Phenolic ester

The hydrolysis of alkyl salicylates often a prolonged process under alkaline conditions can be effected in quantitative yield with trifluoroacetic ackJ. Thus methyl 2-hydroxybenzoate in trifluoroacetic acid (10 moles) sealed in a thick glass tube, after heating at 100°C for 13 hours, gave 2-hydroxybenzoic acid in 100% yield (ref.91). 

Methyl 4-hydroxybenzoate in dioxan reacted at the phenolic group with a solution of aziridine (ethyleneimine) in dioxan added over 30 mins, at 50 C and subsequently for 3 hours at 90°C to furnish 2-(4-methoxycarbonyl phenoxy)ethylamine in 53% yield (ref.92). 

Benzo[b]xanthone formation in 74% yield occurred readily in the reaction of ethyl salicylate and 1-naphthol at elevated temperature in refluxing diphenyl ether during 8 hours (ref.93). 

A pyrazolobenzoxazine derivative has been synthesised from an alkoxycarbonylhydrazone of 2-hydroxyacetophenone by further reaction with methyl salicylate. Thus, the hydrazone in tetrahydrofuran was first treated with excess lithium diisopropylamide in THF at OX to generate a dianion which was then reacted with methyl salicylate. Acidification of the mixture after 2 hours followed by refluxing afforded the produrd in 86% yield ref. 94). 

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Particularly suitable for amines. Obviously cannot be used for any liquids affected by alkalis, e.., acids, phenols, esters. 

Sodium and potassium hydroxides. The use of these efficient reagents is generally confined to the drying of amines (soda lime, barium oxide and quicklime may also be employed) potassium hydroxide is somewhat superior to the sodium compound. Much of the water may be first removed by shaking with a concentrated solution of the alkali hydroxide. They react with many organic compounds (e.g., acids, phenols, esters and amides) in the presence of water, and are also soluble in certain organic liquids so that their use as desiccants is very limited... 

Preliminary indication of the presence of a phenol ester may be obtained by heating the compound with soda-lime esters of phenols and also aromatic hydroxy-acids usually give the phenol. (Likewise amides, Imides, nitriles, substituted hydrazines, uretheines, etc. eifiord ammonia.)... 

The Eries rearrangement of phenol esters gives a mixture of 2- and 4-acylphenols (56). The reaction is cataly2ed by Lewis acids such as aluminum chloride or by Brmnsted acids like hydrogen fluoride. This reaction is used in the production of 4-hydroxyacetophenone [99-93-4] a raw material for... 

FRIES Phenol Esier Rearrangement Rearrangement ol phenol esters to o or p ketophenols Lewis acid catalyzed... 

Aiyl esters, prepared from the phenol and an acid chloride or anhydride in the presence of base, are readily cleaved by saponification. In general they are more readily cleaved than the related esters of alcohols, thus allowing selective removal of phenolic esters. 9-Fluorenecarboxylates and 9-xanthenecarboxylates are also cleaved by photolysis. To permit selective removal, a number of carbonate esters have been investigated aryl benzyl carbonates can be cleaved by hydrogenolysis aryl 2,2,2-trichloroethyl carbonates, by Zn/THF-H20. 

This method is generally selective for phenolic esters. 

Dimethoxybenzyl esters prepared from the acid chloride and the benzyl alcohol are readily cleaved oxidatively by DDQ (CH2CI2, H2O, rt, 18 h, 90-95% yield). A 4-methoxybenzyl ester was found not to be cleaved by DDQ. The authors have also explored the oxidative cleavage (ceric ammonium nitrate, CH3CN, H2O, 0°, 4 h, 65-97% yield) of a variety of 4-hydroxy- and 4-amino-substituted phenolic esters. ... 

BuNH2, benzene, rt, 1-24 h, >85% yield. This method is generally selective for phenolic esters. 

Few methods exist for the protection of sulfonic acids. Imidazolides and phenolic esters are too base labile to be useful in most cases. Simple sulfonate esters often cannot be used because these are obviously quite susceptible to nucleophilic reagents. 

Arenediazonium ions are relatively weak electrophiles, and therefore react only with electron-rich aromatic substrates like aryl amines and phenols. Aromatic compounds like anisole, mesitylene, acylated anilines or phenolic esters are ordinarily not reactive enough to be suitable substrates however they may be coupled... 

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. 

The esters are prepared by first treating estradiol with the appropriate acid chloride. The resulting diester, 27, is then subjected to mild acid or basic hydrolysis in this way, the phenolic ester group is removed selectively. 

B eral, and xylene, phenol, ester, crotonaldehyde, and methylcyclopentane, in particular alcohol... 

A reaction which has proved to be of much use in synthetic organic chemistry is the formation of the ortho and/or the para isomers of a hydroxyketone (CVI and CVTI) by treatment of a phenolic ester (CV) with an acid catalyst, viz. 

Among other compounds used to cleave carboxylic esters have been Dowex-50, Me3SiI, and KOSiMe3. Phenolic esters can be similarly cleaved in fact the reaction is usually faster for these compounds.Phenolic esters have been selectively hydrolyzed in the presence of alkyl esters on alumina, using irradiation... 

The reaction between acyl halides and alcohols or phenols is the best general method for the preparation of carboxylic esters. It is believed to proceed by a 8 2 mechanism. As with 10-8, the mechanism can be S l or tetrahedral. Pyridine catalyzes the reaction by the nucleophilic catalysis route (see 10-9). The reaction is of wide scope, and many functional groups do not interfere. A base is frequently added to combine with the HX formed. When aqueous alkali is used, this is called the Schotten-Baumann procedure, but pyridine is also frequently used. Both R and R may be primary, secondary, or tertiary alkyl or aryl. Enolic esters can also be prepared by this method, though C-acylation competes in these cases. In difficult cases, especially with hindered acids or tertiary R, the alkoxide can be used instead of the alcohol. Activated alumina has also been used as a catalyst, for tertiary R. Thallium salts of phenols give very high yields of phenolic esters. Phase-transfer catalysis has been used for hindered phenols. Zinc has been used to couple... 

For a method of hydrolyzing phenolic esters in the presence of other esters, see Blay, G. Cardona, L. Garcia, B. Pedro, J.R. Synthesis, 1989, 438. 

The exact mechanism has still not been completely worked out. Opinions have been expressed that it is completely intermolecular, completely intramolecular, and partially inter- and intramolecular. " One way to decide between inter- and intramolecular processes is to run the reaction of the phenolic ester in the presence of another aromatic compound, say, toluene. If some of the toluene is acylated, the reaction must be, at least in part, interraolecular. If the toluene is not acylated, the presumption is that the reaction is intramolecular, though this is not certain, for it may be that the toluene is not attacked because it is less active than the other. A number of such experiments (called crossover experiments) have been carried out sometimes crossover products have been found and sometimes not. As in 11-14, an initial complex (40) is formed between the substrate and the catalyst, so that a catalyst/substrate molar ratio of at least 1 1 is required. 

Reduction of phenols, phenolic ethers, or phenolic esters... 

Employing this method, enantioenriched phenol esters 68, amides 69, and carbamates 70 (after Curtius rearrangement of the intermediate acyl azide) were prepared in yields often greater than 90% with ee-values reaching up to 97% (generally 80-95%, see Fig. 37). 

The Fourier Trairsform Infrared (FTIR) spectrum obtained from non-adapted tomato cell walls is very similar to that from the onion parenchyma cell wall (both contain cellulose, xyloglucan and pectin) although there is more protein in the tomato walls (amide stretches at 1550 and 1650 cm-i) (Fig 4). In DCB-adapted tomato cell walls, the spectrum more closely resembles that of either purified pectins or of a commercial polygalacturonic acid sample from Sigma with peaks in common at 1140, 1095, 1070, 1015 and 950 cm-t in the carbohydrate region of the spectrum as well as the free acid stretches at 1600 and 1414 cm-i and an ester peak at 1725 cm-k An ester band at 1740 cm-i is evident in both onion parenchyma and non-adapted tomato cell wall samples. It is possible that this shift in the ester peak simply reflects the different local molecular environment of this bond, but it is also possible that a different ester is made in the DCB-adapted cell walls, as phenolic esters absorb around 1720 cm-i whilst carboxylic esters absorb at 1740 cm-k The... 

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