Experimental and theoretical study of the reaction of POCl(3) (-) with O(2).
The oxidation of the trichlorooxyphosphorus anion (POCl(3) (-)), which takes place in combustion flames, has been examined experimentally at a variety of temperatures and theoretically via ab initio and density functional methods. The reaction was examined in a turbulent ion flow tube and kinetics was measured between 300 and 626 K, estimating an overall reaction barrier of 1.23 kcal/mol. Calculations at the density functional, Moller-Plesset second order perturbation, and coupled cluster levels of theory with basis sets up to augmented triple-zeta quality point to a multistep reaction mechanism involving an initial [OP(Cl)(3)(OO)](-) intermediate, an adduct between triplet O(2) with POCl(3) (-), subsequent formation of a four-membered nonplanar P-O-O-Cl ring transition state, with concomitant breaking of the P-Cl and O-O bonds to provide a transient intermediate [OP(Cl)(2)OO...Cl](-), which, in turn, converts to the product complex (POCl(2) (-))(ClO) upon formation of the Cl-O bond without barrier. The calculated energy of the four-membered transition state is considered to be in good agreement with the small overall barrier found by experiment. The final step is responsible for the large exothermicity of the reaction.
Kerkines
Ioannis S K
IS
Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA.
Morokuma
Keiji
K
Iordanova
Nedialka
N
Viggiano
A A
AA