Chlorination of aromatics

Molecular chlorine is believed to be the active electrophile in uncatalyzed chlorination of aromatic compounds. Simple second-order kinetics are observed in acetic acid. The reaction is much slower in nonpolar solvents such as dichloromethane and carbon tetrachloride. Chlorination in nonpolar solvents is catalyzed by added acid. The catalysis by acids is probably the result of assistance by proton transfer during the cleavage of the Cl-Cl bond. ... 

Schonken et al.211, found that the chlorination of aromatics by chlorine (in the absence of solvent and, therefore, with excess in aromatic) was catalysed by hydrogen chloride and followed the rate expression... 

Allylmagnesium bromide, 41, 49 reaction with acrolein, 41, 49 5-Allyl-l,2,3,4,5-pentachlorocyclopen-tadiene, 43, 92 Allyltriphenyltin, 41, 31 reaction with phenyllithium, 41, 30 Aluminum chloride, as catalyst, for isomerization, 42, 9 for nuclear bromination and chlorination of aromatic aldehydes and ketones, 40, 9 as Friedel-Crafts catalyst, 41, 1 Amidation, of aniline with maleic anhydride, 41, 93... 

Vazquez-Duhalt, R. Ayala, M., and Marquez-Rocha, F. J., Biocatalytic chlorination of aromatic hydrocarbons by chloroperoxidase of Caldariomyces fumago. Phytochemisty, 2001. 58 pp. 929-933. 

Chlorination of aromatic compounds under irradiation has been studied extensively (Wagner, 1969). With benzene, the product is a mixture of stereoisomeric hexachlorocyclohexanes with yields 104pmol.J 1. This certainly points to chain reaction with the initiation either from a dissociation, Cl2 2C1, or from the participation of the first excited singlet state of benzene 0B2u) giving... 

Chlorination of aromatics by radiation has recently been reported by Harmer (H4). High yields are obtained and the product spectrum is identical with that obtained from photo-initiation. In cases where differences are claimed, the data were taken under conditions where no ultraviolet data are available, and so the situation is as yet not clear. 

Development of Optimal Catalytic Systems for Chlorination of Aromatics... 

Regioselective chlorination of aromatics. Phenol undergoes regioselective chlorination at the orf/io-position with 1, but selectivepara-chlorinationwith2. Chlorination of anisole by either reagent results exclusively in para-chlorination, because of steric effects.2 Chlorination of naphthol with 1 and 2 is more regioselective than that of phenol.1... 

Niedan V, Pavasars I, Oberg G (2000) Chloroperoxidase-Mediated Chlorination of Aromatic Groups in Fulvic Acid. Chemosphere 41 779... 

Vazquez-Duhalt F, Ayala M, Marquez-Rocha FJ (2001) Biocatalytic Chlorination of Aromatic Hydrocarbons by Chloroperoxidase of Caldariomyces fumago. Phytochemistry 58 929... 

Figure 16.3 gives the structural formulas of some of the more important aryl halides. These compounds are made by the substitution chlorination of aromatic hydrocarbons, as shown, for example, by the reaction below for the synthesis of a polychlorinated biphenyl ... 

Polyironphenylsiloxane varnish is used as a catalyst for the chlorination of aromatic hydrocarbons in the nucleus and as a thermostabiliser for antiadhesion silicone coatings. 

Kuzina S.I., Demidov S.V., Denisov N.N., Mikhailov A.I. Synchronic reactions of free radicals formation at low-temperature chlorination of aromatic and olefinic carbohydrates. Izv. AN, Ser. Chem., 1999, 335. 

Predict the products of the Birch reduction, hydrogenation, and chlorination of aromatic compounds, and use these reactions in syntheses. Problems 17-45, 51, 53, and 67... 

Another reaction which can be brought about by PCI5 is the conversion of aldehydes and ketones into the corresponding geminal dichlorides and this is illustrated in Protocol 7 by the conversion of terephthalaldehyde 36 into the tetrachloride 37. Unusually for a reaction using PCI5, no HC1 is evolved here and the product is sufficiently unreactive to be isolated using an aqueous work-up. It should be noted that chlorination of aromatic aldehydes in this way is the method of choice for synthesis of benzylidene chlorides since the products obtained from the alternative chlorination of toluenes are always contaminated by the benzyl chlorides and benzotrichlorides. 

Sulfuryl fluoride is not especially reactive, whereas sulfuryl chloride is extensively used in industry. It readily dissociates into SO2 and chlorine, and is widely used for chlorination (particularly selective side-chain chlorination of aromatics) and sulfochlorination (introduction of SO2CI) in organic chemical manufacture for dyes, disinfectants, herbicides, and so on. 

YIELD AND PRODUCT DISTRIBUTIONS FROM THE CHLORINATION OF AROMATIC COMPOUNDS IN TRIFLUOROACETIC ACID ... 

Chlorination of aromatics. By the procedure formulated, NonhebeP chlorinated anthracene to 9-chloroanthracene in very high yield. The progress of the reaction is evident from the conversion of brown cupric chloride to white cuprous chloride. 

Chlorination of aromatics. Although benzene is sufficiently inert to sulfuryl chloride to be used as a solvent (see above), the reagent dichlorinates ethyl 4-hydroxy-benzoate under mild conditions. The reaction is the first step in a synthesis of 2,6-dichlorophenol. 

The use of sulfuryl chloride instead of chlorine as a chlorinating agent eliminates the danger of explosion. It reacts readily with paraffins in a manner similar to that of chlorine. With unsaturated compounds, it forms the chlorine derivatives. It is also used for the chlorination of aromatic compounds but does not react readily in the absence of a catalyst. Halogen carriers are used as catalysts. In the presence of organic peroxides, sulfuryl chloride selectively chlorinates the side chain. Several reviews on the use of sulfuryl chloride as a chlorinating agent are available 18, 22, 66. ... 

Chlorination of aromatics [at end], de la Mare and Suzuki153 examined the chlorination of naphthalene, I-methylnaphthalene, and 2-methylnaphthalene with sulfiiryl chloride and concluded that the main products are generally those of electrophilic substitution. The results are similar to those obtained with molecular chlorine. 

Most of the industrial chlorinations of organic compounds are, at present, performed by free CI2 either in the absence of catalysts or in the presence of Lewis acid catalysts such as the halides of aluminium and iron. The major handicap of the Lewis acid catalysts like FeCb or AICI3, is the difficulty of their disposal, after use in the chlorination reaction, in an environmentally friendly manner. The use of zeolite catalysts in the chlorination processes will avoid corrosion and disposal problems. Work-up procedures to isolate and recover the desired product will also be easier leading to simpler and cleeiner process routes. In addition, if zeolites are used as solid catalysts, one may anticipate that desired changes in selectivity (enhanced para-selectivity in nuclear chlorination of aromatics, for example) may be achieved. Zeolite catalysts are well known to catalyze various synthetic transformations, however, relatively a few reports are available on the selective chlorination of aromatics using zeolite catalysts [1-4],... 

The liquid phase catalytic chlorination of aromatics was performed at atmospheric pressure in a glass reactor equipped with a magnetic stirrer, a reflux condenser, CI2 or N2 gas feed line and a septum. Aromatic, activated cateilyst eind monochloroacetic acid were introduced in the reactor, in the order mentioned. The mixture was then stirred and heated to attain the reaction temperature in the presence of nitrogen gas. The nitrogen gas was disconnected and chlorine gas was supplied at a rate of 0.08 mol/h to conduct the reaction. The reaction products were analyzed by a Hewlett-Packard model 5890 series II gas chromatograph. 

Chlorination of toluene, chlorobenzene, 1,2-dichlorobenzene and naphthalene with chlorine gas is eatalyzed by zeolite catalysts. There is a great potential and possibility for the use of zeolite catalysts in the nuclear chlorination of aromatics in the liquid phase instead of the Lewis acid catalysts like FeCla and AICI3 used at present. The use of zeolites in such cases leads to enhanced yield of the para-isomer thereby lowering the formation of byproducts and the cost of separation. 

The nature of active site and the mechanism of selective chlorination of aromatics by zeolite K-L as predicted hy molecular modelling methods... 

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