Esters aromatic carboxylic

Formation of carboxylic acids ami their derivatives. Aryl and alkenyl halides undergo Pd-catalyzed carbonylation under mild conditions, offering useful synthetic methods for carbonyl compounds. The facile CO insertion into aryl- or alkenylpalladium complexes, followed by the nucleophilic attack of alcohol or water affords esters or carboxylic acids. Aromatic and a,/ -unsaturated carboxylic acids or esters are prepared by the carbonylation of aryl and alkenyl halides in water or alcohols[30l-305]. 

Phenolic esters (1) of aliphatic and aromatic carboxylic acids, when treated with a Lewis acid as catalyst, do undergo a rearrangement reaction to yield ortho- and para-acylphenols 2 and 4 respectively. This Fries rearrangement reaction is an important method for the synthesis of hydroxyaryl ketones. 

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... 

Compared with aldehydes and ketones, carboxylic acids and their derivatives are less reactive toward reduction. Nevertheless, it is still possible to reduce various acid derivatives in aqueous conditions. Aromatic carboxylic acids, esters, amides, nitriles, and chlorides (and ketones and nitro compounds) were rapidly reduced by the Sml2-H20 system to the corresponding products at room temperature in good yields... 

Although acyl imidazoles can be replaced by phenyl esters in some cases,23 acyl imidazoles are more effective for the acylation of nitroalkanes. A combination of diethyl phosphorcyani-dates and triethylamime allows the direct C-acylation of nitromethane by aromatic carboxylic... 

Although the ability of microwaves (MW) to heat water and other polar materials has been known for half a century or more, it was not until 1986 that two groups of researchers independently reported the application of MW heating to organic synthesis. Gedye et al. [1] found that several organic reactions in polar solvents could be performed rapidly and conveniently in closed Teflon vessels in a domestic MW oven. These reactions included the hydrolysis of amides and esters to carboxylic acids, esterification of carboxylic acids with alcohols, oxidation of alkyl benzenes to aromatic carboxylic acids and the conversion of alkyl halides to ethers. 

Exocyclic reactions for aromatic carboxylic esters 174 Exocyclic reactions for aliphatic carboxylic esters 187 Endocyclic reactions for carboxylic esters 191 Carbon acid participation for carboxylic esters 195 Effective molarities 198 Ring size 199 Initiating nucleophile 200 Phosphate and sulphonate esters 200... 

Aromatic halides react with crown ether-complexed K02 by an electron-transfer mechanism and not by nucleophilic attack, as was shown by Frimer and Rosenthal (1976) using esr spectroscopy. The corresponding phenol is the main reaction product (Yamaguchi and Van der Plas, 1977). Esters are saponified by the K02/18-crown-6 complex in benzene, presumably by an addition-elimination pathway (San Fillippo et al., 1976). The same complex has been used to cleave cr-keto-, or-hydroxy-, and or-halo-ketones, -esters, and -carboxylic acids into the corresponding carboxylic acids in synthetically useful quantities (San Fillippo et al., 1976). 

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. 

Rule of thumb The stability of molecular ions roughly decreases in the following order aromatic compounds > conjugated alkenes > alkenes > alicyclic compounds > carbonyl compounds > linear alkanes > ethers > esters > amines > carboxylic acids > alcohols > branched alkanes. [81]... 

Alkene loss via McLafferty rearrangement at the alkoxy group of aliphatic and aromatic carboxylic acid esters competes with yet another reaction path, where two hydrogens instead of one as in the normal McLafferty product are transferred to the charge site. This second pathway leading to alkenyl loss has early been noticed [94] and became known as McLafferty rearrangement with double hydrogen transfer (r2H) ... 

This simple, selective and efficient method was applied to a wide range of aliphatic/ aromatic carboxylic acid derivatives that contain hydroxyl-, halo-, ester and other base-sensitive groups as substituents. 

Aliphatic and aromatic carboxylic esters are also directly converted, in one step, to oxazolines using amino alcohols. As expected, harsh conditions are required for this transformation. Typically, the reaction is performed in refluxing xylene in the presence of catalytic quantities of a Lewis acid such as dibromo- " or dichloro-dimethylstannane. More recently, lanthanide chloride and samarium chloride have also been reported as useful catalysts for this one-pot transformation in refluxing toluene. Representative examples are shown in Table 8.2 (Scheme 8.2). ... 

According to the developer, the technology can treat the following organic solvents alcohols, ketones, aromatic hydrocarbons, ethers, esters, aldehydes, carboxylic acids, thioethers, mercaptans, and amines. 

Steric effects on the reactivity of benzoic acid derivatives are a little more complicated. The first significant point is that the aromatic carboxylic acids and esters are often some two orders of magnitude less reactive than the corresponding aliphatic compounds. Chapman et al. 7, have explained this difference in terms of three co-operative factors (i) the stabilization of the initial state by delocalization in the case of the aromatic compounds, (ii) inductive electron-withdrawal by the ring, which is significant in esterification... 

Thiophene- and benzo[6]thiophene-carboxylic acids undergo all the normal reactions of an aromatic carboxylic acid (63AHC(1)1, 70AHC(11)177). They can be converted to acid chlorides, amides and esters the esters can be used to make hydrazides. Benzo[6]thiophene-2-carboxylic acid chloride has been converted to the methyl ketone with dimethylcadmium and to the diazoketone with diazomethane. Bromodecarboxylation of the silver salts (Hunsdiecker reaction) has been used to prepare the dibromo compounds (340) and (341). 

The m- and p-APha isomers are commercially available. The synthesis of Boc-o-APha-OH and its ethyl and tert-butyl esters by carboxylation of the dianion of Boc-o-methylaniline has been briefly mentioned. 63 Whereas the carboxy group in APha is expected to react normally, the aromatic amino function is expected to be less nucleophilic owing to the delocalization of the nitrogen lone pair. However, deactivation should be less significant than in o- and p-Abz. Only a few hints at this conclusion may be found in the literature. Indeed, coupling of Boc-p-APha-OSu to an aliphatic primary amine was conducted in DMF for 2 h, affording the amide in a 75% yield. 64 ... 

A manufactured fiber in which the fiber-forming substance is any long-chain synthetic polymer composed of at least 85% hy weight of an ester of a substituted aromatic carboxylic acid, including but not restricted to substituted terephlhalnte units ... 

Essential oils are obtained from fruits and dowers (61,62). Volatile esters of short- and medium-chain carboxylic acids or aromatic carboxylic acids with short- and medium-chain alcohols are primary constituents of essential oils, eg, ethyl acetate in wines, brandy, and in fruits such as pineapple benzyl acetate in jasmine and gardenia methyl salicylate in oils of wintergreen and sweet birch. Most of these naturally occurring esters in essential oils have pleasant odors, and either they or their synthetic counterparts are used in the confectionery, beverage, perfume, cosmetic, and soap industries (see Oils,... 

The methods outlined here deal with methylation and other techniques used to prepare samples of oxidation products for GLC analysis. Aliphatic acids have been determined either as free acids or methyl esters. Aromatics have been determined as methyl ethers of phenolics, methyl esters of carboxylic acids, or methyl ether esters of phenolic acids. 

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. 

Nuclear nitration of aromatic carboxylic esters and acids (Expts 6.159 and 6.160). 

Aromatic esters may be prepared by direct esterification methods similar to those already described for aliphatic esters (Section 5.12.3, p. 695). A large range of examples of simple alkyl esters of aromatic carboxylic acids is included in Expt 6.163. Corresponding esterification of a simple aliphatic acid (e.g. acetic acid) with benzyl alcohol is illustrated in Expt 5.142. 

Methyl esters may be prepared by reaction of the aromatic carboxylic acid with diazomethane (cf. Section 4.2.25, p. 433) or, more conveniently, by reaction with a boron trifluoride-methanol reagent. The latter procedure is illustrated by the preparation of methyl m-chlorobenzoate and dimethyl terephthalate (Expt 6.164). t-Butyl esters may be prepared by conversion of the acid into an N-acylimidazole by reaction with N,N -carbonyldiimidazole, followed by reaction with t-butyl alcohol in the presence of DBU62 (Expt 6.165). 

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