KINETIC STUDIES OF PROTON TRANSFER FROM PHENOLS TO TRINITROBENZYL ANION

1966 ◽  
Vol 44 (2) ◽  
pp. 119-124 ◽  
Author(s):  
J. A. Blake ◽  
M. J. B. Evans ◽  
K. E. Russell
Keyword(s):  
Proton Transfer ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Kinetic Studies ◽  
Sodium Cation ◽  
Rate Determining Step ◽  
Rate Of Reaction ◽  
Hammett Relationship ◽  
Measurable Concentration ◽  
Acetic Acids

The rates of reaction of various phenols with the 2,4,6-trinitrobenzyl anion in the solvent ethanol have been determined by a spectrophotometric method. The rate constants at −40 °C are related to the dissociation constants of the phenols in water at 25 °C and the value of α in the Brönsted relation is 0.84 ± 0.07; α drops to 0.44 ± 0.05 if the results for the substituted acetic acids (1) are included. The rate constants for the phenols are also correlated by the Hammett relationship, the ρ value at −40 °C being 1.82 ± 0.2. The activation energies range from 9.4 to 10.9 kcal/mole.The rate of reaction of trinitrobenzyl anion with 3-methylphenol at −30 °C is reduced by a factor of 12 if the phenol is deuterated at the OH group and the solvent is deuteroethanol. The large isotope effect confirms that the rate-determining step involves proton transfer from the OH group of the phenol. Substitution of lithium or potassium cations for the sodium cation does not affect the rate constant at −10 °C.In the reaction with 3-methylphenol, a measurable concentration of trinitrobenzyl anion remains at equilibrium and the equilibrium constant for the reaction is 1.3 ± 0.2 at 25 °C. The heat and entropy changes are approximately −6.5 kcal/mole and −21 e.u./mole respectively.

scholarly journals Rate-determining processes and the number of simultaneously active sites of d-glyceraldehyde 3-phosphate dehydrogenase

1971 ◽  
Vol 122 (1) ◽  
pp. 71-77 ◽  
Author(s):  
D. R. Trentham
Keyword(s):  
Oxidative Phosphorylation ◽  
Active Sites ◽  
Dissociation Constants ◽  
Kinetic Studies ◽  
Competitive Inhibitor ◽  
Low Ph ◽  
Conformation Change ◽  
High Ph ◽  
Rate Determining Step ◽  
Transient Experiments

Transient kinetic studies of the reversible oxidative phosphorylation of d-glyceraldehyde 3-phosphate catalysed by d-glyceraldehyde 3-phosphate dehydrogenase show that all four sites of the tetrameric lobster enzyme are simultaneously active, apparently with equal reactivity. The rate-determining step of the oxidative phosphorylation is NADH release at high pH and phosphorolysis of the acyl-enzyme at low pH. For the reverse reaction the rate-determining step is a process associated with NADH binding, probably a conformation change, at high pH and d-glyceraldehyde 3-phosphate release at low pH. NADH has previously been shown to be a competitive inhibitor of the enzyme with respect to d-glyceraldehyde 3-phosphate and vice versa. This is consistent with the mechanism deduced from transient experiments given the additional proviso that 1-arseno-3-phosphoglycerate has a half-life of about 1min or longer at pH7. The dissociation constants of d-glyceraldehyde 3-phosphate and 1,3-diphosphoglycerate to the NAD+-bound enzyme are too large to measure but are nevertheless consistent with the low Km values of these substrates.

Kinetic studies of the substitution reactions of the cis-dihalotetracarbonylmanganate(I) ions

1969 ◽  
Vol 47 (8) ◽  
pp. 1311-1319 ◽  
Author(s):  
Frank E. Smith ◽  
Ian S. Butler
Keyword(s):  
Halogen Bond ◽  
Kinetic Studies ◽  
Reaction Rates ◽  
Atomic Weight ◽  
Substitution Reactions ◽  
Dissociative Mechanism ◽  
First Order ◽  
Rate Determining Step ◽  
Rate Of Reaction ◽  
Substrate Independent

The substitution reactions of (C2H5)4[cis-Mn(CO)4X2], where X = Br or I, with a variety of ligands, L, were observed to take place with the loss of halide ion, X−, to form cis-Mn(CO)4LX and (C2H5)4NX. The reaction rates in s-tetrachloroethane were first order in substrate, independent of both the nature and the concentration of L, and decreased with increasing atomic weight of the halogen. A dissociative mechanism involving the breaking of a manganese–halogen bond as the rate-determining step is proposed. It is postulated that the order of reactivity of the substrates is most probably the result of an entropy rather than an enthalpy effect. The substitution reactions of (C2H5)4N[cis-Mn(CO)4BrI] in s-tetrachloroethane were also studied kinetically and found to be first order in substrate and independent of the nature and concentration of L. The products of these reactions, however, were mixtures of cis-Mn(CO)4LBr and cis-Mn(CO)4LI, and (C2H5)4NBr and (C2H5)4NI. A solvent study of the reaction between (C2H5)4N[cis-Mn(CO)4Br2] and P(C6H5)3 indicated that the rate of reaction tended to increase with increasing polarity of the solvent.

Homogeneous Hydrogenation of Unsaturated Carboxylic Acids Using Chlororhodate(I) Complexes and Rhodium(I) Diethylsulfide Complexes

1975 ◽  
Vol 53 (6) ◽  
pp. 797-804 ◽  
Author(s):  
Brian R. James ◽  
Flora T. T. Ng
Keyword(s):  
Carboxylic Acids ◽  
Rate Constants ◽  
Maleic Acid ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Homogeneous Hydrogenation ◽  
Chloride Solutions ◽  
Rate Determining Step ◽  
Square Planar ◽  
Unsaturated Carboxylic Acids

N,N-Dimethylacetamide solutions of the cyclooctene complex [Rh(C8H14)2Cl]2, in the presence of excess chloride or diethylsulfide, are effective for the homogeneous hydrogénation of unsaturated carboxylic acids at ca. 80 °C and 1 atm H2. Kinetic studies on the hydrogenation of maleic acid are consistent with a rate determining step involving oxidative addition of H2 to square planar rhodium(I) olefin species. Rate constants and activation parameters agree with those determined previously from similar studies using corresponding rhodium(III) complexes and give confirmation that rhodium(I) catalysts are involved in the rhodium(III) systems. Discussion of the systems is limited by the somewhat uncertain nature of the catalysts; however, chlororhodate(I) species are involved in the chloride solutions, and bis(diethylsulfide) complexes appear likely in the sulfide systems.

scholarly journals Kinetic studies on the effect of uridine diphosphate galactose and manganous ions on the reaction between lactose synthetase A protein from human milk and p-hydroxymercuribenzoate

1974 ◽  
Vol 143 (3) ◽  
pp. 587-590 ◽  
Author(s):  
Barry J. Kitchen ◽  
Patrick Andrews
Keyword(s):  
Human Milk ◽  
Protective Effect ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Kinetic Studies ◽  
Uridine Diphosphate ◽  
First Order ◽  
Pseudo First Order ◽  
Uridine Diphosphate Galactose

The inhibition of lactose synthetase A protein by p-hydroxymercuribenzoate at pH7.5 and 25°C, which involves the reaction of one molecule of inhibitor with each molecule of enzyme, was decreased in rate by UDP-galactose, especially in the presence of Mn2+. Pseudo-first-order rate constants for the reaction between 0.1mm-p-hydroxymercuribenzoate and free enzyme, the enzyme–UDP-galactose complex and the enzyme–Mn2+–UDP-galactose complex were 4.4×10−2, 1.9×10−2 and 0.3×10−2min−1 respectively. The results also indicated that dissociation constants for UDP-galactose in the enzyme–UDP-galactose and enzyme–Mn2+–UDP-galactose complexes were 313 and 16μm respectively, the latter value being similar to the Km for UDP-galactose in the lactose synthetase reaction. The protective effect of UDP-galactose and the role of Mn2+ ions in lactose synthetase are discussed.

scholarly journals Mechanism of Oxidation of (p-Substituted Phenylthio)acetic Acids withN-Bromophthalimide

2011 ◽  
Vol 8 (1) ◽  
pp. 1-8 ◽  
Author(s):  
N. M. I. Alhaji ◽  
A. M. Uduman Mohideen ◽  
K. Kalaimathi
Keyword(s):  
Reaction Rate ◽  
Reaction Medium ◽  
Solvent Mixture ◽  
Kinetics Of Oxidation ◽  
Rate Determining Step ◽  
Water Solvent ◽  
Rate Of Reaction ◽  
Species Effect ◽  
Kinetics Of ◽  
Acetic Acids

The kinetics of oxidation of (phenylthio)acetic acid (PTAA) byN-Bromophthalimide (NBP) in acetonitrile-water solvent mixture at 298 K in the presence of perchloric acid has been followed potentiometrically. The reaction is first-order each in NBP and PTAA and inverse fractional-order in H+. Also, it has been found that the reaction rate is not affected by changes in ionic strength of the reaction medium or by the addition of chemicals such as phthalimide, acrylonitrile and potassium bromide. However, an increase in the water content of the solvent mixture causes an increase in the rate of reaction. These observations have been well analyzed in favour of a SN2-type mechanism, involving NBP itself as the reactive species. Effect of substituents on the reaction rate has been analysed by employing various (p-sustituted phenylthio)acetic acids. The electron-releasing substituent in the phenyl ring of PTAA accelerates the reaction rate while the electron-withdrawing substituent retards the rate. The excellently linear Hammett plot yields a large negative ρ value, supporting the involvement a bromosulphonium ion intermediate in the rate-determining step.

Kinetic studies on the mechanism of the nitraminopyridine rearrangement

1982 ◽  
Vol 35 (10) ◽  
pp. 2035 ◽  
Author(s):  
LW Deady ◽  
OL Korytsky
Keyword(s):  
Sulfuric Acid ◽  
Rate Constants ◽  
Kinetic Studies ◽  
Current Evidence ◽  
Rate Data ◽  
Rate Determining Step

Rate data are reported for the rearrangement, in 92% sulfuric acid at 30�, of a series of 4-X-2-nitra-minopyridines (X = H, Me, Br, CI, MeO, CO2H) and of 4-methyl-2-nitramino(3-D)pyridine. Values of pKa for second protonation of the corresponding pyridin-2-amines were also measured and rate constants for nitration of the monoprotonated pyridinamines were thereby calculated. The results suggest that the rate-determining step occurs prior to formation of the appropriate 3-and 5-nitro σ complexes. The nature of this step is not clear, however, and a key role for the nitramine itself is not proven by the current evidence.

scholarly journals Understanding the reaction mechanism of the regioselective piperidinolysis of aryl 1-(2,4-dinitronaphthyl) ethers in DMSO: Kinetic and DFT studies

2021 ◽  
Vol 46 ◽  
pp. 146867832110274
Author(s):  
Yasmen M Moghazy ◽  
Nagwa MM Hamada ◽  
Magda F Fathalla ◽  
Yasser R Elmarassi ◽  
Ezzat A Hamed ◽  
...  
Keyword(s):  
Carbon Atom ◽  
Density Functional ◽  
Function Analysis ◽  
Density Functional Theory Method ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Nucleophilic Attack ◽  
Common Mechanism ◽  
Slow Step ◽  
Rate Determining Step

Reactions of aryl 1-(2,4-dinitronaphthyl) ethers with piperidine in dimethyl sulfoxide at 25oC resulted in substitution of the aryloxy group at the ipso carbon atom. The reaction was measured spectrophotochemically and the kinetic studies suggested that the titled reaction is accurately third order. The mechanism is began by fast nucleophilic attack of piperidine on C1 to form zwitterion intermediate (I) followed by deprotonation of zwitterion intermediate (I) to the Meisenheimer ion (II) in a slow step, that is, SB catalysis. The regular variation of activation parameters suggested that the reaction proceeded through a common mechanism. The Hammett equation using reaction constant σo values and Brønsted coefficient value showed that the reaction is poorly dependent on aryloxy substituent and the reaction was significantly associative and Meisenheimer intermediate-like. The mechanism of piperidinolysis has been theoretically investigated using density functional theory method using B3LYP/6-311G(d,p) computational level. The combination between experimental and computational studies predicts what mechanism is followed either through uncatalyzed or catalyzed reaction pathways, that is, SB and SB-GA. The global parameters of the reactants, the proposed activated complexes, and the local Fukui function analysis explained that C1 carbon atom is the most electrophilic center of ether. Also, kinetics and theoretical calculation of activation energies indicated that the mechanism of the piperidinolysis passed through a two-step mechanism and the proton transfer process was the rate determining step.

scholarly journals Theoretical insight on the treatment of β-hexachlorocyclohexane waste through alkaline dehydrochlorination

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alicia Bescós ◽  
Clara I. Herrerías ◽  
Zoel Hormigón ◽  
José Antonio Mayoral ◽  
Luis Salvatella
Keyword(s):  
Density Functional ◽  
Kinetic Studies ◽  
Alkaline Treatment ◽  
Functional Study ◽  
Reaction Intermediates ◽  
Preferential Formation ◽  
Reaction Intermediate ◽  
Rate Determining Step ◽  
Dehydrochlorination Reaction ◽  
Theoretical Results

AbstractThe occurrence of 4.8–7.2 million tons of hexachlorocyclohexane (HCH) isomers stocked in dumpsites around the world constitutes a huge environmental and economical challenge because of their toxicity and persistence. Alkaline treatment of an HCH mixture in a dehydrochlorination reaction is hampered by the low reactivity of the β-HCH isomer (HCl elimination unavoidably occurring through syn H–C–C–Cl arrangements). More intriguingly, the preferential formation of 1,2,4-trichlorobenzene in the β-HCH dehydrochlorination reaction (despite the larger thermodynamical stability of the 1,3,5-isomer) has remained unexplained up to now, though several kinetic studies had been reported. In this paper, we firstly show a detailed Density Functional study on all paths for the hydroxide anion-induced elimination of β-HCH through a three-stage reaction mechanism (involving two types of reaction intermediates). We have now demonstrated that the first reaction intermediate can follow several alternative paths, the preferred route involving abstraction of the most acidic allylic hydrogen which leads to a second reaction intermediate yielding only 1,2,4-trichlorobenzene as the final reaction product. Our theoretical results allow explaining the available experimental data on the β-HCH dehydrochlorination reaction (rate-determining step, regioselectivity, instability of some reaction intermediates).

scholarly journals Kinetic Studies of Proton Transfer in the Microenvironment of a Binding Site

1982 ◽  
Vol 121 (3) ◽  
pp. 637-642 ◽  
Author(s):  
Menachem GUTMAN ◽  
Dan HUPPERT ◽  
Esther NACHLIEL
Keyword(s):  
Proton Transfer ◽  
Binding Site ◽  
Kinetic Studies

An experimental study of the reactivity of the hydroxide anion in the gas phase at room temperature, and its perturbation by hydration

1981 ◽  
Vol 59 (11) ◽  
pp. 1615-1621 ◽  
Author(s):  
Scott D. Tanner ◽  
Gervase I. Mackay ◽  
Diethard K. Bohme
Keyword(s):  
Experimental Study ◽  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Room Temperature ◽  
Gas Phase Reactions ◽  
Flowing Afterglow ◽  
Hydroxide Anion

Flowing afterglow measurements are reported which provide rate constants and product identifications at 298 ± 2 K for the gas-phase reactions of OH− with CH3OH, C2H5OH, CH3OCH3, CH2O, CH3CHO, CH3COCH3, CH2CO, HCOOH, HCOOCH3, CH2=C=CH2, CH3—C≡CH, and C6H5CH3. The main channels observed were proton transfer and solvation of the OH−. Hydration with one molecule of H2O was observed either to reduce the rate slightly and lead to products which are the hydrated analogues of the "nude" reaction, or to stop the reaction completely, k ≤ 10−12 cm3 molecule−1 s−1. The reaction of OH−•H2O with CH3—C≡CH showed an uncertain intermediate behaviour.

Sign in / Sign up

Export Citation Format

Share Document