Ascenzi Daniela, Franceschi Pietro, Guella Graziano, Tosi Paolo
Dipartimento di Fisica, Universita di Trento, Povo (TN), Italy.
J Phys Chem A. 2006 Jun 29;110(25):7841-7. doi: 10.1021/jp062406p.
Benzene can be efficiently converted into phenol when it is treated by either corona or dielectric barrier discharge (DBD) plasmas operating at atmospheric pressure in air or mixtures of N(2) and O(2). Phenol produced by corona discharge in an atmospheric pressure chemical ionization source (APCI) has been detected as the corresponding radical cation C(6)H(5)OH(+) at m/z 94 by an ion trap mass spectrometer. On the other hand, phenol has been observed also as neutral product by gas chromatography-mass spectrometry analysis (GC-MS) after treatment in a DBD plasma. Experiments aimed at shading light on the elementary processes responsible for benzene oxidation were carried out (i) by changing the composition of the gas in the corona discharge source; (ii) by using isotopically labeled reagents; and (iii) by investigating some relevant ion-molecule reactions (i.e. C(6)H(6)(+) + O(2), C(6)H(5)(+) + O(2)) via selected guided ion beam measurements and with the help of ab initio calculations. The results of our approach show that ionic mechanisms do not play a significant role in phenol production, which can be better explained by radical reactions resulting in oxygen addition to the benzene ring followed by 1,2 H transfer.
当苯在空气中或氮气与氧气的混合物中于大气压下通过电晕放电或介质阻挡放电（DBD）等离子体处理时，它可以有效地转化为苯酚。在大气压化学电离源（APCI）中通过电晕放电产生的苯酚已被离子阱质谱仪在m/z 94处检测为相应的自由基阳离子C(6)H(5)OH(+)。另一方面，在DBD等离子体中处理后，通过气相色谱-质谱分析（GC-MS）也观察到苯酚为中性产物。为了阐明负责苯氧化的基本过程，进行了以下实验：（i）通过改变电晕放电源中气体的组成；（ii）使用同位素标记的试剂；（iii）通过选定的导向离子束测量并借助从头算计算研究一些相关的离子-分子反应（即C(6)H(6)(+) + O(2)，C(6)H(5)(+) + O(2)）。我们的方法结果表明，离子机制在苯酚生成中不起重要作用，这可以通过导致氧加成到苯环随后进行1,2 H转移的自由基反应更好地解释。
