The retroaldol reaction of cinnamaldehyde

1984 ◽  
Vol 62 (8) ◽  
pp. 1441-1445 ◽  
Author(s):  
J. Peter Guthrie ◽  
Kevin J. Cooper ◽  
John Cossar ◽  
Brian A. Dawson ◽  
Kathleen F. Taylor
Keyword(s):  
Equilibrium Constant ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Alkaline Solutions ◽  
Formation Reaction

Rate and equilibrium constants have been measured for the hydration and retroaldol reactions of cinnamaldehyde. The equilibrium constant for the 1,4-addition of water to cinnamaldehyde is 4.42 × 10−3. The rate constants for hydroxide catalyzed reaction, extrapolated to zero hydroxide concentration (to correct for the addition of hydroxide to the aldol carbonyl), are: [Formula: see text];[Formula: see text]; and [Formula: see text]. The rate of the formation reaction was measured by adding small amounts of acetaldehyde to alkaline solutions of benzaldehyde: [Formula: see text] and Koverall = 1480 M−1. The course of the synthetically useful reaction of acetaldehyde with benzaldehyde is discussed in the light of these results.

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.

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.

Kinetics and mechanisms of the reaction of 2,4,6-trinitrocumene and 2,4,6-trinitroethylbenzene with 1,1,3,3-tetramethylguanidine in N,N-dimethylformamide solvent

1987 ◽  
Vol 65 (5) ◽  
pp. 1007-1011 ◽  
Author(s):  
Mihir K. Biswas ◽  
Arnold Jarczewski ◽  
Kenneth T. Leffek
Keyword(s):  
Carbon Atom ◽  
Complex Formation ◽  
Proton Transfer ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Reaction Parameters ◽  
Deuterium Isotope Effect ◽  
Constant Rate

The reaction of tetramethylguanidine (TMG) with trinitrocumene (TNC) and trinitroethylbenzene (TNEB) in dimethylformamide solvent has been studied with respect to products and kinetics. For TNC only σ-complex formation with the benzene ring was observed, for which the equilibrium constant, rate constants, and activation parameters were measured. For TNEB, both σ-complex formation and proton transfer from the σ-carbon atom of the ethyl group were observed. The equilibrium constants, rate constants, and activation parameters were separately determined for each reaction and a primary deuterium isotope effect, kH/kD = 13.6 (at 20 °C), was found for the proton transfer. The reaction parameters are compared to those for proton transfer from TNT to tetramethylguanidine in DMF solvent.

The influence of fluoride ions on the equilibrium between titanium ions and titanium metal in fused alkali chloride melts

2016 ◽  
Vol 190 ◽  
pp. 421-432 ◽  
Author(s):  
Jianxun Song ◽  
Qiuyu Wang ◽  
Jinyu Wu ◽  
Shuqiang Jiao ◽  
Hongmin Zhu
Keyword(s):  
Equilibrium Constant ◽  
Coordination Compounds ◽  
Least Squares Method ◽  
Equilibrium Constants ◽  
Free Energies ◽  
Stable States ◽  
Alkali Chloride ◽  
Fluoride Ions ◽  
Formation Reaction ◽  
The Right

KF is employed as a source of fluoride ions added to the melt to disclose the influence of fluoride on the disproportionation reactions of titanium ions, 3Ti2+ = 2Ti3+ + Ti, and 4Ti3+ = 3Ti4+ + Ti. The results reveal that the equilibrium transferred to the right direction for the first reaction and the apparent equilibrium constant increased sharply, mainly because of the formation of coordination compounds: TiFi3−i. The accurate values of the equilibrium constants referring to the formation reactions of Ti3+ + iF− = TiFi3−i (i = 1–6) in NaCl–KCl melt at 1023 K were evaluated with a best fit least squares method. It is also revealed that the stable states of the coordination compounds are TiF2+, TiF2+, TiF4− and TiF63−. Moreover, the Gibbs free energies for complex formation were estimated. Ti2+ was undetectable when the concentration of fluoride ion was high enough. The equilibrium constant for the formation reaction, Ti4− + 6F− = TiF62−, was evaluated. The equilibrium constant, Kc2, for the disproportionation reaction 4Ti3+ = 3Ti4+ + Ti, in chloride melt was determined as 0.015.

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.

Chelating equilibria of 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol and 4-(2-pyridylazo)resorcinol with La(III) ions

1988 ◽  
Vol 53 (3) ◽  
pp. 526-542
Author(s):  
Dimitrii Borisovich Gladilovich ◽  
Vlastimil Kubáň ◽  
Josef Havel
Keyword(s):  
Absorption Band ◽  
Organic Solvent ◽  
Aqueous Solutions ◽  
Equilibrium Constant ◽  
Absorption Maximum ◽  
Aqueous Ethanol ◽  
Equilibrium Constants ◽  
Organic Component ◽  
Alkaline Solutions ◽  
Hydrolysis Products

2-(5-Bromo-2-pyridylazo)-5-diethylaminophenol (BrPADAP) with lanthanum(III) ions in 50% (v/v) aqueous ethanol or 30-50% (v/v) aqueous dimethylformamide (DMF) forms unprotonated chelates ML and ML2 characterized by a double absorption band with maxima at 550 and 570 nm. The ML2 species is rather unstable, hydrolyzing readily to the M(OH)L chelate, which exhibits an absorption maximum at 570 nm. The molar absorptivities of the ML, ML2, and M(OH)L species, lying in the regions of 5.3-6.5, 7.0-7.2, and 6.5-7.2 m2 mmol-1, respectively, depend on the kind and fraction of the organic component in the solvent. The conditional equilibrium constants (-log βpqr = 3.3-4.0, 12.2-12.5, and 7.8-8.2, respectively) decrease with increasing fraction of the organic solvent; in systems with high proportions of ethanol orDMF, the formation of higher species is greatly suppressed. 4-(2-Pyridylazo)resorcinol (PAR) with La(III) in acid aqueous solutions forms the MLH and ML species with absorption maxima at 490 and 506 nm, respectively ( ε = 1.2 and 2.5 m2 mmol-1, respectively) and with conditional equilibrium constants –log βpqr = -3.4 and 3.5, respectively. In alkaline solutions with excess PAR, the ML2 species with the absorption maximum at 509 mn (ε = 4.6 m2 mmol-1) and conditional equilibrium constant –log βpqr = 8.1 is formed. This chelate hydrolyses readily forming the M(OH)L species and other hydrolysis products. The ML2 species of the two reagents, forming in ammoniacal buffer at pH 9.0 – 9.5 (PAR) and 8.2 – 8.4 (BrPADAP), can be used for a sensitive (ε = 3.8 and 6.1 m2 mmol-1, respectively) post-column derivatization of lanthanoids after their separation by IEC or HPLC or for their FIA determination.

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.

Oxidation of (1-hydroxybenzyl)ferrocene and its derivatives substituted in phenyl ring with bis(triphenylsilyl) chromate

1982 ◽  
Vol 47 (12) ◽  
pp. 3375-3380 ◽  
Author(s):  
Jaroslav Holeček ◽  
Karel Handlíř ◽  
Milan Nádvorník ◽  
Milan Vlček
Keyword(s):  
Linear Dependence ◽  
Rate Constants ◽  
Oxidation Rate ◽  
Phenyl Ring ◽  
Equilibrium Constants ◽  
Aprotic Solvents ◽  
Protonation Equilibrium ◽  
Oxidation Of Alcohols ◽  
Hammett Σ Constants ◽  
Sulphuric Acid Medium

Kinetics have been studied of oxidation of (1-hydroxybenzyl)ferrocenes substituted in phenyl ring with bis(triphenylsilyl) chromate in benzene solutions as well as protonation of these alcohols in sulphuric acid medium. Logarithms of the oxidation rate constants (kobs, 20-40 °C) and those of the protonation equilibrium constants (KR+, 25 °C) show linear dependence on the Hammett σ constants, the ρ constant values being -0.86 to -0.40 and -2.50, respectively. These negative values suggest that the both processes are influenced by the same effects and confirm the mechanism proposed earlier for oxidation of alcohols with ferrocenyl substituent by action of bis(triphenylsilyl) chromate in aprotic solvents.

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.

scholarly journals Rate constants and equilibrium constants for binding of actin to the 1:1 gelsolin-actin complex

1991 ◽  
Vol 202 (3) ◽  
pp. 1127-1131 ◽  
Author(s):  
Beate SCHOEPPER ◽  
Albrecht WEGNER
Keyword(s):  
Rate Constants ◽  
Equilibrium Constants
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