Acylation of aromatic compounds

A stoichiometric amount of promoter, at least, is required for the reaction to proceed, leading to an environmentally hostile process with gaseous effluents and mineral wastes. With some metal salts, however, an increase in reaction tempera- 

In 1994 preliminary results revealed, surprisingly, that FC acylation could be achieved in the presence of graphite A, under solvent-free conditions, under the 

Entry RCOXli l Conditions (T ax) Productl ] Conversion and yield (%)N  

Entry ArHW RCOXI Craphitel I Conditions (Tm ) Product Conversion and yield (%)  

Acylation of aromatic compounds (Friedel-Crafts (FC) acylation), of great industrial interest, suffers from an important catalysis problem [69]. Most of the Lewis acids used as catalysts (traditionally metal chlorides such as A1C13) complex preferentially 

A stoichiometric amount of promoter, at least, is required for the reaction to proceed, leading to an environmentally hostile process with gaseous effluents and mineral wastes. With some metal salts, however, an increase in reaction temperature sets them free from their complex with the ketone, and a true catalytic reaction becomes possible [73] this is observed for iron(III) chloride [74] and some metal tri-flates [72, 75], including their use under the action of MW heating [76]. 

Entry RCOXh Conditionsc, (Tmax) Productd Conversion and yield (%)e 

The method was also applied to the benzoylation of other aromatic compounds (Tab. 7.7). The benzoylation of benzene itself, volatile and less reactive, seemed more difficult to perform (Tab. 7.7, entry 4). Silyl-substituted aromatics reacted by ipso Si-substitution [77], and were less volatile. With trimethylsilylbenzene, benzoylation occurred with an overall yield higher than for benzene, but the competitive H-substitu-tion was also observed (entry 5). 

CDC Reactions with Molecular Oxygen as the Terminal Oxidant 

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The nitration, sulphonation and Friedel-Crafts acylation of aromatic compounds (e.g. benzene) are typical examples of electrophilic aromatic substitution. 

Friedel-Crafts acylation of aromatic compounds (Section 12 7) Acyl chlorides and carboxylic acid anhydrides acylate aromatic rings in the presence of alumi num chloride The reaction is electrophil ic aromatic substitution in which acylium ions are generated and attack the ring... 

An interesting class ot covalent Inflates are vin l and ar>/ or heteroaryl Inflates Vinyl inflates are used for the direct solvolytic generation of vinyl cations and for the generation of unsaturated carbenes via the a-elimination process [66] A triflate ester of 2-hydroxypyridine can be used as a catalyst for the acylation of aromatic compounds with carboxylic acids [109] (equation 55)... 

Triflates of aluminum, gallium and boron, which are readily available by the reaction of the corresponding chlorides with triflic acid, are effective Fnedel-Crafis catalysis for alkylation and acylation of aromatic compounds [119, 120] Thus alkylation of toluene with various alkyl halides m the presence of these catalysts proceeds rapidly at room temperature 111 methylene chloride or ni-tromethane Favorable properties of the triflates in comparison with the correspond mg fluorides or chlorides are considerably decreased volatility and higher catalytic activity [120]... 

Ferrocene behaves in many respects like an aromatic electron-rich organic compound which is activated toward electrophilic reactions.In Friedel-Crafts type acylation of aromatic compounds with acyl halides, ferrocene is lO times more reactive than benzene and gives yields over 80%. However, ferrocene is different from benzene in respect to reactivity and yields in the Friedel-Crafts alkylation with alkyl halides or olefins. The yields of ferrocene alkylation are often very low. and the separations of the polysubstituted byproducts are tedious. 

Tab. 7.8 Acylation of aromatic compounds in the presence of a small amount of graphite and under the action of MW irradiation [27, 66].

The first example of SILP-catalysis was the fixation of an acidic chloroaluminate ionic liquid on an inorganic support. The acidic anions of the ionic liquid, [AI2CI7] and [AI3CI10], react with free OH-groups of the surface to create an anionic solid surface with the ionic liquid cations attached [72]. The catalyst obtained was applied in the Friedel-Crafts acylation of aromatic compounds. Later, the immobilisation of acidic ionic liquids by covalent bonding of the ionic liquid cation to the surface was developed and applied again in Friedel-Crafts chemistry [73]. 

Bi salts proved to be as active as RET or other metallic triflates in the FC acylation of aromatic compounds using acyl chlorides or anhydrides [13, 66]. While... 

FRIEDEL-CRAFTS ACYLATION OF AROMATIC COMPOUNDS USING... 

The Friedel-Crafts acylation of aromatic compounds is an important synthesis route to aromatic ketones in the production of fine and specialty chemicals. Industrially this is performed by reaction of an aromatic compound with a carboxylic acid or derivative e.g. acid anhydride in the presence of an acid catalyst. Commonly, either Lewis acids e.g. AICI3, strong mineral acids or solid acids e.g. zeolites, clays are used as catalysts however, in many cases this gives rise to substantial waste and corrosion difficulties. High reaction temperatures are often required which may lead to diminished product yields as a result of byproduct formation. Several studies detail the use of zeolites for this reaction (1). 

The importance of aluminum trichloride (and AlBr3 which is more soluble in hydrocarbons) as a catalyst, particularly for Friedel-Crafts alkylation and acylation of aromatic compounds,... 

Cs2 5Ho.5PW 2040 (Cs2.5) catalyzes the acylation of aromatic compounds with benzyl chloride, benzoyl chloride, benzoic anhydride, benzoic acid, or acetic acid (214). As shown in Table XXII, H3PW 2O40 is usually less active than... 

In the RE(OTf)3-catalyzed Friedel-Crafts acylation, the acylation of aromatic compounds with electron-donating substituents, for example anisole and mesity-lene, proceeded smoothly whereas the reactivity of benzene, toluene, and xylenes was low under the same conditions. On the other hand, it was revealed that the catalyst activity of RE(OTf)3 was increased when combined with LiC104, and that the acceleration effect was strongly dependent on the amount of LiC104. 

A mixture of Yb(OTf)3 (620 mg, 1 mmol), anisole (1, 540 pL, 5 mmol), and acetic anhydride (940 pL, 10 mmol) in nitromethane (5mL) was stirred at 50 °C for 4h. After dilution with water (10 mL), the mixture was extracted with dichlorometh-ane. The organic layers were combined and dried over NaS04. After filtration and evaporation of the solvents, the crude mixture was purified by column chromatography on silica gel to afford 4-methoxyacetophenone (2). The aqueous layer was concentrated in vacuo to give a crystalline residue, which was heated at 190 °C for 4h in vacuo to afford 576.6 mg (93 %) Yb(OTf)3 as colorless crystals. The recovered Yb(OTf)3 was reused in the next acylation reaction. All products of the acylation of aromatic compounds shown in this chapter are known compounds and are commercially available. 

In Figure 4.2, log f1/2 is plotted against Hammett substituent constant straight line correlation, and a large negative value of p (—3). Such a result is consistent with that already observed for acylation of aromatic compounds on CeY zeolite[28] and for the conventional acid catalysed Friedel-Crafts acylation. These electronic effects are analogous to those reported in the case of classical electrophilic aromatic substitutions. 

Chiche, B., Finiels, A., Gauthier, C., Geneste, P. The effect of structure on reactivity in zeolite catalyzed acylation of aromatic compounds a p-a+ relationship, Appl. Catal., 1987, 30, 365-369. 

I. Hashimoto, T. Kawaji, F. D. Badea, T. Sawada, S. Mataka, M. Tashiro, G. Fukata, Regioselectivity of Friedel-Crafts Acylation of Aromatic-Compounds with Several Cyclic Anhydrides, Res. Chem. Intermed. 1996, 22, 855-869. 

Primary, secondary, and tertiary carboxylic amides, carboxylic esters, and carboxylic acids are protonated by mineral acids or sulfonic acids at the carboxyl oxygen to a small extent (Figure 6.9). This corresponds to the activation discussed in Section 6.2.3. This activation is used in acid hydrolyses of amides and esters, in esterifications of carboxylic acids and in Friedel-Crafts acylations of aromatic compounds with carboxylic acids. 

The acyl halides (RCOX) on treatment with anhydrous aluminium chloride (AICI3) give a complex, which decomposes to give acyl electrophile, an acylium ion (RCO+). Friedel-Crafts acylation of aromatic compounds involves the formation of a carbocation that acts as an electrophile (see section 2.1.3). 

Aryl-substituted y keto acids are readily obtained by acylation of aromatic compounds with succinic anhydride, e.g., /S-benzoylpropionic acid (85%). ... 

FRIEDEL - CRAFTS AHcylation-Acyiation Akylalion or acylation of aromatic compounds by means of akyl halides, alcohols.alkenes, acyl halides in the presence of Lewis acids... 

It is well known that Friedel-Crafts acylation of aromatic compounds requires more than one equivalent of a Lewis acid relative to the substrate to bring the reaction to the completion, because the ketone produced deactivates the Lewis acid by complexation. Despite this, only 1 mol % TiCl(OTf)3 and 10 mol % TfOH in di-chloromethane or acetonitrile proved sufficient for the acylation shown in Eq. (175) this is, therefore, a catalytic Friedel-Crafts reaction [434]. The high regioselectivity obtained is also useful. 

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