Polyalkylation benzene

To prepare multifunctionalized symmetric organosilicon compounds by the polyalkylation of benzene. (2-chloroethyi)trichlorosilane and (3-chloropropyl)tri-chlorosilane were reacted with benzene. Polyalkylations of benzene with (2-chloroethyl)silane and (3-chloropropyl)silane were carried out in the presence of aluminum chloride catalyst at a reaction temperature of 80 C. The reaction of benzene with excess (2-chloroethyI )trichlorosilanes afforded pcralkylated product, hexakis(2-(trichlorosilyl)ethyl)benzene in good yield (70%). ... 

Concentrated sulphuric acid. The paraffin hydrocarbons, cych-paraffins, the less readily sulphonated aromatic hydrocarbons (benzene, toluene, xylenes, etc.) and their halogen derivatives, and the diaryl ethers are generally insoluble in cold concentrated sulphuric acid. Unsaturated hydrocarbons, certain polyalkylated aromatic hydrocarbons (such as mesitylene) and most oxygen-containing compounds are soluble in the cold acid. 

Deall lation, Transall lation, and Disproportionation. The action of aluminum chloride also removes alkyl groups from alkylbenzenes (dealkylation, disproportionation) (12). Alkylbenzenes, when heated with AlCl, form mixtures of benzene and polyalkylated benzenes ... 

Ethylbenzene can also be produced by catalytic alkylation of benzene with ethylene. Benzene is alkylated with ethylene in a fixed bed alkylator. An excess of benzene is used to suppress the formation of di- and triethyl- benzenes. The excess benzene is removed from the alkylate by fractionation and recycled to the alkylator. The ethylbenzene is separated from the polyalkylated benzenes which are in turn fed to a separate reactor. Here benzene is added to convert the polyalkylated benzenes to monoethylbenzene by transalkylation. 

It should be noted that Scheme 5.1-44 shows idealized Friedel-Crafts allcylation reactions. In practice, there are a number of problems associated with the reaction. These include polyalkylation reactions, since the products of a Friedel-Crafts alkylation reaction are often more reactive than the starting material. Also, isomerization and rearrangement reactions can occur, and can result in a large number of products [74, 75]. The mechanism of Friedel-Crafts reactions is not straightforward, and it is possible to propose two or more different mechanisms for a given reaction. Examples of the typical processes occurring in a Friedel-Crafts alkylation reaction are given in Scheme 5.1-45 for the reaction between 1-chloropropane and benzene. 

The vapor-phase Badger process (Eigure 10-2), which has been commercialized since 1980, can accept dilute ethylene streams such as those produced from ECC off gas. A zeolite type heterogeneous catalyst is used in a fixed bed process. The reaction conditions are 420°C and 200-300 psi. Over 98% yield is obtained at 90% conversion." Polyethylbenzene (polyalkylated) and unreacted benzene are recycled and join the fresh feed to the reactor. The reactor effluent is fed to the benzene fractionation system to recover unreacted benzene. The bottoms... 

In the vapor-phase process, the reaction temperature and pressure are approximately 250°C and 40 atmospheres. Phosphoric acid on Kieselguhr is a commonly used catalyst. To limit polyalkylation, a mixture of propene-propane feed is used. Propylene can be as low as 40% of the feed mixture. A high benzene/propylene ratio is also used to decrease polyalkylation. A selectivity of about 97% based on benzene can be obtained. 

The Fricdel-Crafts type polyalkylation of alkyl-substituted benzenes with 3 becomes easier and faster as the number of electron-donating methyl groups on the phenyl group increases. This is consistent with the fact that the alkylation occurs in the fashion of electrophilic substitution. The tendency of starting incthylben-zenes to form reoriented products also increases in the same order from toluene to mesitylene. 

When (trichloromethyl)silanes reacted with excess benzene in the presence of aluminum chloride at reflux temperature, (triphenylmethyl)silanes were obtained as the major products along with (diphenylmethyl)silanes as minor products (Eq. (17)). Excess benzene was used to avoid the production of polymeric materials due to polyalkylation of one phenyl group. 

DIRECTED ALDOL CONDENSATIONS threo-4-HYDROXY-3-PHENYL-2-HEPTANONE, 54, 49 DIRECTED LITHIATION OF AROMATIC COMPOUNDS (2-DIMETHYL-AMINO- 5-METHYLPHENYL) DI-PHENYLCARBINOL, 53, 56 DIRECT IODINATION OF POLYALKYL-BENZENES IODODURENE, 51, 94 Disiamylborane, 53, 79 Disodium hydroxylaminedisulfo-nate, 52, 83... 

In the polyalkylation reaction of benzene with allylchlorosilanes, trialkylated compounds are the most substituted products obtained in appreciable amount due to increased steric interactions with additional allyltrichlorosilane. This is the case even when more than a four-fold excess of allyltrichlorosilane is used. In addition, multi-step alkylation reactions give the trialkylated products in higher yields than the one-step reaction. 

When benzene reacts with a six-fold excess of Ic in the presence of aluminum chloride at room temperature, the peralkylated product, hexakis[2-(di-chloromethylsilyl)ethyl]benzene is obtained as the major component along with other lower polyalkylated products pentakis-, tetrakis-, tris-, and bis[2-(di-chloromethylsilyl)ethyl]benzene. 

Monoalkylbenzene or other aromatic compounds react more rapidly than benzene itself in alkylation with hydrogen fluoride and the dialkyl-benzene react less rapidly in general to form tri and higher alkylated products. The polyalkylated products require more strenuous conditions. To form the monoalkyl product the alkylating agent should be added slowly to a large excess of the aromatic compound. 

Similar treating procedures can be used on more concentrated aromatic materials such as the polyalkylated benzenes which are formed as heavy by-products in the manufacture of cumene from propylene and benzene (18). 

Di- and polyalkylation can occur during alkylation with alkyl halides since the product alkylbenzenes are more reactive, although the reactivity difference with reactive alkylation systems is small. Toluene, for example, reacts only about 2-5 times faster in some benzylations than benzene.118,119 As alkylbenzenes, however, dissolve preferentially in the catalyst containing layer, heterogeneous systems can cause enhanced polysubstitution. The use of appropriate solvents and reaction conditions as well as of an excess of aromatics allow the preparation of monoalkyl-ated products in high yields. 

In alkylation of benzene with both ethylene and propylene di- and polyalkylates are also formed. In alkylation with propylene 1,2,4,5-tetraisopropylbenzene is the most highly substituted product steric requirements prevent formation of penta-and hexaisopropylbenzene. On the other hand, alkylation of benzene with ethylene readily even yields hexaethylbenzene. Alkylation with higher alkenes occurs more readily than with ethylene or propylene, particularly when the alkenes are branched. Both promoted metal chlorides and protic acids catalyze the reactions. 

The high acidity of the Nafion-H catalyst is further demonstrated by its ability to promote both polyalkylation and isomerization. In reaction between benzene and ethylene at 190°C, 20% of the alkylated products are diethylbenzenes.187 The isomer distribution of the diethylbenzenes is 1 % of the ortho, 75% of the meta, and 24% of the para isomers. This composition is very close to the equilibrium composition of diethylbenzenes determined in solution chemistry with AICI3 catalyst and indicates that the reaction is thermodynamically controlled. 

Conditions for the mononitration of naphthalene, typical of the more reactive polynuclear aromatic hydrocarbons, are to be found in Expt 6.17. Naphthalene can also be nitrated by a mixture of nitric acid and glacial acetic acid, a reagent also suitable for some polyalkylated benzenes. 

Cumene is manufactured by reacting benzene with propylene over a catalyst such as a phosphoric acid derivative at 175 to 250°C and 400 to 600 psi (Fig. 1). A refinery cut of mixed propylene-propane is frequently used instead of the more expensive pure propylene. Benzene is provided in substantial excess to avoid polyalkylation. The yield is near quantitative (in excess of 90 percent) based on propylene. 

Beside isopropyl benzene (IPB) a substantial amount of polyalkylates is formed by consecutive reactions, mostly as C6H5-(C3H7)2 (DIPB) with some C6H5-(C3H7)3 (TPB). The main reaction has a large exothermal effect, of-113kJ/mol in standard conditions. The alkylation reaction is promoted by acid-type catalysts. The synthesis can be performed in gas or liquid phase. Before 1990 gas-phase alkylation processes dominated, but today liquid-phase processes with zeolite catalysts prevail. Recent developments make use of reactive distillation. 

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