18938-12-0Relevant articles and documents
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 (2005)
(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.
Transition-state variation in the nucleophilic substitution reactions of aryl bis(4-methoxyphenyl) phosphates with pyridines in acetonitrile
Lee, Hai Whang,Guha, Arun Kanti,Kim, Chang Kon,Lee, Ikchoon
, p. 2215 - 2222 (2007/10/03)
The kinetics and mechanism of the reactions of Z-aryl bis(4-methoxyphenyl) phosphates, (4-MeOC6H4O)2P(=O) OC6H4Z, with pyridines (XC5H4N) are investigated in acetonitrile at 55.0 °C. In the case of more basic phenolate leaving groups (Z = 4-Cl, 3-CN), the magnitudes of βx (βnuc) and βz (βlg) indicate that mechanism changes from a concerted process (βx = 0.22-0.36, βz = -0.42 to -0.56) for the weakly basic pyridines (X = 3-Cl, 4-CN) to a stepwise process with rate-limiting formation of a trigonal bipyramidal pentacoordinate (TBP-5C) intermediate (βx = 0.09-0.14, βz = -0.08 to -0.28) for the more basic pyridines (X = 4-NH2, 3-CH3). This proposal is supported by a large negative cross-interaction constant (ρxz = -1.98) for the former and a positive ρxz(+0.97) for the latter processes. In the case of less basic phenolate leaving groups (Z = 3-CN, 4-NO2), the unusually small magnitude of βz values is indicative of a direct backside attack TBP-5C TS in which the two apical sites are occupied by the nucleophile and leaving group, ap(NX)-ap(LZ). The instability of the putative TBP-5C intermediate leading to a concerted displacement is considered to result from relatively strong proximate charge transfer interactions between the π-lone pairs on the directly bonded equatorial oxygen atoms and the apical bond (no(eq) - ?*(ap)). These are supported by the results of natural bond orbital (NBO) analyses at the NBO-HF/6-311+G**//B3LYP/6-311+G** level of theory.
Kinetics and mechanism of phosphate-catalyzed hydrolysis of benzoate esters: Comparison with nucleophilic catalysis by imidazole and o-iodosobenzoate
El Seoud, Omar A.,Ruasse, Marie-Francoise,Rodrigues, Wagner A.
, p. 1053 - 1058 (2007/10/03)
Phosphate-catalyzed hydrolysis of 2,4-dinitrophenyl 4-X-benzoate, and 3- or 4-Y-phenyl 3,5-dinitrobenzoates, where X and Y are substituents, has been studied spectrophotometrically. The following conclusions are based on catalytic rate constants, solvent
Electrochemistry of electron transfer probes. α-aryloxyacetoveratrones and implications for the mechanism of photo-yellowing of pulp1
Andersen, Mogens L.,Wayner, Danial D. M.
, p. 830 - 836 (2007/10/03)
Standard potentials (Eo) of a series of substituted α-aryloxyacetoveratrone derivatives have been determined from a correlation of the 13C NMR chemical shifts of the carbonyl group and a similar correlation (Eo vs. 13C NMR shifts) within a series of α-anilinoacetoveratrones. Using these potentials the rate constants for fragmentation of the radical anions were determined by digital simulation of the voltammetric waves. The rate contants for C O cleavage in the radical anions correlate with the pKa of the corresponding phenols. The fragmentations are all in the activated region of a general free energy relationship for this class of compound (α = 0.5). The standard potential and rate constant for fragmention of the α-guaiacoxyacetoveratrone radical anion also were determined. This species is a model compound for one of the lignin substructures. The implication of these results on the currently accepted mechanism for photo-yellowing of lignin rich paper is discussed.
Electrochemistry of electron-transfer probes. The role of the leaving group in the cleavage of radical anions of α-aryloxyacetophenones
Andersen, Mogens L.,Mathivanan,Wayner, Danial D. M.
, p. 4871 - 4879 (2007/10/03)
The formal reduction potential (E°) of α-phenoxyacetophenone has been determined from the voltammetric peak potential obtained by linear sweep voltammetry in combination with the rate constant for fragmentation of the radical anion which had been determin
