Phenol phenyl acetate

Inclusion of Phenols, Phenyl Acetates, and Related Compounds. 72... 

Figure 1 Transformation of the phenol-phenyl acetate mixture over 500 mg of H-BEA-10. Yield in HAP (%) as a function of time (h) in sulfolane and in dodecane solvents...

Kinetic study of the transformation of the phenol-phenyl acetate mixture. 

The oxidation of benzene to phenol, phenyl acetate and biphenyl has been reported to occur in the presence of Pd(II) chloride or acetate complexes and the heteropoly acid acetic acid (120 °C,... 

The ester and catalj st are usually employed in equimoleciilar amounts. With R =CjHs (phenyl propionate), the products are o- and p-propiophenol with R = CH3 (phenyl acetate), o- and p-hydroxyacetophenone are formed. The nature of the product is influenced by the structure of the ester, by the temperature, the solvent and the amount of aluminium chloride used generally, low reaction temperatures favour the formation of p-hydroxy ketones. It is usually possible to separate the two hydroxy ketones by fractional distillation under diminished pressure through an efficient fractionating column or by steam distillation the ortho compounds, being chelated, are more volatile in steam It may be mentioned that Clemmensen reduction (compare Section IV,6) of the hj droxy ketones affords an excellent route to the substituted phenols. 

To hydrolyse an ester of a phenol (e.g., phenyl acetate), proceed as above but cool the alkaline reaction mixture and treat it with carbon dioxide until saturated (sohd carbon dioxide may also be used). Whether a solid phenol separates or not, remove it by extraction with ether. Acidify the aqueous bicarbonate solution with dilute sulphuric acid and isolate the acid as detailed for the ester of an alcohol. An alternative method, which is not so time-consuming, may be employed. Cool the alkaline reaction mixture in ice water, and add dilute sulphuric acid with stirring until the solution is acidic to Congo red paper and the acid, if aromatic or otherwise insoluble in the medium, commences to separate as a faint but permanent precipitate. Now add 5 per cent, sodium carbonate solution with vigorous stirring until the solution is alkaline to litmus paper and the precipitate redissolves completely. Remove the phenol by extraction with ether. Acidify the residual aqueous solution and investigate the organic acid as above. 

Phenyl acetate [122-79-2] M 136.2, b 78°/10mm, d 1.079, n 1.5039. Freed from phenol and acetic acid by washing (either directly or as a soln in pentane) with aqueous 5% Na2C03, then with saturated aqueous CaCl2, drying with CaS04 or Na2S04, and fractional distn at reduced pressure. 

Nishioka and Fujita78) have also determined the Kd values fora- and (S-cyclodextrin complexes with p- and/or m-substituted phenyl acetates through kinetic investigations on the alkaline hydrolysis of the complexes. The Kd values obtained were analyzed in the same manner as those for cyclodextrin-phenol complexes to give the Kd(X) values (Table 5). The quantitative structure-activity relationships were formulated as Eqs. 30 to 32 ... 

Only the hydrophobic and steric terms were involved in these equations. There are a few differences between these equations and the corresponding equations for cyclo-dextrin-substituted phenol systems. However, it is not necessarily required that the mechanism for complexation between cyclodextrin and phenyl acetates be the same as that for cyclodextrin-phenol systems. The kinetically determined Kj values are concerned only with productive forms of inclusion complexes. The productive forms may be similar in structure to the tetrahedral intermediates of the reactions. To attain such geometry, the penetration of substituents of phenyl acetates into the cyclodextrin cavity must be shallow, compared with the cases of the corresponding phenol systems, so that the hydrogen bonding between the substituents of phenyl acetates and the C-6 hydroxyl groups of cyclodextrin may be impossible. 

The phenol ArOH is always a side product, resulting from some ArO that leaks from the solvent cage and abstracts a hydrogen atom from a neighboring molecule. When the reaction was performed on phenyl acetate in the gas phase, where there are no solvent molecules to form a cage (but in the presence of isobutane as a source of abstractable hydrogens), phenol was the chief product and virtually no o- or p-hydroxyacetophenone was found." Other evidence" for the mechanism is that... 

The availability of Nafion on silica has not only lowered the cost of the resin but also has made it versatile (Sun et al., 1997 Harmer et al., 1998). A number of industrially important reactions have been attempted, with considerable success, with these catalysts. Consider the Fries rearrangement of phenyl acetate to p-acetyl phenol (/t-hydroxy acetophenone). This has been accomplished by Hoelderich and co-workers (Heidekum, 1998). In the ca.se of alkylation of benzene with benzyl alcohol, Amberlyst-15 and p-toluene sulphonic acid are ineffective and Nafion on silica works well at 80 °C. 

Figure 1. Hydrolysis pH-rate profiles of phenyl acetate (lower) and a substituted 2-phenyl-l,3-dioxane (HND). Phenyl acetate profile constructed from data of Mabey and Mill (32), HND profile from data of Bender and Silver (33). Phenyl acetate reacts via specific-acid catalyzed, neutral, and base-catalyzed transformation pathways. The pseudo-first-order rate constant is given by Kobs = K(h+) [H+] + Kn + K(qh-) [0H—]. HND hydrolyzes only via an acid-catalyzed pathway the phenolate anion is some 867 times more reactive than its conjugate acid.

An additional example is the observed moderate acceleration in the cleavage of particular phenyl esters in the presence of a cyclodextrin. In such cases, the bound ester is attacked by an hydroxyl group on the cyclodextrin to yield a new ester. There was found to be a significant enhancement of phenol release from meta-substituted phenyl acetate on interaction with cyclodextrin (relative to other esters which do not fit the cavity so well) (Van Etten, Clowes, Sebastian Bender, 1967). During the reaction, the acyl moiety transfers to an hydroxyl group on the... 

In 20% dioxan-water (Milsden and Cohen, 1972). The reference reaction is the formation of phenyl acetate from phenol and acetic acid at 25° (rate constant estimated at 1.5 x 10 10 dm3 mol-1 s 1). These authors very high rate constants for the lactonization of compounds B.2.23-25 (data in parentheses) which lead to much quoted EM s in the region of 10 M, appear to be too high by several orders of magnitude (Caswell and Schmir, 1980)... 

Photolysis of 4- and 3-nitrophenyl acetates (176 —> 177 178 —> 179) in neutral aqueous solution leads to the corresponding phenols with quantum yields 0.002 and O.OO6105 (equation 84). A greater difference in the photoreactivity (quantum yields of 0.002 and 0.129, respectively) is shown between 2-mcthoxy-4-nitrophenyl acetate 180 and 2-methoxy-5-nitrophenyl acetate 182. The nitro substituent clearly exhibits a meta-activating effect in the hydrolysis of phenyl acetates. 

A few acetates of phenols have been used extensively as probes to investigate esterases, e.g., phenyl acetate (7.15), 4-nitrophenyl acetate (7.16), a-naphthyl acetate (7.17) and 7-acetoxy-4-mc(hyl-27/-[l bcnzopyran-2-onc (4-methylumbelliferyl acetate, 7.18). Such substrates are easy to handle and their phenolic metabolite is readily analyzed, allowing convenient monitoring of the reaction. 

Reactions of a wide range of substituted phenyl acetates with six a-effect nucleophiles have revealed little or no difference, compared with phenolate nucleophiles, in the values of the Leffler parameters. As a result, the case for a special electronic explanation of the a-effect is considered unproven. Studies of the kinetics and mechanism of the aminolysis and alkaline hydrolysis of a series of 4-substituted (21) and 6-substituted naphthyl acetates (22) have revealed that, for electron-withdrawing substituents, aminolysis for both series proceeds through an unassisted nucleophilic substitution pathway. 

The hydrolysis of substituted phenyl acetates has been studied in the presence of cyclodextrins (Van Etten et al, 1967a, b). No correlation was found between the rate constants for hydrolysis and a for the substituent group. Specificity was directed towards meta-substituents. m-t-Butylphenyl acetate hydrolyses 240 times faster in the presence of 0-01 M cyclohepta-amylose. Comparison of spectral shifts upon inclusion of p-t-butyl and m-t-butylphenol indicated that benzene rings of p-substituted phenols are included within the cavity of cyclodextrins [45], but that the benzene ring of the meta-isomer... 

The mechanistic origin of the PFR products was a matter of discussion from the beginning. The archetypal rearrangement is that of phenyl acetate (10), which has been widely employed as a model to understand the photoprocess. Its irradiation in solution affords ort/io-hydroxyacetophenone (11), para-hydroxyacetophenone (12), and phenol (13) (Scheme 3). Two alternative mechanistic pathways were... 

If the photo-Fries reaction would occur via a concerted mechanism, the absence of solvent should be of minor importance for the formation of rearranged products. However, conclusive evidence supporting the radical pair mechanism arises from the experiments carried out with phenyl acetate (10) in the vapor phase. The major product in the irradiations of 10 is phenol (13), which accounts for 65% of the photoproducts. Under these conditions, less than 1% of ortho -hydroxyace-tophenone (11) appears to be formed [19,20]. Conversely, when a high cage effect is expected, as in rigid matrixes (i.e., polyethylene), the result is completely different, and phenol is practically absent from the reaction mixtures [29]. In the intermediate situation (liquid solution), both rearranged products and phenol are formed in variable amounts depending on solvent properties. These observations... 

Figure 1 Flash spectra of phenyl acetate)—) and phenol (...) in hexane. Delay time 15 p.sec. (Adapted from Ref. 18.)...

The PFR of phenolic esters is by far the best known of this group of rearrangements. The PFR of phenyl acetate (Scheme 3) is the prototype of all of them. 

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