Rate and equilibrium constants for formation and hydrolysis of 9-formylfluorene oxime: diffusion-controlled trapping of a protonated aldehyde by hydroxylamine

2000 ◽  
Vol 78 (12) ◽  
pp. 1594-1612 ◽  
Author(s):  
RA More O'Ferrall ◽  
D M O'Brien ◽  
D G Murphy
Keyword(s):  
Aqueous Solution ◽  
Acetic Acid ◽  
Reaction Pathway ◽  
Equilibrium Constants ◽  
Diffusion Control ◽  
General Measure ◽  
Hydroxide Ion ◽  
Diffusion Controlled ◽  
Enol Tautomer ◽  
Hydrolysis Of

Equilibrium constants Kadd = 440 and Kox = 3.0 × 108 for formation of a carbinolamine adduct and oxime, respectively from 9-formylfluorene and hydroxylamine, and pKa = –1.62 for protonation of the oxime, have been evaluated at 25°C in aqueous solution, based on measurements in hydroxylamine buffers, acetic acid buffers, and dilute HCl. Rate constants for hydrolysis of the oxime have been measured in the acidity range pH 4–12 M HClO4. At the highest acidities, a reaction pathway via protonated carbinolamine has been identified: evidence is presented that the reverse of this reaction involves rate-determining attack of hydroxylamine upon protonated 9-formylfluorene. By assuming that the attack of hydroxylamine is diffusion-controlled, with rate constant 3 × 109 M –1 s–1, a pKa for O-protonation of the aldehyde (–4.5) is derived. Taking account of the equilibrium constant for enolization of 9-formylfluorene (KE = 16.6), a pKa for for C-protonation of the enol tautomer ((–5.7) may also be obtained. Comparison of this pKa with that of the enol of acetophenone shows that the enol of 9-formylfluorene is less basic by a factor of 1010. By combining pKas for protonation of the aldehyde and oxime with measured or estimated equilibrium constants for addition of water, hydroxide ion, and hydroxylamine to 9-formylfluorene, it is also possible to obtain values of pKR = –5.3, 4.1, and 12.25 for the protonated 9-formylfluorene, protonated oxime, and 9-formylfluorene, respectively. The usefulness of pKR in providing a general measure of equilibrium constants for electrophile-nucleophile combination reactions is discussed.Key words: oxime, formyfluorene, hydrolysis, protonation, diffusion-control.

Determination of Carbaryl Residues in Honey Bees

1965 ◽  
Vol 48 (4) ◽  
pp. 771-774
Author(s):  
D P Johnson ◽  
H A Stansbury
Keyword(s):  
Aqueous Solution ◽  
Acetic Acid ◽  
Quantitative Determination ◽  
Honey Bees ◽  
Methylene Chloride ◽  
Hydrolysis Product ◽  
Separate Analysis ◽  
Yellow Substance ◽  
Hydrolysis Of

Abstract A method has been developed for detecting residues of carbaryl (1-naphthyl methylcarbamate) as well as its hydrolysis product, 1-naphthol, in dead bees. The method is based on extraction of the bees with benzene, followed by a cleanup involving liquid partitioning and chromatography on Florisil. The quantitative determination involves hydrolysis of carbaryl to 1-naphthol and coupling of the latter with p-nitrobenzenediazonium fluoborate in acetic acid to form a yellow substance. For separate analysis, free 1-naphthol is separated from methylene chloride into a basic aqueous solution. The sensitivity of the method is about 0.1 ppm; recoveries averaged 85.6 ± 6.6% for 1- naphthol and 83.8 ± 2.7% for carbaryl.

Base hydrolysis of trans-Halogenoamminebis(dimethylglyoximato) (III). Complexes

1969 ◽  
Vol 22 (12) ◽  
pp. 2569 ◽  
Author(s):  
SC Chan ◽  
PY Leung
Keyword(s):  
Equilibrium Constants ◽  
Base Hydrolysis ◽  
Hydroxide Ion ◽  
First Order ◽  
Rate Determining Step ◽  
Rapid Formation ◽  
Pseudo First Order ◽  
Conjugate Bases ◽  
Hydrolysis Of ◽  
Conjugate Base

The disappearance of trans-[Co(LH)2(NH3)X] (LH = dimethylglyoximate ion, X = chloride or bromide) has been studied in aqueous solutions over a range of alkali concentrations at various temperatures. The kinetics were done with excess of hydroxide ion at a constant ionic strength so that pseudo first-order rate constants were obtained in all the runs. The results were interpreted in terms of the rapid formation of a pre- equilibrium species which then reacts in a rate-determining step to give products. The relatively large equilibrium constants support a conjugate-base pre-equilibrium, in which the proton is lost from oxygen, while the relatively low reactivities of the conjugate-bases are consistent with the absence of electropositive electromeric effects. The similarity in the reactivities of the chloro and the bromo conjugate-bases suggests the possibility of an SN2CB mechanism.

High-Pressure Stopped-Flow Study of the Kinetics of Base Hydrolysis of the Dichromate Ion by Hydroxide Ion, Ammonia, Water, and 2,6-Lutidine in Aqueous Solution

1983 ◽  
Vol 66 (8) ◽  
pp. 2445-2448 ◽  
Author(s):  
Peter Moore ◽  
Yves Ducommun ◽  
Peter J. Nichols ◽  
Andr� E. Merbach
Keyword(s):  
Aqueous Solution ◽  
High Pressure ◽  
Base Hydrolysis ◽  
Stopped Flow ◽  
Hydroxide Ion ◽  
Ammonia Water ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Flow Study

Kinetics and mechanism of gold(III) incorporation into tetrakis(1-methylpyridium-4-yl)porphyrin in aqueous solution

2004 ◽  
Vol 08 (11) ◽  
pp. 1269-1275 ◽  
Author(s):  
Ahsan Habib ◽  
Masaaki Tabata ◽  
Ying Guang Wu
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Kinetic Data ◽  
Ph Dependence ◽  
Equilibrium Constants ◽  
Hydroxyl Group ◽  
Net Charge ◽  
First Order ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of the reaction of the tetrakis(1-methylpyridium-4-yl)porphyrin tetracation, [ H 2( TMPyP )]4+, with gold(III) ions were studied along with equilibria of gold(III) species in aqueous medium at 25°C, I = 0.10 M ( NaNO 3). The equilibrium constants for the formation of [ AuCl 4-n( OH ) n ]- ( n = 0,…,4), defined as β n = [ AuCl 4- n ( OH ) n ]- [ Cl -] n / [ AuCl 4-][ OH -] n were found to be that log β1 = 7.94 ± 0.03, log β2 = 15.14 ± 0.03, log β3 = 21.30 ± 0.05 and log β4 = 26.88 ± 0.05. The overall reaction was first order with respect to each of the total [ Au (III)] and [ H 2 TMPyP 4+]. On the basis of pH dependence on rate constants and the hydrolysis of gold(III), the rate expression can be written as d [ Au ( TMPyP )5+]/ dt = ( k 1[ AuCl 4-] + k2[ AuCl 3( OH )-] + k3[ AuCl 2( OH )2-] + k4[ AuCl ( OH )3-])[ H 2 TMPyP 4+], where k1, k2, k3 and k4 were found to be (2.16 ± 0.31) × 10-1, (6.56 ± 0.19) × 10-1, (1.07 ± 0.24) × 10-1, and (0.29 ± 0.21) × 10-1 M -1. s -1, respectively. The kinetic data revealed that the trichloromonohydroxogold(III) species, [ AuCl 3( OH )]-, is the most reactive. The higher reactivity of [ AuCl 3( OH )]- is explained by hydrogen bonding formation between the hydroxyl group of [ AuCl 3( OH )]- and the pyrrole hydrogen atom of [ H 2( TMPyP )]4+. Furthermore, applying the Fuoss equation to the observed rate constants at different ionic strengths, the apparent net charge of [ H 2( TMPyP )]4+ was calculated to be +3.5.

A Polarographic study of some Wurster salts

1958 ◽  
Vol 11 (2) ◽  
pp. 104 ◽  
Author(s):  
JA Friend ◽  
NK Roberts
Keyword(s):  
Aqueous Solution ◽  
Acetic Acid ◽  
Formation Constant ◽  
Platinum Electrode ◽  
Mercury Electrode ◽  
Diffusion Current ◽  
Polarographic Study ◽  
Polarographic Investigation ◽  
Dropping Mercury Electrode ◽  
Hydrolysis Of

Four related Wurster salts are subjected to a polarographic investigation. In the case of Wurster's blue, results from the dropping mercury electrode, stationary platinum electrode, and rotated platinum electrode are compared. The Wurster salt of p-phenylenediamine is unstable in aqueous solution but is fairly stable in a mixture of methanol, acetic acid, and water and the decrease of diffusion current with time indicates a disproportionation. Wurster's red is also unstable in aqueous solution. In the solvent methanol, acetic acid, and water, a wave is observed with the stationary platinum electrode whose E� compares favourably with the potentiometric E?0. Evidence from the three types of electrodes mentioned previously indicates two one-electron waves for Wurster's blue. The semiquinone formation constant qualitatively appears much greater than that reported from potentiometric work. Decrease of diffusion current with time is perhaps due to a disproportionation (the very unstable di-imine has been shown to revert to the radical in aqueous solution). Polarographic waves given by the Wurster salt of diaminodurene suggest that the radical does not exist in aqueous solution. Waves corresponding to the original amine and duroquinone (formed by hydrolysis of the di-imine) are obtained.

Flow Kinetics of β-Galactosidase Chemically Attached to Nylon Tubing

1975 ◽  
Vol 53 (10) ◽  
pp. 1061-1069 ◽  
Author(s):  
D. Narinesingh ◽  
T. T. Ngo ◽  
K. J. Laidler
Keyword(s):  
Flow Rate ◽  
Substrate Concentration ◽  
Diffusion Control ◽  
Theoretical Treatment ◽  
Enzyme Reactors ◽  
Diffusion Controlled ◽  
Nylon Tubing ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Substrate Concentrations

β-Galactosidase (EC 3.2.1.23) has been attached covalently to the inner surface of nylon tubing. An experimental study has been made of the flow kinetics for the hydrolysis of o-nitrophenylgalactose, the substrate concentration and flow rate being varied. The results were analyzed in the light of the theoretical treatment of Kobayashi and Laidler, three different methods of analysis being employed. It is concluded that at the lower substrate concentrations and flow rates employed, the reactions are largely diffusion controlled; with increase in flow rate and substrate concentration the width of the Nernst diffusion layer decreases, and there is found to be less diffusion control. The values of Km(app) vary with flow rate VF, being linear in VF−1/3, and the value extrapolated to very high flow rate agrees well with the Km value for β-galactosidase in free solution. The theory and results are shown to provide guidelines for the design of open tubular heterogeneous enzyme reactors for industrial, biomedical, and analytical applications.

THE STABILITY OF SOME COMPLEXES OF TRIVALENT COPPER

1953 ◽  
Vol 31 (7) ◽  
pp. 638-652 ◽  
Author(s):  
M. W. Lister
Keyword(s):  
Aqueous Solution ◽  
Sodium Hypochlorite ◽  
Equilibrium Constants ◽  
Copper Ion ◽  
Ion Concentration ◽  
Hydroxide Ion ◽  
New Methods ◽  
Reversible Dissociation ◽  
The Stability ◽  
Complex Ion

New methods are given for the preparation of sodium copper (111) tellurate, Na9Cu(TeO6)2.16H2O, and sodium copper (111) periodate, Na7Cu(IO6)2.20H2O, previously reported by Malatesta. Additional analytical evidence is presented that these are really compounds of trivalent copper. The dissociation of the ions in alkaline aqueous solution was examined through the ability of the uncomplexed copper to catalyze the decomposition of sodium hypochlorite. Evidence is presented that the uncomplexed copper ion is Cu(OH)4−, and this gives both a 1-1 and a 1-2 complex with both tellurate and periodate. The 1-2 complexes appear to be Cu(HTeO6)2−7 and Cu(IO6)2−7 respectively; the 1-1 complexes are less stable. The equilibrium constants for the reversible dissociation of these ions into their simpler constituents in aqueous solution at 40 °C. are as follows: tellurate, 1-1 complex K1 = 1.8 × 10−6; 1-2 complex K2 = 1.1 × 10−11; periodate, 1-1 complex K1 = 3.4 × 10−5; 1-2 complex is K2 = 8.0 × 10−11. The smaller the constant the more stable the complex ion. In the case of the tellurate complex K2 is proportional to the square of the hydroxide ion concentration and these values are for 0.400 M sodium hydroxide; with periodate K2 is independent of the hydroxide concentration. Experiments at various temperatures give 20 kcal. as the heat of the reaction forming the 1-2 tellurate complex from the simple ions, and 71/2 kcal. for the 1-2 periodate complex. The stannate, stibnate, and selenate ions showed no signs of forming analogous compounds.

Kinetics of acetylcholinesterase immobilized on polyethylene tubing

1979 ◽  
Vol 57 (10) ◽  
pp. 1200-1203 ◽  
Author(s):  
T. T. Ngo ◽  
K. J. Laidler ◽  
C. F. Yam
Keyword(s):  
Diffusion Control ◽  
Initial Oxidation ◽  
Diffusion Controlled ◽  
Kinetic Tests ◽  
Acetylthiocholine Iodide ◽  
Carboxylic Groups ◽  
Michaelis Constants ◽  
Polyethylene Tubing ◽  
Kinetics Of ◽  
Hydrolysis Of

Acetylcholinesterase was covalently attached to the inner surface of polyethylene tubing. Initial oxidation generated surface carboxylic groups which, on reaction with thionyl chloride, produced acid chloride groups; these were caused to react with excess ethylenediamine. The amine groups on the surface were linked to glutaraldehyde, and acetylcholinesterase was then attached to the surface. Various kinetic tests showed the catalysis of the hydrolysis of acetylthiocholine iodide to be diffusion controlled. The apparent Michaelis constants were strongly dependent on flow rate and were much larger than the value for the free enzyme. Rate measurements over the temperature range 6–42 °C showed changes in activation energies consistent with diffusion control.

Electrostatic effects of substrate charge on base-catalyzed proton exchange in purines. Implications for the involvement of zwitterions

1980 ◽  
Vol 58 (1) ◽  
pp. 86-91 ◽  
Author(s):  
Spencer E. Taylor
Keyword(s):  
Aqueous Solution ◽  
Transition State ◽  
Exchange Reaction ◽  
Rate Constants ◽  
Electrostatic Interactions ◽  
Equilibrium Constants ◽  
Proton Exchange ◽  
Net Charge ◽  
Hydroxide Ion ◽  
Rate Behaviour

Rates of detritiation from the C-8 position of various ionized purine molecules have been shown to reflect electrostatic interactions occurring within the transition state of the exchange reaction. The purines are capable of existing as protonated, anionic, neutral, and zwitterionic species in aqueous solution, each of which have been shown previously to undergo specific hydroxide ion-catalyzed detritiation. The effects of substrate charge are quantified as the protonactivatingfactor, aniondeactivatingfactor, and zwitterionactivatingfactor. Localized charge and not net charge is shown to govern the reactivities of the various species, especially the zwitterions.Estimation of rate constants for the zwitterionic species (hitherto only postulated to account for the observed rate behaviour) has enabled the calculation of the corresponding zwitterionic equilibrium constants (Kzw). Kzw values calculated in this manner agree with those estimated from suitable literature pKa data.

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