Pyrimidine reactions. XI. Amination rates for two chlorodimethylprimidines without solvent

1965 ◽  
Vol 18 (11) ◽  
pp. 1811 ◽  
Author(s):  
DJ Brown ◽  
JM Lyall
Keyword(s):  
Rate Constants ◽  
Second Order ◽  
Arrhenius Parameters ◽  
First Order ◽  
Order Rate

Second-order rate constants, Arrhenius parameters, and isokinetic temperatures are presented for the reactions of 2-chloro-4,6-dimethylpyrimidine and 4-chloro-2,6-dimethylpyrimidine with some n-alkyl-, branched alkyl-, and dialkylamines in the absence of a solvent. The differences between these values and those available for the same reactions in a solvent are briefly discussed. An equation is derived for satisfactorily converting the apparent first-order rate constants previously reported by us into second-order rate constants.

Micellar effects upon reactions of the 2,2′,4,4′,4″-pentamethoxytrityl cation with nucleophiles

1986 ◽  
Vol 64 (6) ◽  
pp. 1179-1183 ◽  
Author(s):  
Clifford A. Bunton ◽  
Angela Cuenca
Keyword(s):  
Rate Constants ◽  
Sodium Dodecyl ◽  
Order Rate Constant ◽  
Second Order ◽  
Cetyltrimethylammonium Chloride ◽  
Micellar Effects ◽  
First Order ◽  
Order Rate ◽  
Cationic Micelles ◽  
Anionic Micelles

Cationic micelles of cetyltrimethylammonium chloride and bromide (CTACl and CTABr) speed attack of water upon the 2,2′,4,4′,4″-pentamethoxytrityl cation by a factor of ca. 5. The first-order rate constant in water is 5.51 s−1 at 25.0 °C. Anionic micelles of sodium dodecyl sulfate (SDS) have little effect on this reaction, but they strongly inhibit attack of OH−. In water, second-order rate constants for attack of OH−, CN−, and N3− are, respectively, 235, 177, and 2.8 × 105 M−1 s−1. Rate constants of reaction in CTACl go through maxima with increasing [surfactant] and analysis of the data shows that second-order rate constants at the micellar surface are similar to those in water.

Elucidation of the Nucleophilic Potential of Diazocyclopentadiene

Synthesis ◽  
2022 ◽  
Author(s):  
Herbert Mayr ◽  
Manfred Hartnagel ◽  
Armin R. Ofial
Keyword(s):  
Rate Constants ◽  
Second Order ◽  
Order Conditions ◽  
First Order ◽  
Electrophilic Substitutions ◽  
Order Rate ◽  
Nucleophilic Reactivity ◽  
Pseudo First Order

AbstractDiazocyclopentadiene reacts with benzhydrylium ions (Ar2CH+) to give 2,5-dibenzhydryl-substituted diazocyclopentadienes. The kinetics have been determined photometrically in dichloromethane under pseudo-first-order conditions using diazocyclopentadiene in excess. Plots of the second-order rate constants (log k 2) versus the electrophilicity parameters E of the benzhydrylium ions gave the nucleo­philicity parameter N = 4.84 and susceptibility s N = 1.06 for diazo­cyclopentadiene according to the correlation log k(20 °C) = s N(E + N). Diazocyclopentadiene thus has a similar nucleophilic reactivity as pyrrole. Previously reported electrophilic substitutions of diazocyclopentadiene are rationalized by these parameters and new reaction possibilities are predicted.

Coordinated Acylimido Complexes Formed by Reaction of Nitridorhenium and Nitridomolybdenum Porphyrins with Substituted Acetic Anhydrides

1998 ◽  
Vol 02 (03) ◽  
pp. 261-268 ◽  
Author(s):  
CHENG TONG ◽  
LAWRENCE A. BOTTOMLEY
Keyword(s):  
Electrochemical Properties ◽  
Rate Constants ◽  
Second Order ◽  
Formation Reaction ◽  
First Order ◽  
Reactant Concentration ◽  
Initial Reactant ◽  
Spectral Changes ◽  
Order Rate ◽  
Spectral And Electrochemical Properties

Acylimidorhenium and molybdenum porphyrin complexes were prepared by reaction of the corresponding nitridometalloporphyrins with substituted acetic anhydrides and their spectral and electrochemical properties were determined. Analysis of the electronic spectral changes with time and initial reactant concentration confirmed that the acylimido formation reaction was first-order in each reactant and second-order overall. Second-order rate constants for formation of the chloroacetic anhydride complex increased in the order Mn < Cr < Re < Mo . In contrast with the previously reported reactivity of acylimidomanganese and chromium porphyrin complexes, the rhenium and molybdenum derivatives were unreactive towards triphenylphosphine, strained olefins and silyl ethylene ethers.

scholarly journals The pH-dependence of second-order rate constants of enzyme modification may provide free-reactant pKa values

1977 ◽  
Vol 167 (3) ◽  
pp. 859-862 ◽  
Author(s):  
K Brocklehurst ◽  
H B F Dixon
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Second Order ◽  
Quasi Equilibrium ◽  
Pka Values ◽  
First Order ◽  
Order Rate ◽  
Parallel Reactions

1. Reactions of enzymes with site-specific reagents may involve intermediate adsorptive complexes formed by parallel reactions in several protonic states. Accordingly, a profile of the apparent second-order rate constant for the modification reaction (Kobs., the observed rate constant under conditions where the reagent concentration is low enough for the reaction to be first-order in reagent) against pH can, in general, reflect free-reactant-state molecular pKa values only if a quasi-equilibrium condition exists around the reactive protonic state (EHR) of the adsorptive complex. 2. Usually the condition for quasi-equilibrium is expressed in terms of the rate constants around EHR: (formula: see text) i.e. k mod. less than k-2. This often cannot be assessed directly, particularly if it is not possible to determine kmod. 3. It is shown that kmod. must be much less than k-2, however, if kobs. (the pH-independent value of kobs.) less than k+2. 4. Since probable values of k+2 greater than 10(6)M-1.S-1 and since values of kobs. for many modification reactions less than 10(6)M-1.S-1, the equilibrium assumption should be valid, and kinetic study of such reactions should provide reactant-state pKa values. 5. This may not apply to catalyses, because for them the value of kcat./Km may exceed 5 X 10(5)M-1.S-1. 6. The conditions under which the formation of an intermediate complex by parallel pathways may come to quasi-equilibrium are discussed in the Appendix.

A KINETIC INVESTIGATION OF THE REACTION OF METHYLMAGNESIUM BROMIDE WITH BENZOPHENONE

1963 ◽  
Vol 41 (5) ◽  
pp. 1329-1343 ◽  
Author(s):  
Norbert M. Bikales ◽  
Ernest I. Becker
Keyword(s):  
Rate Equation ◽  
Rate Constants ◽  
Second Order ◽  
Magnesium Bromide ◽  
Kinetic Investigation ◽  
First Order ◽  
Order Rate ◽  
Entropy Of Activation ◽  
Time Variables ◽  
Order Rate Equation

The reaction of methylmagnesium bromide with benzophenone in tetrahydrofuran was found to be homogeneous and essentially quantitative. The rates of this reaction were measured by following the decrease in absorbance of benzophenone in the ultraviolet as a function of time. Variables examined were concentrations of reactants, magnesium bromide, and temperature. Values were derived for the rate constants, and the energy and entropy of activation. The reaction was found to be initially first order in each reactant, but the rate decreased faster with time than would be predicted from the simple second-order rate equation. The implications of these findings are discussed.

The thermolysis and photolysis of malonic acid in the gas phase

1986 ◽  
Vol 64 (5) ◽  
pp. 967-968 ◽  
Author(s):  
J.-R. Cao ◽  
R. A. Back
Keyword(s):  
Acetic Acid ◽  
Hydrogen Atom ◽  
Transition State ◽  
Gas Phase ◽  
Malonic Acid ◽  
Rate Constants ◽  
Hydrogen Atom Transfer ◽  
Arrhenius Parameters ◽  
First Order ◽  
Order Rate

The thermolysis of malonic acid has been studied briefly in the gas phase at temperatures from 92 to 151 °C at pressures around 0.1 Torr. Major products were CO2 and acetic acid, while smaller amounts (< 5% of the CO2) of CO, acetone, C2H6, and CH4 were formed. Arrhenius parameters of E = 30.9 kcal/mol and log A (s−1) = 13.27 were obtained, based on first-order rate constants for the formation of CO2. It is suggested that the major products are formed by an internal hydrogen-atom transfer through a 4-centre transition state. The gas-phase photolysis was examined briefly using light of 228.8 nm, and gave products very similar to those of the thermolysis.

Inhibition in Purified Systems and in Human Plasma of Chimaeric Plasminogen Activators Consisting of the NH2-Terminal Region of Tissue-Type Plasminogen Activator and the COOH-Terminal Region of UrokinaseType Plasminogen Activator

1988 ◽  
Vol 60 (02) ◽  
pp. 247-250 ◽  
Author(s):  
H R Lijnen ◽  
L Nelles ◽  
B Van Hoef ◽  
F De Cock ◽  
D Collen
Keyword(s):  
Plasminogen Activator ◽  
Rate Constants ◽  
Plasminogen Activators ◽  
Second Order ◽  
Tissue Type ◽  
Single Chain ◽  
Chain Molecules ◽  
Order Rate ◽  
Type Plasminogen Activator ◽  
Urokinase Type Plasminogen Activator

SummaryRecombinant chimaeric molecules between tissue-type plasminogen activator (t-PA) and single chain urokinase-type plasminogen activator (scu-PA) or two chain urokinase-type plasminogen activator (tcu-PA) have intact enzymatic properties of scu-PA or tcu-PA towards natural and synthetic substrates (Nelles et al., J Biol Chem 1987; 262: 10855-10862). In the present study, we have compared the reactivity with inhibitors of both the single chain and two chain variants of recombinant u-PA and two recombinant chimaeric molecules between t-PA and scu-PA (t-PA/u-PA-s: amino acids 1-263 of t-PA and 144-411 of u-PA; t-PA/u-PA-e: amino acids 1-274 of t-PA and 138-411 of u-PA). Incubation with human plasma in the absence of a fibrin clot for 3 h at 37° C at equipotent concentrations (50% clot lysis in 2 h), resulted in significant fibrinogen breakdown (to about 40% of the normal value) for all two chain molecules, but not for their single chain counterparts. Preincubation of the plasminogen activators with plasma for 3 h at 37° C, resulted in complete inhibition of the fibrinolytic potency of the two chain molecules but did not alter the potency of the single chain molecules. Inhibition of the two chain molecules occurred with a t½ of approximately 45 min. The two chain variants were inhibited by the synthetic urokinase inhibitor Glu-Gly-Arg-CH2CCl with apparent second-order rate constants of 8,000-10,000 M−1s−1, by purified α2-antiplasmin with second-order rate constants of about 300 M−1s−1, and by plasminogen activator inhibitor-1 (PAI-1) with second-order rate constants of approximately 2 × 107 M−1s−1.It is concluded that the reactivity of single chain and two chain forms of t-PA/u-PA chimaers with inhibitors is very similar to that of the single and two chain forms of intact u-PA.

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.

A kinetic standard for precise calibration of spectrophotometer cell temperature.

1981 ◽  
Vol 27 (5) ◽  
pp. 753-755 ◽  
Author(s):  
P A Adams ◽  
M C Berman
Keyword(s):  
Temperature Dependence ◽  
Rate Constants ◽  
Cell Temperature ◽  
First Order ◽  
Order Rate ◽  
Acid Catalyzed ◽  
Pseudo First Order ◽  
Hydrolysis Of

Abstract We describe a simple, highly reproducible kinetic technique for precisely measuring temperature in spectrophotometric systems having reaction cells that are inaccessible to conventional temperature probes. The method is based on the temperature dependence of pseudo-first-order rate constants for the acid-catalyzed hydrolysis of N-o-tolyl-D-glucosylamine. Temperatures of reaction cuvette contents are measured with a precision of +/- 0.05 degrees C (1 SD).

PLATELET AGGREGATION DOES NOT CONFORM TO SIMPLE PARTICLE COLLISION THEORY

1987 ◽  
Author(s):  
Moideen P Jamaluddin
Keyword(s):  
Platelet Aggregation ◽  
Rate Equation ◽  
Rate Constants ◽  
Kinetic Scheme ◽  
Order Type ◽  
Second Order ◽  
Particle Collision ◽  
Collision Theory ◽  
Rate Law ◽  
First Order

Platelet aggregation kinetics, according to the particle collision theory, generally assumed to apply, ought to conform to a second order type of rate law. But published data on the time-course of ADP-induced single platelet recruitment into aggregates were found not to do so and to lead to abnormal second order rate constants much larger than even their theoretical upper bounds. The data were, instead, found to fit a first order type of rate law rather well with rate constants in the range of 0.04 - 0.27 s-1. These results were confirmed in our laboratory employing gelfiltered calf platelets. Thus a mechanism much more complex than hithertofore recognized, is operative. The following kinetic scheme was formulated on the basis of information gleaned from the literature.where P is the nonaggregable, discoid platelet, A the agonist, P* an aggregable platelet form with membranous protrusions, and P** another aggregable platelet form with pseudopods. Taking into account the relative magnitudes of the k*s and assuming aggregation to be driven by hydrophobic interaction between complementary surfaces of P* and P** species, a rate equation was derived for aggregation. The kinetic scheme and the rate equation could account for the apparent first order rate law and other empirical observations in the literature.

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