The Strecker reaction — an examination in terms of no-barrier theory

2008 ◽  
Vol 86 (4) ◽  
pp. 285-289 ◽  
Author(s):  
J Peter Guthrie ◽  
Goonisetty Bhaskar
Keyword(s):  
Aqueous Solution ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Reaction Rate ◽  
Equilibrium Constants ◽  
Reaction Rate Constant ◽  
Cyanide Ion ◽  
Strecker Reaction ◽  
Rate Determining Step ◽  
Iminium Ion

For those examples of the Strecker reaction where information about both rate and equilibrium is available, we have been able to calculate rate constants for the addition of cyanide ion to the iminium ion by the no-barrier theory (NBT) approach. Both experimental and calculated values are for reaction in aqueous solution. Only for the reactions of benzaldehyde with benzyl or allyl amines and HCN are the equilibrium constants and rate constants for the final, rate-determining, step directly available from the literature. For the reactions of acetone with ammonia, methylamine, or dimethylamine and HCN rate constants for the retro-Strecker cleavage and the equilibrium constants for the overall Strecker reaction have been reported. These equilibrium constants, combined with equilibrium constants for iminium ion formation, which can be extracted from information in the literature, allow calculation of the equilibrium constants for the final step of these Strecker reactions. No-barrier theory has already been applied to carbonyl additions, including cyanohydrin formation; this report provides further evidence for the generality of this approach for calculating rate constants without using any kinetic information.Key words: Strecker reaction, rate constant, equilibrium constant, no-barrier theory, computation.

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.

Effect of the acyl substituent on the equilibrium constant for hydration of esters

1980 ◽  
Vol 58 (13) ◽  
pp. 1281-1294 ◽  
Author(s):  
J. Peter Guthrie ◽  
Patricia A. Cullimore
Keyword(s):  
Aqueous Solution ◽  
Equilibrium Constant ◽  
Rate Constant ◽  
Rate Constants ◽  
Acid Catalysis ◽  
Methyl Esters ◽  
Equilibrium Constants ◽  
Free Energies ◽  
General Acid ◽  
Aldehydes And Ketones

Heats of hydrolysis have been measured for the trimethyl orthoesters of isobutyric, propionic, benzoic, methoxyacetic, chloroacetic, and cyanoacetic acids using aqueous acid with an organic cosolvent where necessary, and of the corresponding esters in alkaline solution. Solubilities or free energies of transfer from gas to aqueous solution have been measured, permitting calculation of the free energies of formation of the aqueous orthoesters, and by methods which we have published previously, calculation of the free energies of formation of the covalent hydrates of the esters, and the free energy changes for hydration of these esters.Using estimated pKa values equilibrium constants were calculated for the addition of hydroxide to the esters. The data are in good agreement with the appropriate Marcus equation relating rate and equilibrium constants with a value for b of 8.99 ± 0.17. This line was used to estimate the equilibrium constant for addition of hydroxide, and thence of water, to some additional esters where only the rate constant was available. Rate constants for hydrolysis of methyl esters in aqueous solution at 25 °C were calculated from literature data, correcting for the effect of other conditions as necessary. From the equilibrium constants for addition of water we could estimate the rate constants for uncatalyzed hydrolysis; for the cases where this rate constant has been measured, the agreement was satisfactory. For acid catalyzed hydrolysis the data permit a test of the two alternative mechanisms considered previously, namely specific acid catalysis and general acid catalysis with hydronium ion acting as a general acid. For esters the mechanism is clearly specific acid catalysis, but for aldehydes and ketones it appears very likely that the mechanism is general acid catalysis.

scholarly journals “Transitivity”: A Code for Computing Kinetic and Related Parameters in Chemical Transformations and Transport Phenomena

Molecules ◽  
2019 ◽  
Vol 24 (19) ◽  
pp. 3478 ◽  
Author(s):  
Hugo G. Machado ◽  
Flávio O. Sanches-Neto ◽  
Nayara D. Coutinho ◽  
Kleber C. Mundim ◽  
Federico Palazzetti ◽  
...  
Keyword(s):  
Rate Constants ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
State Theory ◽  
Chemical Transformations ◽  
Graphical Interface ◽  
Arrhenius Behavior ◽  
Reaction Rate Constants ◽  
Kinetic And Thermodynamic Parameters ◽  
Data Documentation

The Transitivity function, defined in terms of the reciprocal of the apparent activation energy, measures the propensity for a reaction to proceed and can provide a tool for implementing phenomenological kinetic models. Applications to systems which deviate from the Arrhenius law at low temperature encouraged the development of a user-friendly graphical interface for estimating the kinetic and thermodynamic parameters of physical and chemical processes. Here, we document the Transitivity code, written in Python, a free open-source code compatible with Windows, Linux and macOS platforms. Procedures are made available to evaluate the phenomenology of the temperature dependence of rate constants for processes from the Arrhenius and Transitivity plots. Reaction rate constants can be calculated by the traditional Transition-State Theory using a set of one-dimensional tunneling corrections (Bell (1935), Bell (1958), Skodje and Truhlar and, in particular, the deformed ( d -TST) approach). To account for the solvent effect on reaction rate constant, implementation is given of the Kramers and of Collins–Kimball formulations. An input file generator is provided to run various molecular dynamics approaches in CPMD code. Examples are worked out and made available for testing. The novelty of this code is its general scope and particular exploit of d -formulations to cope with non-Arrhenius behavior at low temperatures, a topic which is the focus of recent intense investigations. We expect that this code serves as a quick and practical tool for data documentation from electronic structure calculations: It presents a very intuitive graphical interface which we believe to provide an excellent working tool for researchers and as courseware to teach statistical thermodynamics, thermochemistry, kinetics, and related areas.

scholarly journals Enhanced Heterogeneous Photodegradation of Organic Pollutants by a Visible Light Harvesting CoO@meso–CN@MoS2 Nanocomposites

Catalysts ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 722
Author(s):  
Linjer Chen ◽  
Thanh Binh Nguyen ◽  
Yi-Li Lin ◽  
Chung-Hsin Wu ◽  
Jih-Hsing Chang ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Methylene Blue ◽  
Visible Light ◽  
Reaction Rate ◽  
Weight Ratio ◽  
Reaction Rate Constant ◽  
Pollutant Degradation ◽  
New Approach ◽  
Apparent Reaction Rate Constant ◽  
Apparent Reaction Rate

Developing simple and effective synthetic strategies regarding the formation of heterostructure photocatalytic semiconductors remains an intense challenge in research matters. Uniform heterostructure cobalt oxide@meso–CN@MoS2 (CoO@meso–CN@MoS2) photocatalyst exhibits excellent photocatalytic redox performance for pollutant degradation under visible light. By adjusting the weight ratio of CoO@meso–CN and MoS2, we fabricated a CoO@meso–CN@MoS2 heterostructure photocatalyst, and the established heterostructure between CoO@meso–CN and MoS2 was indicated by various physicochemical and morphological characterizations. The photocatalytic response to the fabricated hybrid was determined by rodamine B (RhB), methylene blue (MB), and congo red (CR) degradation in aqueous solution under visible light, and the nanocomposites with a slight content consisting of CoO@meso–CN achieved better catalysis than pure MoS2. This finding confirmed the propriety of this heterostructure as a valuable photocatalyst. The experimental results demonstrated that the apparent reaction rate constant of the 3 wt% CoO@meso–CN modified MoS2 was about two times higher than that of pure MoS2. The present work serves as a new approach for designing highly efficient visible light-induced heterostructure-based photocatalysts for environmental applications in the future.

An Investigation into the Conversion of Propylene Glycol to 2,4-dimethyl-1,3-dioxolane over an Acid Catalyst Using Gas Chromatography

2013 ◽  
Vol 850-851 ◽  
pp. 82-85
Author(s):  
Zuo You Zhang ◽  
Hui Chen ◽  
Xia Li ◽  
Zhao Hui Yang ◽  
Bao Chen Liang
Keyword(s):  
Aqueous Solution ◽  
Reaction Rate ◽  
Acid Catalyst ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
Molar Ratio ◽  
Temperature Reaction ◽  
Gas Chromatograph ◽  
Second Order Reaction ◽  
Operational Parameters

In the presence of an acid catalyst, PG react reversibly with acetaldehyde to form 2,4-dim-ethyl-1,3-dioxolane (24DMD). The effects of different operational parameters on PG conversion had been analyzed in paper, parameters included temperature, reaction time, amount of catalyst and aqueous acetaldehyde/PG molar ratio. Under optimal condition, 85% conversion of PG in aqueous solution was achieved within 180 min of reaction. The analysis of PG was conducted by gas chromatograph. Furthermore, reaction followed the second-order reaction kinetics, and the reaction rate constant was found to be 29.68min-1.

Critical Review of Aqueous Solution Reaction Rate Constants for Hydrogen Atoms

2011 ◽  
Vol 40 (2) ◽  
pp. 023103 ◽  
Author(s):  
Keith P. Madden ◽  
Stephen P. Mezyk
Keyword(s):  
Aqueous Solution ◽  
Rate Constants ◽  
Critical Review ◽  
Reaction Rate ◽  
Hydrogen Atoms ◽  
Reaction Rate Constants ◽  
Solution Reaction

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.

Transient rates of gas sorption. II. Rate equations for transport and adsorption in porous adsorbents

1953 ◽  
Vol 6 (3) ◽  
pp. 234 ◽  
Author(s):  
KL Sutherland ◽  
ME Winfield
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Rate Equations ◽  
Limiting Factor ◽  
Gas Sorption ◽  
Gas Uptake ◽  
Knudsen Flow ◽  
Factor Ii

Equations are derived to describe the rate at which gas passes into a bed of adsorbent under conditions of constant volume and diminishing pressure. Of the processes which may be responsible for the observed rate of gas uptake, the following three are considered : (i) Knudsen flow within the bed, or within the granules of which it is composed, with simultaneous adsorption that is too fast to be a limiting factor ; (ii) chemisorption which is controlled by the rate of Knudsen flow ; (iii) unrestricted chemisorption.It is shown how the rate constants used in the equations are related to the overall reaction rate constant in a catalyst pore.

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