过氧自由基异构化在异戊二烯氧化中的作用。
Peroxy radical isomerization in the oxidation of isoprene.
机构信息
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
出版信息
Phys Chem Chem Phys. 2011 Aug 14;13(30):13607-13. doi: 10.1039/c1cp21330j. Epub 2011 Jun 24.
We report experimental evidence for the formation of C(5)-hydroperoxyaldehydes (HPALDs) from 1,6-H-shift isomerizations in peroxy radicals formed from the hydroxyl radical (OH) oxidation of 2-methyl-1,3-butadiene (isoprene). At 295 K, the isomerization rate of isoprene peroxy radicals (ISO2•) relative to the rate of reaction of ISO2• + HO2 is k(isom)(295)/(k(ISO2•+HO2)(295)) = (1.2 ± 0.6) x 10(8) mol cm(-3), or k(isom)(295) ≃ 0.002 s(-1). The temperature dependence of this rate was determined through experiments conducted at 295, 310 and 318 K and is well described by k(isom)(T)/(k(ISO2•+HO2)(T)) = 2.0 x 10(21) exp(-9000/T) mol cm(-3). The overall uncertainty in the isomerization rate (relative to k(ISO2•+HO2)) is estimated to be 50%. Peroxy radicals from the oxidation of the fully deuterated isoprene analog isomerize at a rate ∼15 times slower than non-deuterated isoprene. The fraction of isoprene peroxy radicals reacting by 1,6-H-shift isomerization is estimated to be 8-11% globally, with values up to 20% in tropical regions.
我们报告了羟基自由基（OH）氧化 2-甲基-1,3-丁二烯（异戊二烯）形成的过氧自由基中 1,6-H-移位异构化形成 C(5)-过氧醛（HPALDs）的实验证据。在 295 K 时，异戊二烯过氧自由基（ISO2•）的异构化速率与 ISO2•+HO2 的反应速率之比为 k(isom)(295)/(k(ISO2•+HO2)(295)) = (1.2 ± 0.6) x 10(8) mol cm(-3)，或 k(isom)(295) ≃ 0.002 s(-1)。通过在 295、310 和 318 K 下进行的实验确定了该速率的温度依赖性，并用 k(isom)(T)/(k(ISO2•+HO2)(T)) = 2.0 x 10(21) exp(-9000/T) mol cm(-3)很好地描述了该依赖性。异构化速率（相对于 k(ISO2•+HO2)）的总不确定度估计为 50%。完全氘代异戊二烯类似物的氧化产生的过氧自由基的异构化速率比未氘代异戊二烯慢约 15 倍。通过 1,6-H-移位异构化反应的异戊二烯过氧自由基的分数估计在全球范围内为 8-11%，在热带地区高达 20%。
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