Jagiella Stefan, Zabel Friedhelm
Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569, Stuttgart, Germany.
Phys Chem Chem Phys. 2008 Apr 7;10(13):1799-808. doi: 10.1039/b712312d. Epub 2008 Feb 12.
Reactions of methylglyoxyl and methylglyoxylperoxy radicals were investigated at a total pressure of 1 bar in oxygen. Methylglyoxyl radicals were generated by stationary photolysis of Br2-CH3C(O)C(O)H-NO2-O2-N2 mixtures at wavelengths > or =480 nm and of Cl2-CH3C(O)C(O)H-NO2-O2-N2 mixtures in the wavelength range 315-460 nm. In the bromine system, rate constant ratios for the reactions CH3C(O)CO --> CH3CO + CO (kdis) and CH3C(O)CO + O2 --> CH3C(O)C(O)O2 (kO2) were measured as a function of temperature in the range 275-311 K. Assuming the constant value kO2 = 5.1 x 10(-12) cm3 molecule(-1) s(-1) for our reaction conditions, kdis = 1.2 x 10(10.0+/-0.7) x exp(-11.7 +/- 3.8 kJ mol(-1)/RT) s(-1) (2sigma errors) was obtained for ptot = 1 bar (M = O2), in good agreement with the kinetic parameters calculated by Méreau et al. [R. Méreau, M.-T. Rayez, J.-C. Rayez, F. Caralp and R. Lesclaux, Phys. Chem. Chem. Phys., 2001, 3, 4712]. CH3C(O)C(O)O2 radicals oxidise NO2, forming NO3, CH3CO and CO2. This experimental result is supported by DFT and ab initio calculations. Possible mechanisms for the observed formation of several % of ketene and bromoacetyl peroxynitrate are discussed. Use of Cl rather than Br atoms to abstract the aldehydic H atom from methylglyoxal leads to chemically activated CH3C(O)CO radicals, thus substantially increasing the fraction of CH3C(O)CO radicals that decompose rather than add O2.
在氧气总压为1巴的条件下，对甲基乙二醛和甲基乙二醛过氧自由基的反应进行了研究。甲基乙二醛自由基通过在波长≥480 nm下对Br₂-CH₃C(O)C(O)H-NO₂-O₂-N₂混合物进行稳态光解，以及在315 - 460 nm波长范围内对Cl₂-CH₃C(O)C(O)H-NO₂-O₂-N₂混合物进行稳态光解产生。在溴体系中，测量了反应CH₃C(O)CO→CH₃CO + CO（kdis）和CH₃C(O)CO + O₂→CH₃C(O)C(O)O₂（kO₂）的速率常数比随温度在275 - 311 K范围内的变化。假设在我们的反应条件下kO₂为恒定值5.1×10⁻¹² cm³·分子⁻¹·秒⁻¹，对于总压ptot = 1巴（M = O₂），得到kdis = 1.2×10⁽¹⁰.⁰⁺/⁻⁰.⁷⁾×exp(-11.7 ± 3.8 kJ·mol⁻¹/RT) 秒⁻¹（2σ误差），这与Méreau等人[R. Méreau, M.-T. Rayez, J.-C. Rayez, F. Caralp和R. Lesclaux, Phys. Chem. Chem. Phys., 2001, 3, 4712]计算的动力学参数高度一致。CH₃C(O)C(O)O₂自由基氧化NO₂，生成NO₃、CH₃CO和CO₂。这一实验结果得到了密度泛函理论（DFT）和从头算计算的支持。讨论了观察到的生成百分之几的乙烯酮和溴乙酰过氧硝酸盐的可能机制。使用Cl原子而非Br原子从甲基乙二醛中夺取醛基H原子会产生化学活化的CH₃C(O)CO自由基，从而显著增加分解而非与O₂加成的CH₃C(O)CO自由基的比例。
