- Evidence of substituent-induced electronic interplay. Effect of the remote aromatic ring substituent of phenyl benzoates on the sensitivity of the carbonyl unit to electronic effects of phenyl or benzoyl ring substituents
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Carbonyl carbon 13C NMR chemical shifts δC(C=O) measured in this work for a wide set of substituted phenyl benzoates p-Y-C 6H4CO2C6H4-p-X (X = NO2, CN, Cl, Br, H, Me, or MeO; Y = NO2, Cl, H, Me, MeO, or NMe2) have been used as a tool to study substituent effects on the carbonyl unit. The goal of the work was to study the cross-interaction between X and Y in that respect. Both the phenyl substituents X and the benzoyl substituents Y have a reverse effect on δC(C=O). Electron-withdrawing substituents cause shielding while electron-donating ones have an opposite influence, with both inductive and resonance effects being significant. The presence of cross-interaction between X and Y could be clearly verified. Electronic effects of the remote aromatic ring substituents systematically modify the sensitivity of the C=O group to the electronic effects of the phenyl or benzoyl ring substituents. Electron-withdrawing substituents in one ring decrease the sensitivity of δC(C=O) to the substitution of another ring, while electron-donating substituents inversely affect the sensitivity. It is suggested that the results can be explained by substituent-sensitive balance of the contributions of different resonance structures (electron delocalization, Scheme 1).
- Neuvonen, Helmi,Neuvonen, Kari,Pasanen, Paavo
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Read Online
- Synthesis and structure-activity relationships of small-molecular di-basic esters, amides and carbamates as flaviviral protease inhibitors
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Inhibitors of the flaviviral serine proteases, which are crucial for the replication of dengue and West-Nile virus, have attracted much attention over the last years. A dibasic 4-guanidinobenzoate was previously reported as inhibitor of the dengue protease with potency in the low-micromolar range. In the present study, this lead structure was modified with the intent to explore structure-activity relationships and obtain compounds with increased drug-likeness. Substitutions of the guanidine moieties, the aromatic rings, and the ester with other functionalities were evaluated. All changes were accompanied by a loss of inhibition, indicating that the 4-guanidinobenzoate scaffold is an essential element of this compound class. Further experiments indicate that the target recognition of the compounds involves the reversible formation of a covalent adduct.
- Sundermann, Tom R.,Benzin, Clarissa V.,Dra?i?, Tonko,Klein, Christian D.
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p. 187 - 194
(2019/05/21)
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- Sodium cyanide-promoted copper-catalysed aerobic oxidative synthesis of esters from aldehydes
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A simple and efficient copper-catalysed procedure for oxidative esterification of aldehydes with alcohols and phenols mediated by sodium cyanide, using air as a clean oxidant, is described. A variety of aromatic aldehydes and structurally different alcohols and phenols reacted efficiently, and the product esters were obtained in good to excellent yields under normal atmospheric and solvent-free conditions.
- Nowrouzi, Najmeh,Abbasi, Mohammad,Bagheri, Maryam
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- Olefins from biomass feedstocks: Catalytic ester decarbonylation and tandem Heck-type coupling
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With the goal of avoiding the need for anhydride additives, the catalytic decarbonylation of p-nitrophenylesters of aliphatic carboxylic acids to their corresponding olefins, including commodity monomers like styrene and acrylates, has been developed. The reaction is catalyzed by palladium complexes in the absence of added ligands and is promoted by alkali/alkaline-earth metal halides. Combination of catalytic decarbonylation and Heck-type coupling with aryl esters in a single pot process demonstrates the viability of employing a carboxylic acid as a "masked olefin" in synthetic processes. This journal is
- John, Alex,Hogan, Levi T.,Hillmyer, Marc A.,Tolman, William B.
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supporting information
p. 2731 - 2733
(2015/03/05)
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- Kinetic study on nucleophilic substitution reactions of 4-Nitrophenyl X-Substituted-Benzoates with potassium ethoxide: Reaction mechanism and role of K+ Ion
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A kinetic study on nucleophilic substitution reactions of 4-nitrophenyl X-substituted-benzoates (7a-i) with EtOK in anhydrous ethanol at 25.0 ± 0.1 °C is reported. The plots of pseudo-first-order rate constants (kobsd) vs. [EtOK] curve upward. Dissection of kobsd into the second-order rate constants for the reactions with the dissociated EtOV and ion-paired EtOK (i.e., kEtO-and kEtOK, respectively) has revealed that the ion-paired EtOK is more reactive than the dissociated EtOV. Hammett plots for the reactions of 7a-i with the dissociated EtOV and ion-paired EtOK exhibit excellent linear correlations with aX = 3.00 and 2.47, respectively. The reactions have been suggested to proceed through a stepwise mechanism in which departure of the leaving-group occurs after the RDS. The correlation of the kEtOK/kEtO{ ratio with the aX constants exhibits excellent linearity with a slope of V0.53. It is concluded that the ion-paired EtOK catalyzes the reaction by increasing the electrophilicity of the reaction center rather than by enhancing the nucleofugality of the leaving group.
- Kim, Song-I,Kim, Min-Young,Um, Ik-Hwan
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p. 225 - 230
(2014/02/14)
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- Aminolysis of Y-substituted-phenyl 2-methoxybenzoates in acetonitrile: Effect of the o-methoxy group on reactivity and reaction mechanism
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Second-order rate constants (kN) were measured for aminolyses of Y-substituted-phenyl 2-methoxybenzoates 2a-i and 4-nitrophenyl X-substituted-benzoates 3a-j in MeCN at 25.0 °C. The Bronsted-type plot for the reactions of 2a-i with piperidine curves downward, indicating that a change in rate-determining step (RDS) occurs. The Hammett plot for the reactions of 3a-j with piperidine consists of two intersecting straight lines, which might be taken as evidence for a change in RDS. However, the nonlinear Hammett plot has been suggested not to be due to a change in RDS but rather to the stabilization of the ground state of substrates possessing an electron-donating group (EDG) (e.g., 3a-c) through a resonance interaction, since the corresponding Yukawa-Tsuno plot exhibits an excellent linear correlation with ρ = 0.54 and r = 1.54. The ρ value found for the reactions of 3a-j in MeCN is much smaller than that reported previously for the corresponding reactions in H2O (i.e., ρ = 0.75). It is proposed that the reactions of 3a-j in MeCN proceed through a forced concerted mechanism due to instability of T± in the aprotic solvent, while the reactions of 2a-i proceed through a stepwise pathway with a stabilized T ± through an intramolecular H-bonding interaction.
- Um, Ik-Hwan,Bae, Ae Ri
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experimental part
p. 7510 - 7515
(2011/11/13)
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- 5,5′-Dimethyl-3,3′-azoisoxazole as a new heterogeneous azo reagent for esterification of phenols and selective esterification of benzylic alcohols under Mitsunobu conditions
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5,5′-Dimethyl-3,3′-azoisoxazole is used as a new efficient heterogeneous azo reagent for the highly selective esterification of primary and secondary benzylic alcohols and phenols with aliphatic and aromatic carboxylic acids via Mitsunobu protocols. The reaction is highly selective for primary benzylic alcohols versus secondary ones, aliphatic alcohols and also phenols. The isoxazole hydrazine byproduct can be simply isolated by filtration and recycled to its azoisoxazole by oxidation.
- Iranpoor, Nasser,Firouzabadi, Habib,Khalili, Dariush
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supporting information; experimental part
p. 4436 - 4443
(2010/11/05)
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- Effective esterification of carboxylic acids using (6-oxo-6H-pyridazin-1-yl)phosphoric acid diethyl ester as novel coupling agents
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(6-Oxo-6H-pyridazin-1-yl)phosphoric acid diethyl esters (3) are efficient and selective coupling agents for equimolar esterification of carboxylic acids and alcohols. Esterification of aliphatic and aromatic carboxylic acids with aliphatic and aromatic alcohols using 3 afforded the corresponding esters chemoselectively in good to excellent yield.
- Won, Ju-Eun,Kim, Ho-Kyun,Kim, Jeum-Jong,Yim, Heong-Seup,Kim, Min-Jung,Kang, Seung-Beom,Chung, Hyun-A.,Lee, Sang-Gyeong,Yoon, Yong-Jin
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p. 12720 - 12730
(2008/03/14)
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- Investigation of a general base mechanism for ester hydrolysis in C-C hydrolase enzymes of the α/β-hydrolase superfamily: A novel mechanism for the serine catalytic triad
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Previous mechanistic and crystallographic studies on two C-C hydrolase enzymes, Escherichia coli MhpC and Burkholderia xenovorans BphD, support a general base mechanism for C-C hydrolytic cleavage, rather than the nucleophilic mechanism expected for a ser
- Li, Jian-Jun,Bugg, Timothy D. H.
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p. 507 - 513
(2008/03/28)
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- Structure-reactivity correlations in nucleophilic substitution reactions of Y-substituted phenyl X-substituted benzoates with anionic and neutral nucleophiles
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A kinetic study is reported for the reactions of 4-nitrophenyl X-substituted benzoates (1a-l) and Y-substituted phenyl benzoates (2a-l) with two anionic nucleophiles (OH- and CN-) and three amines (piperidine, hydrazine, and glycylglycine) in 80 mol% H2O-20 mol% dimethyl sulfoxide (DMSO) at 25.0 ± 0.1 °C. Each Hammett plot exhibits two intersecting straight lines for the reactions of 1a-l with the anionic nucleophiles and piperidine, while the Yukawa-Tsuno plots for the same reactions are linear. The Hammett plots for the reactions of 2a-l with hydrazine and glycylglycine demonstrate much better linear correlations with σ- constants than with σ° or σ constants, indicating that the leaving group departure occurs at the rate determining step (RDS). On the contrary, σ- constants result in poorer Hammett correlation than σ° constants for the corresponding reactions with OH- and CN-, indicating that the leaving group departure occurs after the RDS for the reactions with the anionic nucleophiles. The large ρX value (1.7 ± 0.1) obtained for the reactions of 1a-l with the anionic nucleophiles supports the proposal that the reactions proceed through an addition intermediate with its formation being the RDS. The Royal Society of Chemistry 2006.
- Um, Ik-Hwan,Lee, Ji-Youn,Fujio, Mizue,Tsuno, Yuho
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p. 2979 - 2985
(2008/02/11)
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- Kinetics of the reaction of 4-nitrophenyl benzoates with 4-chlorophenol in the presence of potassium carbonate in dimethylformamide
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The effect of the substituent in the benzoyl group on the relative rate and activation parameters of transesterification of substituted 4-nitrophenyl benzoates with 4-chlorophenol in dimethylformamide in the presence of potassium carbonate was studied by the competing reaction technique. The whole series of benzoates showed the enthalpy-entropy compensation effect. 4-Nitrophenyl benzoates having electronacceptor substituents give rise to isokinetic relationship with an isokinetic temperature β of 382 K. The mechanism of the transesterification process is discussed. Pleiades Publishing, Inc., 2006.
- Os'kina,Vlasov
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p. 865 - 872
(2007/10/03)
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- Polymerizable dichromophoric dichroic azo dyes
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The present invention is directed towards polymerizable dichromophoric dichroic azo dyes comprising azo-chromophores to which polymerizable groups are attached leading to dyes having sufficient solubility in combination with high coloring power and high order parameter.
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Page/Page column 14
(2010/02/14)
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- Synthesis of dinuclear complexes of rhenium(I) as potential metallomesogens
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Seven anisotropic diimines and their corresponding dinuclear complexes of rhenium(i) have been synthesized. The crystal and molecular structures of one of the dimines and two of the complexes were determined. In common with related inline ligands which have been synthesized previously, the new diimines were mesomorphic showing smectic C and nematic phases and, in some cases, smectic I and crystal J phases. However, none of the orthometallated, dinuclear complexes showed any liquid crystal phases. The Royal Society of Chemistry 2000.
- Guillevic, Marie-Andree,Light, Mark E.,Coles, Simon J.,Gelbrich, Thomas,Hursthouse, Michael B.,Bruce, Duncan W.
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p. 1437 - 1445
(2007/10/03)
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- Nucleophilic displacement at the benzoyl centre: A study of the change in geometry at the carbonyl carbon atom
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The second-order rate constants for the reaction between hydroxide ion and phenoxide ion with 4-nitrophenyl esters of substituted benzoic acids in 10% acetonitrile-water (v/v) solution obey Hammett σ correlations. The values of the Hammett ρ of 1.67 (κArO) and 2.14 (κOH) are consistent with a large change in hybridization at the central carbon by comparison with the ρ value for a standard reaction where a full sp2 to sp3 change occurs. The transition state for the concerted reaction thus has a substantially tetrahedral geometry. The observation of the anti-Hammond effect whereby the ρ value for the hydroxide ion exceeds that of the less reactive phenoxide ion is consistent with a concerted, ANDN, mechanism for these reactions. A stepwise mechanism, AN + DN, is unlikely to yield a measurable break in the Hammett correlation for a change in the benzoyl substituent if the partitioning of the putative tetrahedral intermediate involves forward and reverse reactions with Hammett correlations possessing similar ρ values.
- Colthurst, Matthew J.,Williams, Andrew
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p. 1493 - 1497
(2007/10/03)
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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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- MECHANISM OF ESTER AMINOLYSIS IN APROTIC MEDIA AND SPECIFIC SOLVENT EFFECTS
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The n-butylaminolysis of nitro-substituted 4'-nitrophenyl benzoates and cinnamates as well as of phenylacetates in aprotic solvents is governed by a kinetic law implying higher order terms in nucleophile.It is shown that the attacking nucleophile forms a n-? type molecular complex with the substrate before reaching the transition state in the subsequent kinetic step.This molecular complex is a true reaction intermediate as evidenced by the observed negative activation enthalpy.Other nucleophile molecules intervene as general base catalysts.Tertiary amines also catalyse the reaction.Their catalytic activity is linearly related to their hydrogen bond forming ability and it is not a direct function of their proton basicity.By varying the nucleophile structure, an excellent Broensted relationship could be obtained for the first time in aprotic media, the β of which confirms that the catalytic collapse of tetrahedral intermediate is the rate determining step.The reaction of cinnamates turns out to be less sensitive to structural changes of the substrate than is the reaction of benzoates as shown by the corresponding Hammet ? values.The electronic effects of 2-nitro groups are strongly solvent dependent.Once more, it is established that whenever specific solvent effects (?-donor or n-donor ability) are present, they dominate the overall effect.A general reaction mechanism is proposed which not only explains the various roles played by the nucleophile but also accounts successfully for the great variety of kinetic schemes observed in aprotic media.
- Nagy, Otto B.,Reuliaux, Victor,Bertrand, Nicole,Mensbrugghe, Anne Van Der,Leseul, Jean,Nagy, Janos B.
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p. 1055 - 1074
(2007/10/02)
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- The Reactivity of p-Nitrophenyl Esters with Surfactants in Apolar Solvents. VII. Substituent Effects on the Reactivity of 4'-Nitrophenyl 4-Substituted Benzoates in Benzene Solutions of Dodecylammonium Propionate and Butane-1,4-diamine Bis(dodecanoate)
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The rate of decomposition of a series of 4'-nitrophenyl 4-substituted benzoates has been measured at 341 K in benzene solutions of dodecylammonium propionate and butane-1,4-diamine bis(dodecanoate).The bimolecular rate constant due to general acid-general
- O'Connor, Charmian J.,Lomax, Terence D.
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p. 917 - 925
(2007/10/02)
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