Formation of cyclopentadienyl radical from the gas-phase pyrolysis of hydroquinone, catechol, and phenol
Formation of cyclopentadienyl radical from the gas-phase pyrolysis of hydroquinone, catechol, and phenol
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DOI：
10.1021/es051878z
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发表时间：
2006-08-15
影响因子：
11.4
通讯作者：
Dellinger, Barry
中科院分区：
文献类型：
--
作者：
Khachatryan, Lavrent;Adounkpe, Julien;Dellinger, Barry
使用低温基体隔离电子顺磁共振（LTMI EPR）技术研究了在400-750 ℃温度范围内对苯二酚、邻苯二酚和苯酚气相热解自由基的形成。在氮气载气中将来自热解的反应器流出物冷却至77 K产生低温基质，其表现出分辨差的EPR谱。然而，使用二氧化碳作为载气形成了一个矩阵，在退火后，通过缓慢提高矩阵温度，然后快速再冷却到77 K，产生更清晰，可识别的光谱。所有三个样品的退火光谱导致在700 C以上产生具有6条线的EPR光谱，超精细分裂常数类似于6.0G，并且峰到峰宽度类似于3G，基于与文献的比较和理论计算，这很容易被指定为β自由基。在低于700 ℃的温度下热解产生具有高g值（> 2.0040）的二氧化碳基质分离光谱，其归因于含氧自由基，例如半醌或苯氧基。预期的半醌，苯氧基，羟基自由基的结论性鉴定是复杂的，这些自由基存在于碳中心和氧中心的共振结构，可以得到不同的EPR谱的能力。
The formation of radicals from the gas-phase pyrolysis of hydroquinone, catechol, and phenol over a temperature range of 400-750 degrees C was studied using the technique of low-temperature matrix isolation electron paramagnetic resonance (LTMI EPR). Cooling the reactor effluent from pyrolysis in a nitrogen carrier gas to 77 K produces a cryogenic matrix that exhibits poorly resolved EPR spectra. However, using carbon dioxide as a carrier gas formed a matrix that, upon annealing by slowly raising the matrix temperature followed by rapid recooling to 77 K, yielded more resolved, identifiable spectra. Annealed spectra of all three samples resulted in the generation of EPR spectra above 700 C with 6 lines, hyperfine splitting constant similar to 6.0 G, and peak to peak width similar to 3 G that was readily assignable, based on comparison to the literature and theoretical calculations, as that of cyclopentadienyl radical. Pyrolysis at temperatures below 700 C generated a carbon dioxide matrix isolation spectrum with a high g-value (> 2.0040) that is attributed to oxygen-containing radicals such as semiquinone or phenoxyl. Conclusive identification of anticipated semiquinone, phenoxyl, and hydroxycyclopentadienyl radicals was complicated by the ability of these radicals to exist in carbon-centered and oxygen-centered resonance structures that can give different EPR spectra.