- A Lanthanum Macrocycle catalysed Hydrolysis of a Phosphate Triester
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A lanthanum macrocycle is shown to be an effective catalyst for the hydrolysis of the phosphate triester 2,4-dinitrophenyl diethyl phosphate, at pH 9 the rate enhancement using 2.5*1E-3 mol dm-3 catalyst at 25 deg C being ca. 1E3-fold; the reaction is shown to be catalytic rather than stoicheiometric, and possible mechanisms are considered to account for the catalysis.
- Hay, Robert W.,Govan, Norman
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- Footprint Catalysis. III. Inducible Alteration of Substrate Specificities of Silica(Alumina) Gel Catalysts for 2,4-Dinitrophenolysis of Toluic Anhydrides by Footprint Imprinting
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A tailor-made catalyst design was attempted for a required substrate specificity by the authors' footprint imprinting method.Two silica(alumina) footprint catalysts were prepared by imprinting with N-benzoylbenzenesulfonamide (1) and N-(p-toluoyl)-p-toluenesulfonamide (2) from the same aluminium iondoped silica gel.Their catalytic effects upon 2,4-dinitrophenolysis of benzoic anhydride, p-, m-, and o-toluic anhydrides were compared in order to find any difference in substrate specificities.The catalyst prepared by imprinting with 1 showed the largest specificity (kcat/Km) toward benzoic anhydride, whereas the catalyst prepared with 2 showed the largest specificity toward p-toluic anhydride.This finding evidently demonstrated that the substrate specificities of footprint catalytic sites are alterable, as required through selecting appropriate transition state analogs as template molecules for footprint marking.
- Morihara, Kensaku,Tanaka, Eiko,Takeuchi, Yuko,Miyazaki, Kazue,Yamamoto, Nami,et al.
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- Enthalpy-entropy correlations in reactions of 2,4-dinitrophenyl benzoate with phenols in the presence of potassium hydrogen carbonate and with potassium phenoxides in dimethylformamide
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Temperature dependences of the relative reactivity of substituted phenols RC6H4OH in the presence of potassium hydrogen carbonate and of potassium phenoxides RC6H4O-K + toward 2,4-dinitrophenyl benzoate in dimethylformamide were studied using the competitive reactions technique. Correlation analysis of the relative rate constants kR/kH and differences in the activation parameters (ΔΔH{double barred pipe} and ΔΔS{double barred pipe}) of competitive reactions revealed the existence of two isokinetic series for each type of nucleophiles. The mechanism of transesterification was interpreted in terms of an approach based on analysis of the effect of substituent in the nucleophile on the activation parameters. Pleiades Publishing, Ltd., 2011.
- Khalfina,Vlasov
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- Tuning the intramolecular charge transfer (ICT) process in push-pull systems: Effect of nitro groups
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The intramolecular charge transfer (ICT) process in donor-acceptor systems has tremendous importance in various physical and biological systems. Three nitrophenolate salts were synthesized and studied here. The ICT and π → π? transition processes were identified in these derivatives using UV-Vis spectroscopy and theoretical calculations. It was observed that by simple substitution with nitro groups, one can generate and control the ICT process by regulating the charge distribution over the molecule. While for a monosubstitute nitro derivative, only one ICT band was observed, additional ICT processes can be generated at will by introducing a second nitro group. The intensity of this second ICT channel can be regulated with introduction of a third nitro group. Further, the association constants and solvation processes for these potassium nitrophenolate derivatives were found to be drastically dependent on the number of ICT channels present in the molecule. Theoretical studies (MEP analysis) support the experimental observations presented here. The results show that by simply introducing additional acceptor groups to the system, one can tune the ICT band efficiently in a conjugate system.
- Panja, Sumit Kumar,Dwivedi, Nidhi,Saha, Satyen
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p. 105786 - 105794
(2016/11/18)
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- A kinetic study on nucleophilic displacement reactions of aryl benzenesulfonates with potassium ethoxide: Role of K+ ion and reaction mechanism deduced from analyses of LFERs and activation parameters
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Pseudofirst-order rate constants (kobsd) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2,4-dinitrophenyl X-substituted benzenesulfonates 4a-f and Y-substituted phenyl benzenesulfonates 5a-k with EtOK in anhydrous ethanol. Dissection of k obsd into kEtO- and kEtOK (i.e., the second-order rate constants for the reactions with the dissociated EtO - and ion-paired EtOK, respectively) shows that the ion-paired EtOK is more reactive than the dissociated EtO-, indicating that K + ion catalyzes the reaction. The catalytic effect exerted by K + ion (e.g., the kEtOK/kEtO- ratio) decreases linearly as the substituent X in the benzenesulfonyl moiety changes from an electron-donating group (EDG) to an electron-withdrawing group (EWG), but it is independent of the electronic nature of the substituent Y in the leaving group. The reactions have been concluded to proceed through a concerted mechanism from analyses of the kinetic data through linear free energy relationships (e.g., the Bronsted-type, Hammett, and Yukawa-Tsuno plots). K+ ion catalyzes the reactions by increasing the electrophilicity of the reaction center through a cyclic transition state (TS) rather than by increasing the nucleofugality of the leaving group. Activation parameters (e.g., ΔH? and ΔS?) determined from the reactions performed at five different temperatures further support the proposed mechanism and TS structures.
- Um, Ik-Hwan,Kang, Ji-Sun,Shin, Young-Hee,Buncel, Erwin
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supporting information
p. 490 - 497
(2013/03/13)
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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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- Surfactant-mediated solvent-free dealkylative cleavage of ethers and esters and trans-alkylation under neutral conditions
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A simple, surfactant-mediated, one-pot, solvent-free dealkylative cleavage of aryl ethers and esters followed by subsequent optional trans-alkylation under essentially neutral conditions has been developed.
- Bhattacharya, Apurba,Patel, Nitin C.,Vasques, Tomas,Tichkule, Ritesh,Parmar, Gaurang,Wu, Jiejun
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p. 565 - 567
(2007/10/03)
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- Concerted mechanisms of the reactions of methyl aryl carbonates with substituted phenoxide ions
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The reactions of 4-nitrophenyl, 2,4-dinitrophenyl, and 2,4,6-trinitrophenyl methyl carbonates (NPC, DNPC, and TNPC, respectively) with substituted phenoxide ions are subjected to a kinetic study in water at 25.0 °C, ionic strength 0.2 M (KCl). Production of the leaving groups (the nitro derivatives) is followed spectrophotometrically. Under excess of the phenoxide ions pseudo-first-order rate coefficients (kobsd) are found throughout. Plots of kobsd vs substituted phenoxide concentration at constant pH are linear, with the slope (kN) independent of pH. The Broensted-type plots (log kN vs pKa of the phenols) are linear with slopes β = 0.67, 0.48, and 0.52 for the phenolysis of NPC, DNPC, and TNPC, respectively. The magnitudes of these Broensted slopes are consistent with a concerted mechanism. In the particular case of the phenolysis of NPC the expected hypothetical curvature center of the Broensted plot for a stepwise mechanism should be pKa0 = 7.1 (the pKa of 4-nitrophenol). This curvature does not appear within the pKa range of the substituted phenols studied (5.3-10.3), indicating that these reactions are concerted. The phenolysis of DNPC and TNPC should also be concerted in view of the even more unstable tetrahedral intermediates that would be formed if the reactions were stepwise. The reactions of the same substrates with pyridines are stepwise, which means that substitution of a pyridine moiety in a tetrahedral intermediate by a phenoxy group destabilizes the intermediate perhaps to the point of nonexistence. The kN values for the title reactions are larger than those for the concerted phenolysis of the corresponding ethyl S-aryl thiolcarbonates. The kN values found in the present reactions are subjected to a dual regression analysis as a function of the pKa, of both the nucleophile and leaving group, the coefficients being βN = 0.5 and βig = -0.3, respectively. These coefficients are consistent with a concerted mechanism.
- Castro,Pavez,Santos
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p. 3129 - 3132
(2007/10/03)
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- A new, "elongated" oxo ketene intermediate in the dissociative hydrolysis of 2,4-dinitrophenyl (2E,4E)-5-(4′-hydroxyphenyl)pentadienoate
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(matrix presented) Reactivity comparison, Arrhenius parameters, and trapping of the above-depicted unsaturated intermediate strongly suggest that the alkaline hydrolysis of the title ester follows a mechanism of the E1cB type. This is the first observation of the occurrence of a dissociative route in the hydrolysis of an acyl derivative with three π-systems interposed between the hydroxyl group (the internal nucleophile upon ionization) and the reaction center. Comparison with the hydrolysis of 2,4-dinitrophenyl 4′-hydroxybenzoate shows that interposition of the vinylenic groups is beneficial to the dissociative route.
- Cevasco, Giorgio,Vigo, Daniele,Thea, Sergio
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p. 1165 - 1167
(2008/02/09)
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- Thermal Stability of σ Complexes of Aromatic Dinitro Compounds with Alkali Metal Methylates
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Thermal stability of σ complexes of 2,4-dinitroanisole, 2-methoxy-3,5-dinitrobenzamide, 2,4-dinitro-5- and 2,4-dinitro-6-methoxyanisole, and 1-methoxy-2,4-dinitronaphthalene with alkali metal methylates was studied by differential thermal analysis in combination with differential thermogravimetry. The temperature and heat of decomposition of these compounds depend on the nature of substituent in the anion of the σ complex and on the radius of the alkali metal cation. In the first step of the thermolysis the corresponding dinitrophenolates and dinitronaphtholates are formed. The final products of the thermolysis are alkali metal formates.
- Kartashova,Gitis,Atroshchenko,Alifanova,Soldatova,Shakhkel'dyan
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p. 1925 - 1928
(2007/10/03)
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- Kinetics and Equilibria of Reactions between Acetic Anhydride and Substituted Phenolate Ions in Aqueous and Chlorobenzene Solutions
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Potassium acetate, solubilised in chlorobenzene by 18-crown-6, displaces the phenolate ion from substituted phenyl acetates by a second-order (kCl-2) process.Potassium phenolate ions, under similar conditions, react with acetic anhydride via a second order (kCl2) to yield the phenyl acetate.The concentration of the crown does not affect the reactivity unless it is not sufficient to solubilise the reactants.The rate constants correlate with the ionisation of the substituted phenols in water: log kCl2=1.60+/-0.23pKArOH(aq)a - 9.06+/-1.4 log kCl-2=-0.97+/-0.12pKArOH(aq)a + 4.78+/-0.78.The equilibrium constant for transfer of the acetyl group between phenolate ions and acetic anhydride in chlorobenzene has a Broensted βCleq of 2.6 measured against pKArOH(aq)a.The second-order rate constants (k2aq) have been measured for the reaction of substituted phenolate ions with acetic anhydride in water and they obey the Broensted equation: log (k2aq) = 0.56 +/- 0.06 pKArOH(aq)a - 2.52 +/- 0.51 Comparison of the value of the Broensted exponent for the equilibrium constant in chlorobenzene (β = 2.6) compared with that for aqueous solution (β = 1.7) indicates a greater development of effective charge consistent with the weaker solvating power of chlorobenzene.The reaction of substituted phenoxide ion with acetic anhydride has a Leffler α value of 0.33 and 0.62 for aqueous and chlorobenzene solutions, respectively, indicating a more advanced bond formation in the transition state of the reaction in the latter solvent even though the reactions in chlorobenzene are faster than in water.
- Ba-Saif, Salem A.,Maude, Antony B.,Williams, Andrew
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p. 2395 - 2400
(2007/10/02)
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- REACTIONS OF AROMATIC NITRO COMPOUNDS. LVI. REACTION OF POLYNITRODIPHENYL SULFONES WITH ACETONE AND POTASSIUM HYDROXIDE
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The Yanovskii ? complexes of 2,4-dinitrophenyl sulfone and 2,4-dinitro-, 2,4,4'-trinitro-, and 2,2',4,4'-tetranitrodiphenylsulfones were obtained and isolated in the crystalline form.It was established by PMR, IR, and electronic spectroscopy that they are
- Alekhina, N. N.,Gitis, S. S.,Grudtsyn, Yu. D.,Kaminskii, A. Ya.
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p. 1138 - 1142
(2007/10/02)
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- Kinetics and Some Equilibria of Transacylation between Oxy Anions in Aprotic Solvents
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β-Deuterium isotope effects (β-DIE) determined in acetonitrile for the following reactions are: CH3COO- + 4-NO2C6H4O2CCL3 (L = H, D) (PNPA-L3), 0.958 +/- 0.007 (5-45 deg C); CH3COO- + 2,4-(NO2)2C6H3O2CCL3 (DNPA-L3), 0.964 +/- 0.011 (5-20 deg C; OH(1-) + PNPA-L3, 0.972 +/- 0.028 (25 deg C); 4-NO2C6H4O- (PNP-) + CL3COOCOCL3, 1.00 +/- 0.02 (20 deg C); 4-NO-C6H4O- (PNOP-) + CL3COOCOCL3, 1.00 +/- 0.03 (20 deg C). β-DIEs in benzene for two of these reactions are: CH3COO- + PNPA-L3, 0.957 +/- 0.045 (10-20 deg C); CH3COO- + DNPA-L3, 0.985 +/- 0.050 (5-10 deg C).The fraction of tetrahedral character at the transition state (TS) deduced from β-DIEs for reactions of CH3COO- + PNPA is 0.32 in both CH3CN and benzene, of CH3COO- + DNPA is 0.28 in CH3CN and 0.12 in benzene, and of OH- + PNPA is 0.21 in CH3CN.These values are similar to what is found in water and indicate TSs of essentially trigonal geometry.Isotope effects (CH3)2/k(CD3)2> of unity for ester formation from CL3COOCOCL3 with phenoxides might be interpreted by two contributing factors to the observed effect; one of the usual hyperconjugation source and the other from electoststic effect of the label in the departing CL3COO-.An equilibrium isotope effect (CH3)2/K(CD3)2> of 1.03 in the direction of ester formation is calculated.A Hammett correlation of reactions of substituted phenoxides with CH3COOCOCH3 in CH3CN yielded ρ = -2.54.The reaction of CH3COO- in CH3CN could not be effected with phenyl acetate.The reaction was endergonic (ΔG0 = +2.59 kcal/mol)with PNPA and exergonic (ΔG0 = -7.61 kcal/mol) with DNPA.Activation enthalpies of these reactions decrease from H2O to CH3CN to benzene, whereas activation entropies increase in this order.
- Kovach, Ildiko M.
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p. 2235 - 2241
(2007/10/02)
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- TRANSITION STATES OF SOME ACYL TRANSFER REACTIONS IN ACETONITRILE
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β-Deuterium isotope effect (β-DIE) studies of acyl transfer from aryl acetates to acetate ion in acetonitrile indicate the degree of tetrahedral character at the transition state (TS) to be small, and the same as in protic solvents.
- Kovach, Ildiko M.
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p. 4309 - 4312
(2007/10/02)
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