Phenyl-acetic acid acidity constant

Log-log plot of ionization constants of benzoic and phenyl-acetic acids in water at 25°. (From Physical Organic Chemistry by J. S. Hine. Copyright 1962. Used with permission of McGraw-Hill Book Company.)... 

In order to determine the optimum concentration of the acylating agent, phenyl-acetic acid, the amount of amine (0.47 mmol) and enzyme PGA (3.16 units, Rohm-Pharma) were kept constant and the acylating agent was varied from 0.125 to 1.5 mmol (17 mg to 204 mg) (Fig. 9). 

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.

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)... 

For the acid-catalysed reaction, substituent effects have been examined principally in water and acetic acid-water mixtures. The main feature is that the effects are usually small. In Table 3 are also listed the Hammett p-values obtained for acetophenones and arylmethyl phenyl ketones. The slightly negative p-values account for the cationic character of the transition state and for opposite effects on the pre-equilibrium constant and on the elementary rate constant for proton abstraction. 

The values of k2 for ring-substituted phenylacetylenes are well correlated by the Hammett relationship, using a+ constants, and p is very large, — 5-2. The p value compares well with those obtained in the acid-catalysed hydration of arylacetylene derivatives (see Table 1) and is entirely consistent with the formation of a vinyl cation 45 in which the positive charge is at the carbon next to the phenyl ring and is largely shared by it. Interestingly, the p value (by use of a+) based on k2 rate coefficients for the bromination of styrene in acetic acid is — 4-5. 

Aryl esters of 4-hydroxybutyric acid, 5-hydroxyvaleric acid, 2-hydroxyphenylacetic acid, and 3-(2-hydroxyphenyl)propionic acid lactonize with rate constants proportional to iopH picw (Capon et al., 1973). The second-order rate constant at 30° for lactonization of phenyl 4-hydroxybutyrate is ca. 3000 times greater than kOH for hydrolysis of phenyl acetate at 25°. Lactonization of phenyl 4-hydroxybutyrate is catalysed by acetate and phosphate buffers in... 

The Yukawa-Tsuno equation continues to find considerable application. 1-Arylethyl bromides react with pyridine in acetonitrile by unimolecular and bimolecular processes.These processes are distinct there is no intermediate mechanism. The SnI rate constants, k, for meta or j ara-substituted 1-arylethyl bromides conform well to the Yukawa-Tsuno equation, with p = — 5.0 and r = 1.15, but the correlation analysis of the 5 n2 rate constants k2 is more complicated. This is attributed to a change in the balance between bond formation and cleavage in the 5 n2 transition state as the substituent is varied. The rate constants of solvolysis in 1 1 (v/v) aqueous ethanol of a-t-butyl-a-neopentylbenzyl and a-t-butyl-a-isopropylbenzyl p-nitrobenzoates at 75 °C follow the Yukawa-Tsuno equation well, with p = —3.37, r = 0.78 and p = —3.09, r — 0.68, respectively. The considerable reduction in r from the value of 1.00 in the defining system for the scale is ascribed to steric inhibition of coplanarity in the transition state. Rates of solvolysis (80% aqueous ethanol, 25 °C) have been measured for 1-(substituted phenyl)-l-phenyl-2,2,2-trifluoroethyl and l,l-bis(substi-tuted phenyl)-2,2,2-trifluoroethyl tosylates. The former substrate shows a bilinear Yukawa-Tsuno plot the latter shows excellent conformity to the Yukawa-Tsuno equation over the whole range of substituents, with p =—8.3/2 and r— 1.19. Substituent effects on solvolysis of 2-aryl-2-(trifluoromethyl)ethyl m-nitrobenzene-sulfonates in acetic acid or in 80% aqueous TFE have been analyzed by the Yukawa-Tsuno equation to give p =—3.12, r = 0.77 (130 °C) and p = —4.22, r — 0.63 (100 °C), respectively. The r values are considered to indicate an enhanced resonance effect, compared with the standard aryl-assisted solvolysis, and this is attributed to the destabilization of the transition state by the electron-withdrawing CF3 group. 

The free radical arylation of thiazole (391) has been performed either by the Gomberg-Bachmann (392) decomposition of aryldiazonium chlorides (119,393), by the thermal decomposition of benzoyl peroxide (394-397) or N-nitrosoacetanilide (398), or by the photolysis of benzoyl peroxide or iodobenzene (398). The three monophenylthiazoles are obtained in the practically constant proportions 2-phenyl, 60% 5-phenyl, 30% 4-phenyl, 10%, giving the order, 2>5>4, of decreasing reactivity of the three positions of thiazole toward phenyl radicals (398). Competition reactions with nitrobenzene (397) gave an estimation of the globed reactivity of thiazole relative to benzene of 0.75 with the partial rate factors f2 = 2.2, /s=1.9, /4 = 0.5. When the thermolysis of benzoyl peroxide is performed in acetic acid solution, the substrate in reaction is the conjugate acid of thiazole the global reactivity is enhanced to 1.25,... 

The occurrence of general acid-catalyzed hydroxylaminolysis or methoxylaminolysis of thiol esters or amides has been described in Section IIB in terms of kinetically important tetrahedral intermediates. Two kinetically indistinguishable mechanisms for general acid-catalyzed aminolysis reactions are represented by transition states 42 and 43. Mechanism 42 involves a prior protonation of the ester followed by a general base-catalyzed aminolysis mechanism 43 is a general acid-assisted nucleophilic reaction of the amine. Mechanism 42 can be ruled out in the hydrazinolysis of phenyl acetates (Bruice and Benkovic, 1964) and in the hydrazinolysis of S-thiolvalerolactone (Bruice et al., 1963) on the basis of a calculated rate constant which is greater than the diffusion-controlled limit. Mechanism 43 is therefore correct. 

The aromatic acids resemble closely in chemical properties the acids derived from the paraffins, and yield similar derivatives. On account of the negative nature of the phenyl radical they are stronger than the fatty acids. The ionization constant of benzoic acid, CgHb.COOH, for example, is 0.0060, while that of acetic acid is 0.0018. 

Acetic acid, trimethylenediaminetetra-metal complexes equilibrium constants, 784 synthesis. 779 Acetohydroxamic acid metal complexes spectroscopy, 506 Acetohydroxamic acid, A -phenyl-metal complexes, 507 as metal precipitants, 506 Acetone oximes... 

Kinetic studies of aquation of [Fe(phen)3] and derivatives in binary aqueous media remain popular. A group additivity approach has been applied to aquation of [Fe(5N02phen)3] in aqueous alcohols (faster reaction) and formic and acetic acids (slower), to investigate its potential for mechanism diagnosis. Rate constants for dissociation of the parent complex increase tenfold on going from water to 100% dimethylformamide. Aquation rate constants and activation parameters have also been reported for the 5-nitro, 5-phenyl, and 4,7-diphenyl derivatives in water-dioxan mixtures. Both papers contain obscure discussions of solvolysis mechanisms in DMF-rich and dioxan-rich media. In the latter media it seems that ion pairs play a key role, as evidenced by activation entropies. The discussion of reactivities in terms of hydrophobicities of the complexes and their respective transition states represents a qualitative initial state-transition state analysis. An explicit analysis of this type has been published for the iron(II) complexes of the... 

The rates increase with increasing dielectric constant, and H20+Br is the reactive oxidant species. The oxidation of [2-(2- 4-[(4-chlorophenyl)(phenyl)methyl]-l-piperazino ethoxy) acetic acid dihydrochloride (CTZ) by BAT in HCl has a negative fractional dependence in H+ ion, and the rates decrease with increasing dielectric constant of the solvent. CH3C6H5S02NHBr is the reactive BAT species. " The oxidation of cetrizine dihydrochloride (CTZH) with BAT has been investigated both in acid and alkaline medium. A negative fractional order in H+ ion and positive fractional order in HO ion are reported, accompanied by a fractional order in CTZH in both acidic and alkaline media. The rate increases with increasing dielectric constant of the solvent. The reaction in alkaline medium has fractional order in p-toluenesulfonamide (PTS). The oxidation rate of CTZH is faster in acid medium and 4-chlorobenzophenone and (2-piperazine-l-yl-ethoxy)-acetic acid are the oxidation products. ... 

The deaminations of fra 5-2-phenyl- and frans-2-methyl-cyclopropylamine hydrochlorides in acetic acid solution have been examined. The relative amounts of the various products are shown in (26)-(29) and (30)-(33), respectively. The most remarkable feature of these results is the formation of considerable quantities of ring-opened chlorides, which are scarcely formed in deaminations of related open-chain compounds. The addition of chloride ion led to a marked increase in the amount of chloride product. These and other results are interpreted in terms of the formation of a cyclopropyl-diazonium-chloride tight ion pair. The reactions were successfully modelled by ab initio calculations at the B3LYP/6-31G level, including a reaction-field solvent-effect calculation using the dielectric constant of acetic acid. 

Allyl phenyl ethers undergo the rearrangement at temperatures around 200°C in a first-order process in diphenyl ether solvent [8], However, the rate constants drift upward by 10% at 80% reaction, possibly due to formation of the phenol product, which might be a catalyst for the reaction. Further, in the absence of diphenyl ether, the rate constants increased by a factor of 2 at roughly 80% reaction. Perhaps confirming the speculation that phenol is a catalyst, the rate constants obtained upon addition of dimethylamine did not change from the initial rate constants in diphenyl ether solvent alone. However, small amounts of acetic acid had no effect on the reaction. Oxygen also had no effect on the reaction. 

A soln. of 7-chloro-2-methylamino-5-phenyl-4,5-dihydro-3H-l,4-benzodiazepine in 90%-methanol containing acetic acid and Na-acetate trihydrate electrolyzed 3-4 hrs. at constant potential under Ng with a stirred Hg-cathode and a Pt-anode separated by a diaphragm 2-methyl-4-phenyl-6-chloro-3,4-dihydro-quinazoline. Y 80%. H. Oelschlager and H. Hoffmann, Arch. Pharm. 300, 817 (1967). 

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