Aromatics acylation anhydrides

Flavone formation is believed to proceed through a similar mechanism as the synthesis of chromones, albeit aromatic acid anhydrides and their corresponding salts are used. The first step is benzoylation of 12 to give the ester 14. Enolization and o-alkylation then affords the enolbenzoate 15. Enolbenzoate 15 then undergoes an acyl transfer to yield... 

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. 

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... 

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. ... 

Bartoli, G., Bosco, M., Marcantoni, E., Massaccesi, M., Rinaldi, S., and Sambri, L. 2002. LiG104-acyl anhydrides complexes as powerful acylating reagents of aromatic compounds in solvent free conditions. Tetrahedron Lett. 43 6331-6333. 

Table 3.2 Acylation of aromatics with anhydrides catalyzed by dichlorobis(benzonitrile)platinum(Il)-silver hexafluoroantimonate mixture...

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. 

For the gas-phase acylation reaction of aromatics with anhydrides, metal-exchanged zeolites are also employed. In the presence of CeZSM-5, the acylation of benzene with AAN affords AP with 86% conversion of AAN and 95% selectivity on the contrary, unmodified ZSM-5 is found to be less active under the same reaction conditions (71% conversion of AAN, 86% selectivity to AP). If the reaction is carried out with AAC as acylating... 

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]. 

The addition of aromatic or heteroaromatic C-nucleophiles at C-6 of l,2,4-triazin-5-ones 34 proceeds rather smoothly when the reactions are carried out in such solvents as acyl anhydrides or formic acid. There are two reasons (1) the formation of A -acyl-l,2,4-triazinium salts 34 facilitates nucleophilic addition reactions (2) the (j -adducts 37 are stabilized by the A -acyl group, as illustrated by the formation of adducts 37 with phenols, arylamines, pyrroles, and indoles (Scheme 22 Table 8) <1997JHC573, 1997JHC1013,1998RJ0297,1998RJ0452, 2001MC77, 2004RCB1351>. 

The discovery by de Vries and coworkers that acyl complexes formed in the oxidative addition of aromatic carboxylic anhydrides to palladium catalysts decarbonylate in the... 

The conditions are compatible with a variety of other functionality including nitrile and ester, and both aliphatic and aromatic acid anhydrides may be used as the acylating reagent. 

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... 

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. 

Azlactones (anhydrides of a-acylamino acids) are formed by the condensation of aromatic aldehydes with acyl derivatives of glycine in the presence of acetic anhydride and anhydrous sodium acetate. Thus beiizaldehyde and acetyl-... 

Acyl cations (acylium ions) generated by treating an acyl chloride or acid anhydride with aluminum chloride attack aromatic rings to yield ketones The arene must be at least as reactive as a halobenzene Acyl cations are relatively stable and do not re arrange... 

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... 

Acylatmg agents such as acyl chlorides and carboxylic acid anhydrides can react with phenols either at the aromatic ring (C acylation) or at the hydroxyl oxygen (O acylation)... 

Friedel-Crafts acylation (Section 12 7) An electrophilic aro matic substitution in which an aromatic compound reacts with an acyl chloride or a carboxylic acid anhydride in the presence of aluminum chlonde An acyl group becomes bonded to the nng... 

Ketone Synthesis. In the Friedel-Crafts ketone synthesis, an acyl group is iatroduced iato the aromatic nucleus by an acylating agent such as an acyl haUde, acid anhydride, ester, or the acid itself. Ketenes, amides, and nittiles also may be used aluminum chloride and boron ttitiuotide are the most common catalysts (see Ketones). 

Similarly, A[-carboxy-a-amino acid anhydrides react with aromatics such as toluene, xylenes, and mesitylene to give a-amino acylated products ia moderate yields with almost complete retention of configuration of the a-amino acid. 

Sulfonylation. Under Friedel-Crafts reaction conditions, sulfonyl haUdes and sulfonic acid anhydrides sulfonylate aromatics (139), a reaction that can be considered the analogue of the related acylation with acyl haUdes and anhydrides. The products are sulfones. Sulfonyl chlorides are the most frequently used reagents, although the bromides and fluorides also react ... 

Substitution at the Alcohol Group. Acylation of the OH group by acylating agents such as acid chlorides or anhydrides is one of the important high yielding substitution reactions at the OH group of lactic acid and its functional derivatives. AUphatic, aromatic, and other substituted derivatives can be produced. 

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

Liquid crystal polyesters are made by a different route. Because they are phenoHc esters, they cannot be made by direct ester exchange between a diphenol and a lower dialkyl ester due to unfavorable reactivities. The usual method is the so-called reverse ester exchange or acidolysis reaction (96) where the phenoHc hydroxyl groups are acylated with a lower aHphatic acid anhydride, eg, acetic or propionic anhydride, and the acetate or propionate ester is heated with an aromatic dicarboxyHc acid, sometimes in the presence of a catalyst. The phenoHc polyester forms readily as the volatile lower acid distills from the reaction mixture. Many Hquid crystal polymers are derived formally from hydroxyacids (97,98) and thein acetates readily undergo self-condensation in the melt, stoichiometric balance being automatically obtained. 

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