Reaction mechanism between carbonyl oxide and hydroxyl radical: a theoretical study.
The reaction mechanism of carbonyl oxide with hydroxyl radical was investigated by using CASSCF, B3LYP, QCISD, CASPT2, and CCSD(T) theoretical approaches with the 6-311+G(d,p), 6-311+G(2df, 2p), and aug-cc-pVTZ basis sets. This reaction involves the formation of H2CO + HO2 radical in a process that is computed to be exothermic by 57 kcal/mol. However, the reaction mechanism is very complex and begins with the formation of a pre-reactive hydrogen-bonded complex and follows by the addition of HO radical to the carbon atom of H2COO, forming the intermediate peroxy-radical H2C(OO)OH before producing formaldehyde and hydroperoxy radical. Our calculations predict that both the pre-reactive hydrogen-bonded complex and the transition state of the addition process lie energetically below the enthalpy of the separate reactants (DeltaH(298K) = -6.1 and -2.5 kcal/mol, respectively) and the formation of the H2C(OO)OH adduct is exothermic by about 74 kcal/mol. Beyond this addition process, further reaction mechanisms have also been investigated, which involve the abstraction of a hydrogen of carbonyl oxide by HO radical, but the computed activation barriers suggest that they will not contribute to the gas-phase reaction of H2COO + HO.
Theoretical and Computational Chemistry Group, Departament de Química Orgànica Biologica, Institut d'Investigacions Químiques i Ambientals de Barcelona, IIQAB - CSIC, c/ Jordi Girona 18, E-08034 Barcelona, Spain.
Alex
A
Mansergas
Josep M
JM
Anglada
D006859:Hydrogen / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D010087:Oxides / Q000737:chemistry*; D011522:Protons
D010087:Oxides; D011522:Protons; D017665:Hydroxyl Radical; D006859:Hydrogen