Chlorobenzene cleavage

Obtained synthetically by one of the following processes fusion of sodium ben-zenesulphonate with NaOH to give sodium phenate hydrolysis of chlorobenzene by dilute NaOH at 400 C and 300atm. to give sodium phenate (Dow process) catalytic vapour-phase reaction of steam and chlorobenzene at 500°C (Raschig process) direct oxidation of cumene (isopropylbenzene) to the hydroperoxide, followed by acid cleavage lo propanone and phenol catalytic liquid-phase oxidation of toluene to benzoic acid and then phenol. Where the phenate is formed, phenol is liberated by acidification. 

Unlike the case of benzene in which ionization involves loss of a tt electron from the ring electron impact induced ionization of chlorobenzene involves loss of an elec tron from an unshared pair of chlorine The molecular ion then fragments by carbon-chlorine bond cleavage... 

Mars AE, T Kasberg, SR Kaschabek, MH van Agteren, DB Janssen, W Reineke (1997) Microbial degradation of chloroaromatics use of the mefa-cleavage pathway for mineralization of chlorobenzene. J Bacterial 179 4540-4537. 

Zimmerman and co-workers were also able to obtain some information regarding the multiplicities of the excited states responsible for the initial /9-cleavage through quenching and sensitization studies. It was found that both trans-to-cis and cis-to-trans isomerizations could be sensitized by chlorobenzene under conditions where the latter absorbed over 95% of the light. The same product ratio was obtained under these conditions as in the direct irradiation of the ketones. With 1,3-cyclohexadiene or 2,5-dimethyl-2,4-hexadiene as quenchers nearly 90% of the reaction of the trans isomer could be quenched. Again the ratio of the quenched reaction products was the same as in the unquenched reaction. The reaction of the cis isomer, on the other hand, could not be quenched by 1,3-cyclohexadiene or 2,5-dimethyl-2,4-... 

The isolation of benzene and cyclohexane from chlorobenzene and thiophenol, and cyclohexane from fluorobenzene, suggests the preferential reductive cleavage of the substituent prior to hydrogenation of the ring. However, fluorocyclohexane decomposes slowly to cyclohexene, which could give rise to the cyclohexane higher yields of fluorocyclohexane are obtained at lower temperatures. 

Chemical/Physical. Anticipated products from the reaction of chlorobenzene with ozone or OH radicals in the atmosphere are chlorophenols and ring cleavage compounds (Atkinson et al., 1985 Cupitt, 1980). 

Carbomethoxybenzaldehyde, 100 Carbon disulfide, 57 Chlorine, 24 Chloroacetamide, 22 Chloroacetonitrile, 22 Chlorobenzene, 96 lra i-2-CHLOROCYCLOPENTANOL, 24 2-Chloroethyl benzoate, 11 Chloromethylation, 68 1-Chloromethylnaphthalene, 67, 68 Chlorourea, see Monochlorourea Choline, chloride benzoate, 10 Choline, iodide benzoate, 10 Cinnamaldehyde, 75, 77 Cleavage of tetrahydrofuran, 27, 33 Condensation, of aniline and triphenyl carbinol, 5... 

The products of the electrochemical perfluorination of aromatic and heteroaromatic compounds are the corresponding perfluorinated cyclic and heterocyclic alkanes.28 and also per-fluorinated derivatives of the heteroaromatic compounds. Perfluorocyclohexane is the principal product from the electrochemical fluorination of benzene and fluorobenzene. Chloro derivatives of perfluorocyclohexane are produced from chlorobenzenes. Anisoles give fully saturated per-fluoro ethers, together with cleavage products. Extensive cleavage is observed in the fluorination of benzenethiols. Chloropyridines, fluorocarbons and sulfur hexafluoride or nitrogen trifluoride are characteristic byproducts from the above scries of reactions. 

However, like TOL, TOM encodes the meta-fission of the resulting catechol (Figure 11.4). Consequently, it is unproductive in the assimilation of chloroaromatics like chlorobenzene and 2-chlorophenol, which are also metabolized to 3-chlorocatechol because of catechol 2,3-dioxygenase inactivation. To avoid a build-up of this product an ortho-cleavage enzyme and downstream enzymes for the complete catabolism of the product were recruited through the introduction of the 2,4-dichlorophenoxyacetic-acid-degradativeplasmid pROlOl (Kaphammer, Kukor Olsen, 1990). 

STATISTICALLY CORRECTED SECOND-ORDER RATE COEFFICIENTS (l.mole-1. SeC" ) FOR THE CLEAVAGE OF ALKYL-TIN BONDS BY BROMINE IN SOLVENT CHLOROBENZENE AT... 

Table 24. Faleschini and Tagliavini36 stated that for all of the unsymmetrical tetraalkyls they studied, only the smaller alkyl group in each tetraalkyl was split off as RBr. Such selectivity is rather unexpected in view of the poor selectivity observed for brominolysis in solvent chlorobenzene. Indeed, Gielen and coworkers37 have shown that in the brominolysis of EtSnBu"3 in carbon tetrachloride at 35 °C, both the ethyl and the n-butyl groups are split off as alkyl bromides, with a ratio EtBr/Bu"Br of 0.43. Similarly, the ratio Pr"Br/BunBr was 1.3 in brominolysis of Pr"SnBu"3. In view of this work, the rate coefficients recorded by Faleschini and Tagliavini are valid only as overall rate coefficients and (until further work is done) cannot be used as rate coefficients for the cleavage of particular alkyl-tin bonds. Only for the two sets of compounds examined by Gielen and co-workers37 can the rate coefficient data be used to deduce these alkyl-tin rate coefficients, and values calculated by the author are given in Table 24.

By means of laser spectroscopic studies it has been established that chlorobenzene does not quench the triplet state of A,A-dimethylaniline and the reaction is exclusively singlet-mediated402. The radical anion of chlorobenzene could not be observed and its cleavage rate constant is considered to be very high403. Kinetic analysis has shown that the rate constants for the in-cage fragmentation of the radical anion and the back recombina-... 

When chlorobenzene is heated with sodamide, aniline is formed. However, a direct replacement of the halogen does not occur. The reaction proceeds through a highly reactive benzyne formed by elimination in which the cleavage of the C-H bond is the rate-determining step. The amide anion may then attack the symmetrical benzyne at either end of the benzyne triple bond (Scheme 4.9). 

Watanabe et al. reported that the cleavage of sym-dimethojg etramethyldisilane by a molar equivalent of sodium methoxide in THF leads to methoxydimethylsilylsodium, which reacts in situ with bromo- or chlorobenzene to the corresponding methoxydimethylphenylsilane (Scheme 1, la)... 

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