Aromatic compounds, with acyl

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. 

Friedel-Crafts reactions of aromatic compounds with acyl chlorides, anhydrides, or related compounds in the presence of a Lewis acid have been reviewed [429,430], Among a variety of Lewis acids, the most typical is AICI3, although there are reactions as shown in Eqs (172) [431], (173) [432], and (174) [433] in which TiCU was used as the Lewis acid. 

Gallium nonafluorobutanesulfonate (nonaflate) [Ga(ONf)3] (5% mol) shows a very high activity in the acylation of both activated and deactivated aromatic compounds with acyl chlorides without solvent. Some applications are shown in Table 3.12. 

Zinc powder (100% mol) without any treatment promotes Friedel-Crafts acylation of aromatic compounds with acyl chlorides to afford the corresponding aromatic ketones in high yield. Acetylation and benzoylation of a great number of both activated and deactivated aromatic compounds... 

Zinc oxide, an inexpensive and commercially available inorganic solid, can be utilized as an efficient catalyst in the Friedel-Crafts acylation of activated and unactivated aromatic compounds with acyl chlorides at room temperature for 5 to 120 min (Table 4.14). Acylation is claimed to occur exclusively at the para-position of the monosubstituted aromatic compounds. The catalyst can be recovered and reused, after washing with methylene chloride, for at least two further cycles, showing quite similar high yield (-90%) in the model benzoylation of anisole. Mechanistically, it seems that zinc chloride can be the true catalyst, generated in situ by the reaction of zinc oxide with hydrogen chloride. 

Because acylation of an aromatic ring can be accomplished without rearrangement it is frequently used as the first step m a procedure for the alkylation of aromatic compounds by acylation-reduction As we saw m Section 12 6 Friedel-Crafts alkylation of ben zene with primary alkyl halides normally yields products having rearranged alkyl groups as substituents When a compound of the type ArCH2R is desired a two step sequence IS used m which the first step is a Friedel-Crafts acylation... 

A further consequence of association of acylating agents with basic compounds is an increase in the bulk of the reagent, and greater resistance to attack at the more stericaHy hindered positions of aromatic compounds. Thus acylation of chrysene and phenanthrene in nitrobenzene or in carbon disulfide occurs to a considerable extent in an outer ring, whereas acylation of naphthalene leads to extensive reaction at the less reactive but stericaky less hindered 2-position. 

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)... 

While the Friedel-Crafts acylation is a general method for the preparation of aryl ketones, and of wide scope, there is no equivalently versatile reaction for the preparation of aryl aldehydes. There are various formylation procedures known, each of limited scope. In addition to the reactions outlined above, there is the Vdsmeier reaction, the Reimer-Tiemann reaction, and the Rieche formylation reaction The latter is the reaction of aromatic compounds with 1,1-dichloromethyl ether as formylating agent in the presence of a Lewis acid catalyst. This procedure has recently gained much importance. 

Friedel-Crafts acylation reactions usually involve the interaction of an aromatic compound with an acyl halide or anhydride in the presence of a catalyst, to form a carbon-carbon bond [74, 75]. As the product of an acylation reaction is less reactive than its starting material, monoacylation usually occurs. The catalyst in the reaction is not a true catalyst, as it is often (but not always) required in stoichiometric quantities. For Friedel-Crafts acylation reactions in chloroaluminate(III) ionic liquids or molten salts, the ketone product of an acylation reaction forms a strong complex with the ionic liquid, and separation of the product from the ionic liquid can be extremely difficult. The products are usually isolated by quenching the ionic liquid in water. Current research is moving towards finding genuine catalysts for this reaction, some of which are described in this section. 

Diaryl sulfones can be formed by treatment of aromatic compounds with aryl sulfonyl chlorides and a Friedel-Crafts catalyst. This reaction is analogous to Friedel-Crafts acylation with carboxylic acid halides (11-14). In a better procedure, the aromatic compound is treated with an aryl sulfonic acid and P2O5 in polypho-sphoric acid. Still another method uses an arylsulfonic trifluoromethanesulfonic anhydride (ArS020S02CF3) (generated in situ from ArS02Br and CF3S03Ag) without a catalyst. ... 

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). 

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... 

Labelling studies have shown27 that the unusual base-catalysed rearrangement of the P-O-4 lignin model (25) to (27) containing an a-O-4 linkage, proceeds by way of intermediate (26). Acylation of hydroxy aromatic compounds with 2-bromo-2-... 

As discussed in Chapter 2, Shudo and Ohwada found that acetyl and benzoylhexafluoroantimonate salts (CH3CO+SbF6 and CfiHsCO+SbFf,-, respectively) acylate aromatic compounds with increasing reaction rates and greater yields in progressively more acidic media.44 These data are consistent with the formation of the superelectrophilic species 137 and 141 (eq 39).65... 

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. 

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. 

Bottom reaction (as a reminder) chemoselective acylation of an aromatic compound with an activated carboxylic chloride (Friedel-Crafts acylation, cf. Section 5.2.7). 

The reaction of an aromatic compound with an acyl chloride in the presence of a Lewis acid (usually A1C13) results in the substitution of an acyl group onto the aromatic ring. An example of this reaction, known as the Friedel-Crafts acylation, is provided by the following equation ... 

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

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