The design of organic catalysis for epoxidation by hydrogen peroxide

Alder, Roger W.; Davis, Anthony P.

doi:10.1007/s00894-005-0044-4

Cited by 3 publications

(1 citation statement)

References 21 publications

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“…Several catalysts for molecular oxygen activation have been developed, the purpose of which has been to produce active peroxide groups. ,,,,− Indeed, the destabilization of the O 2 molecule upon peroxide formation is so great (∼3 eV) that the actual process of epoxidation has been seen as a limiting property of an O 2 activating catalyst, rather than a separate problem with its own peculiarities. It is generally accepted that a peroxide species is required to break the double bond and enabling epoxide to be formed.…”

Section: Discussionmentioning

confidence: 99%

Quantum Chemical Modeling of Ethene Epoxidation with Hydrogen Peroxide: The Effect of Microsolvation with Water

2007

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Quantum chemical calculations were performed to study the mechanism of ethene epoxidation with hydrogen peroxide. The calculations were carried out at the B3LYP/6-311+G(d,p) level of theory. The applicability of this functional to the problem at hand, including basis set effects, was validated by CCSD(T) and CASSCF based multireference MP2 calculations. A mechanism was determined where hydrogen peroxide becomes polarized in the transition state upon binding to the ethene molecule. The distant hydroxide fragment of the attached hydrogen peroxide molecule becomes partly negatively charged, while the other part of the molecule involves a proton and becomes partly positively charged. In the absence of water an activation energy of 139.7 kJ mol(-1) was determined for the isolated H(2)O(2) + C(2)H(4) system. By microsolvating with water, the impact of a hydrogen-bonded network on the activation energy was addressed. A 43.7 kJ mol(-1) lowering of the activation energy, DeltaE(a), was observed when including up to 4 water molecules in the model. This effect results from the stabilization of the proton and hydroxide fragments in the transition state. The findings are discussed in the context of previous theoretical studies on similar systems. Effects of adding or removing a proton to mimic acidic and alkaline conditions are addressed and the limitations of the model in solvating the excess charge are discussed.

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