Aromatic esters methyl benzoate

Aromatic Esters Ethyl benzoate Benzyl benzoate Methyl salicylate... 

Triflic acid-catalyzed Friedel-Crafts acylation reactions of aromatics with methyl benzoate give benzophenone products in good to excellent yields (eq 33). To explain the high level of electrophilic reactivity of this system, protosolvated species are proposed as possible intermediates (eq 32). In the triflic acid-catalyzed cyclization of some ethylene dications, protonation of the ester group is thought to be a key activation step. Reaction of a-(methoxycarbonyl)diphenylmethanol with TfOH gives the fluorene product in 94% yield (eq 34). ... 

It is not possible to prepare biaryls containing a free carboxyl group directly by the diazo reaction. No biaryl is formed when (a) diazotized aniline and sodium benzoate, (b) diazotized anthranilic acid and aqueous sodium benzoate, or (c) diazotized anthranilic acid and benzene are used as components in the reaction.13 On the other hand, the reaction proceeds normally if methyl benzoate is used in reaction (a) or when methyl anthranilate replaces the anthranilic acid in (b) and in (c). The success of the diazohydroxide reaction appears to lie in the ability of the non-aqueous liquid to extract the reactive diazo compound from the aqueous layer.4 However, esters and nitriles can be prepared from esters of aromatic amino acids and cyanoanilines and also by coupling with esters of aromatic acids, and from the products the acids can be obtained by hydrolysis. By coupling N-nitrosoacetanilide with ethyl phthalate, ethyl 4-phenylphthalate (VIII) is formed in 37% yield. 

Aromatic esters are hydrogenated without solvent or in alcohol. Ethyl benzoate (eq. 11.49),11 ethyl phenyl acetate,183 methyl salicylate (eq. 11,50),86a and diethyl phthalate (eq. 11.51)183 were hydrogenated almost quantitatively to the corresponding cyclohexane derivatives over Ni-kieselguhr at 150-200°C. The hydrogenation of the ethyl... 

Aromatic carboxylic esters may be reduced to produce the corresponding primary alcohol by electrolysis at a mercury, lead or cadmium cathode. - For example, methyl benzoate is readily reduced to benzyl alcohol (91%) at a mercury cathode in MeOH containing Me4NCl. Ring substituents in the ben-... 

Prelab Exercise Draw the complete mechanism for the nitration of methyl benzoate. Show the resonance forms that make the methyl ester group a meta director and deactivator of the aromatic ring. 

Voltammetric data for ester reductions are available for several aromatic esters [51-54], and in particular cyclic voltammetry shows clearly that in the absence of proton donors reversible formation of anion radical occurs [51]. In dimethylfonnamide (DMF) solution the peak potential for reduction of methyl benzoate is —2.29 V (versus SCE) for comparison dimethyl terephthalate reduces at —1.68 V and phthalic anhydride at —1.25 V [4]. Half-wave potentials for reduction of aromatic carboxylate esters in an unbuffered solution of pH 7.2 are linearly correlated with cr values [51] electron-withdrawing substituents in the ring or alkoxy group shift Ei/o toward less negative potentials. Generally, esters seem to be more easily reducible than the parent carboxylic acids. Anion radicals of methyl, ethyl, and isopropyl benzoate have been detected by electron paramagnetic resonance (epr) spectroscopy upon cathodic reduction of these esters in acetonitrile-tetrapro-pylammonium perchlorate [52]. The anion radicals of several anhydrides, including phthalic anhydride, have similarly been studied [55]. 

Acylations. Catalyzed by graphite the Friedel-Crafts acylation as well as the transformation of ethers to esters by acyl halides in refluxing 1,2-dichloroethane are realized. Although aliphatic chlorides are inferior to aromatic halides this method is quite general as shown by the synthesis of benzoates (e.g., allyl benzoate from allyl benzyl ether and methyl benzoates from methyl f-butyl ether). 

Other reductions. Miller et report reduction of benzoic acid and of methyl benzoate to benzyl alcohol and of n-butyl caproate to n-butanol and n-hexanoL Russian investigators" report reduction of aliphatic and aromatic esters to aldehydes, of ortho esters to acetals, of acetals to ethers, and of benzyl ethyl ether to toluene. 

The fluorescence of 2-ethoxynaphthalene is quenched by methyl benzoate through an exciplex. The importance of the rate of formation of exciplexes and radical ions in the encounters of excited aromatic esters with aliphatic amines has been stressed by Costa and Macanita. A charge-transfer mechanism is clearly demonstrated in the quenching of excited aromatic esters by triethylamine. ... 

A chemical/chromatographic method has been used to determine the first double bond position in the unsaturated anacardic acid constituents of Pistacia vera (ref. 9). The isolated constituent was methylated, dihydroxylated with performic acid, hydrolysed to remove some formate ester, oxidised with potassium periodate in acidic solution and the aldehydes formed reduced with sodium borohydride to the primary alcohols (refs. 226). The retention time of the aromatic product methyl 2-methoxy-6-(8-hydroxyoctyl)benzoate (C8 side chain) was compared with those of the Cl, C3, C7 and CIO synthetic analogues and from the linear plot of retention time against methylenic carbon chain length, the double bond could be readily assigned to the 8-position. Nevertheless mostly on account of limited sample availability and the time involved in purely synthetic verification. 

Saponification of hindered aromatic esters This is a typical example of an enhanced microwave-specific effect related to the difficulty of the reaction, which presumably proceeds via later and later TS. Whereas essentially thermal effects are observed (approx. 200 °C) with methyl and octyl benzoate, a microwave-specific effect is increasingly apparent with hindered esters and becomes optimum with mesitoyl oc-tanoate (Eq. (73), Table 4.23) [157]. 

Synthesis of Aromatic Nitriles from Esters. A one-flask method has been developed for the conversion of aromatic esters to the corresponding nitriles by use of NaHMDS in a sealed tube at 185 °C in a mixture of THF and 1,3-dimethyl-2-imidazolidinone (DMEU) (eq 20). The transformation proceeded with good to excellent yields. The synthetic strategy is only apphcable to aromatic esters that bear an electron-donating substituent such as hydroxy or methoxy. In the latter case, con tetitive 0-demethyla-tion is observed, thus leading to a mixture of nitrile products. The reaction has been also applied to indole-3-carboxylate. However, simple unsubstituted methyl benzoate failed to give the desired product. 

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