20227-79-6Relevant academic research and scientific papers
Kinetics and mechanistic study of the reaction of cyclic anhydrides with substituted phenols. Structure-reactivity relationships
Andres, Gabriel O.,De Rossi, Rita H.
, p. 1445 - 1449 (2007/10/03)
(Chemical Equation Presented) The kinetic of the reactions of phthalic and maleic anhydrides with different substituted phenols (Z-PhOH with Z = H, m-CH3, p-CH3, m-Cl, p-Cl, and m-CN) were studied in aqueous solution. Two kinetic processes well separated in time were observed. The fast one is attributed to the formation of the aryl ester in equilibrium with the anhydride and allows the determination of the rate of nucleophilic attack of the phenol on the anhydride (k-A). From the slow kinetic process, the equilibrium constant for this reaction was determined. The Broensted-type plots for the nucleophilic attack of substituted phenols on the anhydrides were linear with slopes βNuc of 0.45 and 0.56 for phthalic and maleic anhydride, respectively. The results are consistent with a mechanism involving rate-determining nucleophilic attack and also with a concerted mechanism. The calculated effective charge on the atoms involved in the reactions and the Broensted β values are consistent with a mechanism involving a concerted or enforced concerted mechanism where a tetrahedral intermediate with significant lifetime is not formed along the reaction coordinate. The latter mechanism is preferred over the stepwise process.
Mechanistic change in the reactivity of substituted phenyl acetates over phenyl thiolacetates toward imidazole in aqueous phase
Rajarathnam,Jeyakumar,Nadar, P. Ananthakrishna
, p. 211 - 221 (2007/10/03)
The kinetics of aminolysis of several substituted phenyl acetates by imidazole is studied in aqueous medium at 20°C and an ionic strength of 0.1 M (KCl). By following the leaving groups spectrophotometrically (λ max = 272-401 nm), under excess free imidazole, pseudo-first-order rate constants (κobs) are obtained. For the esters with good nucleofuges, the reaction follows clean second-order kinetics and the plots of (κobs - κH) against free imidazole concentration are linear at constant pH. The macroscopic nucleophilic substitution rate constants (κN) are obtained as the slopes of these plots and found to be pH independent. For the esters with poor nucleofuges, a rate dependence on more than first power of the free imidazole and a linear dependence of κ′2 on free imidazole is observed. Accordingly, the microscopic rate constants for the assisted paths viz. κga and κgb have been disseminated besides for simple bimolecular attack. The Broensted-type plots and Hammett plots were constructed whose slope values are consistent with a stepwise mechanism through a bipolar tetrahedral addition intermediate whose formation or breakdown being rate determining for various paths. Comparison of this reaction of oxyesters with the earlier reported works on similar reaction of analogue thiolesters under identical reaction conditions showed remarkable mechanistic differences which are discussed in detail. The discussion is extended to include the details on previously studied ammonolysis of these two types of esters wherein thiolesters showed differed reactivity than that reported in the present study.
Acid dissociation constants of phenols and reaction mechanism for the reactions of substituted phenyl benzoates with phenoxide anions in absolute ethanol
Um, Ik-Hwan,Hong, Yeon-Ju,Kwon, Dong-Sook
, p. 5073 - 5082 (2007/10/03)
Acid dissociation constants of 10 substituted phenols have been measured by a kinetic method together with second-order rate constants for the reactions of aryl benzoates (X-C6H4CO-OC6H4-Y) with Z-substituted phenoxide (Z-C6H4O-) and EtO- in absolute ethanol at 25.0 ± 0.1°C. The kinetic results support a stepwise mechanism for the present acyl-transfer reaction.
ALKALINE HYDROLYSIS OF SUBSTITUTED PHENYL ACETATES CATALYZED BY QUATERNARY AMMONIUM SALTS
Kulic, Jiri,Sussenbek, Jiri,Ptacek, Ales
, p. 2891 - 2895 (2007/10/02)
Alkaline hydrolysis of the phenyl acetates CH3COOC6H4X (X = 4-NO2, 3-NO2, 3-Cl, H, 4-CH3, 3-CH3, and 4-OCH3) in the presence of hexadecyltris(2-hydroxyethyl)ammonium chloride, bis(2-hydroxyethyl)hexadecyl(methyl)ammonium bromide, and hexadecyltrimethylamm
The Effect of Hydrogen Bonding between Methyl-Substituted Phenols and Dipolar Aprotic Solvents on the Rate Constants for Protonation of Anthracene Anion Radical
Nielsen, Merete Folmer,Hammerich, Ole
, p. 883 - 896 (2007/10/02)
The kinetics for the protonation of anthracene anion radical (A-anion radical) by phenol and 13 methyl-substituted phenols (ArOH) have been studied by derivative cyclic voltammery in dimethyl sulfoxide, N,N-dimethylformamide, propylene carbonate and acetonitrile.The observed rate constants were corrected for the stoichiometric effects of formation of the homoconjugation complexes, ArOH/ArO- and Ar/OH/ArOH/ArO- and the kinetic contributions from protonation of A-anion radical by ArOH dimers.Available data for equilibrium (1) show that ArOH exists in solution predominantly as the ArOH/solvent hydrogen bond complex with only minor amounts of the 'free' ArOH present.It is suggested that the protonation of A-anion radical involves only the free ArOH in the proton transfer step (II).The unique rate constants corrected for the effect of equilibrium (I) were between two and three orders of magnitude higher than those usually referred to as the second-order rate constants for protonation of A-anion radical.ArOH/solvent ArOH + solvent (I) A-anion radical + ArOH AH-radical + ArO- (II).The kinetic effect of methyl substituents in the 2,6-positions of the phenol was observed to depend on the solvent.It was found that these effects could be satisfactority accounted for by the influence of the 2,6-methyl substituents on the magnitude of K1.The 'best' values of the substituent constants, ?b2 and ?b2.6, defined by the protonation of A-anion radical were found to be between those defined by equilibrium (1) and those defined by the unique equilibrium acidity of the phenols.This is taken as an indication that the phenol O-H bond is stretched considerably in the transition state for protonation of A-anion radical.From the relation between kII and ΔG deg it was found that the Broensted α value for the process is close to 0.5.
Aminopyrine and Antipyrine Free Radical-cations: Pulse Radiolysis Studies of One-electron Transfer Reactions
Forni, Luigi G.,Mora-Arellano, Victor O.,Packer, John E.,Willson, Robin L.
, p. 1579 - 1584 (2007/10/02)
Absolute rate constants for the reaction of a variety of electrophilic free radicals with the pyrazoline derivatives aminopyrine and antipyrine have been measured by pulse radiolysis.In the case of aminopyrine the resulting radical cation is a particularly stable species ε325 5.35*103 dm3 mol-1 cm-1).Both compounds are readily oxidised to their respective radical-cations with the one-electron oxidation potential of antipyrine (E0 1.1-1.6 V) being higher than that of aminopyrine (E0 0.26-0.5 V).Studies of the reaction of the radical-cations with reducing agents suggest that aminopyrine in particular may prove to be a useful reference compound in studies of free radical one-electron oxidations.
