CPL - Chalmers Publication Library
| Utbildning | Forskning | Styrkeområden | Om Chalmers | In English In English Ej inloggad.

Quantum chemical Modeling of ethene epoxidation with hydrogen peroxide: The effect of microsolvation with water

Angelica Lundin ; Itai Panas (Institutionen för kemi- och bioteknik, Oorganisk miljökemi) ; Elisabet Ahlberg
JOURNAL OF PHYSICAL CHEMISTRY A (1089-5639). Vol. 111 (2007), 37, p. 9080-9086 .
[Artikel, refereegranskad vetenskaplig]

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 H2O2 + C2H4 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, Delta E-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.

Nyckelord: TITANIUM-BASED EPOXIDATION; MOLECULAR-ORBITAL METHODS; SELF-INTERACTION ERROR; OLEFIN EPOXIDATION; HYDROPEROXO COMPLEXES; ELECTRON CORRELATION; CORRELATION-ENERGY; OXYGEN REDUCTION; BASIS SETS; DENSITY



Denna post skapades 2007-10-22. Senast ändrad 2010-01-26.
CPL Pubid: 55847

 

Institutioner (Chalmers)

Institutionen för kemi (2001-2011)
Institutionen för kemi- och bioteknik, Oorganisk miljökemi (2005-2014)

Ämnesområden

Kvantkemi

Chalmers infrastruktur