Aromatic hydrocarbons acylation

Gattermann-Koch reaction Formylation of an aromatic hydrocarbon to yield the corresponding aldehyde by treatment with CO, HCl and AICI3 at atmospheric pressure CuCl is also required. The reaction resembles a Friedel-Crafts acylation since methanoyl chloride, HCOCl, is probably involved. 

TTie true ketones, in which the >CO group is in the side chain, the most common examples being acetophenone or methyl phenyl ketone, C HjCOCH, and benzophenone or diphenyl ketone, C HjCOC(Hj. These ketones are usually prepared by a modification of the Friedel-Crafts reaction, an aromatic hydrocarbon being treated with an acyl chloride (either aliphatic or aromatic) in the presence of aluminium chloride. Thus benzene reacts with acetyl chloride... 

For aromatic hydrocarbons some very efficient formytation and acylation procedures are known (e.g. Friedel-Crafts, Vilsmeier, Gattermann-Koch), They are treated in introductory text books. 

Preparation of Arylcarboxylic Acids and Derivatives. The general Friedel-Crafts acylation principle can be successfully appHed to the preparation of aromatic carboxyUc acids. Carbonyl haUdes (phosgene, carbonyl chloride fluoride, or carbonyl fluoride) [353-50-4] are diacyl haUdes of carbonic acid. Phosgene [75-44-5] or oxalyl chloride [79-37-8] react with aromatic hydrocarbons to give aroyl chlorides that yield acids on hydrolysis (133) ... 

Acylation. In chlorinated solvents, maleic anhydride reacts with aromatic hydrocarbons (ArH) in the presence of aluminum chloride... 

Acylation. Aryl chloroformates are good acylating agents, reacting with aromatic hydrocarbons under Eriedel-Crafts conditions to give the expected aryl esters of the aromatic acid (38). 

A surpnsing feature of the reactions of hexafluoroacetone, trifluoropyruvates, and their acyl imines is the C-hydroxyalkylation or C-amidoalkylaOon of activated aromatic hydrocarbons or heterocycles even in the presence of unprotected ammo or hydroxyl functions directly attached to the aromatic core Normally, aromatic amines first react reversibly to give N-alkylated products that rearrange thermally to yield C-alkylated products. With aromatic heterocycles, the reaction usually takes place at the site of the maximum n electron density [55] (equaUon 5). 

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

Reaction conditions reflux of a mixture of the aromatic compound, N-benzoylimid-azole, and trifluoroacetic acid in a molar ratio of 1 1.2 10. This method for acylating aromatic hydrocarbons works without the use of classical Friedel-Crafts catalysts. 

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. 

Aromatic hydrocarbons, Trifluoromethanesulfonic acid See Trifluoromethanesulfonic acid Acyl chlorides, etc. 

Trifluoromethanesulfonic acid, Acyl chlorides, Aromatic hydrocarbons, 0375 Trimethyl phosphate, 1318... 

Several metal oxides could be used as acid catalysts, although zeolites and zeo-types are mainly preferred as an alternative to liquid acids (Figure 13.1). This is a consequence of the possibility of tuning the acidity of microporous materials as well as the shape selectivity observed with zeolites that have favored their use in new catalytic processes. However, a solid with similar or higher acid strength than 100% sulfuric acid (the so-called superacid materials) could be preferred in some processes. From these solid catalysts, nation, heteropolyoxometalates, or sulfated metal oxides have been extensively studied in the last ten years (Figure 13.2). Their so-called superacid character has favored their use in a large number of acid reactions alkane isomerization, alkylation of isobutene, or aromatic hydrocarbons with olefins, acylation, nitrations, and so forth. 

The lower members of the homologous series of 1. Alcohols 2. Aldehydes 3. Ketones 4. Acids 5. Esters 6. Phenols 7. Anhydrides 8. Amines 9. Nitriles 10. Polyhydroxy phenols 1. Polybasic acids and hydro-oxy acids. 2. Glycols, poly-hydric alcohols, polyhydroxy aldehydes and ketones (sugars) 3. Some amides, ammo acids, di-and polyamino compounds, amino alcohols 4. Sulphonic acids 5. Sulphinic acids 6. Salts 1. Acids 2. Phenols 3. Imides 4. Some primary and secondary nitro compounds oximes 5. Mercaptans and thiophenols 6. Sulphonic acids, sulphinic acids, sulphuric acids, and sul-phonamides 7. Some diketones and (3-keto esters 1. Primary amines 2. Secondary aliphatic and aryl-alkyl amines 3. Aliphatic and some aryl-alkyl tertiary amines 4. Hydrazines 1. Unsaturated hydrocarbons 2. Some poly-alkylated aromatic hydrocarbons 3. Alcohols 4. Aldehydes 5. Ketones 6. Esters 7. Anhydrides 8. Ethers and acetals 9. Lactones 10. Acyl halides 1. Saturated aliphatic hydrocarbons Cyclic paraffin hydrocarbons 3. Aromatic hydrocarbons 4. Halogen derivatives of 1, 2 and 3 5. Diaryl ethers 1. Nitro compounds (tertiary) 2. Amides and derivatives of aldehydes and ketones 3. Nitriles 4. Negatively substituted amines 5. Nitroso, azo, hy-drazo, and other intermediate reduction products of nitro com-pounds 6. Sulphones, sul-phonamides of secondary amines, sulphides, sulphates and other Sulphur compounds... 

Solid Catalysts. Nafion-H is an active catalyst for acylation with aroyl halides and anhydrides.60,61 The reaction is carried out at the boiling point of the aromatic hydrocarbons. Yields with benzoyl chloride using 10-30% Nafion-H for benzene, toluene, and p-xylene are 14%, 85% and 82%, respectively. Attempted acylation with acetyl chloride, however, led to HC1 evolution and ketene formation. Nation resin-silica nanocomposite materials containing a dispersed form of the resin within silica exhibits significantly enhanced activity in Friedel-Crafts acylations.62,63... 

The only formic acid derivative that allows the direct formylation of aromatics is formyl fluoride1617 since others (halides and the anhydride) that could be used in Friedel-Crafts-type acylations are quite unstable. Other related methods, however, are available to transform aromatic hydrocarbons to the corresponding aldehydes. The most frequently used such formylations are the Gattermann-Koch reaction16 17 and the Gattermann synthesis.10 16 17... 

Under the reaction conditions the direct acylation of the aromatic hydrocarbons with the acylium ion does not take place. Instead, the intermediate vinyl carboca-tion reacts with the aromatics to form the 20 aryl-substituted vinyl ketones. 

The route offers the possibility of further simplification, since aromatic hydrocarbons are readily acylated under Friedel-Crafts conditions. Thus, the acetylation of toluene in the presence of perchloric acid yields the trisubstituted pyrylium compound (27CB716). Alkoxy-benzenes behave in a similar manner and anisole gives a good yield of 2,4-di-(4-methoxyphenyl)-6-methylpyrylium perchlorate (51JCS726). 

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. 

Reaction XX. (6) Action of certain Anhydrous Metallic Halides (Aluminium Chloride, Aluminium Bromide, Aluminium and Hydrogen Chloride, Ferric Chloride) on a mixture of an Aromatic Hydrocarbon or certain Derivatives, and an Acyl Halide. (Friedel-Crafts.) (A. Ch., [6], 1, 518.)—This is an even more important application of the Friedel-Crafts synthesis than the methods of synthesising hydrocarbons (pp. 58, 60). The reactions involved are more readily controlled since the products, in presence of aluminium chloride, do not undergo further condensations. Usually these products have also the advantage of being more easily separated, for, as shown below in (iii.), the formation of isomers can be avoided. 

Reaction XX. (c) Action of a Mixture of Aluminium and Mercuric Chloride on a Mixture of an Aromatic Hydrocarbon and an Acyl Halide. 

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