Aryl esters preparation

Aryl 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. Esters of electron-deficient phenols are good acylating agents for alcohols and amines. 

The substituted aryl esters prepared and examined as potential acylating agents are too numerous to be described here. They are discussed in a comprehensive review article [24]. Yet, the studies of J. Pless and R.A. Biossonnas [25] should be mentioned even in this brief presentation. Based on an extensive comparison of substituted phenyl esters, they chose the 2,4,5-tri-chlorophenyl esters of iV-acylamino acids as practical acylating agents, a choice fairly well accepted by several laboratories. The powerful pentafluorophenyl esters introduced by J. Kovacs, L. Kisfaludi and M.Q. Ceprini in 1967 [26] has gained importance in recent years through their application in solid phase peptide synthesis. 

CH OfiSj, H2C(S03H)2- a colourless, crystalline solid which readily absorbs water vapour decomposes on distillation. The potassium salt is prepared by heating methylene chloride with an aqueous solution of potassium sulphite under pressure at 150-I60" C. The free acid is obtained by decomposing the sparingly soluble barium salt with sulphuric acid. The aryl esters are very stable, but the alkyl esters decompose on heating to give ethers. Resembles malonic acid in some of its reactions. 

Fischer esterification m which a phenol and a carboxylic acid condense m the pres ence of an acid catalyst is not used to prepare aryl esters... 

Naphthol is mainly used in the manufacture of the insecticide carbaryl (59), l-naphthyl A/-methyicarbamate/ iJ-2j5 - (Sevin) (22), which is produced by the reaction of 1-naphthol with methyl isocyanate. Methyl isocyanate is usually prepared by treating methylamine with phosgene. Methyl isocyanate is a very toxic Hquid, boiling at 38°C, and should not be stored for long periods of time (Bhopal accident, India). India has developed a process for the preparation of aryl esters of A/-alkyl carbamic acids. Thus l-naphthyl methylcarbamate is prepared by refluxing 1-naphthol with ethyl methylcarbamate and POCl in toluene (60). In 1992, carbaryl production totaled > 11.4 x 10 t(35). Rhc ne-Poulenc, at its Institute, W. Va., facihty is the only carbaryl producer in United States. 

The best known aryl ester is O-acetylsalicylic acid, better known as aspirin. It is prepared by acetylation of the phenolic hydroxyl group of salicylic acid ... 

Thiol acids and thiol esters can be prepared in this manner, which is analogous to 10-8 and 10-24. Anhydrides and aryl esters (RCOOAr) are also used as substrates, but the reagents in these cases are usually SH and SR. Thiol esters can... 

Block, H.-D. and Frohlen, H.-G., Preparation of Alkane Phosphonic and Phos-phinic Acid Aryl Esters, U.S. Patent 4,377,537, 1983. 

For the preparation of aryl esters from phosphorus oxychloride, a Lewis acid is generally added as a catalyst. Commonly, aluminum chloride with an excess of phosphorus oxychloride added to the phenol provides excellent yields (Equation 4.2).4... 

Aryl esters of retinoids have also received some interest. The 4-(acet-amido)phenyl ester of (all- )-retinoic acid, for example, showed topical activity in various animal models but was ineffective for the local treatment of acne in patients [86]. This difference is probably due to the prodrug being readily hydrolyzed in mice skin homogenates but not in human skin preparations. 

Ortho- and para-rearrangement and phenol formation on uv-irradiation of aryl esters are accompanied in several cases by decarboxylation,37,60,62,64,80,81 represented for 3,5-di-t-butylphenyl benzoate by the equation 118 -> 119-122. It was shown that this reaction cannot be sensitized,64 but the dramatic differences in product distribution could be observed by changing of the solvent.60,84 The results in Table VI indicate that in polar solvents the decarboxylation process is minimized while the formation of the photo-Fries rearrangement 119 is enhanced. The reverse appears to be true when nonpolar ethereal solvents are used. A considerable amount of biaryls are formed, and hence this reaction may prove useful for the preparation of biaryls and alkylary Is. 

Polyesters [2] find use in fibers [poly(ethylene terephthalate), poly(ethylene oxybenzoate), poly(ester ethers), poly(ester amides), etc.] [1], coatings (especially unsaturated polyesters) [4], plasticizers, adhesives, polyurethane base resins, films, etc. Cross-linked polyesters prepared from glycerol and phthalic anhydride (alkyd resins) have been reviewed [20], High-melting poly aryl esters have been investigated for high-temperature applications. 

The 5,7-dioxopyrimido[4,5-rf]pyrimidine-5,7-dione (254) can be obtained by fusion of the amide (253) with urea (68JMC568). This amide is prepared by hydrolysis of the corresponding cyanopyrimidine in concentrated sulfuric acid. 4-Aminopyrimidine-5-carboxamides can also be condensed with alkyl and aryl esters to give pyrimido[4,5-d]pyrimidin-4-ones... 

Enolates prepared by deprotonation of carboxylic acid derivatives can also undergo elimination to yield ketenes. This is rarely seen with amides, but esters, thiolesters, imides, or N-acylsulfonamides can readily decompose to ketenes if left to warm to room temperature (Scheme 5.58). At -78 °C, however, even aryl esters can be converted into enolates stoichiometrically without ketene formation [462, 463],... 

This procedure, however, was not applicable to the preparation of aryl esters. 

Ester-based cascades (e.g., 107) have been prepared[77 80i by using 5-(tert-butyldime-thylsiloxy)isophthaloyl dichloride (108), which was synthesized in high yield from 5-hydroxy-isophthalic acid (Scheme 5.26). The dendron wedges were prepared by treatment of siloxane 108 with phenol to give bis(aryl ester) 109, which was hydrolyzed, or desilylated (HC1, acetone), to generate a new phenolic terminus. Treatment of this free phenolic moiety with monomer 108, followed by hydrolysis, afforded the next tier (110). Repetition of the sequence followed by reaction of the free focal phenols with a triacyl chloride core, (e.g., 86), afforded the fourth tier dendrimer 107 of the polyester aryl series. It was noted that the choice of base (N, A-dimethylaniline) used in the final esterification was critical, since with pyridine bases (pyridine or 4-(dimethylamino)pyridine) facile transesterification resulting in branch fragmentation occurred. 

Anhydrides—Continued reduction to alcohols, 155 reduction to lactones, 535 Arenes, see Hydrocarbons, aromatic Amdt-Eistert reaction, 433, 487, 573 Aryl esters. Fries rearrangement, 344 hydrolysis, 169 preparation, 169 Aryl halides, see Halides Atyloxy acids, preparation, by aceto-acetic ester synthesis, 430 by malonic ester synthesis, 429 from atyloxy alcohols, 419 from atyloxy cyanides, 414 preparations listed in table 48, 460 Aryloxy acyl halides, preparation, 547 preparations listed in table 61, 553 Aryloxy esters, preparations listed in table 55, 516... 

Phenolic esters, see Aryl esters Phenolic ketones, preparation, 321, 344... 

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