scholarly journals Kinetics of the reaction of 5-substituted orotic acids with diazodiphenylmethane

2004 ◽  
Vol 69 (11) ◽  
pp. 949-953 ◽  
Author(s):  
Bratislav Jovanovic ◽  
Fathi Assaleh ◽  
Aleksandar Marinkovic
Keyword(s):  
Rate Constants ◽  
Steric Effect ◽  
Substituent Effects ◽  
Electrical Effect ◽  
Kinetics Of

Rate konstants for the reaction of eight 5-substituted orotic acids with diazodiphenylmethane (DDM) in dimethylformamide (DMF) were determined at 30 ?C by the known spectrophotometricmethod. The determined rate constants were correlated with the equations: logk2 = ??1+??R+h logk2 = ??1+??R+??+h to detect the presence and investigate the influence of both electrical and steric substituent effects. The obtained results show that the electrical effect (the localized ? field and delocalized ? resonance) is predominant and that the steric effect, althought present, is releatively small in this reaction.

Kinetics of hydrolyses of o-methylbenzylideneaniline and o-hydroxybenzylideneaniline

1968 ◽  
Vol 46 (9) ◽  
pp. 1589-1592 ◽  
Author(s):  
Alfred V. Willi ◽  
José F. Siman
Keyword(s):  
Hydrogen Bond ◽  
Schiff Base ◽  
Rate Constants ◽  
Experimental Error ◽  
Steric Effect ◽  
Hydrolysis Rate ◽  
Aqueous Methanol ◽  
Buffer Solutions ◽  
Acid Catalyzed ◽  
Kinetics Of

Rates of hydrolysis have been measured for o-methylbenzylideneaniline, o-hydroxybenzylideneaniline, and benzylideneaniline in various buffer solutions in 20% (by volume) aqueous methanol at 29.9 °C. Rate constants for the o-CH3 compound and the unsubstituted Schiff base agree within experimental error which indicates that there is no appreciable rate retarding steric effect. The o-OH group decreases the hydrolysis rate at pH = 5.6 – 6.6 by approximately one power of ten. This effect is caused by the hydrogen bond between the OH group and the azomethine N, which renders the Schiff base less accessible to acid-catalyzed hydrolysis.

Kinetics of Methylation of Methyl 5-Deoxy-α/β-D-xylofuranosides

2004 ◽  
Vol 69 (10) ◽  
pp. 1877-1888
Author(s):  
Mária Oščendová ◽  
Jitka Moravcová
Keyword(s):  
Sodium Hydroxide ◽  
Methyl Iodide ◽  
Rate Constants ◽  
Reaction Rate ◽  
Steric Effect ◽  
Order Reaction ◽  
Half Time ◽  
First Order ◽  
Consecutive Reactions ◽  
Kinetics Of

The kinetics of methylation of methyl 5-deoxy-α-D-xylofuranoside (1), methyl 5-deoxy-β-D-xylofuranoside (2) and their partly methylated derivatives with methyl iodide in the presence of sodium hydroxide in acetonitrile was studied. The reaction rate was independent of the base concentration during the first half-time only and the methylation proceeded as a first-order reaction. The rate constants of all side and consecutive reactions were calculated and the influence of both polar and steric effect is discussed. The methylation of 1 was highly regioselective giving almost exclusively 5-deoxy-2-O-methyl-α-D-xylofuranoside.

Kinetics of reactions of para-substituted phenyl isocyanates with amines and alcohols

1991 ◽  
Vol 56 (8) ◽  
pp. 1662-1670 ◽  
Author(s):  
Ivan Danihel ◽  
Falk Barnikol ◽  
Pavol Kristian
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Rate Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Stopped Flow ◽  
Partial Charges ◽  
Hammett Correlation ◽  
One Step ◽  
Kinetics Of

The reaction of para-substituted phenyl isocyanates with amines and alcohols was studied by stopped-flow method. The Hammett correlation obtained showed that the sensitivity of the above mentioned reactions toward substituent effects is the same as that of analogous reactions of phenyl isothiocyanates (ρ ~ 2). The rate constants of these reactions were found to be affected more by steric effects than by solvent effects. An one step multicentre mechanism with partial charges in transition state has been proposed for the title reactions.

scholarly journals The kinetics of formation of horseradish peroxidase compound I by reaction with peroxobenzoic acids. pH and peroxo acid substituent effects

1976 ◽  
Vol 157 (1) ◽  
pp. 247-253 ◽  
Author(s):  
D M Davies ◽  
P Jones ◽  
D Mantle
Keyword(s):  
Horseradish Peroxidase ◽  
Active Site ◽  
Rate Constants ◽  
Ph Effect ◽  
Substituent Effects ◽  
Nucleophilic Attack ◽  
Compound I ◽  
Active Intermediate ◽  
Kinetics Of Formation ◽  
Kinetics Of

1. The kinetics of formation of horseradish peroxidase Compound I were studied by using peroxobenzoic acid and ten substituted peroxobenzoic acids as substrates. Kinetic data for the formation of Compound I with H2O2 and for the reaction of deuteroferrihaem with H2O2 and peroxobenzoic acids, to form a peroxidatically active intermediate, are included for comparison. 2. The observed second-order rate constants for the formation of Compound I with peroxobenzoic acids decrease with increasing pH, in the range pH 5-10, in contrast with pH-independence of the reaction with H2O2. The results imply that the formation of Compound I involves a reaction between the enzyme and un-ionized hydroperoxide molecules. 3. The maximal rate constants for Compound I formation with unhindered peroxobenzoic acids exceed that for H2O2. Peroxobenzoic acids with bulky ortho substituents show marked adverse steric effects. The pattern of substituent effects does not agree with expectations for an electrophilic oxidation of the enzyme by peroxoacid molecules in aqueous solution, but is in agreement with that expected for a reaction involving nucleophilic attack by peroxo anions. 4. Possible reaction mechanisms are considered by which the apparent conflict between the pH-effect and substituent-effect data may be resolved. A model in which it is postulated that a negatively charged ‘electrostatic gate’ controls access of substrate to the active site and may also activate substrate within the active site, provides the most satisfactory explanation for both the present results and data from the literature.

Hydride transfer reactions. Substituent effects in oxidation of N-benzylacridans by π acceptors

1983 ◽  
Vol 61 (11) ◽  
pp. 2544-2551 ◽  
Author(s):  
Allan K. Colter ◽  
Charles C. Lai ◽  
Terry W. Williamson ◽  
Raymond E. Berry
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Second Order ◽  
Face To Face ◽  
Order Rate ◽  
Linear Free Energy ◽  
Donor And Acceptor ◽  
Kinetics Of

The kinetics of oxidation of a series of eight N-(substituted benzyl)acridans (3, NBA's) by 1,4-benzoquinone (BQ), p-chloranil (CA), 2,3-dicyano-1,4-benzoquinone (DCBQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and tetracyanoethylene (TCNE) in acetonitrile (AN) and by BQ in 50:50 (v/v) AN-water were measured at 25 °C. Equilibrium constants for pseudobase formation, [Formula: see text], from the corresponding acridinium ions (4) were measured in water at 25 °C. Hammett correlations of the second-order rate constants for reaction of the NBA's without ortho substitutents (3a–e) led to ρ values of −0.29 (BQ, AN), −0.55 (CA), −0.56 (DCBQ), −0.64 (TCNQ), −0.41 (TCNE), and −0.47 (BQ, 50:50 AN–water). The second-order rate constants for 3a–e also give good linear free energy correlations with the [Formula: see text] values of 4a–e. These correlations and the [Formula: see text] values for the ortho-substituted acridinium ions (4f, g, h) are used to calculate rate constants for oxidation of the corresponding ortho-substituted NBA's (3f, g, h). The rate constants calculated in this way are 4.7 to 6.6 times and 6.4 to 12 times larger, respectively, than the observed rate constants for N-(2,4,6-trimethylbenzyl) and N-(2,6-dichlorobenzyl)acridan (3g and h). The variations in ρ values are attributed mainly to differences in the amount of electrostatic stabilization in the transition state resulting from differences in the separation of donor and acceptor and the degree of delocalization of the negative charge. The rate retarding effect of a pair of ortho substituents is attributed to sterie effects in a preferred face-to-face transition state.

Submerged upflow biotower operation and computer simulation

1994 ◽  
Vol 30 (11) ◽  
pp. 143-146
Author(s):  
Ronald D. Neufeld ◽  
Christopher A. Badali ◽  
Dennis Powers ◽  
Christopher Carson
Keyword(s):  
Computer Simulation ◽  
Benzoic Acid ◽  
Computer Model ◽  
Rate Constants ◽  
Batch Mode ◽  
Operational Conditions ◽  
First Order ◽  
Low Concentrations ◽  
Biological Transformation ◽  
Kinetics Of

A two step operation is proposed for the biodegradation of low concentrations (< 10 mg/L) of BETX substances in an up flow submerged biotower configuration. Step 1 involves growth of a lush biofilm using benzoic acid in a batch mode. Step 2 involves a longer term biological transformation of BETX. Kinetics of biotransformations are modeled using first order assumptions, with rate constants being a function of benzoic acid dosages used in Step 1. A calibrated computer model is developed and presented to predict the degree of transformation and biomass level throughout the tower under a variety of inlet and design operational conditions.

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