The Aldol Condensation of Acetaldehyde: the Equilibrium Constant for the Reaction and the Rate Constant for the Hydroxide Catalyzed RetroAldol Reaction

1974 ◽  
Vol 52 (11) ◽  
pp. 2037-2040 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Equilibrium Constant ◽  
Rate Constant ◽  
Aldol Condensation ◽  
Aldol Reaction ◽  
Enthalpy Change

An indirect thermochemical estimate of the equilibrium constant for the aldol condensation of acetaldehyde suggested that this reaction was much less irreversible than has been believed. The rate of the hydroxide catalyzed retroaldol reaction has been measured; k21 = 2.8 × 10−3 M−1 s−1 at 25°, so that the equilibrium constant is 4.0 × 102 M−1. The γ value for acetaldehyde as addend is 0.40. The enthalpy change for the aldol reaction is −9.84 kcal/mol.

An efficient click synthesis of chalcones derivatized with two 1-(2-quinolon-4-yl)-1,2,3-triazoles

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Mohammed B. Alshammari ◽  
Ashraf A. Aly ◽  
Alan B. Brown ◽  
Md Afroz Bakht ◽  
Ahmed M. Shawky ◽  
...  
Keyword(s):  
Aldol Condensation ◽  
Aldol Reaction ◽  
Click Synthesis

Abstract Chalcones derivatized with 1-(2-quinolonyl)-1,2,3-triazoles were synthesized by reaction of 4-azido-2-quinolones with 1-phenyl-3-(4-propargyloxyphenyl)prop-2-en-1-one, or by aldol reaction of 4-{[1-(2-oxo-1,2-dihydroquinolin-4-yl)-1H-1,2,3-triazol-4-yl]methoxy}benzaldehydes with acetophenone. Whereas, chalcones bearing two 1-(2-quinolonyl)-1,2,3-triazoles were synthesized by reaction of 1,3-bis(4-propargyloxyphenyl)prop-2-en-1-one with 4-azido-2-quinolones, or by aldol condensation between 4-{4-[(4-acetylphenoxy)methyl]-1H-1,2,3-triazol-1-yl}quinolin-2(1H)-ones and 4-{[1-(2-oxo-1,2-dihydroquinolin-4-yl)-1H-1,2,3-triazol-4-yl]methoxy}benzaldehydes.

The uptake of atropine and related drugs by intestinal smooth muscle of the guinea-pig in relation to acetylcholine receptors

1965 ◽  
Vol 163 (990) ◽  
pp. 1-44 ◽  
Keyword(s):  
Smooth Muscle ◽  
Binding Site ◽  
Equilibrium Constant ◽  
Rate Constant ◽  
Binding Sites ◽  
Acetylcholine Receptors ◽  
Kinetic Properties ◽  
Kinetic Behaviour ◽  
Kinetics Of ◽  
Bound Drug

In an attempt to study the properties of acetylcholine receptors in intestinal smooth muscle, measurements have been made of the uptake of tritium-labelled atropine and methylatropinium, and of 14 C-labelled methylfurmethide by the longitudinal muscle of guinea-pig small intestine in vitro . Substantial amounts of atropine were taken up from very dilute solutions, a clearance of 160 ml. per g tissue (wet weight) being achieved at the lowest concentration tested (1.5 × 10 -10 M). Analysis of the curve relating atropine uptake at equilibrium to the bath concentration, which was explored over a concentration range 1.5 × 10 -10 M to 2.5 × 10 -3 M, enabled three components to be distinguished: (1) A binding site with a capacity of 180 pmoles/g, and equilibrium constant 1.1 × 10 -9 M. (2) A binding site of capacity about 1000 pmoles/g and equilibrium constant about 5 × 10 -7 M. (3) A compartment with a clearance of 4.7 ml./g (nonsaturable). The equilibrium constant of the first binding site agreed exactly with that measured for acetylcholine antagonism in the same tissue. Methylatropinium was taken up in rather smaller amounts than atropine, and analysis of the uptake curve showed a binding site of capacity about 90 pmoles/g with an equilibrium constant 6.5 × 10 -10 M, an ill-defined series of binding sites with much higher equilibrium constants, and a constant clearance of about 0.4 ml. /g. Analysis of this curve was much less clear cut than that of atropine. The equilibrium constant for blockade of acetylcholine receptors by methylatropinium was 4.7 × 10 -10 M. Atropine was not taken up appreciably by striated muscle, nerve or tendon of the guineapig; hydrolysed atropine was not taken up by smooth muscle (and lacks atropinic activity); cocaine and d -tubocurarine in high concentrations did not affect atropine uptake; lachesine and benzhexol blocked atropine uptake competitively at low concentrations, and with lachesine the equilibrium constant for this interaction agreed with that measured for acetylcholine antagonism (1.4 × 10 -9 M). These findings suggested that the atropine taken up could be related to receptor-bound drug. The kinetics of atropine uptake and washout were studied over the concentration range 0.5-5 × 10 -9 M. Uptake and washout took place approximately exponentially between 2½ and 50 min, and the rate constant was 4.5-5 × 10 -4 s -1 for both uptake and washout. The uptake rate constant did not increase with concentration. This contrasted with the kinetics of receptor blockade, which took place much faster, with a rate constant which increased linearly with concentration, in accordance with the theoretical kinetic behaviour of a single binding site. This finding precluded a simple identification of atropine taken up with receptor-bound drug. Studies with various metabolic inhibitors suggested that no metabolic energy was required for the accumulation of atropine, and by dialysis experiments, the atropine taken up was shown to be bound in homogenized tissue. A theoretical study, using an analogue computer, was made of the kinetic properties of three passive binding systems, in order to see whether the observed kinetic behaviour could be simulated. It was found that a system of four binding sites in series, with only one communicating directly with the surrounding medium, could show these kinetic properties, and the outermost binding site could still show the kinetic behaviour of receptors. Experimental testing of this model demands more accurate kinetic measurements than can be made by the method used in this study. The acetylcholine-like stimulant, methylfurmethide, was taken up very slowly (taking more than 24 h to reach equilibrium), reaching a clearance of about 5 ml. /g after 6 h. This uptake was unaffected by atropine in a concentration sufficient to block 80% of acetylcholine receptors, but was blocked by depolarization in high potassium solution, suggesting that it was behaving passively as a slowly permeant cation. No uptake referable to acetylcholine receptors was detected. These findings are discussed in relation to the abundance and chemical behaviour of acetylcholine receptors in smooth muscle, and in relation to current theories of drug action.

Chemical kinetics and thermodynamics of tin ionization in H2-O2-N2 flames and the proton affinity of SnO

1998 ◽  
Vol 76 (10) ◽  
pp. 1437-1446 ◽  
Author(s):  
John M Goodings ◽  
QingFeng Chen
Keyword(s):  
Equilibrium Constant ◽  
Proton Affinity ◽  
Rate Constant ◽  
Detailed Balance ◽  
Zero Point ◽  
Recombination Coefficient ◽  
Published Data ◽  
Free Electrons ◽  
Flame Ionization ◽  
Good Agreement

A small amount (<10-6 mol fraction) of tin was introduced into five, fuel-rich, H2-O2-N2 flames in the temperature range 1820-2400 K at atmospheric pressure. Ions in a flame were observed by sampling the flame along its axis through a nozzle into a mass spectrometer. The major neutral tin species in these flames were SnO (>97%) and Sn (<3%). The principal tin ions observed were SnOH+ and Sn+. Thermodynamic functions for SnOH+, Sn+, SnO, and Sn were calculated by statistical mechanics using published data from ab initio calculations and spectroscopy. The SnOH+ ion was formed initially by proton transfer to SnO by H3O+, a natural flame ion, with which it is in equilibrium. It was also produced by chemi-ionization of SnO reacting with H; SnOH+ rapidly equilibrates with Sn+. Ion ratio measurements of SnOH+/H3O+ led to the proton affinity PA°298 (SnO) = 911 ± 21 kJ mol -1 (218 ± 5 kcal mol-1). A calculated equilibrium constant provided the SnOH+/Sn+ ion ratio. When electron-ion recombination of SnOH+ with free electrons was made dominant by the addition of CH4 and K, the measured recombination coefficient of SnOH+ was (0.116 ± 0.065)T-(1.66±0.16) cm3 molecule-1 s-1; the temperature dependence is in good agreement with the T-1.5 dependence predicted by simple theory. The rate constant for chemi-ionization could not be measured due to impurity ions from potassium and sodium, but the equilibrium constant for chemi-ionization/recombination was calculated to be 0.004 863 exp (-52 070/T). Assuming detailed balance and the experimental recombination coefficient, the relatively small rate constant for chemi-ionization was given by 3.27 × 10-10 exp (-48 630/T) cm3 molecule-1 s-1. Finally, calculated values were obtained for the bond energy D°0(HO-Sn+) = 408 ± 21 kJ mol-1, and the standard zero-point enthalpy of formation deltafH°0(SnOH+) = 637 ± 21 kJ mol-1.Key words: flame ionization, chemi-ionization, proton affinity, mass spectrometry, tin.

Kinetics of the reaction H + C2H6 → H2 + C2H5 in the temperature region of 1000 K

1984 ◽  
Vol 62 (1) ◽  
pp. 86-91 ◽  
Author(s):  
J.-R. Cao ◽  
M. H. Back
Keyword(s):  
Equilibrium Constant ◽  
Rate Constant ◽  
Temperature Region ◽  
Recent Measurement ◽  
Hydrogen Atoms ◽  
Elementary Reactions ◽  
Temperature Range ◽  
Hydrogen Molecules ◽  
Kinetics Of ◽  
Rate Controlling Step

A system for the measurement of rate constants for elementary reactions of hydrogen atoms in the temperature region of 1000 K is described. The concentration of hydrogen atoms is controlled by the equilibrium constant for dissociation of hydrogen molecules. The kinetics of the rate of conversion of ethane to ethylene in this system has been studied over the temperature range 876–1016 K. The results show that the rate-controlling step is[Formula: see text]and the value obtained for the rate constant is[Formula: see text](R = 1.987 cal mol−1 deg−1). This value is compared with values obtained from other methods over the temperature range 300–1400 K. Combination with a recent measurement of the rate constant for the reverse reaction yields an experimental value for the equilibrium constant for the reaction.

scholarly journals REACTION KINETICS OF Cu ELECTRO-DEPOSITION ON THE SURFACE OF TiO2/GRAPHITE

2015 ◽  
Vol 8 (2) ◽  
pp. 116
Author(s):  
Fitria Rahmawati ◽  
Wanodya Anggit Mawasthi ◽  
Patiha
Keyword(s):  
Equilibrium Constant ◽  
Rate Constant ◽  
Reaction Rate ◽  
Reaction Order ◽  
Electrode Reaction ◽  
Deposition Process ◽  
Anodic Reaction ◽  
Electro Deposition ◽  
First Order ◽  
Kinetics Of

Research on the kinetics of electrode reaction during copper electro-deposition on the surface of TiO2/graphite has been conducted. The aims of this research are to determine the ratio of anodic reaction rate to cathodic reaction rate , the ratio of anodic rate constant to cathodic rate constant , the equilibrium constant when the reaction reach equilibrium condition and to study the polarization in the electro-deposition reaction. Copper was deposited electrochemically from CuSO4 solution at various concentration i.e. 0.1 M; 0.2 M; 0.3 M; 0.4 M; 0.5 M. In every 5 minutes during electro-deposition process, the pH changes in anode cell was recorded and the change of Cu2+ concentration was also analyzed by spectrophotometric method. The result shows that the reaction order of Cu2+ reduction is first order and the oxidation of H2O in anodic cell is zero order. The ratio of anodic rate constant to cathodic rate constant, is 4.589´10-3 ± 0.071´10‑3. It indicates that the reaction rate  in cathode is larger than the reaction rate in anode and it allowed polarization.  The electrochemical cell reached equilibrium after 25 minutes with the equilibrium constant is 8.188´10-10 ± 1.628´10-10.

Sign in / Sign up

Export Citation Format

Share Document