Chlorine atoms aromatic hydrocarbons, reactions with

Chlorine atoms react with aromatic hydrocarbons, but only at a significant rate with those having saturated side chains from which the chlorine atom can abstract a hydrogen or unsaturated side chains to which it can add. For example, the rate constant for the Cl atom reaction with benzene is 1.3 X 10"15 enr3 molecule-1 s-1 (Shi and Bernhard, 1997). On the other hand, the rate constants for the reactions with toluene and p-xylene are 0.59 X 10-10 and 1.5 X 10-l() enr3 molecule"1 s"1, respectively (Shi and Bernhard, 1997), and that for reaction with p-cymene is 2.1 X 10"10 cm3 molecule"1 s-1 (Finlayson-Pitts et al., 1999). Hence... 

By comparing the results for chlorinated polypropylene with those for polypropylene, it can be concluded that the two materials undergo very different pyrolytic reactions. Typical for polypropylene is the formation of fragments of the polymeric backbone with formation of monomer, dimer, etc., or with cleavage of the backbone in random places and formation of compounds with 3n, 3n-1, and 3n+1 carbon atoms (see Section 6.1). Pyrolysis of the chlorinated compound leads to a significant amount of HCI and also char. Very few chlorinated compounds are identified in the pyrolysate, since the elimination of HCI leaves very few chlorine atoms bound to carbons. Some aromatic hydrocarbons are formed by a mechanism similar to that of poly(vinyl chloride) pyrolysis. The elimination of HCI leads to the formation of double bonds, and the breaking of the carbon backbone leads to cyclization and formation of aromatic compounds. The reactions involved in this process are shown below for the case of formation of 1,3-dimethylbenzene ... 

The kinetics of the reactions of many xenobiotics with hydroxyl and nitrate radicals have been examined under simulated atmospheric conditions and include (1) aliphatic and aromatic hydrocarbons (Tuazon et al. 1986) and substituted monocyclic aromatic compounds (Atkinson et al. 1987c) (2) terpenes (Atkinson et al. 1985a) (3) amines (Atkinson et al. 1987a) (4) heterocyclic compounds (Atkinson et al. 1985b) and (5) chlorinated aromatic hydrocarbons (Kwok et al. 1995). For PCBs (Anderson and Hites 1996), rate constants were highly dependent on the number of chlorine atoms, and calculated atmospheric lifetimes varied from 2 days for 3-chlorobiphenyl to 34 days for 2,2, 3,5, 6-pentachlorbiphenyl. It was estimated that loss by hydroxylation in the atmosphere was a primary process for removal of PCBs from the environment. It was later shown that the products were chlorinated benzoic acids produced by initial reaction with a... 

It has been proposed that aromatic solvents, carbon disulfide, and sulfur dioxide form a complex with atomic chlorine and that this substantially modifies both its overall reactivity and the specificity of its reactions.126 For example, in reactions of Cl with aliphatic hydrocarbons, there is a dramatic increase in Ihe specificity for abstraction of tertiary or secondary over primary hydrogens in benzene as opposed to aliphatic solvents. At the same time, the overall rate constant for abstraction is reduced by up to two orders of magnitude in the aromatic solvent.1"6 The exact nature of the complex responsible for this effect, whether a ji-coinplex (24) or a chlorocyclohexadienyl radical (25), is not yet resolved.126- 22... 

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