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Benzo[//]quinoline 7,8-Benzoquinoline

Similarly, benzo[/]quinoline = 5,6-benzoquinoline.

The second approach for endocyclic N-PACs is to use replacement nomenclature, in which the term aza is a prefix to the corresponding PAH. The position of the N-atom in the fused-ring system of the PAH precedes the term aza. Thus, for example, quinoline is I-azanaphthalene. We generally use this convention for three or more ring N-PACs with endocyclic nitrogen heteroatoms.

Substitutive nomenclature is employed for exo-cyclic N-PACs (and the O- and S-PACs). Functional groups such as amino (-NH2), cyano (- C=N), nitro (-N02), and hydroxyl (-OH) are attached as prefixes to the parent PAH, e.g., 1-nitropyrene, VI.

3. Solubilities and Vapor Pressures

PAHs have low solubilities in water (Table 10.6) as expected from their nonpolar character. These decrease dramatically in going from the 2- and 3-ring compounds (e.g., naphthalene, with a solubility of 31 mg L-1) through the 3- and 4-ring semivolatile organ-ics (e.g., fluoranthene, with a solubility of 0.26 mg L-1) to 5-ring BaP, with a solubility of only 0.0038 mg L~1 (Mackay et al., 1992).

However, reactions of PAHs in ambient air to form more polar species (e.g., nitro-PAHs, ketones, quinones, lactones, and dicarboxylic acids) greatly enhance their solubilities in aqueous systems. This has major implications when one considers the distribution of PAHs, and their atmospherically formed PAC derivatives, through the air, water, and soil environments. These increases in solubility upon reaction are important not only from an environmental chemistry perspective but also in terms of possible impacts on public health and ecosystems, e.g., in both the exposure and the health effect portions of risk assessments of PAHs (e.g., see Mackay et al., f992; Schwarzenbach et al., 1993; Neilsen, 1998; Baum, 1998; the review by Mackay and Callcott, 1998; and references therein).

Values recommended by Mackay et al. (1992) and Mackay and Callcott (1998) for the vapor pressures of a number of PAHs of atmospheric interest and several properties used in theoretical calculations of their gas-particle partitioning in ambient air are given in Table 10.6: for examples of their use, see discussion of gas-particle partitioning theory in Chapter 9.D and references cited above.

Measured vapor densities of several volatile and semivolatile PAHs over a temperature range from 10 to 50°C have been used by Sonnefeld and co-workers (1983) to generate vapor pressures as a function of temperature:

log P° = -A/T + B Values for A and B are given in Table f0.7.

10. AIRBORNE PAHs: CHEMISTRY ANL) TOXICOLOGICAL IMPLICATIONS

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