Chlorinated benzenes, proposed

Proposed Test Rules. 7/18/80 - Chloromethane. 7/18/80 - Chlorinated Benzenes. 

EPA. 1980a. TSCA chemical assessment series, assessment of testing needs chlorinated benzenes, support document for proposed health effects test rule. Washington, DC U.S. Environmental Protection Agency. EPA 560/11-80-014. NTIS No. PB80-220296. 

Chlorinated benzenes are widely used in industry and are sometimes encountered in drinking-water from surface sources. They usually give rise to taste and odour problems at concentrations below the health-based guideline value, where one has been proposed. 

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... 

Over recent years, the electrochlorination of a wide range of substrates has been reported. The direct halogenation of benzene has been studied at Pt and Rh electrodes and the in situ spectro-electrochemical monitoring of the process with confocal microprobe Raman methods allowed optimization of the reaction conditions [80]. Toluene has been chlorinated at DSAs and the kinetics of this process have been explored in detail [81]. The electrochlorination of 1,4-dimethoxy-2-tert-butylbenzene has been reported in CCI4 and in acetonitrile environments [82]. A difference in mechanism has been proposed to explain the observation of l,4-dimethoxy-2-tert-butyl-5-chlorobenzene and l,4-dimethoxy-2-tert-butyl-6-chlorobenzene, respectively, as the main products. Succinimide is electrochlo-rinated to give A -chlorosuccinimide at platinum electrodes, but the process has been reported to be relatively inefficient due to side reactions (when compared... 

To substantiate this mechanism, haloquinolines (75) were used. The strategy was to hinder sterically the addition of superoxide. In the case of 6-chloroquinoline, the products were the same as those formed from quinoline, except that they were chlorinated, which was expected because position 6 is not involved in either mechanism. Halogen substitution on the pyridine moiety in part directed oxygen addition to the benzene moiety, which was consistent with superoxide addition onto the more accessible positions on the benzene ring of the halogenated radical cation. This result supports the fact that a cycloaddition mechanism can take place in the photocatalytic degradation of quinoline. This mechanism has been proposed in the case of other aromatics, such as 4-chlorophenol (76) and 4-chloro-catechol (77). 

Propose a mechanism for the aluminum chloride-catalyzed reaction of benzene with chlorine. 

According to Tsao et al. [62], three possible structures of benzene-chlorine complex were obtained (Figure 13.1). The first one is high symmetric C(,v) hexahapto-complex with chlorine atom over the centre of the benzene ring (Figure 13.1a), which was firstly proposed by Russel [63]. The second and third structures had Cs symmetry the chlorine atom was located over the carbon-hydrogen bond... 

Although a stable dibromide cannot be isolated for a similar study of the bromination of benzene, the kinetics of the iodine catalyzed bromina-tion of benzene is identical with that of phenanthrene.26 Consequently it is very probable that the mechanism of the halogenation of benzene is the same as that proposed for phenanthrene. The kinetics of chlorination,27 bromination,28 and iodination by iodine chloride29 are also in agreement with this interpretation. The halogenation of phenols, however, appears to be a different, more complex process. 0... 

Under the proposed operating conditions the composition of the liquid product will be constant for any one run. Different products will be obtained for different ratios of benzene and chlorine fed to the reactor. Compute the composition of the liquid product for the case where 1.4 moles chlorine/mole benzene are fed to the reactor. 

Of all the schemes proposed for the addition chlorination of benzene, the continuous cocurrent glass-pipe chlorinator designed by Stormon and modified to include external cooling by Govemale and Clark is the most interesting from an engineering standpoint (Fig. 6-19). 

Wastes containing PAHs may be effectively destroyed by various incineration processes as mentioned briefly in the above section. Weber et al. (2001) have studied the mechanisms of formation of polychlorinated diben-zofurans (PCDF), polychlorinated biphenyls (PCB), polychlorinated naphthalenes (PCN) and polychlorinated benzenes (PCBz) from the degradation of PAHs in two types of incinerators, the stoker type- and the fluidized bed incinerators. Their studies have revealed the occurrence of a sequence of steps, such as the cleavage of C-C bond in the PAHs, chlorination at these cleaved positions, further chlorination or oxygen insertion at the ortho positions to the chlorine atoms in the intermediate chlorinated species. A perylene structure in soot is proposed as the basis for the observed PCDF pattern in the fluidized bed incinerators. Polychlorinated dibenzo-dioxins (PCDD) and the polychlorinated... 

Two examples of nucleophilic aromatic substitution for hydrogen reactions were described from which we have proposed two new atomically efficient processes for the manufacturing of commercially relevant aromatic amines. Our mechanistic studies have revealed that the direct oxidation of a-complex intermediates by either nitro groups or O2 can eliminate the need for chlorination of benzene as a starting point for the manufacturing of aromatic amines. Accordingly, these reactions demonstrate the key objective of alternate chemical design which is not to make the waste in the first place. 

In these cases, the chlorobenzenes act as electron acceptors while the benzidine molecule behaves as an electron donor. The effect of chlorine substitution on the aromaticity of the planar benzene ring of the chlorobenzene derivatives is assessed from the nucleus independent chemical shift (NICS) criterion proposed by Schleyer et al. [338]. Among the various global and local molecular descriptors, electrophilicity (m) is found to be the most appropriate reactivity parameter regarding toxicity... 

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