Acylation of aromatic hydrocarbons

As reported in the literature, the acylation of aromatic hydrocarbons can be carried out by using zeolites as catalysts and carboxylic acids or acyl chlorides as acylating agents. Thus toluene can be acylated by carboxylic acids in the liquid phase in the presence of cation exchanged Y-zeolites (ref. 1). The acylation of phenol or phenol derivatives is also reported. The acylation of anisole by carboxylic acids and acyl chlorides was obtained in the presence of various zeolites in the liquid phase (ref. 2). The acylation of phenol by acetic acid was also carried out with silicalite (ref. 3) or HZSM5 (ref. 4). The para isomer has been generally favoured except in the latter case in which ortho-hydroxyacetophenone was obtained preferentially. One possible explanation for the high ortho-selectivity in the case of the acylation of phenol by acetic acid is that phenylacetate could be an intermediate from which ortho-hydroxyacetophenone would be formed intramolecularly. 

Nafion-H has also been found to be an effective catalyst for heterogeneous acylation of aromatic hydrocarbons with aroyl chlorides and anhydrides.367... 

When (253) reacts with phosgene the 1-acyl chloride product (254) can react with amines to give amides (79LA1756X while in a further transfer reaction with ketones the compounds (255) and (256) are produced (Scheme 146) (80H(14)97). Acylation of aromatic hydrocarbons using 1-acylimidazoles in the presence of trifluoracetic acid gives high yields provided that the aryl compounds are electron rich, e.g. p-dimethoxybenzene, thiophene, anisole <80BCJ1638). 

Diarylketones are also the important fine chemical intermediates, which could be prepared by the acylation of aromatic hydrocarbon with benzoyl chloride and benzoic anhydride. The ionic liquids have also been used to catalyze the synthesis of diarylke-tone. Earle et al. [105] have reported the benzoylation of benzene, derivants of benzene (toluene, anisole, isobutyl benzene, phenyl chloride and fluoride) to synthesize the diarylketone by use of chloroindate (III) ionic liquids as the green dual catalysts and solvents. As a result, good yields (75-96%) were obtained under proper conditions with the ionic liquids as the clean reaction medium and recyclable catalysts. 

The conventional method of preparation of these aromatic ketones is the homogeneous Friedel-Crafts acylation of aromatic hydrocarbons with carboxylic acid derivatives using Lewis acids (A1C13, FeCl3, BF3, ZnCl2, TiCl4) or Bronsted acids (polyphosphoric acid, HF). For this purpose, stoichiometric to excess amounts of the catalyst are required for the reaction to proceed (ref. 1). 

Sreekumar, R. and Padmakumar, R. 1997. Friedel-Crafts acylation of aromatic hydrocarbons using zeolites. Synth. Commun. 27 777-780. 

Acylation reactions of arenes using zeolites may become industrially important because of their high selectivity. The Friedel-Crafts acylation of aromatic hydrocarbons by carboxylic, acids has been studied by Chiche et al. (1986) [see also Brunei et al. (1989)]. 

The experiments in Sections 15.2 and 15.3 illustrate the Friedel-Crafts alkylation and acylation of aromatic hydrocarbons, respectively. A complication of Friedel-Crafts reactions is apparent in the alkylation experiment, wherein rearrangements of the carbo-cations generated from the alkyl halide provide mixtures of substitution products. The acylation reaction of Section 15.3 provides an example of how a combination of electronic and steric effects can affect the orientation of electrophilic attack on an aromatic ring. 

Aluminum chloride is noteworthy as a Lewis acid and is extensively used as such in the Friedel-Crafts alkylation and acylation of aromatic hydrocarbons. This property is evidenced in the structure of the compound. While the crystal consists of an ionic lattice, with each aluminum ion surrounded by six chloride ions in an octahedral array, the compound becomes a dimeric molecule in the nonconducting liquid phase and in the gas phase. This molecule, AI2CI6, consists of tetrahedrally coordinated aluminum with two chlorine atoms bridging the two aluminum atoms, effectively a Lewis acid-base adduct of one monomer to another. 

Intramolecular Friedel-Crafts acylation of diaryl ketones Oxidation of phenols or aromatic amines Oxidation of aromatic hydrocarbons... 

Acyl chlorides, Aromatic hydrocarbons EfFenberger, F. et al., Angew. Chem. (Intern. Ed.), 1972, 11, 300 Addition of catalytic amounts (1%) of the acid (stronger even than perchloric acid) to mixtures of acyl chlorides and aromatic hydrocarbons causes more or less violent evolution of hydrogen chloride, depending on the reactivity of the Friedel-Crafts components. 

Among the wide variety of organic reactions in which zeolites have been employed as catalysts, may be emphasized the transformations of aromatic hydrocarbons of importance in petrochemistry, and in the synthesis of intermediates for pharmaceutical or fragrance products.5 In particular, Friede 1-Crafts acylation and alkylation over zeolites have been widely used for the synthesis of fine chemicals.6 Insights into the mechanism of aromatic acylation over zeolites have been disclosed.7 The production of ethylbenzene from benzene and ethylene, catalyzed by HZSM-5 zeolite and developed by the Mobil-Badger Company, was the first commercialized industrial process for aromatic alkylation over zeolites.8 Other typical examples of zeolite-mediated Friedel-Crafts reactions are the regioselective formation of p-xylene by alkylation of toluene with methanol over HZSM-5,9 or the regioselective p-acylation of toluene with acetic anhydride over HBEA zeolites.10 In both transformations, the p-isomers are obtained in nearly quantitative yield. 

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,... 

Chatteijee, A., Bhattacharya, D., Iwasaki, T. and Ebina, T. A computer simulation study on acylation reaction of aromatic hydrocarbons over acidic zeolites, J. Catal., 1999,185,23-32. 

Di-(l-naphthylmethyl)sulphone forms an excimer but does not react to give an intramolecular cycloaddition product like the corresponding ether but rather fragments to give sulphur dioxide and (l-naphthyl)methyl radicals (Amiri and Mellor, 1978). I-Naphthylacetyl chloride has a very low quantum yield of fluorescence and this is possibly due to exciplex formation between the acyl group and the naphthalene nucleus (Tamaki, 1979). Irradiation leads to decarbonylation. It is known that acyl chlorides quench the fluorescence of aromatic hydrocarbons and that this process leads to acylation of the aromatic hydrocarbon (Tamaki, 1978a). The decarboxylation of anhydrides of phenylacetic acids [171] has been interpreted as shown in (53), involving... 

These media have also proved to be suitable stoichiometric solvents for Friedel-Craft acylation reactions of aromatic hydrocarbons and ferrocene [42],... 

These materials, which were initially designed as large-pore zeolites, are not strongly acid but are, rather, quite effective as mild acid catalysts [4], catalyzing reactions such as the oligomerization of propene [5,6] and butene [7], the alkylation of aromatic hydrocarbons [8-10], the acylation of activated aromatics... 

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