Kinetics of the reduction of 1-methylquinolinium cations by 1-benzyl-1,4-dihydronicotinamide

1985 ◽  
Vol 63 (3) ◽  
pp. 655-662 ◽  
Author(s):  
John W. Bunting ◽  
Norman P. Fitzgerald
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Hydride Transfer ◽  
Second Order ◽  
Hydroxide Ion ◽  
Order Rate ◽  
Kinetic Isotope ◽  
One Step ◽  
High Concentrations ◽  
Kinetics Of

The reduction of a series of 3-W-1-methylquinolinium cations (1: W = H, Br, CONH2, CO2CH3, CN, NO2) by 1-benzyl-1,4-dihydronicotinamide has been investigated. In all cases the kinetically controlled product from these reactions is the appropriate 3-W-1,4-dihydro-1-methylquinoline. Only for W = Br is any significant amount of the 1,2-dihydro isomer obtained (15% in this case). This kinetic preference for C-4 attack over C-2 attack in dihydronicotinamide reductions contrasts with the kinetically preferred attack at C-2 by hydroxide ion and in borohydride reductions. Rates of reduction were measured for each 1 and also 1,2-dimethyl- and 1,4-dimethylquinolinium cations in 20% CH3CN – 80% H2O, ionic strength 1.0 at 25 °C, under pseudo-first-order conditions. Kinetic saturation due to nonproductive 1:1 complex formation was observed for several cations at high concentrations (> 0.1 M). Second-order rate constants [Formula: see text] were evaluated for each W, and also kinetic isotope effects from second-order rate constants [Formula: see text] for reduction by 1-benzyl-4,4-dideuterio-1,4-dihydronicotinamide. Second-order rate constants are correlated with σp− for W with ρ = 4.5, and are also closely correlated with [Formula: see text] for pseudobase formation at C-4 of these quinolinium cations by: [Formula: see text]. Values of [Formula: see text] vs. [Formula: see text] describe a Westheimer curve reaching a maximum of 5.8 for W = Br and falling to 1.5 for W = NO2 and 4.2 for W = H. These data are consistent with an intrinsic barrier of 2.9 ± 0.5 kcal/mol for hydride transfer between this 1,4-dihydronicotinamide and quinolinium cations. However, quinolinium cations display a dramatically enhanced rate of dihydronicotinamide reduction relative to hydroxide ion attack when compared with isoquinolinium cations. This observation, and the predominance of C-4 rather than C-2 reduction, suggests that these reactions may not be simple one-step hydride transfer processes.

Hydride transfer reactions. A kinetic study of oxidation of 10-methyl-9-phenylacridan by some π acceptors and a one-electron oxidant

1985 ◽  
Vol 63 (8) ◽  
pp. 2237-2240 ◽  
Author(s):  
Allan K. Colter ◽  
A. Gregg Parsons ◽  
Karen Foohey
Keyword(s):  
Kinetic Study ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Hydride Transfer ◽  
Transfer Reactions ◽  
Kinetics Of Oxidation ◽  
Kinetic Isotope ◽  
One Step ◽  
The One ◽  
Kinetics Of

The kinetics of oxidation of 10-methyl-9-phenylacridan (1(H)) and 9-deuterio-10-methyl-9-phenylacridan (1(D)) to 10-methyl-9-phenylacridinium ion (3) by eight oxidants have been investigated. The oxidants included the π-acceptors 1,4-benzoquinone (BQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), p-bromanil (BA), p-chloranil (CA), tetracyanoethylene (TCNE), 2,3-dicyano-1,4-benzoquinone (DCBQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in acetonitrile (AN), BQ in 50:50 (v/v) AN-water, and the one-electron oxidant tris(2,2′-bipyridyl)cobalt(III), [Formula: see text] in AN. The seven π acceptors cover a 109-fold range of reactivity from BQ to DDQ and the deuterium kinetic isotope effect varies from 11.9 (BQ in AN) to 5.8 (DDQ). For π acceptors (BQ, TCNQ, CA, TCNE, and DCBQ) previously investigated with 10-methylacridan (NMA), 1(H) is less reactive than NMA by factors ranging from 9.1 (BQ) to 1.7 × 102 (TCNE). The isotope effects and relative reactivities for the π acceptor oxidations are most simply explained by a one-step hydride transfer mechanism.

scholarly journals Comparative kinetic isotope effects on first- and second-order rate constants of soybean lipoxygenase variants uncover a substrate-binding network

2019 ◽  
Vol 294 (48) ◽  
pp. 18069-18076 ◽  
Author(s):  
Shenshen Hu ◽  
Adam R. Offenbacher ◽  
Edbert D. Lu ◽  
Judith P. Klinman
Keyword(s):  
Rate Constants ◽  
Substrate Binding ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Second Order ◽  
Soybean Lipoxygenase ◽  
Order Rate ◽  
Kinetic Isotope

Determination of the Nucleophilicity of Tricarbonyliron Coordinated Cyclohepta-1,3,5-triene

1999 ◽  
Vol 64 (11) ◽  
pp. 1770-1779 ◽  
Author(s):  
Herbert Mayr ◽  
Karl-Heinz Müller
Keyword(s):  
Gibbs Energy ◽  
Ambient Temperature ◽  
Rate Constants ◽  
Second Order ◽  
Order Rate ◽  
Electrophilic Additions ◽  
Kinetics Of

The kinetics of the electrophilic additions of four diarylcarbenium ions (4a-4d) to tricarbonyl(η4-cyclohepta-1,3,5-triene)iron (1) have been studied photometrically. The second-order rate constants match the linear Gibbs energy relationship log k20 °C = s(E + N) and yield the nucleophilicity parameter N(1) = 3.69. It is concluded that electrophiles with E ≥ -9 will react with complex 1 at ambient temperature.

KINETICS OF THE AQUEOUS ALKALINE HOMOGENOUS HYDROLYSIS OF HIGH EXPLOSIVE 1, 3,5,7-TETRAAZA- 1, 3,5,7-TETRANITROCYCLOOCTANE (HMX)

1994 ◽  
Vol 30 (3) ◽  
pp. 53-61 ◽  
Author(s):  
Harro M. Heilmann ◽  
Michael K. Stenstrom ◽  
Rolf P. X. Hesselmann ◽  
Udo Wiesmann
Keyword(s):  
Temperature Dependence ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Elevated Temperatures ◽  
Second Order ◽  
Order Rate ◽  
Subsequent Calculation ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Order Rate Equation

In order to get basic data for the design of a novel treatment scheme for high explosives we investigated the kinetics for the aqueous alkaline hydrolysis of 1,3,5,7-tetraaza-1,3,5,7-tetranitrocyclooctane (HMX) and the temperature dependence of the rate constants. We used an HPLC procedure for the analysis of HMX. All experimental data could be fit accurately to a pseudo first-order rate equation and subsequent calculation of second-order rate constants was also precise. Temperature dependence could be modeled with the Arrhenius equation. An increase of 10°C led to an average increase in the second-order rate constants by the 3.16 fold. The activation energy of the second-order reaction was determined to be 111.9 ±0.76 kJ·moJ‒1. We found the alkaline hydrolysis to be rapid (less than 2.5% of the initial HMX-concentration left after 100 minutes) at base concentrations of 23 mmol oH‒/L and elevated temperatures between 60 and 80°C.

AM1 calculational and experimental evidence that a β-nitroxyl group significantly enhances the thermodynamic and kinetic acidities of ketones

1994 ◽  
Vol 72 (11) ◽  
pp. 2348-2350 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
Chandra Deo Roy
Keyword(s):  
Experimental Evidence ◽  
Gas Phase ◽  
Carbonyl Group ◽  
Rate Constants ◽  
Second Order ◽  
Nitroxyl Group ◽  
Order Rate ◽  
Kinetics Of

The kinetics of NaOD-catalysed H/D exchange of 3,3,5,5-tetramethylcyclohexanone (1), 1-hydroxy-4-oxo-2,2,6,6-tetrame-thylpiperidine (2), 4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl (3), 9-hydroxynorpseudopelletierine (4), and norpseudopelle-tierine-9-oxyl (5) have been studied in 60:40 dioxane–D2O(v/v) at 25.0 °C. The second-order rate constants are 9.20 × 10−3, 6.39 × 10−2, 1.59, 2.20 × 10−2, and 5.67 × 10−1 L mol−1 s−1 for 1, 2, 3, 4, and 5, respectively. Gas-phase enthalpies of ionization (the values are 363.0, 359.4, 352.0, 360.7, and 354.1 kcal mol−1 for 1, 2, 3, 4, and 5, respectively) calculated with AM1 correlate with the relative rates of enolization. Thus replacement of the β-hydroxylamino groups of 2 and 4 with a nitroxyl group produces sizable increases in the kinetic and thermodynamic acidities of the hydrogens α to the carbonyl group.

Kinetik der Reaktion von Papain mit Bromacetamid / Kinetics of the reaction of papain with bromoacetamide

1971 ◽  
Vol 26 (1) ◽  
pp. 43-46 ◽  
Author(s):  
Hans-Gerhard Löffler ◽  
Friedhelm Schneider ◽  
Helmut Wenck
Keyword(s):  
Rate Constants ◽  
Turning Point ◽  
Ph Dependence ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Ph Range ◽  
Kinetics Of

The pH-dependence of the second order rate constants of the reaction of papain with bromoacetamide in the pH-range 5,5-8,5 is described by a curve with a turning point corresponding to a pK 7,3 ± 0,1 at 25°. This is the pK of a catalytically essential imidazole residue. The activation parameters of the reaction of papain with bromoacetamide were determined. The second order rate constants at pH 7 for the reaction is 200 times greater than for the reaction of bromoacetamide with simple SH-compounds.

Effect of pH on the reaction of 1,3-dihydro-1-hydroxy-3-oxo-1,2-benziodoxole with 2-mercaptoethanol, 2-mercaptoethylamine, and glutathione

1970 ◽  
Vol 48 (19) ◽  
pp. 3104-3107 ◽  
Author(s):  
James Leslie
Keyword(s):  
Rate Constants ◽  
Ionic Species ◽  
Second Order ◽  
Hydrogen Ion ◽  
Effect Of Ph ◽  
Order Rate ◽  
Rate Determining Step ◽  
Ion Activity ◽  
Kinetics Of ◽  
Linear Manner

The kinetics of the oxidation of 2-mercaptoethanol, 2-mercaptoethylamine, and glutathione with 1,3-dihydro-1-hydroxy-3-oxo-1,2-benziodoxole (1) have been examined at pH 4–5.6. The reaction is second-order, which can be explained by a rate-determining step involving the reaction of one molecule of the thiol with one molecule of 1. The second-order rate constants vary in a linear manner with the reciprocal of the hydrogen ion activity. The ionic species involved in the reaction are discussed.

Primary isotope effects and mechanism of base initiated β-elimination reactions of di-(p-nitrophenyl)fluoroethanes

1977 ◽  
Vol 55 (10) ◽  
pp. 1696-1700 ◽  
Author(s):  
Jan Kurzawa ◽  
Kenneth T. Leffek
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Elimination Reactions

The second-order rate constants have been determined for the β-elimination reactions of 2,2-di-(p-nitrophenyl)-1,1,1-trifluoroethane, 2,2-di-(p-nitrophenyl)-1-fluoroethane, and their β-deuterated analogues with sodium methoxide in methanol. The primary isotope effects and activation parameters for these reactions are reported. It is suggested that the trifluoro-compound reacts via the pre-equilibrium carbanion mechanism (ElcB)R and that the monofluoro compound follows the E2 mechanism via a carbanion-like transition state.

Experimental and AM1 calculational studies of the deprotonation of bicyclo[2.2.2]octane-2,5-dione and bicyclo[2.2.2]octane-2,6-dione: a study of homoconjugation, inductive, and steric effects on the rates and diastereoselectivities of α enolization

1995 ◽  
Vol 73 (3) ◽  
pp. 460-463
Author(s):  
Nick Henry Werstiuk ◽  
Chandra Deo Roy
Keyword(s):  
Carbonyl Group ◽  
Rate Constants ◽  
Second Order ◽  
Polar Effect ◽  
Steric Effects ◽  
Order Rate ◽  
Kinetics Of

The kinetics of NaOD-catalyzed H/D exchange (enolization) at C3 α to the carbonyl group of bicyclo[2.2.2]octane-2,5-dione (1) and bicyclo[2.2.2]octane-2,6-dione (2) have been studied in 60:40 (v/v) dioxane–D2O at 25.0 °C. The second-order rate constants for exchange are (9.7 ± 1.5) × 10−1 and (3.4 ± 1.2) × 10−5 L mol−1 s−1 for 1 and 2, respectively. Thus, 1, exchanges 76 times faster than bicyclo[2.2.2]octan-2-one (3) (k = (1.27 ± 0.02) × 10−2 L mol−1 s−1), but the 2,6-dione 2 unexpectedly is much less reactive (2.7 × 10−3) than the monoketone. Unlike the large exo selectivity of 658 observed in the case of bicyclo[2.2.1]heptan-2-one, small and opposite selectivities, exo (1.2) for 1 and endo (2.1) for 2, are found for the isomeric [2.2.2] ketones. The results indicate that the incipient enolate of 1 is stabilized by a polar effect of the β carbonyl group at C5, not by homoconjugation. The source of the surprising low reactivity of 2 is unknown at this stage. The small diastereoselectivities, exo (1.2) for 1 and endo (2.1) for 2, correlate with relative energies of the diastereomeric pyramidal enolates calculated with AM1. Keywords: enolization, bicyclo[2.2.2]octane-2,5-dione, bicyclo[2.2.2]octane-2,6-dione, AM1, thermodynamic acidities.

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