The reaction kinetics of dimethyl carbonate (DMC) and OH radicals were investigated behind reflected shock waves over the temperature range of 872-1295 K and at pressures near 1.5 atm. Reaction progress was monitored by detecting OH radicals at 306.69 nm using a UV laser absorption technique. The rate coefficients for the reaction of DMC with OH radicals were extracted using a detailed kinetic model developed by Glaude et al. (Proc. Combust. Inst. 2005, 30(1), 1111-1118). The experimental rate coefficients can be expressed in Arrhenius form as: kexpt'l = 5.15 × 10(13) exp(-2710.2/T) cm(3) mol(-1) s(-1). To explore the detailed chemistry of the DMC + OH reaction system, theoretical kinetic analyses were performed using high-level ab initio and master equation/Rice-Ramsperger-Kassel-Marcus (ME/RRKM) calculations. Geometry optimization and frequency calculations were carried out at the second-order Møller-Plesset (MP2) perturbation level of theory using Dunning's augmented correlation consistent-polarized valence double-ζ basis set (aug-cc-pVDZ). The energy was extrapolated to the complete basis set using single point calculations performed at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory. For comparison purposes, additional ab initio calculations were also carried out using composite methods such as CBS-QB3, CBS-APNO, G3 and G4. Our calculations revealed that the H-abstraction reaction of DMC by OH radicals proceeds via an addition elimination mechanism in an overall exothermic process, eventually forming dimethyl carbonate radicals and H2O. Theoretical rate coefficients were found to be in excellent agreement with those determined experimentally. Rate coefficients for the DMC + OH reaction were combined with literature rate coefficients of four straight chain methyl ester + OH reactions to extract site-specific rates of H-abstraction from methyl esters by OH radicals.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Research reported in this publication was supported by the King Abdullah University of Science and Technology (KAUST) under the Clean Combustion Research Center's CCF program on Future Fuels. Dr Milán Szőri acknowledges Hungarian Academy of Sciences (BO/00113/15/7) for a János Bolyai Research Scholarship and a Magyary Zoltán Fellowship provided by the State of Hungary and the European Union within the framework of TÁMOP 4.2.4.A/2-11-1-2012-0001 “National Excellence Program” under the respective grant number of A2-MZPD-12-0139. He further acknowledges the support provided by the “Establishment of collaboration between the higher education and industry (FIEK) involving University of Miskolc for advanced materials and intelligent technologies” under the program (GINOP-2.3.4-15-2016-00004). The computations described in this work were performed on the research computing facilities at KAUST, the computing facility at the University of Szeged, Hungary, and the International University Laboratory for Computational Biochemistry, Institute for Computational Science and Technology at Ho Chi Minh City, Vietnam. The authors further thank László Müller and Máté Labádi of University of Szeged for administrating the computing systems.