Effects of the Nucleophile Structure on the Mechanisms of Reaction of 1-Chloro-2,4-dinitrobenzene with Aromatic Amines in Aprotic Solvents

1999 ◽  
Vol 64 (10) ◽  
pp. 1583-1593 ◽  
Author(s):  
Norma Sbarbati Nudelman ◽  
Cecilia E. Silvana Alvaro ◽  
Monica Savini ◽  
Viviana Nicotra ◽  
Jeannette Yankelevich
Keyword(s):  
Hydrogen Bond ◽  
Tertiary Amine ◽  
Aromatic Amines ◽  
Order Rate Constant ◽  
Aprotic Solvents ◽  
Nucleophilic Substitutions ◽  
Hydrogen Bond Acceptor ◽  
Mixed Aggregates ◽  
Kinetics Of

The kinetics of reactions of 1-chloro-2,4-dinitrobenzene with aniline and several substituted aromatic amines, B, in toluene shows a quadratic dependence of the second-order rate constant, kA, on [B], which is preserved even in the presence of increasing amounts of dimethylaniline, while the reaction with N-methylaniline shows a linear dependence of kA vs [B]. All these results are interpreted by the "dimer nucleophile" mechanism, and confirmed by the effects of a non-nucleophilic hydrogen bond acceptor tertiary amine which show the relevance of the structure of the nucleophile and the role of mixed aggregates in defining the mechanisms of aromatic nucleophilic substitutions with amines in aprotic solvents.

On the potential role of the amino nitrogen atom as a hydrogen bond acceptor in macromolecules

1998 ◽  
Vol 279 (5) ◽  
pp. 1123-1136 ◽  
Author(s):  
Ben Luisi ◽  
Modesto Orozco ◽  
Jiri Sponer ◽  
Francisco J Luque ◽  
Zippora Shakked
Keyword(s):  
Hydrogen Bond ◽  
Nitrogen Atom ◽  
Potential Role ◽  
Amino Nitrogen ◽  
Hydrogen Bond Acceptor ◽  
Amino Nitrogen Atom

scholarly journals Reactivity of cyclohex-1-enylcarboxylic and 2-methylcyclohex-1-enylcarboxylic acids with diazodiphenylmethane in aprotic solvents

2000 ◽  
Vol 65 (12) ◽  
pp. 839-846
Author(s):  
Jasmina Nikolic ◽  
Gordana Uscumlic ◽  
Vera Krstic
Keyword(s):  
Hydrogen Bond ◽  
Rate Constants ◽  
Kinetic Data ◽  
Linear Regression Analysis ◽  
Spectroscopic Method ◽  
Reaction Rates ◽  
Aprotic Solvents ◽  
Experimental Conditions ◽  
Hydrogen Bond Acceptor ◽  
Protic Solvents

Rate constants for the reaction of diazodiphenylmethane with cyclohex-1-enylcarboxylic acid and 2-methylcyclohex-1-enylcarboxylic acid were determined in nine aprotic solvents, as well as in seven protic solvents, at 30?C using the appropriate UV-spectroscopic method. In protic solvents the unsubsituted acid displayed higher reaction rates than the methyl-substituted one. The results in aprotic solvents showed quite the opposite, and the reaction rates were considerably lower. In order to explain the obtained results through solvent effects, reaction rate constants (k) of the examined acids were correlated using the total solvatochromic equation of the form: log k=logk0+s?*+a?+b?, where ?* is the measure of the solvent polarity, a represents the scale of the solvent hydrogen bond donor acidities (HBD) and b represents the scale of the solvent hydrogen bond acceptor basicities (HBA). The correlation of the kinetic data were carried out by means of multiple linear regression analysis and the opposite effects of aprotic solvents, as well as the difference in the influence of protic and aprotic solvents on the reaction of the two examined acids with DDM were discussed. The results presented in this paper for cyclohex-1-enylcarboxylic and 2-methylcyclohex-1-enylcarboxylic acids were compared with the kinetic data for benzoic acid obtained in the same chemical reaction, under the same experimental conditions.

scholarly journals Purification and kinetic mechanism of the major glutathione S-transferase from bovine brain

1989 ◽  
Vol 257 (2) ◽  
pp. 541-548 ◽  
Author(s):  
P R Young ◽  
A V Briedis
Keyword(s):  
Decanoic Acid ◽  
Kinetic Mechanism ◽  
Order Rate Constant ◽  
Bovine Brain ◽  
Glutathione S Transferase ◽  
Rate Acceleration ◽  
Hydrophobic Binding ◽  
Kinetics Of ◽  
Kinetics Of Inhibition

The major glutathione S-transferase isoenzyme from bovine brain was isolated and purified approx. 500-fold. The enzyme has a pI of 7.39 +/- 0.02 and consists of two non-identical subunits having apparent Mr values of 22,000 and 24,000. The enzyme is uniformly distributed in brain, and kinetic data at pH 6.5 with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate suggest a random rapid-equilibrium mechanism. The kinetics of inhibition by product, by GSH analogues and by NADH are consistent with the suggested mechanism and require inhibitor binding to several different enzyme forms. Long-chain fatty acids are excellent inhibitors of the enzyme, and values of 1nKi for hexanoic acid, octanoic acid, decanoic acid and lauric acid form a linear series when plotted as a function of alkyl chain length. A free-energy change of -1900 J/mol (-455 cal/mol) per CH2 unit is calculated for the contribution of hydrophobic binding energy to the inhibition constants. The turnover number of the purified enzyme dimer is approx. 3400/min. When compared with the second-order rate constant for the reaction between CDNB and GSH, the enzyme is providing a rate acceleration of about 1000-fold. The role of entropic contributions to this small rate acceleration is discussed.

Kinetic Studies on Oxidation of Veratryl Alcohol by Laccase-Mediator System. Part 1. Effects of Mediator Concentration

Holzforschung ◽  
2000 ◽  
Vol 54 (2) ◽  
pp. 165-170 ◽  
Author(s):  
Mikhail Yu. Balakshin ◽  
Chen-Loung Chen ◽  
Josef S. Gratzl ◽  
Adrianna G. Kirkman ◽  
Harald Jakob
Keyword(s):  
Kinetic Studies ◽  
Veratryl Alcohol ◽  
Alcohol Oxidation ◽  
Order Rate Constant ◽  
Molar Ratio ◽  
Active Centers ◽  
First Order ◽  
System Part ◽  
Kinetics Of

Summary Kinetics of the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diamonium salt (ABTS), the mediator, were studied to elucidate the possible reaction mechanism and the role of the mediator in this reaction. The reaction follows a pseudo-first order reaction law. The first order rate constant (κ) is dependent on the Mediator/Substrate (M/S) ratio and has a maximum at M/S molar ratio of 0.15. The kinetic studies show that the mechanism of veratryl alcohol oxidation with dioxygen-laccase-ABTS is rather complex and includes different reaction pathways. The mediator is involved in competitive reactions. It has been suggested that at low mediator concentration, the veratryl alcohol is oxidized via the laccase redox cycle. The mediator acts mostly as a laccase activator at a M/S ratio lower than 0.15. With increasing ABTS concentration with respect to the substrate concentration, ABTS acts increasingly as a cosubstrate competing with the original substrate for active centers of the laccase. This results in inhibition of veratryl alcohol oxidation in the enzyme cycle and increases the role of substrate oxidation by an oxidized mediator.

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