The reaction of nickel(II) bis(diethyldithiocarbamate) with N,N,N',N'-tetraethyl thiuramdisulphide

1985 ◽  
Vol 50 (8) ◽  
pp. 1648-1660 ◽  
Author(s):  
Ernest Beinrohr ◽  
Andrej Staško ◽  
Ján Garaj
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants

The oxidation of nickel(II) bis(diethyldithiocarbamate) (NiL2) by N,N,N',N'-tetraethyl thiuramdisulphide (tds) can be described by the equation 2 NiL2 + tds ⇄ 2 NiL3 (NiL3 = tris(diethyldithiocarbamate) nickel(III)). The equilibrium constant of the reaction depends on the polarity of the solvent (4.4 . 10-3 in toluene, 1.3 . 10-3 in chloroform, and 8 . 10-4 in acetone and methanol). The rate constants k1 and k-2 and the ratio k2/k-1 were found for the reaction steps NiL2 + tds ⇄ NiL3 + L. and NiL2 + L. ⇄ NiL3, where L. is the (C2H5)2NCS2. radical.

Modelling the adsorption of phospholipid vesicles to a silicon dioxide surface using Langmuir kinetics

2022 ◽  
Author(s):  
Iad Alhallak ◽  
Peter J. N. Kett
Keyword(s):  
Silicon Dioxide ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Lipid Vesicles ◽  
Phospholipid Vesicles ◽  
Adsorption And Desorption ◽  
Langmuir Kinetics

The rate constants and equilibrium constant for the adsorption and desorption of lipid vesicles from a SiO2 surface have been determined.

Dynamics of the Bis-Tris and High Spin-Low Spin Equilibria of 2-(2′-Pyridyl)imidazoleiron(II) Complexes in Dimethyl Sulfoxide Solutions

1988 ◽  
Vol 41 (9) ◽  
pp. 1315 ◽  
Author(s):  
JK Beattie ◽  
KJ Mcmahon
Keyword(s):  
Relaxation Time ◽  
Dimethyl Sulfoxide ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Temperature Jump ◽  
Free Ligand ◽  
Relaxation Curve ◽  
Dissociation Equilibrium ◽  
Laser Temperature Jump ◽  
Equilibrium Transition

Ultrasonic and temperature-jump relaxation kinetics have been used to observe, respectively, the spin equilibrium and tris-bis ligand dissociation equilibrium of the 2-(2′-pyridyl) imidazoleiron (II) complexes in dimethyl sulfoxide solutions. In the ultrasonic experiments a single relaxation curve describes the excess sound absorption with a relaxation time of 73�3 ns. This was identified as perturbation of the singlet-quintet spin equilibrium by comparison with previous laser temperature-jump measurements in other solvents and by the temperature dependence of the relaxation amplitude. The equilibrium constant for the singlet-quintet transition was determined by the Evans n.m.r . method to be 0.48 at 298 K. From the relaxation time and the equilibrium constant the rate constants for the spin-equilibrium transition can be calculated to be k15 of 4.5×106 s-1 and k51 of 9.4×106s-1. In the temperature-jump experiments a millisecond relaxation time was observed. The dependence of the relaxation time on the concentration of the free ligand is of the form kobs = a + b[L]. From the ratio b/a an equilibrium constant for the perturbed process can be calculated. An independent measure of this equilibrium constant was obtained from spectrophotometric measurements. The rate constants for the formation and dissociation of the tris complex are calculated to be 2.8 × 104 dm3 mol-1 s-1 and 2.1 × 102 s-1, respectively, at 298 K.

The retroaldol reaction of 3-methyl-2-butenal

1983 ◽  
Vol 61 (1) ◽  
pp. 171-178 ◽  
Author(s):  
J. Peter Guthrie ◽  
Brian A. Dawson
Keyword(s):  
Sodium Hydroxide ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Aqueous Sodium Hydroxide ◽  
Initial Increase ◽  
Aqueous Sodium ◽  
Rate Determining Step ◽  
Kinetics Of

In aqueous sodium hydroxide solutions at 25 °C, 3-methyl-2-butenal, 1c, undergoes retroaldol cleavage to acetone and acetaldehyde. The kinetics of the retroaldol reaction were followed spectrophotometrically at 242 nm and showed simple first order behavior. When 3-methyl-3-hydroxybutanal, 2c, was added to aqueous sodium hydroxide solutions at 25 °C, there was an initial increase in absorbance at 242 nm, attributed to formation of 1c, followed by a 20-fold slower decrease; the rate of the slow decrease matches the rate of disappearance of 1c under the same conditions. Analysis of the kinetics allows determination of the three rate constants needed to describe the system: khyd = 0.00342; kdehyd = 0.00832; kretro = 0.0564; all M−1 s−1. The equilibrium constant for enone hydration is 0.41. Rate constants for the analogous reactions for acrolein and crotonaldehyde could be obtained from the literature. There is a reasonable rate–equilibrium correlation for the retroaldol step. For the enone hydration step, rate and equilibrium constants respond differently to replacement of hydrogen by methyl. It is proposed that this results from release of strain after the rate-determining step by rotation about a single bond; this decrease in strain is reflected in the equilibrium constant but not in the rate constant.

Isothiazole chemistry. IV. Cyanide cleavage of the S-N bond in 3-hydroxyisothiazole

1967 ◽  
Vol 20 (12) ◽  
pp. 2729 ◽  
Author(s):  
WD Crow ◽  
I Gosney
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants ◽  
Nucleophilic Attack ◽  
Effect Of Temperature ◽  
Cyanide Ion ◽  
Equilibrium Studies ◽  
Conjugate Acid ◽  
Ph Range ◽  
Rate Profile ◽  
Direct Attack

Nucleophilic attack on 3-hydroxyisothiazole by cyanide ion, yielding cis-3-thiocyanoacrylamide, has been investigated over the pH range 0.00-5.50. Rate constants have been measured both for direct attack by cyanide ion and from the effect of cyanide ion in retarding the cyclization of the thiocyanoacrylamide; in both cases the derived rate constants agree. The pH-rate profile of the reaction reveals the existence of two kinetically discrete mechanisms. Within the range 5.50-4.00 the dominating mechanism is one involving a slow direct attack on 3-hydroxyisothiazole itself, while at pH less than 3.50 the conjugate acid of this molecule is subjected to a much faster attack. Equilibrium studies have been made for the system, and the effect of temperature on the equilibrium constant has been used to derive thermodynamic parameters.

scholarly journals Evolution of enzyme catalytic power. Characteristics of optimal catalysis evaluated for the simplest plausible kinetic model

1977 ◽  
Vol 163 (1) ◽  
pp. 111-116 ◽  
Author(s):  
Keith Brocklehurst
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants ◽  
Catalytic Efficiency ◽  
Kinetic Mechanism ◽  
Enzyme Concentration ◽  
Forward Rate ◽  
Power Characteristics ◽  
Evolutionary Changes ◽  
Order Of Magnitude ◽  
Km Value

1. Evolutionary changes in the structure of an enzyme that provide an increase in its Km value are considered. Provided that Km increases as a result of increases in the forward rate constants of the catalysis relative to the reverse rate constants, the enzyme catalyses the conversion of a fixed concentration of its substrate more rapidly when its structure provides that Km>[S] than when Km<[S]. 2. Catalytic efficiency of enzymes is discussed in terms of the simplest plausible model, the Haldane [(1930) Enzymes, Longmans, London] reversible three-step model: [Formula: see text] The rate equation for the forward reaction of this model (formation of P) may be written in the simple form: [Formula: see text] Keq. is the equilibrium constant (=[P]eq./[S]eq.), and kcat.=V/[E]T, where [E]T is the total enzyme concentration. 3. To assess the effectiveness of an enzyme, it is necessary only to determine the extent to which the constraints of a particular kinetic mechanism permit v2 (v when Km»[S]) to approach vd (the diffusion-limited rate). 4. The value of the optimal rate of catalysis (vopt., the maximal value of v2) is dictated by the equilibrium constant for the reaction, Keq.; v2=vd/a, where [Formula: see text] when k+1 is assumed equal to k−3, and vopt.=vd/amin.. When Keq.≥1, it is necessary that k+2»k−1 for a to take its minimum value, amin.; when Keq.«1, it is necessary only that k+2»Keq.·k−1, i.e. a can equal amin. even if k+2<k−1. When Keq.»1, vopt.=vd; when Keq.=1, vopt.=vd/2, and when Keq.«1, vopt.=Keq.·vd. 5. The analysis, together with predicted effects of evolutionary pressure, suggests that in practice the rates of the fastest enzyme-catalysed freely reversible reactions might be expected to be lower than the value of k+1[E]T[S] by about an order of magnitude, particularly if Keq.<1. 6. The existing literature suggests that, in general, appropriate values of Km have evolved for the provision of high rates of catalysis but that many values of kcat. are not large enough to provide optimal rates of catalysis unless the value of k+1in vivo is lower than its value in free solution.

Carbonyl oxygen exchange of glycol monoesters. Rate and equilibrium constants for the formation of a tetrahedral intermediate

1979 ◽  
Vol 57 (12) ◽  
pp. 1531-1540 ◽  
Author(s):  
R. A. McClelland ◽  
M. Ahmad ◽  
J. Bohonek ◽  
S. Gedge
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Carbonyl Oxygen ◽  
Ester Hydrolysis ◽  
Oxygen Exchange ◽  
Ortho Ester ◽  
Kinetic Investigations ◽  
Relationship Of ◽  
The Relationship

Kinetic investigations of the hydrolysis of the 2-phenyl-4,4,5,5-tetramethyl-1,3-dioxolenium ion and 2-phenyl-2-methoxy-4,4,5,5-tetramethyl-1,3-dioxolane furnish rate constants for all three reaction stages of the ortho ester hydrolysis: (1) generation of the dioxolenium ion, (2) hydration of this ion to form hydrogen ortho ester, and (3) breakdown of this species to pinacol monobenzoate. The equilibrium constant for stage (2) can also be obtained. This study complements a previous investigation of 2-phenyl-2-alkoxy-1,3-dioxolanes where similar information was obtained.The rate constants for carbonyl oxygen exchange of the ester products of these reactions, pinacol monobenzoate and ethylene glycol monobenzoate, have been measured. This reaction is shown to proceed by a different mechanism to that normally associated with exchange of carboxylic acid derivatives: cyclization of the glycol monoester to form hydrogen ortho ester, followed by loss of the labelled exocyclic OH group to give 1,3-dioxolenium ion. Reversal of these steps, initiated by an unlabelled water molecule, results in exchange. The relationship of this mechanism with that of the ortho ester hydrolysis is obvious; it is shown that the exchange provides rate constants for the reverse of stage (3). This means that both the forward and reverse rates of this process have been obtained, and this provides the equilibrium constant.

Mutarotation of D(+)-glucose. II. Volumes of activation for the uncatalysed and copper(II)-catalysed rates

1983 ◽  
Vol 36 (2) ◽  
pp. 279 ◽  
Author(s):  
CJ O'Conner ◽  
AL Odell ◽  
AAT Bailey
Keyword(s):  
High Pressure ◽  
Reaction Mechanism ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Reaction Mechanisms ◽  
Sodium Perchlorate ◽  
Continuous Series ◽  
Aqueous Sodium ◽  
The Individual ◽  
Individual Rate

The effect of high pressure on the rate of mutarotation of α-and β-D(+)-glucose in aqueous sodium perchlorate solutions has been evaluated. The observed rate constant kΨ = kα + kβ increases with pressure while the equilibrium constant Keq = kα /kβ is nearly unchanged from the 1.7 found at 1 bar. From the experimental results, the individual rate constants kα and kβ and the corresponding activation volumes ∆V‡α and ∆V‡β can be evaluated. The values obtained, -10.7 � 0.1 and -10.0 � 0.1 cm3 mol-1, are discussed in relation to the reaction mechanism. In the presence of Cu(ClO4)2 the values of ∆V: form a continuous series, dependent upon the pH and the concentration of copper(II) catalyst, up to + 1.3 cm3 mol-1. The activation volumes for mutarotation by monomeric and dimeric copper(II) catalysts, ∆V‡(Cu2+) and ∆V‡ {CU((OH)2Cu)2+}, are -1.2 � 0.2 and + 3.6 � 0.2 cm3 mol-1 respectively. Reaction mechanisms are discussed to account for these values of ∆V‡.

Aromatic substitutions with carbanion nucleophiles. IV. The kinetics and mechanism of the reaction of picryl bromide with diethylmalonate anion

1977 ◽  
Vol 55 (14) ◽  
pp. 2664-2669 ◽  
Author(s):  
Kenneth T. Leffek ◽  
Anna E. Matinopoulos-Scordou
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants ◽  
Activation Parameters ◽  
Solvent System ◽  
Stopped Flow ◽  
Substitution Product ◽  
Picryl Chloride ◽  
Uv Visible ◽  
The Individual ◽  
Mechanism Of The Reaction

The reaction of picryl bromide with sodium diethylmalonate has been studied in benzene–DMSO 7:1 v/v by means of stopped-flow and uv–visible spectrophotometers. A Meisenheimer-like intermediate was detected, decomposing to yield the stable violet anion of the substitution product. The rate constants of the individual steps have been measured and the activation parameters calculated. Comparison with those obtained for picryl chloride support a bimolecular substitution via the 1,1-complex. The reaction with 1,3,5-trinitrobenzene is too fast to be measured in the same solvent system. The equilibrium constant is estimated to be of the order of 104–105.

Demonstrating the relation between rate constants and the equilibrium constant

1970 ◽  
Vol 47 (9) ◽  
pp. 646 ◽  
Author(s):  
Edwin F. Meyer ◽  
Edward Glass
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants
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