demonstrated to give excellent results that agree very well with previous experimental values. − The thermodynamic magnitudes were obtained by vibrational calculation. The Gibbs energies were obtained via a thermodynamic cycle using corrections to Gibbs energies in the gas phase at 298.15 K using standard state 1 M and corrected electronic energies in solution.…”

“…The experimental results performed in ref represent a good opportunity to prove that our mechanism is reliable in FA, as was shown previously in dichloromethane . Thus, employing the experimental rate constants obtained in the mentioned work at various temperatures and using classical transition state theory, we calculated the corresponding Δ G ‡ values at 298.15 K. These values were 22.00 and 20.79 kcal/mol for the oxidation of 4-methylacetophenone and 3,4-dimethoxyacetophenone by PFA in FA, respectively.…”

“…We can see in Table that the TS calculated in ref presents a considerable Δ G ‡ for the catalyzed addition step, even after inclusion of the thermodynamic correction for the liquid phase . As mentioned above, these authors selected the catalyzed TS1 structure for the addition step used by Okuno and Grein (see Figure b), which was shown to have a higher energy than ours (Figure a).…”

“…To prove the arguments above, we decided to model the mechanism proposed in ref , as well as ours, for both steps of the BV oxidation of acetophenones, R-COCH 3 (R = phenyl, 4-methylphenyl, 3,4-dimethoxyphenyl), with PFA, using FA as both catalyst and solvent (Figure ).…”