66291-20-1Relevant articles and documents
Kinetics of deprotonation of arylnitromethanes by benzoate ions in acetonitrile solution. Effect of equilibrium and nonequilibrium transition-state solvation on intrinsic rate constants of proton transfers
Gandler, Joseph R.,Bernasconi, Claude F.
, p. 631 - 637 (1992)
Second-order rate constants for benzoate ion promoted deprotonation reactions of (3-nitropbenyl)nitromethane, (4-nitrophenyl)nitromethane, and (3,5-dinitrophenyl)nitromethane have been determined in acetonitrile solution at 25 °C. These data were obtained at low benzoate buffer concentrations (a= 21.7; (4-nitromethyl)nitromethane, pKa = 20.6; and (3,5-dinitrophenyl)nitromethane, pKa, = 19.8. A Br?nsted βB value of 0.56 and an αCHlue of 0.79 have been calculated for the benzoate, 3-bromobenzoate, and 4-nitrobenzoate ion promoted reactions of (3,5- dinitrophenyl)nitromethane and for the benzoate ion promoted reactions of (3- nitrophenyl)nitromethane and (3,5-dinitrophenyl)nitromethane, respectively; (4-nitrophenyl)nitromethane deviates negatively from the Bronsted plot due to the resonance effect of the 4-nitro group. The logarithms of the intrinsic rate constants for benzoate promoted deprotonations of (3-nitrophenyl)nitromethane, (4-nitro phenyl)nitromethane, and (3,5-dinitrophenyl)nitromethane are 4.81, 4.58, and 5.27, respectively, and these values are 1.43, 1.70, and 1.30 log units, respectively, higher in acetonitrile than in dimethyl sulfoxide. Transfer activity coefficients from dimethyl sulfoxide (D) to acetonitrile (A) solution, log DγA, for (3-nitropbenyl)nitroimethyl anion (0.28), (4-nitrophenyl)nitromethyl anion (0.56), (3-nitrophenyl)nitromethane (0.18), and (4-nitrophenyl)nitromethane (0.16) have been calculated, and log DγA for benzoic acid (～ 1.9) and the benzoate ion (～0.25) have been estimated. The solvent effects on the intrinsic rate constants are analyzed within the framework of the Principle of Nonperfect Synchronization (PNS) in terms of contributions by late solvation of the arylnitromethyl anion, late solvation of the benzoic acid (produced as a product of the reaction), early desolvation of the benzoate ion and the arylnitromethane, and by a classical solvent effect. The results are also compared with predictions by a theoretical model recently proposed by Kurz. For the comparison of intrinsic rate constants in water and dimethyl sulfoxide there is good agreement between the Kurz model and the experimental results as well as the PNS analysts, but there is a discrepancy between the results and the predictions of the Kurz model for the comparison of intrinsic rate constants in dimethyl sulfoxide and acetonitrile solutions.
Hydrolysis of substituted α-nitrostilbenes: Dissection of rate coefficients for individual steps in the four-step mechanism. Estimates of intrinsic rate constants and transition-state imbalances
Bernasconi, Claude F.,Fassberg, Julianne
, p. 514 - 522 (2007/10/02)
A kinetic study of the hydrolysis of substituted α-nitrostilbenes (NS-Z with Z = 4-Me, H, 4-Br, 3-NO2, and 4-NO2) in 50% Me2SO-50% water (v/v) at 20 °C is reported. The mechanism consists of four steps: nucleophilic addition to NS-Z of water (k1H2O) and OH- (k1OH) to form PhCH(OH)C(Ar)NO2- (TOH-); carbon protonation of TOH- by water (k2H2O), H3O+ (k2H), and buffer acids (k2BH) to form PhCH(OH)CH(Ar)NO2 (TOH0); rapid oxygen deprotonation of TOH0 (KaOH) to form PhCH(O-)CH(Ar)NO2 (TO-); collapse of TO- (k4) into benzaldehyde and arylnitromethane anion. The aci-form of TOH0, PhCH(OH)CH(Ar)NO2H (TOH,aci0), can also be generated as a transient by reaction of TOH- with strong acid. A combination of kinetic experiments involving the reaction of the olefin with water and OH-, the reaction of TOH- with acid, and the reaction of independently synthesized TOH0 with base allowed the dissection of the rate coefficients of most of the individual steps. From the substituent dependence of these rate coefficients, it is concluded that water and OH- addition to NS-Z (k1H2O and k1OH) as well as the collapse of TO- to benzaldehyde and ArCH=NO2- (k4) is characterized by substantial transition-state imbalances, reminiscent of the imbalance observed in the deprotonation of ArCH2NO2. It is also shown that the intrinsic rate constants for the k1OH and k4 steps are low compared to those for the corresponding steps in the hydrolysis of other olefins of the type PhCH=CXY (XY = (H, NO2), (CO)2C6H4, (COO)2C(CHj)2, and (CN)2). This again parallels the behavior in the deprotonation of ArCH2NO2.
