Bosa Elisabetta, Paradisi Cristina, Scorrano Gianfranco
INTM del CNR - Sezione di Padova, Dipartimento di Chimica Organica, Università di Padova, Via Marzolo 1, 35131 Padova, Italy.
Rapid Commun Mass Spectrom. 2003;17(1):1-8. doi: 10.1002/rcm.870.
This paper presents a report on the ionization/dissociation of some representative chlorofluorocarbons (CFCs) induced by corona discharges in air at atmospheric pressure. Both positive and negative ions formed from Freons 1,1,1-trichlorotrifluoroethane (CFC 113a), 1,1,2-trichlorotrifluoroethane (CFC 113), and 1,1,1,2-tetrachlorodifluoroethane (CFC 112a) were analyzed using an atmospheric pressure chemical ionization mass spectrometry (APCI-MS) instrument. Energy-resolved mass spectra were obtained by modulating the kinetic energy of the ions via adjustment of the sampling cone potential (V(cone)). Positive ion spectra of the CFCs (M) at low V(cone) show no signals due to either M(+)* or MH(+) but only those due to species M - Cl and CX(3)(+) (X = Cl, F), likely formed via C-Cl and C-C bond cleavages following ionization via charge exchange. Charge localization in the products of C-C bond cleavage in M(+)* is driven by the stability of the neutral fragment. At low V(cone) the hydrates M - Cl(H(2)O) are also observed. In the case of 1,1,2,-trichlorotrifluoroethane, M - F species also form as a result of ion-molecule reactions. As V(cone) is increased collision-induced dissociation of M - Cl and M - F, i.e., the perhalogenated cations C(2)X(5)(+) (X = Cl, F), takes place via carbene elimination. In some cases such elimination is preceded or accompanied by rearrangements involving transfer of halogen from one carbon to the other. Evidence is also presented for the occurrence of a condensation reaction of C(2)Cl(3)F(2)(+) with water to form a C(2)Cl(2)F(2)HO(+) species via elimination of HCl. Negative ion spectra are dominated by Cl(-) and its ion-neutral complexes with M and with water. Additional components of the plasma include ion-neutral complexes O(3)(-)(M), the molecular anion M(-) (observed only with 1,1,2-trichlorotrifluoroethane), and an interesting species corresponding to M - Cl + O. The origin and structure of these M - Cl + O species are discussed in terms of available thermochemical and reactivity data and current mechanistic views concerning reaction of O(2)(-) with halogenated compounds. The observation of both positive and negative ions containing oxygen is of special relevance to development of new processes for the treatment of volatile organic compounds (VOCs) based on oxidative decomposition induced by corona discharges in air at room temperature and pressure.
本文介绍了关于在大气压力下空气中电晕放电诱导一些代表性氯氟烃（CFCs）发生电离/解离的报告。使用大气压化学电离质谱仪（APCI-MS）对由氟利昂1,1,1-三氯三氟乙烷（CFC 113a）、1,1,2-三氯三氟乙烷（CFC 113）和1,1,1,2-四氯二氟乙烷（CFC 112a）形成的正离子和负离子进行了分析。通过调整采样锥电位（V(cone)）来调制离子的动能，从而获得能量分辨质谱。在低V(cone)下，CFCs（M）的正离子谱未显示出由于M(+)*或MH(+)产生的信号，而仅显示出由于M - Cl和CX(3)(+)（X = Cl，F）物种产生的信号，这些物种可能是通过电荷交换电离后C-Cl和C-C键断裂形成的。M(+)*中C-C键断裂产物中的电荷定位是由中性片段的稳定性驱动的。在低V(cone)下还观察到水合物M - Cl(H(2)O)。对于1,1,2-三氯三氟乙烷，M - F物种也是离子-分子反应的结果。随着V(cone)增加，M - Cl和M - F，即全卤化阳离子C(2)X(5)(+)（X = Cl，F）的碰撞诱导解离通过卡宾消除发生。在某些情况下，这种消除之前或伴随着涉及卤素从一个碳转移到另一个碳的重排。还提供了证据表明C(2)Cl(3)F(2)(+)与水发生缩合反应，通过消除HCl形成C(2)Cl(2)F(2)HO(+)物种。负离子谱主要由Cl(-)及其与M和水的离子-中性络合物主导。等离子体的其他成分包括离子-中性络合物O(3)(-)(M)、分子阴离子M(-)（仅在1,1,2-三氯三氟乙烷中观察到）以及对应于M - Cl + O的有趣物种。根据现有的热化学和反应性数据以及关于O(2)(-)与卤代化合物反应的当前机理观点，讨论了这些M - Cl + O物种的起源和结构。观察到含氧化合物的正离子和负离子对于基于室温常压下空气中电晕放电诱导的氧化分解开发挥发性有机化合物（VOCs）处理新工艺具有特别重要的意义。
