Halogen compounds, aromatic identification

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. 

Ethers can be prepared under mild conditions from aromatic halogen compounds that contain ortho- or para-nitro groups.772"775 Alkyl 2,4-di-nitrophenyl ethers are obtained from 1 -fluoro-2,4-dinitrobenzene and alcohols in the presence of triethylamine,776 a reaction that can be used for identification of alcohols. 

Table 2.9.2 presents some of the halogenated hydrocarbons that can be effectively extracted out from aqueous and nonaqueous matrices by liquid-liquid or other nonpurge and trap extraction. Such compounds include di-, tri-, tetra-, penta-, and hexahalo- substituents aromatics and cyclohexanes, and haloderiva-tives of alkanes with carbon number greater than 6. Characteristic mass ions for GC/MS identification are also presented for some of these listed compounds. 

Polynitro compounds with aromatic hydrocarbons give solid derivatives, many of which are suitable for identification purposes. These addition compoimds are usually intensely colored and are formed by the mixing of both components in a suitable solvent (benzene, methanol, ethanol, chloroform) they can also crystallize from a melt of both components. The ability of nitro compounds to form the mentioned complexes increases with the number of nitro groups in the molecule. The presence of halogens, amino groups, and hydroxy groups can also increase this ability, while methyl groups have an opposite effect. 

Procedures for the identification of this class of compounds can be divided into methods for the identification of alkyl and cycloalkyl halogenides and methods for the identification of aromatic halo compounds. The type of bond between the halogen and the rest of the molecule is decisive for the choice of the identification procedure. While the procedures for the identification of halo compounds with halogen atom boimd to an aliphatic carbon are based on the exchange of a halogen by a suitable residue, the identification of compounds with halogen bound to an aromatic nucleus is generally carried out by additional substitution of the aromatic nucleus. 

Many commercial products are complex chemical or physical mixtures. In some cases the use of the type of search scheme described above is not always useful. Sometimes, all that is required is a broad based characterization or a generic identity in terms of a product type. A good example is a polychlorinated biphenyl (a PCB), such as the Arochlor 1254 shown in Figure 8. This time the identification of the individual component polychlorinated compounds would not be useful. Therefore in this case a normal absolute scoring scheme is preferred where the material is treated as a single entity. The computer interpretation (Table 6) accurately classifies the sample as an aromatic material with multiple halogen (ring) substituents. 

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

---