Hydrolysis of phenyl salicylate

The rate of hydrolysis of phenyl salicylate remains independent of [HO] within its range 0.005 to 0.060 M at 30°C. The [HO]-independent hydrolysis of phenyl salicylate is expected to involve either H2O and PS" (ionized phenyl salicylate) or kinetically indistinguishable HO and PSH (nonionized phenyl salicylate) as the reactants. The occurrence of these kinetically indistinguishable reaction steps has been resolved satisfactorily and it has been concluded that pH-independent hydrolysis involves H2O and PS as the reactants. The rates of pH-independent hydrolysis and alkanolysis of phenyl salicylate have been shown to be increased by lO -fold owing to the intramolecular GB (2-0 group) assistance through an intramolecular intimate ion-pair (IIP). 

Recently, induced intramolecularity in the reference reaction has been concluded to be responsible for the low rate enhancement (usually < 10-fold) of intramolecular (3A-GB-assisted intermolecular nucleophilic reactions. " But an approximate 10 -fold rate enhancement of intramolecular GB-assisted hydrolysis of phenyl salicylate is certainly large enough to cast doubt on invoking the concept... 

Capon, B., Ghosh, B.C. The mechanism of the hydrolysis of phenyl salicylate and catechol monohenzoate in the presence and absence of horate ions. J. Chem. Soc., (B) 1966, 472-478. 

Khan, M.N. Effects of anionic micelles on the intramolecular general-base-cata-lyzed hydrazinolysis and hydrolysis of phenyl salicylate evidence for a porous cluster micelle. J. Chem. Soc. Perkin Trans. 2. 1990, 445 57. 

Khan, M.N., Ismail, E., Yusoff, M.R. Effects of pure non-ionic and mixed nonionic-cationic surfactants on the rates of hydrolysis of phenyl salicylate and phenyl benzoate in alkaline medium. J. Phys. Org. Chem. 2001,14, 669-676. 

The rate of hydrolysis of phenyl salicylate in aqueous solvent was found to be [HO-]-independent within the [HO ] range -0.002 to 0.070 and under such conditions, the hydrolysis reactions of salicylate esters involved ionized salicylate ester and H2O as the reactants. A brief mechanism for [HO"]-independent hydrolysis of PS" is shown in Scheme 4.1, in which IIP and HP represent intramolecular intimate ion-pair (highly reactive intermediate) and internally hydrogen-bonded highly reactive intermediate, respectively. Although micelles accelerate or decelerate the rate of a reaction, it is very rare that they change the mechanism of the reaction with the change in the reaction environment from aqueous pseudophase to the micellar pseudophase." It is, therefore, reasonable to assume that the mechanism of hydrolysis of PS- remains the same in both the aqueous and micellar pseudophases. 

Pseudo-first-order rate constants (k bs) for pH-independent hydrolysis of phenyl salicylate and phthalimide, obtained at constant post-CMC [CTABrJr and varying values of [CigEjoJp have been found to fit to Equation 3.49, which is derived by the use of PP model (i.e.. Equation 3.2) coupled with an empirical equation (Equation 3.32) as described in Chapter 3. The linear increase in with increase in [CjjEjsIt from 0.0 to 0.015 M at constant [CTABrlj (= 0.01,0.02, and 0.03 indicates that 1 K[C E ]t (where n = 12 and m = 23) and, consequently. Equation 3.49 is reduced to Equation 5.2 under such conditions. 

Herrington, K.L., Kaler, E.W., Miller, D.D., Zasadzinski, J.A., Chiruvolu, S. Phase behavior of aqueous mixtures of dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS). J. Phys. Chem. 1993, 97(51), 13792-13802. Khan, M.N., Ismail, E., Yusoff, M.R. Effects of pure non-ionic and mixed non-ionic-cationic surfactants on the rates of hydrolysis of phenyl salicylate and phenyl benzoate in alkaline medium. J. Phys, Org. Chem. 2001,14, 669-676. 

Neighbouring-group participation in the hydrolysis of esters and amides has been reviewed. The effects of urea, Na+ and Li+ on the intramolecular general-base-catalysed glycolysis of phenyl salicylate (217) in glycol-acetonitrile solvent at constant water concentration have been reported. ... 

The aminolysis and methanolysis of ionized phenyl salicylate (189) have been examined under micellar conditions. The effect of CTABr on the rates of aminolysis of (189) by -butylamine, piperidine, and pyrrolidine is to bring about a rate decrease (up to 17-fold with pyrrolidine). The results are interpreted in terms of binding constants for the amines with CTABr and the pseudo-phase model.The effects of mixed surfactants SDS and CTABr on the methanolysis of (189) and the alkaline hydrolysis of phenyl benzoate suggest that micellar aggregates are involved in the processes.The effects of NaOH and KBr on the intramolecular general base-catalysed methanolysis of (189) in the presence of CTABr has been investigated. Pseudo-first-order rate constants were not affected by either additive but other changes were noted. The effect of mixed MeCN-water solvents on the same reaction has also been probed. 

The presence of B(OH>3 increases the rate of hydrolysis of ionized phenyl salicylate (PS ) by nearly 10 -fold compared to the rate of hydrolysis of phenyl benzoate under essentially similar conditions (Equation 2.34). However, the hydrolysis of PS crtn also occur with measurable rate in the absence of B(OH)3. Nearly 10 -fold rate enhancement due to the presence of boric acid is attributed to the boric-acid-induced intramolecular reaction involving transition state TS,6. An alternative and kinetically indistinguishable mechanism involving transition state TSiy has been ruled out on the basis of the absence of enhanced nucleophilic reactivity of tertiary and secondary amines toward phenyl salicylate in the presence of borate buffer. 

The rates of hydrolysis of phenyl and methyl salicylates became independent of [HO ] within the [HOi range of 0.002 to 0.070 M in the absence of micelles. The values of ionization constants, K, for phenyl salicylate and methyl salicylate in water solvent are 5.67 x 10 ° M and 2.48 x 10 ° M, respectively. Thus, within the [HO ] range of - 0.002 to 0.070 M, both phenyl and methyl salicylates exist in fully ionized forms. The pH-independent rate of hydrolysis of salicylate esters involve ionized salicylate ester and H2O as the reactants. Intramolecular general base catalysis has been shown to occur in the aminolysis of ionized phenyl salicylate in both aqueous pseudophase and micellar pseudophase of SDS. - The brief reaction scheme for hydrolysis or alkanolysis of salicylate ester or any substrate containing an easily ionizable proton in the presence of micelles, D , may be given in terms of PP model of micelle as depicted in 8cheme 4.2... 

Khan, M.N. Effect of anionic micelles on the intramolecnlar general base-catalyzed hydrolysis of phenyl and methyl salicylates. J. Mol. Catal A 1995, 102, 93-101. 

Khan, M.N. Effects of mixed anionic and cationic surfactants on rate of trans-estrification and hydrolysis of esters. J. Colloid Interface Sci. 1996,182,602-605. Khan, M.N., Arifin, Z. Kinetics and mechanism of intramolecular general base-catalyzed methanolysis of phenyl salicylate in the presence of cationic micelles. Langmuir 1996, 72(2), 261-268. 

The kinetics of the alkaline hydrolysis of 2-methylpentyl salicylate (24) have been studied in various aqueous propanol and r-butanol mixtures and in mixtures of water and ethane-l,2-diol. ° Further smdies of the aminolysis of ionized phenyl salicylate (25) have been reported, in which it was observed that, in mixed acetonitrile-water solvents, glycine, 1,2-diaminoethane and 3-aminopropanol all reacted as did simple amines, via an intramolecular general-base-catalysed process. ... 

He, B., Huang, W Guo, X., and Yu, Y Catalysis by condensation polymers containing salicylic acid for hydrolysis of p-nitro-phenyl acetate in aqueous solution, Gaofenzi Tongxun, 416,1982 Chem. Abstr., 99,21670,... 

Pharmaceutical Incompat, (from Remington s Pharmaceutical Sciences) Aspirin forms a damp to pasty mass when triturated with acetanilide, phenacetin, antipyrine, amidopyrine, methenamine, phenol or phenyl salicylate. Powders containing aspirin with an alkali salt such as sodium bicarbonate become gummy on contact with atmospheric moisture. Hydrolysis oecnrs in admixture with salts contg water of crystallization. Solns of the alkaline acetates and citrates, as well as alkalies themselves, dissolve aspirin but the result -ing solns hydrolyze rapidly to form salts of acetic and salicylic acids. Sugar and glycerol have been shown to hinder this decompn. Aspirin very slowly liberates hydriodic acid from potassium or sodium iodide. Subsequent oxidation by air produces free iodine. 

The effect of cetyltrimethylammonium bromide on the rate constants of hydrolysis of ethyl glycinate hydrochloride has been reported. " Cationic and non-ionic micelles inhibited and anionic micelles accelerated the acid hydrolysis of A-p-tolyl-benzohydroxamic acid (189). The rates of acid hydrolysis of acetohydroxamic acid, MeCONHOH, benzohydroxamic acid, PhCONHOH, and A-phenylbenzohydroxamic acid, PhCON(OH)Ph, were increased by perfiuorooctanoic acid and by sodium 1-dodecanesulfonate and sodium dodecyl sulfate (SDS). " The effects of micelles of SDS upon the rates of reaction of ionized phenyl salicylate with Bu"NH2, piperidine and pyrroiidine have been reported. 

Let us examine few models. The rate of hydrolysis of the ester function of the phenyl and salicyl esters of pyridine-2,6-dicarboxylic acid is significantly enhanced upon complexation with Ni(II) or Zn(II) ions (225). 

Also obtained by hydrolysis of p-(salicyloyl)phenyl salicylate [346]. 

The catalytic effect of nickel(n) on hydrolysis rates of the salicyl and phenyl esters of pyridine-2,6-dicarboxylic acid is ascribed to the intermediacy of a 1 1 complex between the ester and the nickel(n). Rates of hydrolysis and of reaction with hydroxide are reported.Kinetic and equilibrium studies have... 

Khan, M.N., Arifin, Z. Effects of cationic micelles on the intramolecular general base-catalyzed hydrolysis of ionized phenyl salicylate at different temperatures. J. Chem. Res. (S) 1995, 132-133. 

The experimental test of Equation 3.49 has been carried out by smdying the effects of [C, E2o]t on the rate of pH-independent hydrolysis of phthalimide (PT)132,i33 phenyl salicylate (PS)02 at constant [PT] or [PS], [NaOH], [CTABr], and at 35°C. The observed data (k bs vs. [CigE2o]x) revealed a good fit to Equation 3.49 (where [QE ,]x = [CipEijoIt) and the nonlinear least-squares calculated values of F and K are summarized in Table 3.7. The calculated values... 

Pseudo-first-order rate constants, k bs, for hydrolysis of ionized phenyl salicylate in the presence of different concentrations of CTABr were used to calculate k Kg and Kg (considered to be unknown parameters) from Equation 3.2 and such calculated values of k Kg and Kg are 0.61 + 0.24 Af- sec and (6.3 1.1) X 10 M respectively. These values of k Kg and Kg yielded k as 9.6 X 10 sec , which is exactly the same as the one calculated from Equation 3.2 considering k and Kg as unknown parameters. The quality of the data fit of a set of observed data to Equation 3.2 remained unchanged with the change in the choice of unknown parameters from k, and Kg to k Kg and Kg. This analysis thus rules out the inherent perception of a possible compensatory effect between the calculated values of k and Kg when they, rather than k, Kg and Kg, are considered unknown parameters in using Equation 3.2 for data analysis. 

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