The cleavage of aspirin by α- and β-cyclodextrins in basic aqueous solution

1985 ◽  
Vol 63 (12) ◽  
pp. 3540-3544 ◽  
Author(s):  
Oswald S. Tee ◽  
Bryan K. Takasaki
Keyword(s):  
Aqueous Solution ◽  
Rate Constant ◽  
Dissociation Constants ◽  
Hydroxide Ion ◽  
Saturation Kinetics

The deacetylation of aspirin is promoted by α- and β-cyclodextrins (αCD and βCD) in basic aqueous solution. From saturation kinetics the dissociation constants (Kd) for the aspirin anion – CD complexes are 12 mM (αCD) and 20 mM (βCD). At pH 12.25 the limiting rate constant for ester cleavage is 14 times (αCD) and 7 times (βCD) that in the medium alone. For the 4-chloroaspirin anion (Kd = 3.8 mM) the cleavage induced by αCD is 240 times that in the medium, but 5-chloroaspirin shows a very small effect. The results are discussed in terms of a model derived from that of Bender and co-workers (1967) and are compared to earlier work. For the αCD anion, the 4-chloroaspirin anion is almost as good as "substrate" as m-chloro-and m-tert-butylphenyl acetates. Compared to hydroxide ion, the αCD anion is better at cleaving 4-chloroaspirin (2000×) and aspirin (36×).

Catalysis of the deprotonation of β-keto esters by cyclodextrins

1993 ◽  
Vol 71 (12) ◽  
pp. 2139-2143
Author(s):  
Oswald S. Tee ◽  
N. Rani Iyengar ◽  
Bryan K. Takasaki
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Ethyl Acetoacetate ◽  
Substrate Selectivity ◽  
Hydroxide Ion ◽  
Alkoxyl Group ◽  
Keto Esters ◽  
Saturation Kinetics ◽  
Carbon Acids ◽  
Marked Dependence

The rates of deprotonation of several β-keto esters in basic aqueous solution are elevated by α- and β-cyclodextrin (α- and β-CD). In most cases saturation kinetics are observed that indicate fairly strong binding of the esters to the CDs (Kd = 0.22–11 mM); catalytic ratios (kc/ku) are in the range 1.9–17. For esters of the form RCO-CH2COOEt with both α- and β-CD the values of Kd and kc/ku show little sensitivity to the acyl group, RCO (R = Me, Et, Pr, i-Pr), and for 2-carboethoxycyclopentanone, a cyclic analogue, these parameters are similar. In contrast, for R-COCH2CO-OR′ (R = Me or Et; R′ = Me, Et, allyl) there is a marked dependence of the parameters on the alkoxyl group, OR′. These results suggest that the β-keto esters studied bind to the CDs with their alkoxyl groups in the CD cavity and that the catalysis ensues from the complexes thus formed. Variations in two other kinetic parameters, k2 = kc/Kd (substrate selectivity) and KTS = ku/k2 (apparent constant for dissociation of CD from the transition state) support this interpretation. Apparent second-order rate constants for the reaction of the esters with neutral CD (k2 = kc/Kd) are 1900–360 000 M−1 s−1 (at pH ≈ 10), whereas for hydroxide ion attack on ethyl acetoacetate kOH = 5500 M−1 s−1. Assuming the pKas of the CDs are 12.2 and 12.3, deprotonation of the esters by the CD anions has rate constants of 105 to 5 × 107 M−1 s−1. Thus, binding of the β-keto esters in the CD cavities, adjacent to a basic oxyanion site, enhances the reactivity of the CD anions towards these weak carbon acids by at least 2–4 orders of magnitude.

THE OXIDATION OF NITRITE AND IODATE IONS BY HYPOCHLORITE IONS

1961 ◽  
Vol 39 (8) ◽  
pp. 1645-1651 ◽  
Author(s):  
M. W. Lister ◽  
P. Rosenblum
Keyword(s):  
Activation Energy ◽  
Aqueous Solution ◽  
Rate Constant ◽  
Hypochlorous Acid ◽  
Slow Stage ◽  
Iodate Ions

The oxidation of nitrite ions and of iodate ions by hypochlorite ions in aqueous solution has been examined. The oxidation of nitrite is really a reaction of hypochlorous acid, with the slow stage HOCl + NO2− + H2O → H3O+ + Cl− + NO3−. The rate constant is given by log k = 7.36−6450/RT (time in minutes, and the activation energy in calories). The oxidation of iodate is chiefly a reaction of hypochlorite ions, probably ClO− + IO3− → Cl− + IO4−, although the rate is somewhat increased by a higher concentration of hydroxide ions. The rate constant is given by log k = 16.15−26,100/RT. These results are compared with other oxidations by hypochlorite ions, to see if any general trends are apparent.

Binding of boronic acids with sugars in aqueous solution at physiological pH - Estimation of association and dissociation constants using spectroscopic method

2017 ◽  
Vol 227 ◽  
pp. 37-43 ◽  
Author(s):  
Geethanjali H.S. ◽  
R.M. Melavanki ◽  
Nagaraja D. ◽  
Bhavya P. ◽  
R.A. Kusanur
Keyword(s):  
Aqueous Solution ◽  
Dissociation Constants ◽  
Spectroscopic Method ◽  
Boronic Acids

scholarly journals EFFECT OF DIATOMEAOUS EARTH TREATMENT USING HYDROGEN CHLORIDE AND SULFURIC ACID ON KINETICS OF CADMIUM(II) ADSORPTION

2010 ◽  
Vol 2 (2) ◽  
pp. 107-112
Author(s):  
Nuryono Nuryono ◽  
Narsito Narsito
Keyword(s):  
Aqueous Solution ◽  
Sulfuric Acid ◽  
Hydrogen Chloride ◽  
Rate Constant ◽  
Diatomaceous Earth ◽  
Adsorption Rate ◽  
Physical Interaction ◽  
First Order ◽  
Adsorption Rate Constant ◽  
Kinetics Of

In this research, treatment of diatomaceous earth, Sangiran, Central Java using hydrogen chloride (HCl) and sulfuric acid (H2SO4) on kinetics of Cd(II) adsorption in aqueous solution has been carried out. The work was conducted by mixing an amount of grounded diatomaceous earth (200 mesh in size) with HCl or H2SO4 solution in various concentrations for two hours at temperature range of 100 - 150oC. The mixture was then filtered and washed with water until the filtrate pH is approximately 7 and then the residue was dried for four hours at a temperature of 70oC. The product was used as an adsorbent to adsorb Cd(II) in aqueous solution with various concentrations. The Cd(II) adsorbed was determined by analyzing the rest of Cd(II) in the solution using atomic absorption spectrophotometry. The effect of treatment was evaluated from kinetic parameter of adsorption rate constant calculated based on the simple kinetic model. Results showed  that before equilibrium condition reached, adsorpstion of Cd(II) occurred through two steps, i.e. a step tends to follow a reaction of irreversible first order  (step I) followed by reaction of reversible first order (step II). Treatment with acids, either hydrogen chloride or sulfuric acid, decreased adsorption rate constant for the step I from 15.2/min to a range of 6.4 - 9.4/min.  However, increasing concentration of acid (in a range of concentration investigated) did not give significant and constant change of adsorption rate constant. For step II process,  adsorption involved physical interaction with the sufficient low adsorption energy (in a range of 311.3 - 1001 J/mol).     Keywords: adsorption, cdmium, diatomaceous earth, kinetics.

Observation of a radical intermediate in the one electron oxidation of 5-methyl-1-thia-5-azacyclooctane by •Br2−

1984 ◽  
Vol 62 (9) ◽  
pp. 1874-1876 ◽  
Author(s):  
Warren Kenneth Musker ◽  
Parminder S. Surdhar ◽  
Rizwan Ahmad ◽  
David A. Armstrong
Keyword(s):  
Aqueous Solution ◽  
Rate Constant ◽  
Half Life ◽  
Cation Radical ◽  
Order Rate Constant ◽  
Type Structure ◽  
Radical Intermediate ◽  
Text Type ◽  
First Order ◽  
The One

The one electron oxidant •Br2− reacts with 5-methyl-1-thia-5-azacyclooctane (4) in aqueous solution at high pH with an overall rate constant of ~2 × 108 M s−1. The radical intermediate produced has a broad maximum at 500 nm with ε = 2400 M−1 cm−1 and at pH 10 decays with a first order rate constant of 2.3 ± 0.3 × 104 s−1, first half-life of 30 ± 5 μs. Its characteristics do not correspond to those of the [Formula: see text] species reported by Asmus and co-workers. The species appears to be the same as the cation radical reported earlier in the one electron oxidation of 4 in acetonitrile. This species is considered to have an [Formula: see text] type structure, which provides transannular stabilization.

Dissociation constants of toluic acids in aqueous solution at different temperatures and study of related thermodynamic parameters

1978 ◽  
Vol 23 (2) ◽  
pp. 103-107 ◽  
Author(s):  
M. Sengupta ◽  
K. Pal ◽  
A. Chakravarti ◽  
P. Mahapatra
Keyword(s):  
Aqueous Solution ◽  
Thermodynamic Parameters ◽  
Dissociation Constants ◽  
Different Temperatures ◽  
Toluic Acids

Inline Raman Spectroscopy and Indirect Hard Modeling for Concentration Monitoring of Dissociated Acid Species

2020 ◽  
pp. 000370282097327
Author(s):  
Alexander Echtermeyer ◽  
Caroline Marks ◽  
Alexander Mitsos ◽  
Jörn Viell
Keyword(s):  
Aqueous Solution ◽  
Raman Spectroscopy ◽  
Process Analytical Technology ◽  
Dissociation Constants ◽  
A Priori ◽  
Calibration Procedure ◽  
Acid Dissociation ◽  
Multivariate Curve Resolution ◽  
Least Squares Regression ◽  
Fitting Ideal

We propose an approach for monitoring the concentration of dissociated carboxylic acid species in dilute aqueous solution. The dissociated acid species are quantified employing inline Raman spectroscopy in combination with indirect hard modeling (IHM) and multivariate curve resolution (MCR). We introduce two different titration-based hard model (HM) calibration procedures for a single mono- or polyprotic acid in water with well-known (method A) or unknown (method B) acid dissociation constants p Ka. In both methods, spectra of only one acid species in water are prepared for each acid species. These spectra are used for the construction of HMs. For method A, the HMs are calibrated with calculated ideal dissociation equilibria. For method B, we estimate p Ka values by fitting ideal acid dissociation equilibria to acid peak areas that are obtained from a spectral HM. The HM in turn is constructed on the basis of MCR data. Thus, method B on the basis of IHM is independent of a priori known p K a values, but instead provides them as part of the calibration procedure. As a detailed example, we analyze itaconic acid in aqueous solution. For all acid species and water, we obtain low HM errors of < 2.87 × 10−4mol mol−1 in the cases of both methods A and B. With only four calibration samples, IHM yields more accurate results than partial least squares regression. Furthermore, we apply our approach to formic, acetic, and citric acid in water, thereby verifying its generalizability as a process analytical technology for quantitative monitoring of processes containing carboxylic acids.

Theory of amphoteric electrolytes. Part II.

1905 ◽  
Vol 74 (497-506) ◽  
pp. 271-280 ◽  
Author(s):  
James Walker
Keyword(s):  
Aqueous Solution ◽  
Dissociation Constants

In a previous paper it was shown that if HXOH is an amphoteric electrolyte, it is possible to express the concentration of the various ions present in its aqueous solution in terms of the concentration of the unionised substance, the dissociation constants of the substance acting as acid and as base respectively, and the ionisation constant of water.

Cation-anion combination reactions. II. Reactions of p-nitrobenzenediazonium ion with hydroxide ion in aqueous solution

1971 ◽  
Vol 93 (10) ◽  
pp. 2425-2428 ◽  
Author(s):  
Calvin D. Ritchie ◽  
David J. Wright
Keyword(s):  
Aqueous Solution ◽  
Hydroxide Ion
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