Aromatics acylation aliphatic carboxylic acids

The experimental evidence obtained has shown that the reactivity of the estos of the aromatic and aliphatic carboxylic acids under study in the reaction of alcoholysis with cellulose changes substantially with changes in the chemical constitution of the acyl radical. According to existing con<%ptions (52), the alcoholysis of esters in the presence of an alkaline catalyst at the rate-determining step involves the attack of the alkoxy ion on the carbon atom erf the carbonyl group in the case of... 

Table 3.11 Europium-bistriflimide-catalyzed acylation of aromatics with aliphatic carboxylic acids ...

This reaction was first reported by Bernthsen in 1878It is one of the earliest methods for the synthesis of acridine by heating diphenylamine hydrochloride with benzonitrile. Therefore, this reaction is generally known as the Bernthsen reaction. In the modified method, the mixture of diphenylamine, an aromatic or aliphatic carboxylic acid, and zinc chloride is heated at 200-270°C for 20 Heating zinc chloride with fV-acyldiphenylamine or a mixture of diphenylamine and acyl chloride also affords acridines. ... 

Bandgar et al. reported a general route for the synthesis of acyl azides from aryl, heteroaryl, alkylaryl and alkyl acids with cyanuric chloride (297) in the presence of sodium azide and (V-methylmorpholine. Acid activation can also be achieved using triphosgene. In fact, aromatic and aliphatic carboxylic acids react with triphosgene in the presence of sodium azide and triethylamine giving acyl azides in good yield (e.g. synthesis of 301). 

Friedel-Crafts Acylation. Catalytic Friedel-Crafts acylation of benzene and unactivated benzenes, such as chlorobenzene and fluorobenzene, has been successfully carried out using FIf(OTf)4 and trifluoromethanesulfonic acid as catalysts. Both aromatic and aliphatic carboxylic acid chlorides reacted smoothly under these conditions to afford the corresponding aromatic ketones in good yields (eq 22). ... 

The classes of compounds that are conveniently considered together as derivatives of carboxylic acids include the acyl chlorides, carboxylic acid anhydrides, esters, and amides. In the case of simple aliphatic and aromatic acids, synthetic transformations... 

Aromatic carboxylic acids show many properties that parallel those of aliphatic carboxylic acids. Thus acyl chlorides are formed on treatment with thionyl chloride and esters are obtained on treatment with the alcohol and an add catalyst. Benzoate and 3,5-dinitrobenzoate esters are used in the characterization of alcohols and are prepared using the reaction of the acyl halide with the alcohol. 

Sodium 1-methylethanetellurolate and hexadecanetellurolate were obtained from sodium hydrogen telluride and the appropriate alkyl halide in THF or THF/ethanol. The sodium hydrogen telluride was prepared from tellurium and sodium borohydride in water. Equimolar amounts of disodium telluride combined with aliphatic carboxylic acid chlorides in tetrahydrofuran at — 30" and with aromatic carboxylic acid chlorides in tetrahydrofuran at 0° to give sodium tellurolates that have an acyl group bonded to the tellurium atom. These tellurolates, the sodium salts of tellurolocarboxylic acids, are dark-red substances that were obtained in almost quantitative yields. 

More interestingly, carboxylic acids can be employed in the acylation of aromatic compounds. The acylation of toluene and anisole with C2-C42 aliphatic carboxylic acids can be carried out with CsPW, affording the corresponding products in 41%-71% yield. These solid acids are superior in activity to the conventional acid catalysts such as sulfuric acid and zeolites, and can be reused after a simple workup, albeit with reduced activity. 

Activation of Carboxylic Acids Synthesis of Acyl Imidazoles. iV,AA-Carbonyldiimidazole (1) converts carboxylic acids into the corresponding acylimidazoles (2) (eq 1). The method can be applied to a wide range of aliphatic, aromatic, and heterocyclic carboxylic acids, including some examples (such as formic acid and vitamin A acid) where acid chloride formation is difficult. The reactivity of (2) is similar to that of acid chlorides, but the former have the advantage that they are generally crystalline and easily handled. Isolation of (2) is sirr5>le, but often unnecessary further reaction with nucleophiles is usually performed in the same reaction vessel. Conversion of (2) into acid chlorides (via reaction with HCl), hydrazides, hydroxamic acids, and peroxy esters have all been described. Preparation of the more irr5)ortant carboxylic acid derivatives is described below. 

Aromatic compounds (eqs 16 and 17) are acylated by PhCOCI in the presence of a Lewis acid such as AICI3, TiCU, BF3, SnCU, ZnClz, or FeClz, or of a strong acid such as polyphos-phoric acid or CF3SO3H. Metallic A1 or Fe and iodine (in situ formation of a Lewis acid) can also act as a catalyst. Various solvents that have been used to perform this reaction are CSz, CH2CI2, 1,2-dichloroethane, nitrobenzene, and nitromethane. PhCOCI is less reactive than aliphatic carboxylic acid chlorides (with benzene in nitromethane the relative reaction rates are Ph-COCl MeCOCl = 6 100). As for all electrophilic substitutions, the rate and the regioselectivity of the acylation closely depend on the nature and on the position of the substituents on the aromatic system (eqs 16 and 18 ). The nature of the solvent can also exert a strong influence. ... 

Dimsyl anion 88 reacts with esters of aromatic carboxylic acids and aliphatic acids which do not have a readily transferable proton, to give /5-ketosulfoxides114,133,138-141. There are not many cases in which acyl chlorides were used142,143. However, the reaction... 

Salts of aliphatic or aromatic carboxylic acids can be converted to the corresponding nitriles by heating with BrCN or CICN. Despite appearances, this is not a substitution reaction. When R COO was used, the label appeared in the nitrile, not in the C02, and optical activity in R was retained. The acyl isocyanate... 

A related convenient and mild method for the preparation of aliphatic and aromatic aldehydes in high yield from carboxylic acids is the reductive cleavage of l-acyl-3-methylimidazole-2-thiones by tributylstannane. 

The chemical diversity of carboxylic acid esters (R-CO-O-R ) originates in both moieties, i.e., the acyl group (R-CO-) and the alkoxy or aryloxy group (-OR7). Thus, the acyl group can be made up of aliphatic or aromatic carboxylic acids, carbamic acids, or carbonic acids, and the -OR7 moiety may be derived from an alcohol, an enol, or a phenol. When a thiol is involved, a thioester R-CO-S-R7 is formed. The model substrates to be discussed in Sect. 7.3 will, thus, be classified according to the chemical nature of the -OR7 (or -SR7) moiety, i.e., the alcohol, phenol, or thiol that is the first product to be released during the hydrolase-catalyzed reaction (see Chapt. 3). Diesters represent substrates of special interest and will be presented separately. 

The reaction of sulfur tetrafluoride with carboxylic acids (aliphatic, aromatic, and heterocyclic) is of particular importance as the most general and simplest route to trifluorotnethyl derivatives. The reaction proceeds in two steps, the first step gives acyl or aroyl fluorides 1, and then catalysis in the second step by hydrogen fluoride released in the first step results in the tri-fluoromethyl derivatives 2.41... 

In connection with the elaboration of specific procedures for the manufacture of both of the isosorbide mononitrates, methods were developed to shift, with high regioselectivity, the course of the acylation reaction either towards the 5 (endo) or the 2 (exo) position, depending on the conditions applied.104-106 Thus, isosorbide 5-acylates are obtained in 70-85% yield when 3 is treated with the appropriate acid anhydride in the presence of lead(II) oxide or acetate for 20 to 40 h at room temperature. To avoid transesterifications to the appropriate 2-acylate, the workup procedures, especially during the distillation, have to be conducted under strictly neutral conditions. The contrary effect, a remarkable enrichment by the isosorbide 2-acylate (up to 90%) is realized by a transesterification process mediated by a small proportion of sodium or potassium carbonate, hydroxide, or meth-oxide, which are added to the acylation mixture from isosorbide at HOMO0, and subsequent removal of the 2-acylate by vacuum distillation.104 These two regioselective acylation methods may be used for aliphatic, as well as for aromatic, carboxylic acid anhydrides. 

Fries rearrangement—that is, the transformation of phenolic esters to isomeric hydroxyphenyl ketones—is related to Friedel-Crafts acylations.392,393 Olah et al.394 have found a convenient way to perform the Fries rearrangement of a variety of substituted phenolic esters in the presence of Nafion-H in nitrobenzene as solvent [Eq. (5.153)]. A catalytic amount of Nafion-H is satisfactory, and the catalyst can be recycled. In contrast, Nafion-silica nanocomposites, in general, exhibit low activities in the Fries rearrangement of phenyl acetate to yield isomeric hydroxyacetophe-nones.239,395 In a recent study, BF3-H20 was found to be highly efficient under mild conditions (80°C, 1 h) to transform phenolic esters of aliphatic and aromatic carboxylic acids to ketones (71-99% yields).396 In most cases the para-hydroxyphenyl isomers are formed with high (up to 94%) selectivity. 

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