Benzene reactions with chlorine

Benzene, toluene and homoiogues chlorinated hy reaction with chlorine gas. 

Benzene undergoes a substitution reaction with chlorine only in the presence of halogen carriers. An addition reaction takes place in the absence of a carrier, leading to the formation of benzene hexa-chloride. Iron is the only halogen carrier used extensively in industry, a suitable form being fine iron powder. 

Example The reaction of benzene (C6H6) with chlorine produces chlorobenzene when one... 

Detergents, which now rival soap in demand, are based largely on petroleum the variety of structures which confer detergent properties have led to some interesting syntheses. Alkyl aryl sulfonates are made by alkylation of benzene either with chlorinated kerosene or with a highly-branched olefin made from propylene. Long chain olefins for secondary sulfates were made from paraffin wax. Secondary alkyl sulfonates were made by direct sulfonation of paraffins with sulfur dioxide and chlorine, a reaction discovered in America in the 193O s. 

Benzene is halogenated at room temperature by reaction with chlorine or bromine, in the presence of a catalyst. For example, chlorine reacts with benzene in the presence of iron(III) chloride. A chlorine atom is substituted for hydrogen in the benzene ring and chlorobenzene is formed ... 

Chlorine alone does not react with benzene, in contrast to its instantaneous addition to cyclohexene. However, in the presence of a Lewis acid catalyst, such as ferric chloride or aluminum chloride (Section 4.7), benzene reacts with chlorine to give chlorobenzene and HCl. As shown in the following mechanism, this reaction involves a series of Lewis acid/base reactions. 

Chlorination is carried out m a manner similar to brommation and provides a ready route to chlorobenzene and related aryl chlorides Fluormation and lodmation of benzene and other arenes are rarely performed Fluorine is so reactive that its reaction with ben zene is difficult to control lodmation is very slow and has an unfavorable equilibrium constant Syntheses of aryl fluorides and aryl iodides are normally carried out by way of functional group transformations of arylammes these reactions will be described m Chapter 22... 

Chlorine and bromine add to benzene in the absence of oxygen and presence of light to yield hexachloro- [27154-44-5] and hexabromocyclohexane [30105-41-0] CgHgBr. Technical benzene hexachloride is produced by either batch or continuous methods at 15—25°C in glass reactors. Five stereoisomers are produced in the reaction and these are separated by fractional crystallization. The gamma isomer (BHC), which composes 12—14% of the reaction product, was formerly used as an insecticide. Benzene hexachloride [608-73-17, C HgCl, is converted into hexachlorobenzene [118-74-17, C Clg, upon reaction with ferric chloride in chlorobenzene solution. 

The hquid-phase chlorination of benzene is an ideal example of a set of sequential reactions with varying rates from the single-chlorinated molecule to the completely chlorinated molecule containing six chlorines. Classical papers have modeled the chlorination of benzene through the dichlorobenzenes (14,15). A reactor system may be simulated with the relative rate equations and flow equation. The batch reactor gives the minimum ratio of... 

Commercial chlorination of benzene today is carried out as a three-product process (monochlorobenzene and 0- and -dichlorobenzenes). The most economical operation is achieved with a typical product spHt of about 85% monochlorobenzene and a minimum of 15% dichlorobenzenes. Typically, about two parts of -dichlorobenzene are formed for each part of (9-isomer. It is not economical to eliminate the coproduction of the dichlorobenzenes. To maximize monochlorobenzene production (90% monochlorobenzene and 10% dichlorobenzene), benzene is lightly chlorinated the density of the reaction mixture is monitored to minimize polychlorobenzene production and the unreacted benzene is recycled. 

In non-polar solvents, the reaction with piperidine is best represented by a two-term kinetic form indicating a mixed 2nd- and 3rd-order reaction. Also, base catalysis by tri-ri-butylamine was observed. This kinetic pattern is strongly reminiscent of the results obtained with nitro-activated benzenes.Another interesting result is that stepwise replacement of chlorine atoms by amino groups results in marked... 

After filtering the reaction mixture resulting from the second chlorination, the filtrate was again mixed with a smaller quantity of benzene and again chlorinated in a similar manner. 

The reactivity of Ce, C7, Cg aromatics is mainly associated with the benzene ring. Aromatic compounds in general are liable for electrophilic substitution. Most of the chemicals produced directly from benzene are obtained from its reactions with electrophilic reagents. Benzene could be alkylated, nitrated, or chlorinated to important chemicals that are precursors for many commercial products. 

With 77 % aqueous acetic acid, the rates were found to be more affected by added perchloric acid than by sodium perchlorate (but only at higher concentrations than those used by Stanley and Shorter207, which accounts for the failure of these workers to observe acid catalysis, but their observation of kinetic orders in hypochlorous acid of less than one remains unaccounted for). The difference in the effect of the added electrolyte increased with concentration, and the rates of the acid-catalysed reaction reached a maximum in ca. 50 % aqueous acetic acid, passed through a minimum at ca. 90 % aqueous acetic acid and rose very rapidly thereafter. The faster chlorination in 50% acid than in water was, therefore, considered consistent with chlorination by AcOHCl+, which is subject to an increasing solvent effect in the direction of less aqueous media (hence the minimum in 90 % acid), and a third factor operates, viz. that in pure acetic acid the bulk source of chlorine ischlorineacetate rather than HOC1 and causes the rapid rise in rate towards the anhydrous medium. The relative rates of the acid-catalysed (acidity > 0.49 M) chlorination of some aromatics in 76 % aqueous acetic acid at 25 °C were found to be toluene, 69 benzene, 1 chlorobenzene, 0.097 benzoic acid, 0.004. Some of these kinetic observations were confirmed in a study of the chlorination of diphenylmethane in the presence of 0.030 M perchloric acid, second-order rate coefficients were obtained at 25 °C as follows209 0.161 (98 vol. % aqueous acetic acid) ca. 0.078 (75 vol. % acid), and, in the latter solvent in the presence of 0.50 M perchloric acid, diphenylmethane was approximately 30 times more reactive than benzene. 

In the second process the /z-paraffins are partially chlorinated with chlorine gas in a multistage reactor. The resulting product, a mixture of /z-paraffins and chloroparaffins, is fed, together with excess benzene, into a reactor where AlCl3-catalyzed alkylation is performed. The catalyst suspended or dissolved in the crude alkylate is then separated, while the benzene and unconverted ti-paraffins are recovered by distillation and recycled to the previous reaction stages. In the last step of the process, the LAB is separated from the heavy alkylates. This second process needs to be integrated with a chlorine production unit and with an additional industrial transformation plant which makes use of the corrosive HC1 byproduct. 

DMSO or other sulfoxides react with trimethylchlorosilanes (TCS) 14 or trimefhylsilyl bromide 16, via 789, to give the Sila-Pummerer product 1275. Rearrangement of 789 and further reaction with TCS 14 affords, with elimination of HMDSO 7 and via 1276 and 1277, methanesulfenyl chloride 1278, which is also accessible by chlorination of dimethyldisulfide, by treatment of DMSO with Me2SiCl2 48, with formation of silicon oil 56, or by reaction of DMSO with oxalyl chloride, whereupon CO and CO2 is evolved (cf also Section 8.2.2). On heating equimolar amounts of primary or secondary alcohols with DMSO and TCS 14 in benzene, formaldehyde acetals are formed in 76-96% yield [67]. Thus reaction of -butanol with DMSO and TCS 14 gives, via intermediate 1275 and the mixed acetal 1279, formaldehyde di-n-butyl acetal 1280 in 81% yield and methyl mercaptan (Scheme 8.26). Most importantly, use of DMSO-Dg furnishes acetals in which the 0,0 -methylene group is deuter-ated. Benzyl alcohol, however, affords, under these reaction conditions, 93% diben-zyl ether 1817 and no acetal [67]. 

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