Chlorination of alkylbenzenes

Keefer and Andrews253 measured the rates of chlorination of alkylbenzenes by chlorine catalysed by zinc chloride in acetic acid in solvent. They analysed the data in terms of a catalysed and an uncatalysed reaction (equation 129 and Table 66)... 

Catalysis by stannic chloride in the chlorination of alkylbenzenes in the absence of solvent has been shown to be first-order in catalyst so that the kinetic equation... 

Zeolite-X catalyzed liquid-phase chlorination of alkylbenzenes and halobenzenes was first reported by researchers from Philips laboratories128 and following by Japanese workers129,130 who studied L, X and Y zeolites. Mild temperatures are used and the para ortho selectivity is marginally higher than what have been obtained with conventional... 

CUorinatiou of alkylbeieents. Chlorination of alkylbenzenes with PNCS at 100-140° for 16-20 hr. yields exclusively products of aromatic substitutions. In contrast chlorination of alkylbenzenes under the same conditions with N-chlorosuccinimide (NCS) yields a mixture of products resulting from chlorination of the benzene ring and of the alkyl group(s). The difference in specificity between PNCS and NCS is attributed to the influence of the polymeric backbone in PNCS. Indeed, chlorination of alkylbenzenes with NCS in the presence of succinimide results mainly in chlorination of the benzene ring. Cf. N-Bromopolymaleimide, this volume. 

As in the free-radical halogenation of alkanes, chlorination of alkylbenzenes is less selective than bromination. Given the relative rates per hydrogen for hydrogen atom abstraction from 1-phenylbutane by chlorine for the elementary step shown, calculate the percentage of 1-chloro-1-phenylbutane in the C10H13CI product. 

Kinetic data are available for the nitration of a series of p-alkylphenyl trimethylammonium ions over a range of acidities in sulphuric acid. - The following table shows how p-methyl and p-tert-h xty augment the reactivity of the position ortho to them. Comparison with table 9.1 shows how very much more powerfully both the methyl and the tert-butyl group assist substitution into these strongly deactivated cations than they do at the o-positions in toluene and ferf-butylbenzene. Analysis of these results, and comparison with those for chlorination and bromination, shows that even in these highly deactivated cations, as in the nitration of alkylbenzenes ( 9.1.1), the alkyl groups still release electrons in the inductive order. In view of the comparisons just... 

The comparative ease with which a benzylic hydrogen is abstracted leads to high selectivity m free radical halogenations of alkylbenzenes Thus chlorination of toluene... 

The kinetics of the chlorination of some alkylbenzenes in a range of solvents has been studied by Stock and Himoe239, who again found second-order rate coefficients as given in Table 57. Although the range of rates varies by a factor of 104, there was no marked change in the toluene f-butylbenzene reactivity ratio, and it was, therefore, concluded that the Baker-Nathan order is produced by a polar rather. than a solvent effect. 

There is an additional problem that has important implications for the bioremediation of contaminated sites when two substrates such as a chlorinated and an alkylated aromatic compound are present. The extradiol fission pathway is generally preferred for the degradation of alkylbenzenes (Figure 9.17), although this may be incompatible with the degradation of chlorinated aromatic compounds since the 3-chlorocatechol produced inhibits the activity of the catechol-2,3-oxygenase (Klecka and Gibson 1981 Bartels et al. 1984). 

Also other Type B and C series from Table II are consistent with the above elimination mechanisms. The dehydration rate of the alcohols ROH on an acid clay (series 16) increased with the calculated inductive effect of the group R. For the dehydrochlorination of polychloroethanes on basic catalysts (series 20), the rate could be correlated with a quantum-chemical reactivity index, namely the delocalizability of the hydrogen atoms by a nucleophilic attack similar indices for a radical or electrophilic attack on the chlorine atoms did not fit the data. The rates of alkylbenzene cracking on silica-alumina catalysts have been correlated with the enthalpies of formation of the corresponding alkylcarbonium ions (series 24). Similar correlations have been obtained for the dehydrosulfidation of alkanethiols and dialkyl sulfides on silica-alumina (series 36 and 37) in these cases, correlation by the Taft equation is also possible. The rate of cracking of 1,1-diarylethanes increased with the increasing basicity of the reactants (series 33). 

Thus hydrochloric acid is a derivative of chlorine. About 93% of it is made by various reactions including the cracking of ethylene dichloride and tetrachloroethane, the chlorination of toluene, fluorocarbons, and methane, and the production of linear alkylbenzenes. It is also a by-product of the reaction of phosgene and amines to form isocyanates. 

Linear alkylbenzenes are made from -paraffms (Cio-Cu) by either partial dehydrogenation to olefins and addition to benzene with HF as catalyst (60%) or chlorination of the paraffins and Friedel-Crafts reaction with benzene and an aluminum chloride catalyst (40%). See Chapter 24 for more information. 

Light-induced, radical chlorination or bromination of alkylbenzenes with molecular chlorine or bromine was discussed previously (Section 14-3C). Under these conditions, methylbenzene reacts with chlorine to give successively phenylchloromethane, phenyldichloromethane, and phenyltrichloromethane ... 

Sulfuryl chloride (40) under the influence of heat or ultraviolet light chlorinates alkanes and alkylbenzenes to give a mixture of products thus, with toluene (47), the free radical process yields compounds (48), (49) and (50), (Scheme 34). The radical process involves the formation of the intermediate stabilised benzyl radical leading to chlorination of the side chain. 

Production of alkylbenzene derivatives in the 1940 s was linked to the Fischer-Tropsch synthesis. In 1941, IG Farbenindustrie began to produce chloroparaffins by chlorination of a Fischer-Tropsch alkane mixture rich in n-paraffins with an average chain length of C14 the chloroparaffin was made to react with benzene under Friedel-Crafts conditions and subsequently sulfonated to yield an alkylbenzene sulfonate. The product was given the trade name Tgepal NA . 

Linear alkylbenzene sulfonates are produced from the reaction of benzene and secondary monochloroparaffins the latter are obtained by chlorination of n-paraffins. A requirement of this process was the availability of pure n-paraffins, which was made possible by the introduction of molecular sieves. The n-paraffins can be separated with molecular sieves from kerosene or gas oil, since they have a smaller diameter (ca. 4.9 A) than the branched paraffins. 

The chlorination of paraffins first produces a so-called chloro-oil , which contains around 30% alkyl chlorides and 70% paraffins. The chloro-oil is dehydro-chlorinated in a dehydrochlorination column, with a bottom temperature of around 300 °C. The resulting olefin/paraffin mixture is mixed with a larg molar excess of benzene and fed into the reactor, which is fitted with a powerful stirrer and cooling pipes. Here, the benzene is alkylated in the presence of hydrogen fluoride at a temperature below 50 °C. The reaction product is then separated into two layers in a separation vessel the upper layer, the crude alkylate, is split by distillation into benzene, an inter-cut, paraffin, alkylbenzene and a higher-boiling tail product. The hydrogen fluoride, which is present in the lower layer, is recirculated. 

Zeolites have been used to enhance the / r i-selectivity of chlorination reactions. For example, anisole has been chlorinated using sulfuryl chloride and ZF520 zeolite under reflux conditions [10]. A yield of 81% was achieved with a para to ortho product ratio of 74 26. Smith et al. reported complete conversion of alkylbenzenes using tertiary-butyl hypochlorite and HNaX zeolite at room temperature with para to ortho ratios of greater than 90 10 [11]. Molecular chlorine in the liquid phase with KL zeolite as the catalyst has been reported to give excellent para selectivity and good yields for deactivated benzenes [12]. 

Three basic processes have been practiced for linear alkylbenzene manufacture. The most prevalent route of alkylbenzene manufacture is by partial dehydrogenation of paraffins, followed by alkylation of benzene with a mixed olefin/paraffin feedstock, using liquid hydrogen fluoride catalyst. A second route is via partial chlorination of paraffins, followed by alkylation of the chloroparaffin/paraffin feedstock in the presence of an aluminium chloride catalyst. The third process uses partial chlorination, but includes a dehydrochlorination to olefin step prior to alkylation with aluminium chloride or hydrogen fluoride. 

Other sources of by-product HCl include allyl chloride, chlorobenzenes, chlorinated paraffins, linear alkylbenzene, siHcone fluids and elastomers, magnesium, fluoropolymers, chlorotoluenes, benzyl chloride, potassium sulfate, and agricultural chemicals. 

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