Aromatic compounds, identification

An important enhancement to the mass resolving and mass determining capabilities of mass spectrometry is using it in sequence with chromatographic separation techniques. Indeed, most aromatic compounds identification when MS is applied result from the combination with chromatographic methods. This allows the sample separation prior to ionization in the mass spectrometer and we can even refer this as a requirement for complex mixtures. Combined methods will be described below in this chapter. 

Safe, S., et al. Photodecomposition of Halogenated Aromatic Compounds. Identification and Analysis of Organic Pollutants in Water. Ann Arbor Science 1976... 

Nitration at a rate independent of the concentration of the compound being nitrated had previously been observed in reactions in organic solvents ( 3.2.1). Such kinetics would be observed if the bulk reactivity of the aromatic towards the nitrating species exceeded that of water, and the measured rate would then be the rate of production of the nitrating species. The identification of the slow reaction with the formation of the nitronium ion followed from the fact that the initial rate under zeroth-order conditions was the same, to within experimental error, as the rate of 0-exchange in a similar solution. It was inferred that the exchange of oxygen occurred via heterolysis to the nitronium ion, and that it was the rate of this heterolysis which limited the rates of nitration of reactive aromatic compounds. 

In earlier chapters we have been concerned with the identification of the effective electrophile in nitrations carried out under various conditions. We have seen that very commonly the nitronium ion is the electrophile, though dinitrogen pentoxide seems capable of assuming this role. We now consider how the electrophile, specifically the nitronium ion, reacts with the aromatic compound to cause nitration. 

Figure 13.16 LC separation of urban air particulate exrtact (a), along with the GC/FID cliro-matogram (b) of an oxy-PAC fraction (transfeired via a loop-type interface). Reprinted from Environmental Science and Technology, 29, A. C. Lewis et al., On-line coupled LC-GC-ITD/MS for the identification of alkylated, oxygenated and nirtated polycyclic aromatic compounds in urban air particulate exti acts , pp. 1977-1981, copyright 1995, with permission from the American Chemical Society.

A. C. Eewis, R. E. Robinson, K. D. Bartle and M. J. Pilling, On-line coupled EC-GC-ITD/MS for the identification of alkylated, oxygenated and nitr-ated polycyclic aromatic compounds in urban ah particulate extr acts . Environ. Sci. Technol. 29 1977-1981 (1995). 

I. L. Davies, K. D. Battle, P. T. Williams and G. E. Andrews, On-line fractionation and identification of diesel fuel polycyclic aromatic compounds by two-dimensional microbore liigh-peiformance liquid-cliromatography/capillary gas-cliiomatography . Anal. Chem. 60 204-209 (1988). 

Sulfur Compounds. All crude oils contain sulfur in one of several forms including elemental sulfur, hydrogen sulfide, carbonyl sulfide (COS), and in aliphatic and aromatic compounds. The amount of sulfur-containing compounds increases progressively with an increase in the boiling point of the fraction. A majority of these compounds have one sulfur atom per molecule, but certain aromatic and polynuclear aromatic molecules found in low concentrations in crude oil contain two and even three sulfur atoms. Identification of the individual sulfur compounds in the heavy fractions poses a considerable challenge to the analytical chemist. 

If an aromatic compound reacts with an OH radical to form a specific set of hydroxylated products that can be accurately identified and quantified in biological samples, and one or more of these products are not identical to naturally occurring hydroxylated species, i.e. not produced by normal metabolic processes, then the identification of these unnatural products can be used to monitor OH radical activity therein. This is likely to be the case if the aromatic detector molecule is present at the sites of OH radical generation at concentrations sufficient to compete with any other molecules that might scavenge OH radical. 

Fig. 5a-c. A typical distribution of polycyclic aromatic hydrocarbons in a atmospheric fallout sample, Alexandria City - Egypt b bottom incineration ash leachate of municipal solid waste - USA c hydrothermal petroleum, Escanaba Trough, NE Pacific Ocean. PAH Compound identifications N = naphthalene, MN = methylnaphthalene, DMN = dimethylnaphthalenes, P = phenanthrene, MP = methylphenanthrene, Fl = fluoranthene, Py = pyrene, BaAN = benzol anthracene, DH-Py = dihydropyrene, 2,3-BF = 2,3-benzofluorene, BFL = benzo[fc,/c]fluoranthene, BeP = benzo[e]pyrene, BaP = benzo[a]pyrene, Per = perylene, Cx-228 = methyl-228 series, Indeno = indeno[ l,2,3-c,d]pyrene, DBAN = dibenz[a,/z]anthracene, BPer = benzo[g,/z,z] perylene, AAN = anthanthrene, DBTH = dibenzothiophene, Cor = coronene, DBP = dibenzo [a,e]pyrene, DBPer = dibenzo [g,h,i] perylene... 

Safe, S., Bunce, N.J., Chittin, B., Hutzinger, 0., and Rnzo, L.O. Photodecomposition of halogenated aromatic compounds, in Identification and Analysis of Pollutants in Water, Keith, L.H., Ed. (Ann Arbor, Ml Ann Arbor Science Publishers, 1976), pp. 35-46. 

One major reaction of aromatic compounds is electrophilic substitution and it was therefore natural to submit the present systems to electrophiles. Thus l,2-dihydro-2-methylbenz[e][l,2]azaborine (113 R = Me) is brominated and chlorinated in its 3-position to give compounds (186), of which (186 X = C1) was prepared authentically for identification, starting from w-chloro-2-aminostyrene. The main reaction was, however, deboronation to w-halo-2-aminostyrenes. 

The lifetimes and kinetic behavior of many triplet states of molecules, particularly of aromatic compounds, have been studied by Porter and his coworkers. The identification of the absorption spectra of methyl radicals, of HCO radicals and of NH2 radicals, mainly in Herzberg s laboratory at Ottawa, has permitted flash photolysis to be used directly to measure the rates of radical reactions. 

In addition to acyclic ketones, dolichoderine ants in the genus Azteca generate an alarm signal with 2-methylcyclopentanone (xxxi),cis-l-acetyl-2-methylcyclopentane (XXXII), and 2-acetyl-3-methylcyclopentene (XXXIII) (128). That some ant species utilize aromatic compounds as alarm pheromones is demonstrated by the identification of methyl 6-methyl salicylate (XXXIV) in the... 

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