Alkylation of Aromatics with Olefins

Ethylbenzene is the key intermediate in the manufacture of styrene, one of the most important industrial monomers. Almost all ethylbenzene is synthesized from benzene and ethylene. 

In the conventional ethylbenzene technology, an aluminum chloride —hydrogen chloride combination is the most widely used catalyst. The highly corrosive nature of aluminum chloride requires special resistance materials in the construction of the reaction vessel and product handling equipment. The polluting nature of aluminum chloride further necessitates treatment of the product for disposal of spent catalysts. 

The Alkar process using boron trifluoride supported on alumina introduced in 1958 was a high pressure fixed-bed process. The process permitted the utilization of the light olefins (ethylene + propylene) of the refiners gas, which had been burnt as a fuel. The quality of ethylbenzene and isopropyl benzene was excellent. However, commerical experience showed that corrosion problems were still substantial and product pretreatment was necessary to remove boron trifluoride. 

With the introduction of faujasite zeolite into petroleum cracking, interest in vapor phase alkylation was renewed. There were several reported studies on the use of faujasite or mordenite to ethylate benzene.They were very active, but associated with rapid aging attributed to coke formation. Therefore, a feasible commercial alkylation using faujasite as a catalyst never evolved. 

In 1976, the Mobil/Badger ethylbenzene process was announced.This is a vapor-phase, fixed-bed process that utilizes ZSM-5. Because of the unique characteristics of the catalysts, aging rate is low and yields of nonselective byproducts are also low. The first commercial unit with a capacity of 50,000 t/y was streamed by the American Hoechst Corp. in 1980. Alkylation is carried out in the gas-phase at about 

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

The pioneer work in this field was carried out on polystyrene-supported acid catalysts [161]. Thereafter, several works on the use of sulfonic, strong acidic cation exchangers as acid catalysts were reported for alkylation, hydration, etherification, esterification, cleavage of ether bonds, dehydration, and aldol condensation [162,168-171], Besides, industrial applications of these materials were evaluated with reactions related to the chemistry of alkenes, that is, alkylation, isomerization, oligomerization, and acylation. [163,169], Also, Nation, an acid resin which has an acid strength equivalent to concentrated sulfuric acid, can be applied as an acid catalyst. It is used for the alkylation of aromatics with olefins in the liquid or gas phases and other reactions however, due to its low surface area, the Nation resin has relatively low catalytic activity in gas-phase reactions or liquid-phase processes where a nonpolar reactant or solvent is employed [166],... 

Diphenyl carbonate from dimethyl carbonate and phenol Dibutyl phthalate from butanol and phthalic acid Ethyl acetate from ethanol and butyl acetate Recovery of acetic acid and methanol from methyl acetate by-product of vinyl acetate production Nylon 6,6 prepolymer from adipic acid and hexamethylenediamine MTBE from isobutene and methanol TAME from pentenes and methanol Separation of close boiling 3- and 4-picoline by complexation with organic acids Separation of close-boiling meta and para xylenes by formation of tert-butyl meta-xyxlene Cumene from propylene and benzene General process for the alkylation of aromatics with olefins Production of specific higher and lower alkenes from butenes... 

There are many examples of the alkylation of aromatics with olefins to produce alkylbenzene In textbooks, the open literature, and In numerous patents. This reaction Is catalyzed by both proton and Lewis acids In a homogeneous phase and In heterogeneous phases. The latter systems are characterized by both proton (H FO ) and Lewis acids (BF ) on supports and the amorphous and crystalline alumina silicates. And, the reaction has been studied extensively. However, up until the start of this Investigation (1969) there had not been a systematic investigation of the kinetic parameters nor an adequate catalyst aging study on the alkylation of benzene with propylene over a crystalline alumina silicate. 

The industrial alkylation of aromatics with olefins is one of the major examples of development of environmentally friendly processes with solid acid catalysts [221, 222]. The principal products obtained are ethylbenzene (EB), cumene (CUM), p-diethylbenzene, p-diisopropylbenzene, Cio-Ci4linear alkylbenzenes (LAB) and cymene. Figure 2.28 summarizes several aromatic alkylations industrially applied for the preparation of important chemical intermediates [222]. These reactions include the most important aromatic substrates, benzene, toluene and xylene, and different olefins. They also include two different kinds of alkylation electrophilic alkylation on the aromatic ring catalyzed by acids and side-chain alkylation catalyzed by bases. In terms of production volume, add-catalyzed alkylations are by far the most... 

While alkylation of aromatics with olefins or alcohols occurs at the aromatic ring over acid catalysts, alkylation of the alkyl groups proceeds over basic catalysts. Pines and coworkers reported that the side-chain alkylation of toluene with ethylene is effectively catalyzed by the use of a mixture of sodium and a promotor such as anthracene or o-chlorotoluene. ... 

Acid-catalyzed reactions of aromatics with monoolefins result in nuclear alkylation. But the base-catalyzed reactions of aromatics with olefins do not result in nuclear alkylation as long as benzylic hydrogens are available. This is true even with aromatics, such as cumene, which have deactivated benzylic hydrogens resulting in facile metalation of the ring. Apparently phenyl carbanions do not readily add to olefins. Pines and Mark (20) found that in the presence of sodium and promoters only small yields of alkylate were produced at 300° in reactions of benzene with ethylene and isobutylene and of t-butylbenzene with ethylene. With potassium, larger yields may be obtained at 190° (24)-... 

Just as in the case of aromatic compounds isoparaffins can be alkylated with sources of alkyl groups other than olefins. Alkyl halides, alcohols, ethers, mercaptans, sulfides, etc., can be used. When olefins are used some alkyl fluorides from a combination of olefin and hydrogen fluoride are always formed. The quantity of this in the product can be greatly reduced by providing conditions under which the alkyl fluoride is used in alkylation. The apparent paradox is provided, in that the fluoride content of the product is lessened by further treatment with hydrogen fluoride. A more thorough treatment of the details of the alkylation of isoparaffins with olefins is found elsewhere in this volume. 

Dialkylhalonium ions are reactive alkylating agents. The alkylation of Jt-donor (aromatic and olefinic) and w-donor bases with dialkylhalonium ions has been studied.353 Alkylation of aromatics with dialkylhalonium ions was found to be not significantly different from conventional Friedel-Crafts alkylations, showing particular similarities in the case of alkylation with alkyl iodides. Alkylation of w-donor bases with dialkylhalonium salts provides a simple synthetic route to a wide variety of onium ions. 

To conclude this section, it is necessary to state that besides their application in catalytic cracking, amorphous silica-alumina acid catalysts have been applied in other hydrocarbon transformations, such as isomerization of olefins, paraffins, and alkyl aromatics, the alkylation of aromatics with alcohols and olefins, and in olefin oligomerization [55],... 

In 1945 Mamedaliev published a book in Baku (213) reporting the research carried out in his laboratory on the alkylation of aromatics and isoparaffins with olefins in the presence of a number of catalysts. Subsequent information indicates that Mamedaliev has developed a continuous process of alkylation of benzene with olefins. He also described alkylation of benzene with propylene in the presence of activated clay (214). 

Alkylation of Aromatics with Liquid Catalysts. Forty years ago, ethylbenzene, cumene, and dodecyl benzenes were produced by alkylation reactions of benzene with liquid catalysts. Although some production processes still involve these catalysts, solid catalysts such as zeolites are now often the preferred catalysts. Olefins are generally employed for commercial alkylation reactions. The chemistry discussed next will involve liquid catalysts that are protonic acids or Friedel-Crafts catalysts. 

Polynuclear Aromatics. The alkylation of polynuclear aromatics with olefins and olefin-producing reagents is effected by acid catalysts. The alkylated products are more compHcated than are those produced by the alkylation of benzene because polynuclear aromatics have more than one position for substitution. For instance, the alkylation of naphthalene [91-20-3] with methanol over mordenite and Y-type zeoHtes at 400—450°C produces 1-methylnaphthalene [90-12-0] and 2-methylnaphthalene at a 2-/1- ratio of about 1.8. The selectivity to 2-methylnaphthalene [91-57-6] is increased by applying a ZSM-5 catalyst to give a 2-/1- ratio of about 8 (102). 

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 0/7/fo-alkylation of aromatic ketones with olefins can also be achieved by using the rhodium bis-olefin complex [C5Me5Rh(C2H3SiMe3)2] 2, as shown in Equation (9).7 This reaction is applied to a series of olefins (allyltrimethyl-silane, 1-pentene, norbornene, 2,2 -dimethyl-3-butene, cyclopentene, and vinyl ethyl ether) and aromatic ketones (benzophenone, 4,4 -dimethoxybenzophenone, 3,3 -bis(trifluoromethyl)benzophenone, dibenzosuberone, acetophenone, />-chloroacetophenone, and />-(trifluoromethyl)acetophenone). 

It has been found that the disproportionation of toluene over ZSM-5 catalyst can be directed such that p-xylene is the predominant xylene isomer (14-17). This reaction, designated STOP, is one of several in which disubstituted aromatics rich in the para isomer are produced. Others are the alkylation of toluene with methanol to produce p-xylene (15,18) and with ethylene to produce p-ethyltoluene (19,20), as well as the aromatization of olefins (20), paraffins (20) and of methanol... 

The reaction of toluene with propylene and higher olefins is similar to that of toluene with ethylene. In contrast to the acid-catalyzed alkylation of aromatics, the base-catalyzed reaction of toluene with propylene takes place less rapidly than the reaction with ethylene. With more severe conditions, such as temperatures of 225-250°, the reaction of toluene with propylene may be made to proceed satisfactorily, but butylenes yield only small amounts of products even at 300°, as reported by Pines and Mark 20). Such conditions result not only in more hydrogen transfer, but alkyl-group... 

Acidic mixed oxides, including alumina and silica, as well as natural clays, and natural or synthetic aluminosilicates, are sufficiently (although mildly) hydrated to be effective as solid protic acids for the alkylation of aromatic hydrocarbons with olefins. The most studied of these catalysts are zeolites that are used in industrial... 

Study of the reactivity of aromatic C-H bonds in the presence of transition metal compounds began in the 1960s despite the quite early discovery of Friedel-Crafts alkylation and acylation reactions with Lewis acid catalysts. In 1967, we reported Pd(II)-mediated coupling of arenes with olefins in acetic acid under reflux [1], The reaction involves the electrophilic substitution of aromatic C-H bonds by a Pd(II) species, as shown in Scheme 2, and this is one of the earliest examples of aromatic C-H bond activation by transition metal compounds. Al-... 

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