Lewis acid catalysts aluminium chloride

Obara et al. (95) co-carbonized a petroleum pitch which gave a coke of mosaic size of optical texture with the strong Lewis acid catalyst, aluminium chloride,which promoted the size of the optical texture and extents of hydrogen transfer to added anthracene. A correlation was established between size of optical texture of the resultant cokes and extents of formation of 9,10-dihydroanthracene plus evolved hydrogen gas. 

All acids but especially Lewis acids (particularly aluminium chloride), give rise to dangerous interactions with nitrated derivatives and nitrates (there is not much information about nitrates). Aluminium chloride causes a large number of accidents due to nitrobenzene and sometimes nitromethane when used as a solvent in Friedel-Crafts reactions for which aluminium chloride is the common catalyst. 

Sulfonylation involves the replacement of a hydrogen atom by the sulfonyl (RSO2) group. The early work on the chemistry of sulfones was reported by Suter and the mechanism of sulfonylation has been reviewed by Taylor. In sulfonylation, the reaction is catalysed by Lewis acids and aluminium chloride is usually the favoured catalyst since the relative activities of the catalysts in methylsulfonation are as depicted (Figure 2). ... 

As mentioned several times Lewis acids are highly valuable catalysts but the most commonly used ones such as aluminium chloride and boron trifluoride are highly water sensitive and are not usually recovered at the end of a reaction, leading to a significant source of waste. In recent years there has been much research interest in lanthanide triflates (trifluoro-methanesulfonates) as water stable, recyclable Lewis acid catalysts. This unusual water stability opens up the possibility for either carrying out reactions in water or using water to extract and recover the catalyst from the reaction medium. 

An alternative route to anthraquinone, which involves Friedel-Crafts acylation, is illustrated in Scheme 4.3. This route uses benzene and phthalic anhydride as starting materials. In the presence of aluminium(m) chloride, a Lewis acid catalyst, these compounds react to form 2-benzoyl-benzene-1-carboxylic acid, 74. The intermediate 74 is then heated with concentrated sulfuric acid under which conditions cyclisation to anthraquinone 52 takes place. Both stages of this reaction sequence involve Friedel-Crafts acylation reactions. In the first stage the reaction is inter-molecular, while the second step in which cyclisation takes place, involves an intramolecular reaction. In contrast to the oxidation route, the Friedel-Crafts route offers considerable versatility. A range of substituted... 

Mixtures of C4 alkene isomers (largely isobutene) are polymerised commercially in contact with low levels of aluminium chloride (or other Lewis acid) catalysts. The highly exothermic runaway reactions occasionally experienced in practice are caused by events leading to the production of high local levels of catalyst. Rapid increases in temperature and pressure of 160°C and 18 bar, respectively, have been observed experimentally when alkenes are brought into contact with excess solid aluminium chloride. The runaway reaction appears to be more severe in the vapour phase, and a considerable amount of catalytic degradation contributes to the overall large exotherm. 

Anthraquinone itself is traditionally available from the anthracene of coal tar by oxidation, often with chromic acid or nitric acid a more modern alternative method is that of air oxidation using vanadium(V) oxide as catalyst. Anthraquinone is also produced in the reaction of benzene with benzene-1,2-dicarboxylic anhydride (6.4 phthalic anhydride) using a Lewis acid catalyst, typically aluminium chloride. This Friedel-Crafts acylation gives o-benzoylbenzoic acid (6.5) which undergoes cyclodehydration when heated in concentrated sulphuric acid (Scheme 6.2). Phthalic anhydride is readily available from naphthalene or from 1,2-dimethylbenzene (o-xylene) by catalytic air oxidation. 

Lewis acid catalyst is normally required when ammonium polyhalides are used, although recourse does not have to be made to strong acids, such as aluminium trichloride. Bromination and iodination reactions are normally conducted in acetic acid in the presence of zinc chloride [32], but chlorination using the ammonium tetrachloroiodate in acetic acid does not require the additional presence of a Lewis acid [33]. Radical chlorination of toluenes by benzyltrimethylammonium tetrachloroiodate in the presence of AIBN gives mixtures of the mono-and dichloromethylbenzenes [34], Photo-catalysed side-chain chlorination is less successful [35], Radical bromination using the tribromide with AIBN or benzoyl peroxide has also been reported [36, 37],... 

Abstract The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 °C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of then-cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis. 

With bromine and excess aluminium chloride, 2-acetylfuran was converted into a mixture of 2-acetyl-4,5-dibromofuran (major product) and about equal quantities of the 4- and 5-bromo derivatives. The swamping catalyst effect is operating here. Coordination of the catalyst with the carbonyl function makes the substituent more electronegative, and in the presence of a large excess of Lewis acid catalyst, positions ortho and para to the substituent are deactivated more than the me/a-position [68AG(E)519 82AHC(30)167]. In terms of a 2-acylfuran, this means that... 

Almost all ethylbenzene is produced commercially by alkylating benzene with ethylene, either in the liquid phase with aluminium chloride catalyst or in the vapour phase with a synthetic zeolite or Lewis acid catalyst (Coty et al., 1987 Cannella, 1998). 

Aluminium chloride is often used as a Lewis acid catalyst (equations 68 and 69), although there are many other suitable catalysts (equations 70 and 71). Strong electrophiles such as chlorosulphonyl isocyanate or an aluminium salt do not require catalysis (equations 72 and 73). 

The catalyst may serve to generate the reactive species. For example, many electrophiles are generated by mineral acid or Lewis acid catalysts. Bromine reacts with iron(III) bromide to give the bromonium ion (1.62), whilst acetyl chloride in the presence of aluminium trichloride reacts as an acylium ion (1.63). 

Titanium(II) arene complexes, (r -arene)Ti(AICl4)2, are readily obtained from the reaction between TiC, aluminium powder and aluminium chloride in refluxing aromatic solvent [182]. Metal halides have been used as Lewis acid catalysts for various... 

Friedel-Crafts alkylation involves the alkylation of an aromatic ring and an alkyl halide using a strong Lewis acid catalyst. With anhydrous aluminium chloride as a catalyst, the alkyl group attaches at the former site of the chloride ion. 

Different methods for the preparation of Novel Lewis-Acid Catalysts (NLACs) consisting of ionic liquids immobilised on mesoporous support materials are presented. The focus will be placed on materials bound to the carrier via the organic cation of the ionic liquid, either by grafting or by the preparation of organically modified HMS. After addition of aluminium(III)chloride the materials were used as catalysts e.g. in Friedel-Crafts alkylations, in which they displayed high activities and selectivities. 

The rearrangement of phenolic esters to either o-and/or p-phenolic ketones on being heated upon with anhydrous aluminium chloride or other Lewis acid catalysts is known as Fries Reaction or Rearrangement, as depicted below ... 

Diastereoselective complexation of a chiral [antagonist] ketone with a racemic aluminium Lewis acid catalyst effectively removes one enantiomer of the latter, leaving the uncomplexed antipode free to function as a chiral Lewis acid. E Asym. heterodiene synthesis. 0.1 eq. D-3-bromocamphor, 1.05 eqs. startg. siloxydiene, and benzaldehyde added sequentially to 0.1 eq. of the racemic aluminium complex in degassed methylene chloride at —78°, stirred for 3 h, then subjected to acidic work-up (2S,3S)-product. Y 78% (e.e. 82%, upgraded to > 98% by one recrystallization with ca. 60% recovery). F.e.s. K. Maruoka, H. Yamamoto, J. Am. Chem. Soc. Ill, 789-90 (1989). 

Aluminium chloride (AICI3) as the Lewis acid (catalyst) with cupric chloride (CuCb) as the oxidizing agent was the best catalyst-oxidant combination used by Kovacic et al. for the polymerization of benzene. Polymerization occurred under mild conditions (36-37°C, 15 minutes), with water as a co-catalyst, and the yield of poly-(p-phenylene) was found to depend on the aluminium chloride to cupric chloride ratio. 

While hundreds of Lewis acid catalysts have been developed for organic reactions, Brousted acid catalysts have been paid less attention until recently. Conventional Lewis acids, such as titanium chloride and aluminium chloride, are known to be incompatible with aqueous media. On the other hand, Bronsted acids are stable toward water and oxygen. Thus, they are potential candidates as activators of electrophilic substrates in water. It was found that among various Bronsted acids, HBF4 efficiently catalyzed Mannich -type reactions of silyl enol ethers with aromatic aldehydes derived from activated imines to afford the corresponding p-amino ketones (Scheme 3.1). ... 

The methylsulfonylation of toluene by reaction with methylsulfonyl chloride in the presence of aluminium chloride catalyst affords methyl tolyl sulfone (52% yield) with an ortho meta para isomer ratio of 53 14 33. Attempts have been made to obtain greater selectivity in sulfonylations a supported Lewis acid catalyst has been recommended for selective sulfonylation, but it did not give good results in the methylsulfonylation of toluene. The best pura-selectivity... 

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