Alkylation, of aromatics

The product consisted of two liquid layers. The upper layer comprised benzene and methylated benzenes. The lower layer was a red-brown oily complex of the catalyst and the same methylbenzenes as those found in the upper layer, and which could be liberated by hydrolysis. 

Similarly, a product believed to be n-amylbenzene was formed by the reaction of amyl chloride with benzene in the presence of aluminum chloride. It is quite probable, however, that the product reported at boiling at 185-190°C contained much. vec-amy I ben zenes and possibly even a small amount of tert- amylbenzene. In fact, isomerization often accompanies alkylation of aromatic hydrocarbons. 

Shortly after the work of Friedel and Crafts, Balsohn discovered that ethylene also reacted with benzene in the presence of AICI3 to give ethylbenzene.76 Other 

Besides aluminum chloride, the most often used and studied Friedel-Crafts catalyst, many other acid catalysts are effective in alkylation. Although Friedel-Crafts alkylation was discovered and explored mainly with alkyl halides, from a practical point of view, alkenes are the most important alkylating agents. Others include alcohols, ethers, and esters. 

Detailed coverage of Friedel-Crafts-type alkylations is to be found in relevant reviews and monographs,77-86 and the reader is advised to consult these for detailed information. 

Electrophilic alkylation of aromatics can be carried out with a variety of alkylating agents such as alkenes, alcohols and halogenated hydrocarbons. Aromatic alkylation is a good example of a reaction where the shape selectivity of the zeolite plays an important role in controlling the distribution of products. 

One of the most important industrial alkylations is the production of 1,4-xylene from toluene and methanol (Reaction 2). ZSM-5, in the proton exchanged form, is used as the catalyst because of its enhanced selectivity for para substituted products. para-Xylene is used in the manufacture of terephtha-lic acid, the starting material for the production of polyester fibres such as Terylene. The selectivity of the reaction over HZSM-5 occurs because of the difference in the rates of diffusion of the different isomers through the channels. This is confirmed by the observation that selectivity increases with increasing temperature, indicating the increasing importance of diffusion limitation. The diffusion rate of para-xylene is approximately 1000 times faster than that of the meta and ortho isomers.14 

The selective methylation of meta-xylene to produce 1,2,4-trimethylbenzene (TMB) has been studied by Raj et al.16 The most effective catalysts were those based on the medium pore 10 ring MEL structure. They found that isomor-phous substitution of framework Al for Ga or Fe significantly enhanced the yield of 1,2,4-TMB. The reason for the higher yields was attributed to the weaker acid sites on the Ga and Fe substituted materials compared to the Al 

One of the unique features of zeolites in alkylation reactions is their shape selectivity. In many zeolite-catalysed reactions, however, shape-selective catalysis occurring on the inside of the zeolite can be affected by non-selective catalysis on the external surfaces. Paparatto et al. have reported that during aromatic alkylation, the para isomer is formed selectively within the zeolite, whereas isomerisation occurred only on the external surfaces, decreasing para product selectivity.17 

Several methods have been reported to deactivate the catalytic activity of the external surfaces of zeolites. Bhat et al. have modified the catalytic behaviour of ZSM-5 by chemical vapour deposition (CVD) of tetraethyl orthosilicate (TEOS).18 The CVD technique does not affect the channel size or acidity of the zeolite but deactivates the external surfaces by coating them with an inert layer of silica. As a result, the shape selectivity of the zeolite is greatly enhanced. 

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We will show here the classification procedure with a specific dataset [28]. A reaction center, the addition of a C-H bond to a C=C double bond, was chosen that comprised a variety of different reaction types such as Michael additions, Friedel-Crafts alkylation of aromatic compounds by alkenes, or photochemical reactions. We wanted to see whether these different reaction types can be discerned by this... 

Acid-catalyzed alkylation of aromatics with alcohols themselves is widely used. Whereas tertiary (and secondary) alcohols react with rel-... 

Because acylation of an aromatic ring can be accomplished without rearrangement it is frequently used as the first step m a procedure for the alkylation of aromatic compounds by acylation-reduction As we saw m Section 12 6 Friedel-Crafts alkylation of ben zene with primary alkyl halides normally yields products having rearranged alkyl groups as substituents When a compound of the type ArCH2R is desired a two step sequence IS used m which the first step is a Friedel-Crafts acylation... 

Ring formation readily occurs ia the alkylation of aromatics with di- and polyhaUdes, eg, the reaction of di- and ttihalomethanes with aromatics ia the presence of aluminum chloride. In the reaction of dichioromethane and ben2ene, besides diaryknethanes, anthracene derivatives are also formed (54). 

In addition, boron, aluminum, and gallium tris(triduoromethanesulfonates) (tridates), M(OTf)2 and related perduoroalkanesulfonates were found effective for Friedel-Crafts alkylations under mild conditions (200). These Lewis acids behave as pseudo haUdes. Boron tris(tridate) shows the highest catalytic activity among these catalysts. A systematic study of these catalysts in the alkylation of aromatics such as benzene and toluene has been reported (201). 

Another type of soHd supetacid is based on perfluorinated resin sulfonic acid such as the acid form of Du Font s Nafion resin, a copolymer of a perfluorinated epoxide and vinylsulfonic acid or soHd, high molecular weight petfluotoalkanesulfonic acids such as petfluotodecanesulfonic acid, CF2(CF2)qS02H. Such sohd catalysts have been found efficient in many alkylations of aromatic hydrocarbons (225) and other Friedel-Crafts reactions (226). 

Catalysis. As of mid-1995, zeoHte-based catalysts are employed in catalytic cracking, hydrocracking, isomerization of paraffins and substituted aromatics, disproportionation and alkylation of aromatics, dewaxing of distillate fuels and lube basestocks, and in a process for converting methanol to hydrocarbons (54). 

The first step in the catalytic alkylation of aromatics is the conversion of an olefin or olefin-producing reagent into a carbonium ion or polari2ed complex. Then, this carbonium ion or complex, which is a powerful electrophile, attacks the aromatic ring (32). 

Alkylation of isobutylene and isobutane in the presence of an acidic catalyst yields isooctane. This reaction proceeds through the same mechanism as dimerization except that during the last step, a proton is transferred from a surrounding alkane instead of one being abstracted by a base. The cation thus formed bonds with the base. Alkylation of aromatics with butylenes is another addition reaction and follows the same general rules with regard to relative rates and product stmcture. Thus 1- and 2-butenes yield j -butyl derivatives and isobutylene yields tert-huty derivatives. 

General process for the alkylation of aromatics with olefins Alkylation... 

Molecular sieves placed in hags or porous containers Alkylation of aromatics Crossland, U.S. Patent 5,04.3,506 (1991)... 

Bts(perfluoroacyl) peroxides allow also the alkylation of aromatic compounds [7 2, 153] (equations 132 and 133)... 

Many of the reactions of BF3 are of the Friedel-Crafts type though they are perhaps not strictly catalytic since BF3 is required in essentially equimolar quantities with the reactant. The mechanism is not always fully understood but it is generally agreed that in most cases ionic intermediates are produced by or promoted by the formation of a BX3 complex electrophilic attack of the substrate by the cation so produced completes the process. For example, in the Friedel-Crafts-type alkylation of aromatic hydrocarbons ... 

The reductive alkylation of aromatic nitro compounds using H +Pd/G in the presence of 40% aqueous formaldehyde gives directly dimethylamino derivatives in good yield (Tq. 6.43. ... 

Details of two related patents for the alkylation of aromatic compounds with chloroaluminate(III) ionic or chlorogallate(III) ionic liquid catalysts have become available. The first, by Seddon and co-workers [81], describes the reaction between ethene and benzene to give ethylbenzene (Scheme 5.1-51). This is carried out in an... 

Scheme 5.1-51 The alkylation of aromatic compounds in chloroaluminate(lll) or chlorogallate(lll) ionic liquids.

Flowever, information concerning the characteristics of these systems under the conditions of a continuous process is still very limited. From a practical point of view, the concept of ionic liquid multiphasic catalysis can be applicable only if the resultant catalytic lifetimes and the elution losses of catalytic components into the organic or extractant layer containing products are within commercially acceptable ranges. To illustrate these points, two examples of applications mn on continuous pilot operation are described (i) biphasic dimerization of olefins catalyzed by nickel complexes in chloroaluminates, and (ii) biphasic alkylation of aromatic hydrocarbons with olefins and light olefin alkylation with isobutane, catalyzed by acidic chloroaluminates. 

The method illustrates the ability of the sodium hydride-dimethylformamide system to effect the alkylation of aromatic sulfonamides under mild conditions and in good yield. The method appears to be fairly general. The submitters have prepared N,N-diethyl- and N,N-di- -butyl- >-toluenesulfonamide as well as 2-(/ -tolyIsuIfonyl)benz[/]isoindoline from 2,3-bis-(bromomethyl)naphthalene, and 1 %-tolylsulfony])pyrrolidine from 1,4-dichIorobutane the yield of purified product exceeded 75% in each case. 

Unsolvated organomagnesium compounds have been recommended for the synthesis of organometallic derivatives of mercury, boron, aluminum, silicon, germanium, tin, phosphorus, arsenic, and antimony6-8 and have been used in procedures for the alkylation of aromatic rings and for the production of various polymerization catalysts.4 9... 

The kinetics of alkylation of aromatics with sulphonic acid esters have been... 

Reaction No. 5 (Table 11) is part of a synthetically useful method for the alkylation of aromatic compounds. At first the aromatic carboxylic acid is reductively alkylated by way of a Birch reduction in the presence of alkyl halides, this is then followed by an eliminative decarboxylation. In reaction No. 9 decarboxylation occurs probably by oxidation at the nitrogen to the radical cation that undergoes decarboxylation (see... 

The alkylation of aromatic rings, called Friedel-Crafts alkylation, is a reaction of... 

Alkylation of aromatic rings with ethylene oxide... 

In this section, the reactivities of organosilicon compounds for the Friedel-Crafts alkylation of aromatic compounds in the presence of aluminum chloride catalyst and the mechanism of the alkylation reactions will be discus.sed, along with the orientation and isomer distribution in the products and associated problems such as the decomposition of chloroalkylsilanes to chlorosilanes.. Side reactions such as transalkylation and reorientation of alkylated products will also be mentioned, and the insertion reaction of allylsilylation and other related reactions will be explained. 

Monoalkylation products, 3-aryl-1,1 -dichloro-1 -silabutanes, were obtained from the alkylation of aromatic compounds with I in the presence of aluminum chloride catalyst in good isolated yields (60-80%) along with small amounts of higher alkylation products. Dialkylation products were obtained in yields ranging from 2 to 8% when a 5-fold excess of the aromatic compounds with respect to 1 was used. The amount of dialkylated products can be further reduced by using a greater excess of the aromatic compounds. 

Vinylchlorosilanes react with aromatic compounds in the presence of Lewis acid to give the alkylation products 2-(chlorosilyl)ethylarenes. In the Friedel-Crafts alkylation of aromatic compounds, the reactivity of vinylchlorosilanes is slightly lower than that of allylchlorosilanes.Friedel-Crafts alkylation of benzene derivatives with vinylsilanes to give 2-(chlorosilyl)ethylarenes was first reported by the Andrianov group (Eq. (5))." The reactivity of vinylsilanes in the... 

The Friedel-Crafts alkylation of aromatic compounds with alkyl halides in the presence of Lewis acid is well defined in organic chemistry. However, alky-... 

Among the Friedel-Crafts alkylations of aromatic compounds with (chlorinated alkyl)silanes, the alkylation of benzene with (tt>-chloroalkyl)silanes in the presence of aluminum chloride catalyst was generally affected by two factors the spacer length between the Cl and silicon and the electronic nature of substituents on the silicon atom of (w-chloroalkyl)silanes. As the spacer length between the C—Cl and silicon increases from (chloromethyl)silane to (/i-chloroethyl)silane to (/-chloropropyl)silane, the reactivity of the silanes increases. As the number of chloro-groups on the silicon decreases from (chloromethyl)trichlorosilanes to (chloromethyl)methyldichlorosilanes to (chloromethyl)trimethylsilanes, the... 

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