- Ph3P-I2 mediated aryl esterification with a mechanistic insight
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In order to better understand the reaction mechanism and to obtain optimal conditions, the Ph3P-I2/Et3N mediated aryl esterification reaction was thoroughly investigated. Using a specific reagent addition sequence, the reaction proceeds remarkably well especially with acidic substrates. 31P NMR studies revealed that the formation of an aryloxyphosphonium salt is crucial in governing the reaction path toward the formation of phenolic esters.
- Phakhodee, Wong,Duangkamol, Chuthamat,Pattarawarapan, Mookda
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supporting information
p. 2087 - 2089
(2016/04/26)
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- Benzoyl peroxide-imidazole: A novel and efficient reagent for the mild conversion of alcohols or phenols into benzoates
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A very mild, one-pot, and expedient protocol for the conversion of alcohols and phenols into their corresponding benzoates using imidazole and benzoyl peroxide as a novel reagent is described.
- Nowrouzi, Najmeh,Alizadeh, Seyedeh Zahra
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p. 2412 - 2414
(2013/06/26)
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- Hydrolysis of 1-(X-substituted-benzoyl)-4-aminopyridinium ions: Effect of substituent X on reactivity and reaction mechanism
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A kinetic study is reported for hydrolysis of 1-(X-substituted-benzoyl)-4- aminopyridinium ions 2a-i, which were generated in situ from the nucleophilic substitution reaction of 2,4-dinitrophenyl X-substituted-benzoates 1a-i with 4-aminopyridine in 80 mol% H2O/20 mol% DMSO at 25.0 ± 0.1 °C. The plots of pseudo-first-order rate constants kobsdvs. pyridine concentration are linear with a large positive intercept, indicating that the hydrolysis of 2a-i proceeds through pyridine-catalyzed and uncatalyzed pathways with the rate constant kcat and ko, respectively. The Hammett plots for kcat and ko consist of two intersecting straight lines, which might be taken as evidence for a change in the rate-determining step (RDS). However, it has been proposed that the nonlinear Hammett plots are not due to a change in the RDS but are caused by stabilization of 2a-i in the ground state through a resonance interaction between the π-electron-donor substituent X and the carbonyl functionality. This is because the corresponding Yukawa-Tsuno plots exhibit excellent linear correlations with ρX = 1.45 and r = 0.76 for kcat while ρX = 1.39 and r = 0.72 for ko. A possibility that the hydrolysis of 2a-i proceeds through a concerted mechanism has been ruled out on the basis of the large ρX values. Thus, the reaction has been concluded to proceed through a stepwise mechanism in which the leaving group departs after the RDS since OH- is more basic and a poorer nucleofuge than 4-aminopyridine. The Royal Society of Chemistry 2011.
- Um, Ik-Hwan,Kim, Eun-Hee,Kang, Ji-Sun
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experimental part
p. 8062 - 8067
(2012/01/04)
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- Kinetics and mechanism of nucleophilic displacement reactions of Y-substituted phenyl benzoates with cyanide Ion
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Second-order rate constants (kCN-) have been measured for nucleophilic substitution reactions of Y-substituted phenyl benzoates (1a-r) with CN- ion in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Bronsted-type plot is linear with βlg = -0.49, a typical βlg value for reactions reported to proceed through a concerted mechanism. Hammett plots correlated with σo and σ-constants exhibit many scattered points. In contrast, the Yukawa-Tsuno plot for the same reaction exhibits excellent linearity with pY = 1.37 and r = 0.34, indicating that a negative charge develops partially on the oxygen atom of the leaving aryloxide in the rate-determining step (RDS). Although two different mechanisms are plausible (i.e., a concerted mechanism and a stepwise pathway in which expulsion of the leaving group occurs at the RDS), the reaction has been concluded to proceed through a concerted mechanism on the basis of the magnitude of βlg and pY values.
- Kim, Song-I,Kim, Eun-Hee,Um, Ik-Hwan
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experimental part
p. 689 - 693
(2010/08/19)
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- Nonlinear Hammett plots in pyridinolysis of 2,4-dinitrophenyl X-substituted benzoates: Change in RDS versus resonance contribution
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Second-order rate constants (kOH-) have been measured for nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzoates (1a-j) with Z-substituted pyridines in 80 mol% H2O/20 mol% DMSO at 25.0 ± 0.1 °C. The Hammett plots for the reactions of 1a-j with pyridines consist of two intersecting straight lines, i.e., a large ρ value for the reactions of substrates (1a-c) possessing an electron-donating group (EDG) in the benzoyl moiety and a small one for substrates (1e-j) bearing an electron-withdrawing group (EWG). The nonlinear Hammett plots have been attributed to stabilization of the ground state of substrates 1a-c through resonance interactions between the electron-donating substituent and the carbonyl functionality, since the corresponding Yukawa-Tsuno plots exhibit excellent linear correlations with large r values. It has been shown that substrates 1e-j are not unusually more reactive than would be expected from the Hammett substituent constants, but rather, substrates 1a-c exhibit lower reactivity than would be predicted. The Bronsted-type plots for pyridinolysis of 1a-j are linear with βnuc = 0.74-0.98, indicating that the reaction proceeds through a stepwise mechanism in which the second step is the RDS. It has been concluded that the electronic nature of the substituent X in the benzoyl moiety does not influence the RDS, but the degree of bond formation (or the effective charge on the nucleophilic site) in the transition state becomes more significant as the substituent X changes from a strong EDG to a strong EWG.
- Um, Ik-Hwan,Im, Li-Ra,Kim, Eun-Hee,Shin, Ji Hye
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experimental part
p. 3801 - 3806
(2010/09/06)
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- Aminolysis of 2,4-dinitrophenyl X-substituted benzoates and Y-substituted phenyl benzoates in MeCN: Effect of the reaction medium on rate and mechanism
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Second-order rate constants (kN) have been determined spectrophotometrically for the reactions of 2,4-di-nitrophenyl X-substituted benzoates (1a-f) and Y-substituted phenyl benzoates (2a-h) with a series of alicyclic secondary amines in MeCN at
- Um, Ik-Hwan,Jeon, Sang-Eun,Seok, Jin-Ah
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p. 1237 - 1243
(2008/09/18)
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- Zinc oxide (ZnO) as a new, highly efficient, and reusable catalyst for acylation of alcohols, phenols and amines under solvent free conditions
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Zinc oxide (ZnO) is a highly efficient catalyst for the acylation of a variety of alcohols, phenols and amines with acid chlorides or acid anhydrides under solvent free conditions. Primary, secondary, tertiary, allylic and benzylic alcohols, diols and phenols with electron donating or withdrawing substituents can be easily acylated in good to excellent yield.
- Hosseini Sarvari, Mona,Sharghi, Hashem
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p. 10903 - 10907
(2007/10/03)
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- Effects of amine nature and nonleaving group substituents on rate and mechanism in aminolyses of 2,4-dinitrophenyl x-substituted benzoates
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Second-order rate constants have been measured for the reactions of 2,4-dinitrophenyl X-substituted benzoates (1a-f) with a series of primary amines in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Bronsted-type plot for the reactions of 1d with primary amines is biphasic with slopes β1 = 0.36 at the high pKa region and β2 = 0.78 at the low pKa region and the curvature center at pKa° = 9.2, indicating that the reaction proceeds through an addition intermediate with a change in the rate-determining step as the basicity of amines increases. The corresponding Bro nsted-type plot for the reactions with secondary amines is also biphasic with β1 = 0.34, β2 = 0.74, and pKa° = 9.1, indicating that the effect of amine nature on the reaction mechanism and pKa° is insignificant. However, primary amines have been found to be less reactive than isobasic secondary amines. The microscopic rate constants associated with the aminolysis have revealed that the smaller k 1 for the reactions with primary amines is fully responsible for their lower reactivity. The electron-donating substituent in the nonleaving group exhibits a negative deviation from the Hammett plots for the reactions of 1a-f with primary and secondary amines, while the corresponding Yukawa-Tsuno plots are linear. The negative deviation has been ascribed to stabilization of the ground state of the substrate through resonance interaction between the electron-donating substituent and the carbonyl functionality.
- Um, Ik-Hwan,Kim, Kyung-Hee,Park, Hye-Ran,Fujio, Mizue,Tsuno, Yuho
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p. 3937 - 3942
(2007/10/03)
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- Mechanism of catalysis with triethylamine of phenols benzoylation in dioxane. New quality experiment
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Acylation kinetics with benzoyl chloride in the presence of triethylamine in dioxane at 25°C was studied for substituted nitrophenols (R = 2,4,6-(NO2)3, 2,5-(NO2)2, 2,4-(NO2)2, 4-NO2/
- Belousova,Simanenko,Savelova,Suprun
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p. 1656 - 1664
(2007/10/03)
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- A new highly regioselective reaction of unprotected sugars for chemical synthesis of 6-acyl-D-glycopyranosides
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New methodologies developed to synthesize 6-acyl-D-glycopyranosides are described. Thus, regioselective acylation of non protected glycopyranosides was performed using acyl-p-nitrothiophenol esters and acyl-2,4-dinitrophenol esters as the acylating reagen
- Xia,Hui
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p. 2235 - 2251
(2007/10/02)
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- Imidazole-Catalyzed Hydrolysis of Substituted Benzoate Esters. A Detailed Kinetic and Mechanistic Study
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Kinetic and mechanistic details of the imidazole-catalyzed hydrolysis of substituted phenyl benzoates in 10percent acetonitrile in water (V/V) were examined.The following 4 ester series were studied: p-nitrophenyl p-X-benzoates (X = CH3, H, Cl, CN, NO2, series I), p-Y-phenyl p-nitrobenzoates (Y = CH3, H, Cl, CN, NO2, series II), 2,4-dinitrophenyl p-X-benzoates (X = CH3O, H, Cl, CN, NO2, series III) and p-Y-phenyl 2,4-dinitrobenzoates (Y = CH3, H, Cl, CN, NO2, series IV).Based on: catalytic rate constants, activation parameters, kinetic solvent isotope effects, Hammett (ρ) values and the spectroscopic detection of the reaction intermediates, the following conclusions were reached: a) imidazole acts as a nucleophilic catalyst, i.e., the hydrolysis occurs via the intermediate formation of acylimidazole; b) the leaving group is the phenoxide ion; c) the rate limiting step is the decomposition of the tetrahedral intermediate that precedes the acylimidazole (series I, II and IV) or the attack of imidazole on the acyl group of the ester (series III). Keywords: Acylimidazoles / Catalysis / Chemical Kinetics / Isotope Effects / Reaction Mechanism
- Menegheli, Paulo,Farah, Joao P. S.,Seoud, Omar A. El
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p. 1610 - 1615
(2007/10/02)
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- Water-Soluble Acylating Agents: Preparation of 2-Acylthio-1-alkylpyridinium Salts and Acylation of Phenols, Acids, and/or Amines with These Salts in an Aqueous Phase
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Reaction of phenols, amines, and acids with 2-benzoylthio-1-methylpyridinium chloride prepared in situ from benzoyl chloride and 1-methyl-2(1H)-pyridinethione, afforded the corresponding benzoyl derivatives in good yields.In the reaction of p-nitrophenol, even catalytic amount of 1-methyl-2(1H)-pyridinethione proved to be effective.Similar reactions of p-nitrophenol with isobutyryl chloride and acetyl chloride in the presence of 1-methyl-2(1H)-pyridinethione afforded p-nitrophenyl isobutyrate and p-nitrophenyl acetate in 63 and 44percent yields, respectively. 2-Benzoylthio-, 2-acetylthio-, and 2-isobutyrylthio-1-ethylpyridinium tetrafluorobora tes were prepared by treatment of the corresponding 2-acylthiopyridines with triethyloxonium tetrafluoroborate.These pyridinium salts also acted as acylating agents in an aqueous phase. some competitive reactions of 2-aminoethanol and phenols with 2-benzoylthio-1-methylpyridinium chloride were also investigated.
- Sakakibara, Tohru,Watabe, Yukie,Yamada, Masahide,Sudoh, Rokuro
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p. 247 - 254
(2007/10/02)
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- POLY(ETHYLENE GLYCOL) DERIVATIVES AS COMPLEXING AGENTS AND PHASE-TRANSFER CATALYSTS, VII. BEHAVIOUR OF ANIONS IN THE PRESENCE OF DIFFERENT PHASE-TRANSFER CATALYSTS
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The changes in anion reactivity in the organic phase on addition of excess onium salts to a phase-transfer system containing poly(ethylene glycol) complex cations have been studied.The results permit conclusions concerning the behaviour of various phase-t
- Szabo, G. T.,Geroe, K.,Toeke, L.
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- POLYETHYLENE GLYCOLS AS COMPLEXING AGENTS AND PHASE-TRANSFER CATALYSTS, V; REACTION RATES IN THE ORGANIC PHASE
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Rates of the reaction between benzoyl chloride and 2,4-dinitrophenolates have been studied in benzene solution containing polyethers.Tertiary amines have been found to accelerate these reactions.A model was proposed for tertiary amine catalyzed phase-tran
- Szabo, G. T.,Aranyosi, K.,Toeke, L.
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p. 225 - 230
(2007/10/02)
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