Anhydrides carboxylic

Most anhydrides are prepared from carboxylic acids by exchange with the readily available acetic anhydride. Heating these and then distilling the acetic acid and excess acetic anhydride shifts the equilibrium toward the higherboiling product (Eq. 6.15) [21]. Five- and six-membered cyclic anhydrides usually form simply on heating the dicarboxylic acid to about 120°C. 

Unsymmetric anhydrides that react selectively on one side are useful. Although formic anhydride is unstable above 10°C, acetic formic anhydride can be prepared by stirring sodium formate with acetyl chloride in ether (64% yield, bp 27-28°C) [22]. It is useful for the formylation of alcohols and amines. A stable solid formylating agent is the mixed anhydride prepared in 89% yield from p-methoxybenzoyl chloride and sodium formate catalyzed by a polymeric pyridine oxide [23]. Ethyl chlorofor-mate gives mixed anhydrides with various carboxylic acids which are then susceptible to nucleophilic substitution at the carboxylic carbonyl carbon. 

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 

This approach represents a convenient method for utilizing carboxylic acid substrates in small-scale laboratory applications. However, while it avoids the formation of stoichiometric salt waste that needs to be separated from the products, the reagent 

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Pyrano[3,4-b]indol-3-ones are the most useful equivalents of the indol-2,3-quinodimethane synthon which are currently available for synthetic application. These compounds can be synthesized readily from indole-3-acetic acids and carboxylic anhydrides[5,6]. On heating with electrophilic alkenes or alkynes, adducts are formed which undergo decarboxylation to 1,2-dihydro-carbazoles or carbazoles, respectively. 

Methylnorbornene-2,3-dicarboxylic anhydride (5-methylnorborn-5-ene-2-endo-3-endo-di-carboxylic anhydride) [25134-21-8] M 178.2, m 88.5-89 . Purified by thin layer chromatography on AI2O3 (previously boiled in EtOAc) and eluted with hexane- C6Hg (1 2) then recrystd from CgH -hexane. The free acid has m 118.5-119.5 . [Miranov et al. Tetrahedron 19 1939 1963.]... 

Ruonnated carboxylic anhydrides and acyl halides as common acylating reagents to convert amines to amides and to acy late suitable heterocyclic nitiogen atoms have already been described in the first edition [10] Like in the acylation at oxygen, much synthetic activity was concentrated m the past few years on the denvatization of biomolecules by fluoroacylation reactions, that is, tnfluoroacetylation of amino sugars,... 

As acylating agent, a carboxylic anhydride may be used instead of the acyl halide. The reaction then yields the arylketone together with a carboxylic acid, each of which forms a complex with the Lewis acid used. The catalyst therefore has to be employed in at least twofold excess ... 

Condensation of aromatic aldehydes with carboxylic anhydrides... 

The aldol-like reaction of an aromatic aldehyde 1 with a carboxylic anhydride 2 is referred to as the Perkin reaction. As with the related Knoevenagel reaction, an o ,/3-unsaturated carboxylic acid is obtained as product the /3-aryl derivatives 3 are also known as cinnamic acids. 

The reaction mechanism involves deprotonation of the carboxylic anhydride 2 to give anion 4, which then adds to aldehyde 1. If the anhydride used bears two a-hydrogens, a dehydration takes place already during workup a /3-hydroxy carboxylic acid will then not be isolated as product ... 

The general procedure is to heat a mixture of aldehyde 1 and carboxylic anhydride 2 together with a base to a temperature of 170-200 °C for several hours. As base the sodium salt of the carboxylic acid corresponding to the anhydride is most often used. 

Small amounts of water present will lead to partial hydrolysis of the acyl chloride to give the carboxylic acid 7, which then may further react with the acyl chloride to give a carboxylic anhydride 8 ... 

Other examples of the photochemical a-cleavage of cyclic sulfoxides have been noted. Lawesson and coworkers22 have proposed that the mixed sulfenic-carboxylic anhydride (16) is formed on photolysis of 17, by a-cleavage followed by the loss of benzaldehyde. The... 

The graphitic layers remain unchanged while the pore volume increases [93, 94]. Toebes et at. showed that the most predominant effect is the opening of the inner tubes of the fibers [93]. The oxidation did not only occur at the surface but also developed 2-3 run into the subsurface [93]. Carbonyl groups are formed, which are subsequently converted into carboxyls and carboxylic anhydrides [92]. 

Smith et al. (1998) have reported selective para acetylation of anisole, phenetole, and diphenyl ether with carboxylic anhydrides at 100 °C, in the presence of catalytic quantities of zeolites H-beta. The zeolite can be recovered and recycled to give essentially the same yield as that given by fresh zeolite. 

Particularly, some newly developed drags, which incorporate the N-acyl sulfonamide moiety [8-10], are synthesized from the parent sulfonamides, by their coupling with acid chlorides or carboxylic anhydrides in basic conditions [11-15]. Unfortunately all these methods lead to substantial waste products. Less common reports mentioning this transformation under acidic conditions (Bronsted or Lewis acids) do not systematically examine the purpose and limitations of the reaction [16]. 

The best yields are obtained when the ketene has an electronegative substituent, such as halogen. Simple ketenes are not very stable and must usually be generated in situ. The most common method for generating ketenes for synthesis is by dehydrohalo-genation of acyl chlorides. This is usually done with an amine such as triethylamine.167 Other activated carboxylic acid derivatives, such as acyloxypyridinium ions, have also been used as ketene precursors.168 Ketene itself and certain alkyl derivatives can be generated by pyrolysis of carboxylic anhydrides.169... 

Intramolecular acylations are very common, and the normal conditions involving an acyl halide and Lewis acid can be utilized. One useful alternative is to dissolve the carboxylic acid in polyphosphoric acid (PPA) and heat to effect cyclization. This procedure probably involves formation of a mixed phosphoric-carboxylic anhydride.54... 

Benzyl groups are cleaved from amines heated with inorganic acids (15), carboxylic anhydrides (16) or cyanogen bromide (17). 

Scheme 18 Branch-selective hydroacylation via hydrogen-mediated coupling of vinyl arenes to carboxylic anhydrides...

Scheme 19 Selective acyl transfer in reductive hydroacylations involving mixed carboxylic anhydrides derived from pivalic acid...

Scheme 21 Hydrogenative coupling of ethylene to a carboxylic anhydride to form an ethyl ketone...

The reactive 1-acyl-3-alkylimidazolium species also plays a role in acylation of alcohols with carboxylic anhydrides or carboxylic acid chlorides using 1-substituted imidazoles as catalysts.[145] In this case the reactive species is formed in situ ... 

Another Pd-catalyzed reaction of aryl- and alkylzinc halides used carboxylic anhydrides as starting organic compounds (Scheme 127).328 One of the advantages of this method is that anhydrides can be synthesized in situ from the corresponding sodium salts of carboxylic acids and ethyl chloroformate. The scope of the method includes aliphatic and aromatic anhydrides, phenyl-, ethyl-, isopropyl-, and n-butylzinc iodides. 

Trivalent phosphorus-halogen reagents have been noted to be of use in obtaining simple Abramov-type products with chloral199 200 and with aldimines.201 Similarly, phosphorus-carboxylate anhydrides have been useful in overcoming the stereochemical difficulties associated with alkyl transfer for obtaining Abramov-type products in a direct manner.202 205... 

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