The aniline catalysed decarboxylation of oxaloacetic acid

1965 ◽  
Vol 18 (3) ◽  
pp. 337 ◽  
Author(s):  
RW Hay
Keyword(s):  
Aqueous Solution ◽  
Transition State ◽  
Ethanol Solution ◽  
Keto Group ◽  
Fast Process ◽  
Schiff’S Base ◽  
Oxaloacetic Acid ◽  
Single Proton ◽  
Rate Determining Step ◽  
Rate Profile

Aniline catalysis of the decarboxylation of oxaloacetic acid, HO2CCOCH2CO2H + CH3COCO2H + CO2, has been studied in water and ethanol as solvent at 25�. In aqueous solution a maximum occurs in the pH-rate profile at pH 3.9, indicating the participation of a single proton in the transition state. Experiments with the half ester HO2CCOCH2CO2Et, which does not decarboxylate in the presence of amines, suggest that in aqueous solution the intermediate in the reaction is a carbinolamine formed between the amine and the keto group of the acid, and not a Schiff's base as has been previously suggested. In ethanol solution the intermediate is a Schiff's base, and formation of the Schiff's base is the rate-determining step, the actual decarboxylation being a fast process.

EFFECTS OF COMPLEXING ON THE HOMOGENEOUS REDUCTION OF MERCURIC SALTS IN AQUEOUS SOLUTION BY MOLECULAR HYDROGEN

1956 ◽  
Vol 34 (10) ◽  
pp. 1372-1381 ◽  
Author(s):  
G. J. Korinek ◽  
J. Halpern
Keyword(s):  
Aqueous Solution ◽  
Molecular Hydrogen ◽  
Hydrogen Molecule ◽  
Bimolecular Reaction ◽  
Mercury Atom ◽  
Complexing Agents ◽  
Mercuric Ion ◽  
Rate Determining Step ◽  
Homogeneous Reduction

The effects of various complexing agents on the homogeneous reduction of mercuric salts by molecular hydrogen in aqueous solution were determined. In all cases the kinetics suggest that the rate-determining step is a bimolecular reaction between a mercuric ion or complex and a hydrogen molecule, probably leading to the formation of an intermediate mercury atom. The reactivity of various mercuric complexes was found to decrease in the following order: HgSO4 > Hg++ > HgAc2, HgPr2 > HgCl2 > HgBr2 > Hg(EDA)2++. Addition of anions such as OH−, CO3=, Ac−, Pr−, and Cl−, in excess of the amounts required to form stable mercuric complexes, was found to increase the rate. An interpretation of these effects is given.

Effect of Medium on Reactivity for Alkaline Hydrolysis of p-Nitrophenyl Acetate and S-p-Nitrophenyl Thioacetate in DMSO-H2O Mixtures of Varying Compositions: Ground State and Transition State Contributions

2021 ◽  
Author(s):  
Ik-Hwan Um ◽  
Seungjae Kim
Keyword(s):  
Transition State ◽  
Alkaline Hydrolysis ◽  
Ground State ◽  
Rate Constants ◽  
Kinetic Data ◽  
Reaction Medium ◽  
Stepwise Mechanism ◽  
Rate Determining Step ◽  
Leaving Group ◽  
Hydrolysis Of

Second-order rate constants (kN) for reactions of p-nitrophenyl acetate (1) and S-p-nitrophenyl thioacetate (2) with OH‒ have been measured spectrophotometrically in DMSO-H2O mixtures of varying compositions at 25.0 ± 0.1 oC. The kN value increases from 11.6 to 32,800 M‒1s‒1 for the reactions of 1 and from 5.90 to 190,000 M‒1s‒1 for those of 2 as the reaction medium changes from H2O to 80 mol % DMSO, indicating that the effect of medium on reactivity is more remarkable for the reactions of 2 than for those of 1. Although 2 possesses a better leaving group than 1, the former is less reactive than the latter by a factor of 2 in H2O. This implies that expulsion of the leaving group is not advanced in the rate-determining transition state (TS), i.e., the reactions of 1 and 2 with OH‒ proceed through a stepwise mechanism, in which expulsion of the leaving group from the addition intermediate occurs after the rate-determining step (RDS). Addition of DMSO to H2O would destabilize OH‒ through electronic repulsion between the anion and the negative-dipole end in DMSO. However, destabilization of OH‒ in the ground state (GS) is not solely responsible for the remarkably enhanced reactivity upon addition of DMSO to the medium. The effect of medium on reactivity has been dissected into the GS and TS contributions through combination of the kinetic data with the transfer enthalpies (ΔΔHtr) from H2O to DMSO-H2O mixtures for OH‒ ion.

Ligand substitution at five-coordinate copper(II) centres by cyanate, chloride and bromide ions

1980 ◽  
Vol 33 (6) ◽  
pp. 1381 ◽  
Author(s):  
JH Coates ◽  
PR Collins ◽  
SF Lincoln
Keyword(s):  
Aqueous Solution ◽  
Transition State ◽  
Ligand Substitution ◽  
Aqua Ligand ◽  
Stopped Flow ◽  
Bromide Ions ◽  
Ethyl Amine ◽  
Ligand Bond

The substitution of the aqua[tris{2-(dimethylamino)ethyl}amine]copper(II) ion by cyanate, chloride and bromide ions has been studied in aqueous solution by static and stopped-flow spectrophoto-metric techniques. This process is unusually slow for ligand substitution at a copper(II) centre and appears to proceed through an interchange mechanism in which the copper(II)-aqua ligand bond makes a major contribution to the transition state energetics.

Synthesis of “three-legged” tri-dentate podand ligands incorporating long-chain aliphatic moieties, for water remediators, and for isolating metal ions in non-aqueous solution

2018 ◽  
Vol 3 (11) ◽  
Author(s):  
Justin Pothoof ◽  
Michal Ruprecht ◽  
Ben D. Sliwinski ◽  
Ben M. Sosnowski ◽  
Polly R. Fitzgerald ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Aqueous Solutions ◽  
Metal Ions ◽  
Ambient Temperature ◽  
Water Remediation ◽  
Schiff’S Base ◽  
Aliphatic Aldehydes ◽  
Long Chain

Abstract Two molecules, each including tris-2-amino-ethyleneamine (tren), have been produced using a Schiff’s base condensation and long-chain, aliphatic aldehydes. The syntheses are straightforward and can be run in air at ambient temperature. The ability of these molecules to complex with metal ions makes them good candidates for water remediation. The ability of these ligands to hold metal ions in 0.03 M non-aqueous solutions was unexpected. Their syntheses and characterization are discussed.

scholarly journals Design and Characterization of Ethosomes for Transdermal Delivery of Caffeic Acid

Pharmaceutics ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 740
Author(s):  
Supandeep Singh Hallan ◽  
Maddalena Sguizzato ◽  
Paolo Mariani ◽  
Rita Cortesi ◽  
Nicolas Huang ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Caffeic Acid ◽  
High Performance ◽  
Drug Stability ◽  
Ethanol Solution ◽  
Correlation Spectroscopy ◽  
Poloxamer 407 ◽  
Transdermal Administration ◽  
Antioxidant Power ◽  
Acid Diffusion

The present investigation describes a formulative study aimed at designing ethosomes for caffeic acid transdermal administration. Since caffeic acid is characterized by antioxidant potential but also high instability, its encapsulation appears to be an interesting strategy. Ethosomes were produced by adding water into a phosphatidylcholine ethanol solution under magnetic stirring. Size distribution and morphology of ethosome were investigated by photon correlation spectroscopy, small-angle X-ray spectroscopy, and cryogenic transmission electron microscopy, while the entrapment capacity of caffeic acid was evaluated by high-performance liquid chromatography. Caffeic acid stability in ethosome was compared to the stability of the molecule in water, determined by mass spectrometry. Ethosome dispersion was thickened by poloxamer 407, obtaining an ethosomal gel that was characterized for rheological behavior and deformability. Caffeic acid diffusion kinetics were determined by Franz cells, while its penetration through skin, as well as its antioxidant activity, were evaluated using a porcine skin membrane–covered biosensor based on oxygen electrode. Ethosome mean diameter was ≈200 nm and almost stable within three months. The entrapment of caffeic acid in ethosome dramatically prolonged drug stability with respect to the aqueous solution, being 77% w/w in ethosome after six months, while in water, an almost complete degradation occurred within one month. The addition of poloxamer slightly modified vesicle structure and size, while it decreased the vesicle deformability. Caffeic acid diffusion coefficients from ethosome and ethosome gel were, respectively, 137- and 33-fold lower with respect to the aqueous solution. At last, the caffeic acid permeation and antioxidant power of ethosome were more intense with respect to the simple solution.

Aminolysis of naphthyl acetates catalyzed by cyclodextrins

1999 ◽  
Vol 77 (5-6) ◽  
pp. 950-959 ◽  
Author(s):  
Oswald S Tee ◽  
Michael J Boyd
Keyword(s):  
Aqueous Solution ◽  
Transition State ◽  
Rate Constants ◽  
Nucleophilic Attack ◽  
Reactivity Ratios ◽  
Aryl Group ◽  
First Order ◽  
Free Amine ◽  
Transition State Stabilization ◽  
Pseudo First Order

The effects of cyclodextrins (CDs) on the rate of nucleophilic attack on 1- and 2-naphthyl acetates (1-NA and 2-NA) in aqueous solution have been investigated. Analysis of the variation of the pseudo-first-order rate constants with [nucleophile] and [CD] affords rate constants for reaction of the nucleophiles with free ester (kN) and with ester bound to the CD (kcN). The reaction of 1-NA and 2-NA with the trifluoroethoxide anion is slowed down by β-CD as the ratios kcN/kN are 0.11 and 0.30, respectively. For reaction with the anion of 2-mercaptoethanol in the presence of α-CD, β-CD, "hydroxypropyl-β-CD" (hp-β-CD) and γ-CD, the reactivity ratios kcN/kN vary between 0.04 and 2.4, ranging from strong retardation to modest catalysis; the retardations arise with β-CD and hp-β-CD, which bind the esters strongly. By contrast, the attack of primary alkylamines is generally accelerated, and in many cases substantially so. For the aminolysis of 1-NA in the presence of β-CD, values of kcN/kN range from 7 to 460, assuming that free amine reacts with CD-bound ester. Alternatively, if the CD-catalyzed reaction involves free ester reacting with CD-bound amine, with rate constant kNc, the ratios kNc/kN vary from 43 to 140. Either way, there is appreciable catalysis of the aminolysis of 1-NA by β-CD. For the aminolysis of 2-NA, the effects are less dramatic: the ratios kcN/kN range from 0.19 to 17, and values of kNc/kN vary from 17 to 110. The reaction of 1-NA with n-hexylamine is also catalyzed by γ-CD. The variations of kinetic parameters with alkylamine chain length suggest that the CD-catalyzed aminolysis basically takes place by the attack of CD-bound amine on the free ester. However, there must be some stabilizing interactions between the aryl group of the ester and the CD during the reaction, since the transition state stabilization is different for 1-NA and 2-NA, as well for other esters.Key words: aminolysis, catalysis, cyclodextrin, ester cleavage, kinetics.

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