Aromatic acylation anhydrides

Silica sol-gel inunobihzed La(OTf)3 (Scheme 48.2B) previously used in the acylation of a series of alcohols and activated aromatic compounds using acetic anhydride as acylating agent, showed a poor activity compared with other various sihca sol-gel inunobihzed triflate derivatives (tert-butyl-dimethylsilyl-trifluoromethane-sulfonate (BDMST), or trifhc acid (HOTf)). Acylation at the aromatic ring occurred over the BDMST and HOTf catalysts, while the La(OTl)3 catalysts only led to O-acetylated products [22]. Such behavior is characteristic... 

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 classes of compounds which are conveniently considered together as derivatives of carboxylic acids include the carboxylic acid anhydrides, acyl chlorides, esters, and amides. In the case of simple aliphatic and aromatic acids, synthetic transformations among these derivatives are usually a straightforward matter involving such fundamental reactions as ester saponification, formation of acyl chlorides, and the reactions of amines with acid anhydrides or acyl chlorides ... 

There are solid phase enthalpy of formation data for four aromatic acyl peroxides dibenzoyl peroxide and the bis-o- and bis-p-toluyl derivatives and dicinnamoyl peroxide. The last three were reported in the same publication . The first disconcerting observation is that the p-methyl substituted benzoyl peroxide is less stable than the ortho isomer by nearly 50 kJmol. We cannot reconcile the large difference between the enthalpies of formation of these two isomers, especially since the corresponding anhydrides have comparable enthalpies of formation, —521.0 + 7.9 (p ) and —533.5 + 7.9 (o )kJmol . However, they too exhibit an unexpected stability order and were measured by the same... 

These hydroxyl groups in polymers are also usually determined by acetylation [9,21] or bromination [23]. However, it should be noted that acetylation with acid anhydrides and acyl chlorides that only total hydroxyl groups in these resins can be determined [7], Aromatic sulfonyl chlorides, however, react selectively with phenolic hydroxyls [26]. 

The typical reaction with benzoic anhydride as acylating agent was carried out as follows a solution of 20 mmol of aromatic substrate in 50 ml dry chlorobenzene were introduced in the flask and magnetically stirred under nitrogen atmosphere. 

The aromaticity of the imidazole nucleus ensures stability towards reduction, and when benzimidazole (27) is hydrogenated over Adams catalyst in acetic acid the carbocyclic ring is reduced first to give the tetrahydrobenzimidazole (28). However, if the solvent is changed to acetic anhydride, A(-acylation promotes the reduction of the heterocycle and the 1,3-diacetylbenzimidazoline (29) is then formed (Scheme 1). Imidazole (30) under these conditions gives 1,3-diacetylimidazoline (31). Imidazolium salts (32) are easily reduced and treatment with excess sodium borohydride in 95% aqueous ethanol culminates in the formation of 1,2-diamines, (33) or (34). Either N—C bond may cleave, although if the substituent R is benzyl the major products are benzylamines (33 R = Bn). ... 

The recent application of sonochemistry to the reaction of aroyl chlorides with KCN in acetonitrile is very interesting. Aromatic acyl cyanides could also be prepared by reaction of aroyl chlorides with KCN impregnated onto XAD resins. A number of patents describe the results of the two-phase interactions of alkali metal cyanides with a solution of acyl halides or anhydrides in aprotic organic solvents, which in general run in the presence of Cu salts. ... 

Use of bismuth(III) triflate allows achieved acylation of both activated and deactivated aromatic compounds with anhydrides and acyl chlorides. Thus, the acylation of aromatics such as trifluoromethoxybenzene, toluene, benzene, fluorobenzene, and chlorobenzene can be achieved in high... 

The reaction can be extended to different methoxyarenes and mesi-tylene with different aliphatic and aromatic acyl chlorides and anhydrides (48%-91% yield). Some cases merit special comment the benzoylation of... 

Acylation of anisole with A AN is carried out in a mixture of GALDEN SV 135, a suitable fluorous solvent, and chlorobenzene in the presence of hafnium tetra[bis(perfluorooctanesulfonyl)amide] (1% mol) at 70°C-120°C for 1 to 5 h, giving para-methoxyacetophenone in 80% yield and 100% selectivity. It is significant to underline that aluminum chloride gives the mentioned product in only 2% yield under the present mild reaction conditions. The catalyst can be very easily recycled by directly reusing the lower fluorous catalytic phase in the successive reaction with another mixture of reactants, affording the product more than three times without decrease in catalytic activity. The catalytic process can be applied to dimethoxybenzenes and mesitylene with both aliphatic and aromatic acyl chlorides and anhydrides (80%-97% yield). Benzoylation of toluene gives para-methylbenzophenone in 35% yield. 

Izumi et al. pioneered the use of heteropoly acids as catalysts for aromatic acylation. Silica-supported acids H4[SiWi204o] and H3[PWi204o] were found to effectively catalyse the acylation of p-xylene with benzoyl chloride. Cs2.5Ho.5[PWi204o] showed high efficiency in the acylation of activated arenes, such as p-xylene, anisole, mesitylene, etc., by acetic and benzoic anhydrides and acyl chlorides. This catalyst provided higher yields of acylated arenes than the parent acid H3[PWi204o], the latter being partly soluble in the reaction mixture. ... 

The aromatic acylation with carboxylic acids (Eq. 3) instead of acid anhydrides and acyl chlorides has attracted interest, because it is an environmentally benign reaction, resulting in the formation of water as the only by-product. It has been attempted with zeolites and clays as catalysts. Heteropoly acids have proved to be more active catalysts for this... 

In aromatic acylation, present industrial practice involves stoichiometric amounts of metal halides as "catalysts" and of acylating agents. Aromatic heterocycles present exceptions. For example, catalytic amounts of SnCU promote the reaction of benzofuran with acetic anhydride to give 4()% 2-acetyl-benzofuran [1]. 

In this paper, we give some examples of ethylaluminum dichloride (EtAlCl2)-induced acylations with different acylating agents such as saturated acyl chlorides, dicarboxylic acid dichlorides, cyclic anhydrides, unsaturated acyl chlorides, and aromatic and heteroaromatic acyl chlorides. 

Metal triflates that can be easily prepared from metal halides and triflic acid at -78°C [14] show several unique properties compared with the corresponding metal halides. The use of bismuth(III) triflate allows for acylation of both activated and deactivated aromatic compounds with anhydrides and acyl chlorides [15]. Thus, the acylation of deactivated aromatics such as trifluoromethoxyben-zene, fluorobenzene, and chlorobenzene can be achieved in high yields with benzoyl chloride in the presence of bismuth(III) triflate (10% mol) without solvent. The />ara-acylation product is the most abundant in all cases (trifluoromethoxybenzene 87% yield, ortho.para 4 96 fluorobenzene 86% yield, orthoipara 0 100 chlorobenzene 89% yield, ortho para 13 87). 

Iodine (2% mol) can be used as a catalyst for the acetylation of electron-rich aromatic compounds with aliphatic and aromatic acyl chlorides or anhydrides in 25-93% yields [8]. In successful acylations, the violet-colored refluxing mixture disappears after 15-30 min. Heterocyclic compounds such as furan and thiophene derivatives undergo easy acylation in the presence of variable amounts of iodine. The process is of particular synthetic interest since these heterocycle compounds are... 

Covalent acyl nitrites formed from nitrous acid and various carboxylic acids react readily with aromatic amines, and they are used often for nitrosating water-insoluble amines . The mechanism must be similar to that for nitrous anhydride. In aqueous buffer solutions of carboxylic acids, however, the bulk of the reaction is brought about by nitrous anhydride itself. Acyl nitrites are formed, but these react more readily with the very basic nitrite ion, always present at pH > 3-5, than with tlae amine directly . ... 

Acylation of both aromatic and aliphatic compounds can be carried out with relative ease using acyl halides, acid anhydrides, ketenes, nitriles, amides, acids and esters in the presence of Friedel-Craft catalysts to give ketones. Similar substitution reactions with formic acid derivatives are therefore expected to yield the appropriate aldehydes. However, since the anhydride and acyl halides of formic acid, with the exception of formyl fluoride, are either not known or are not sufficiently stable to be used in Friedel-Crafts type acylation reactions, this objective cannot be fully realized. Table 1.1 compares the main ketone syntheses (based on acylating reagents) with the corresponding aldehyde syntheses (based on formylating reagents). 

More practically, in the presence of trifluoroacetic anhydride (TFAA), acylation of aromatic compounds with carboxylic acid catalyzed by AIPW10O40 (3 mol%) proceeded at room temperature (Scheme 6.10) [10]. 

The acetylation (with AC2O and HC104) and Vilsmeier formylation of sterically hindered phenols have been investigated. Substituted o-hydroxy-benzophenones have been prepared in 18-68% yields by treatment of the HMPT complexes of bromomagnesium phenoxides with aromatic aldehydes. " Phenolic O- vs. C-benzoylation has been studied, with particular reference to 3,4-disubstituted phenols. Previous work on the use of trifluoroacetic anhydride to promote aromatic acylation has been extended to the preparation of symmetrical and unsymmetrical benzophenones via reaction between the methyl and benzyl ethers of orcinol and the same ethers of phloroglucinolcarboxylic acid. " Other phenolic acylations include some chalcone syntheses and the acetylation and benzoylation of 2-hydroxy-4-methoxyacetophenone (peonol). ... 

A facile conversion of several aliphatic and aromatic acyl peroxides, halides, and anhydrides to the "per" acids has been effected by treatment with H2O2 and a threefold excess of base in the presence of a soluble magnesium saltl > The magnesium salt Is proposed to stabilize the "per" acid as it is formed, and to prevent its decomposition. 

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