Gas Chromatography Mass Spectrometry Identification of Labile Radicals Formed during Pyrolysis of Catechool, Hydroquinone, and Phenol through Neutral Pyrolysis Product Mass Analysis
Catechol, hydroquinone, and phenol are known to be environmental pollutants due to their ability to generate environmentally free radicals, which cause millions of deaths worldwide. Recently, efforts have been done to precisely identify the origin and the nature of those free radicals employing EPR-LTMI technique. All the three precursors generate cyclopentadienyl radical as major pyrolysis products and phenoxyl radical as both pyrolysis and photolysis products which were obtained from phenol; ortho-semiquinone and para-semiquinone were seen, respectively, from the pyrolysis of catechol and hydroquinone. However, it has been suspected that the solely use of the EPR-LTMI did not allow the isolation of the more labile radicals that is supposedly terminated by radical-radical or radical-surface interaction. The present study reports the gas chromatography mass analysis of the pyrolysis products from catechol, hydroquinone, and phenol. Naphthalene , indene, and hydroxyindene were observed as the pyrolysis products of hydroquinone, while fluorene, 1H-indenol and its isomer 1H-inden-1-one 2,3 dihydro, acenaphthylene, benzofuran-7-methyl, and benzofuran-2-methyl were observed as pyrolysis products of catechol. Dibenzo dioxin and dibenzo furan were observed from pyrolysis of catechol and hydroquinone. Those products result from the combination of radicals such as cyclopentadienyl, para-semiquinone, ortho-semiquinone, hydroxyl-cyclohexadienyl, phenoxyl, and most importantly Hydroxycyclopentadienyl which was not identified by EPR-LTMI. 1. Introduction Combustion-generated Particulate Matter (PM) has been extensively reported in the literature [1–8]. They are known as the cause of environmental pollution with its toll of diseases and deaths [9–16]. Particulate Matter (PM) has been categorized as Fine Particulate Matter (FP) and Ultra-fine Particulate Matter (UFP). FPs have an aerodynamic diameter less than 2.5？μm while UFPs have an aerodynamic diameter less than 0.1？μm [17, 18]. The smaller the size of fine particles, the more potent and biologically destructive they are [19–23]. Fine particles’ toxicity has been attributed to their association with free radicals [24–26]. Persistent Free Radicals (PFRs) are chemical compounds with one or more unpaired electrons, sufficiently stable towards decomposition, and resistant to further reaction and can exist for long period of time in the atmosphere. These free radicals that potentially include semiquinone-type and phenoxyl-type radicals are highly resonance stabilized and are supposed to form in combustion systems or
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