Kinetics of the hydrolysis of thiochloroformate esters in pure water

1970 ◽  
Vol 48 (4) ◽  
pp. 522-527 ◽  
Author(s):  
A. Queen ◽  
T. A. Nour ◽  
M. N. Paddon-Row ◽  
K. Preston
Keyword(s):  
Isotope Effect ◽  
Structural Changes ◽  
Pure Water ◽  
Activation Parameters ◽  
Deuterium Isotope Effect ◽  
Hydro Carbon ◽  
Electron Donation ◽  
Kinetics Of ◽  
Hydrolysis Of

The effects of structural changes on the rates of hydrolysis of a series of thiochloroformate esters in water have been investigated. The reactivity is enhanced by increased electron donation by the hydro carbon group. These results, the activation parameters for the hydrolysis of methyl thiochloroformate and the solvent deuterium isotope effect, are shown to be consistent with the operation of the SN1 mechanism.

Kinetics of the hydrolysis of acyl chlorides in pure water

1967 ◽  
Vol 45 (14) ◽  
pp. 1619-1629 ◽  
Author(s):  
A. Queen
Keyword(s):  
Pure Water ◽  
Activation Parameters ◽  
Acyl Chlorides ◽  
Reversible Addition ◽  
Electron Donation ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Chlorine Bond ◽  
Oxygen Bond ◽  
Bimolecular Mechanism

The activation parameters ΔH≠, ΔS≠, and ΔCP≠ for the hydrolyses of a series of alkyl chloroformates and dimethylcarbamyl chloride in water have been determined. The results indicate that, with increasing electron donation to the chlorocarbonyl group, the mechanism changes from bimolecular to unimolecular (SN1) displacement at this position. For isopropyl chloroformate, some concurrent alkyl–oxygen bond fission is also indicated. The bimolecular mechanism involves reversible addition of water to the carbonyl group followed by ionization of the carbon–chlorine bond.

Kinetics and Mechanism for the Hydrolysis of Chlorothionoformate and Chlorodithioformate Esters in Water and Aqueous Acetone

1972 ◽  
Vol 50 (9) ◽  
pp. 1401-1406 ◽  
Author(s):  
D. M. McKinnon ◽  
A. Queen
Keyword(s):  
Isotope Effect ◽  
Structural Changes ◽  
Activation Parameters ◽  
Aqueous Acetone ◽  
Kinetics And Mechanism ◽  
Solvent Isotope Effect ◽  
Hydrocarbon Group ◽  
Solvent Isotope ◽  
Electron Donation ◽  
Hydrolysis Of

The effects of structural changes on the rates of hydrolysis of a series of chlorothionoformate esters and the analogous chlorodithioformate esters have been studied. For both classes of compound, the reactivity is enhanced by increased electron donation by the hydrocarbon group. These results, the activation parameters for the hydrolyses of the methyl compounds, and the solvent isotope effect are shown to be consistent with the operation of the SN1 mechanism.

Kinetics of Proton Transfer Reactions of Carbon Acids. IV. Primary Deuterium Isotope Effect in the Reaction of Di-(4-nitrophenyl)methane-d2 with t-Butoxide

1974 ◽  
Vol 52 (4) ◽  
pp. 592-596 ◽  
Author(s):  
Jae-Hang Kim ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Isotope Effect ◽  
Activation Parameters ◽  
Proton Transfer Reaction ◽  
Transfer Reactions ◽  
Deuterium Isotope Effect ◽  
Enthalpy Of Activation ◽  
Proton Transfer Reactions ◽  
Carbon Acids ◽  
Kinetics Of

The primary deuterium isotope effect has been measured for the proton transfer reaction from di-(4-nitrophenyl)methane to t-butoxide ion in a solvent consisting of 10% v/v toluene in t-butanol at a series of temperatures between 20 and 45 °C. The isotopic rate ratio, kH/kD, is 7.3 at 25 °C. The activation parameters showed an enthalpy of activation difference (ΔHD≠ − ΔHH≠) of only ca. [Formula: see text] kcal mol−1 and an entropy isotope effect (ΔSD≠ − ΔSH≠) of −2.4 cal mol−1 deg−1. The latter indicates, according to the theory of Bell, that tunnelling of the proton through the energy barrier is unimportant in this reaction. This result is compared to other reactions in the literature, in which tunnelling has been postulated to occur.

scholarly journals The influence of crown ethers on the kinetics of E1cB and E2 β-elimination reactions of di(4-nitrophenyl)fluoroethanes with sodium methoxide in methanol

1982 ◽  
Vol 60 (24) ◽  
pp. 3077-3080
Author(s):  
Kenneth T. Leffek ◽  
Grzegorz Schroeder
Keyword(s):  
Isotope Effect ◽  
Crown Ethers ◽  
Rate Constant ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Activation Parameters ◽  
Deuterium Isotope Effect ◽  
Kinetic Order ◽  
Elimination Reactions ◽  
Kinetics Of

The addition of crown ethers 1,4,7,10,13-pentaoxacyclopentadecane (15C5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18C6) in quantities equimolar to the base, to β-elimination reactions of 1,1,1-trifluoro-2,2-di(4-nitrophenyl)ethane and 1-fluoro-2,2-di(4-nitrophenyl)ethane promoted by sodium methoxide in methanol, has been investigated. In the E2 reaction of the monofluoro compound, the crown ethers caused no change in the kinetic order and only small changes in the second-order rate constants and activation parameters. The primary deuterium isotope effect was also unaltered by the presence of crown ethers.For the (E1cB)R reaction of the trifluoro compound, no change in kinetic order was found, but slightly larger rate constant changes and an increase in the isotope effect from kH/kD = 1.0 to 1.25 at 25 °C was observed. This is interpreted as an alteration in mechanism from (E1cB)R towards (E1cB)I.

scholarly journals Substituent effect on lysozyme-catalysed hydrolysis of some β-aryl di-N-acetylchitobiosides

1969 ◽  
Vol 114 (3) ◽  
pp. 529-534 ◽  
Author(s):  
C. S. Tsai ◽  
J. Y. Tang ◽  
S. C. Subbarao
Keyword(s):  
Isotope Effect ◽  
Rate Constants ◽  
Substituent Effect ◽  
Deuterium Isotope Effect ◽  
Catalytic Rate ◽  
Electron Donating Groups ◽  
First Time ◽  
Kinetics Of ◽  
Hydrolysis Of

Measurements are reported on the kinetics of the lysozyme-catalysed hydrolysis of several β-aryl di-N-acetylchitobiosides, some of which have been synthesized for the first time. The catalytic rate constants (kcat.) at 45° yield a curved Hammett plot (concave up) and the plot of ΔH‡ versus ΔS‡ has a sharp break. Substrates with electron-withdrawing groups exhibit a kinetic deuterium isotope effect (kHcat./kDcat.), whereas those with electron-donating groups show no such isotope effect. The results suggest the operation of different mechanisms for the two types of substrates.

Fractionation of Hydrogen Isotopes in Aqueous Lithium Chloride Solutions

1988 ◽  
Vol 43 (5) ◽  
pp. 449-453 ◽  
Author(s):  
Masahisa Kakiuchi
Keyword(s):  
Oxygen Isotope ◽  
Isotope Effect ◽  
Lithium Chloride ◽  
Structural Changes ◽  
Platinum Catalyst ◽  
Pure Water ◽  
Free Water ◽  
Hydrogen Gas ◽  
Water Molecules ◽  
Chloride Solutions

The D/H ratio of hydrogen gas in equilibrium with water vapor over aqueous lithium chloride solutions was measured at 25 °C, using a hydrophobic platinum catalyst. Experimental details are described. The hydrogen isotope effect between the solution and pure water depends linearly on the LiCl concentration up to ca. 12 m, and at higher concentrations a marked deviation from linearity takes place, as was also observed for the oxygen isotope effect measured by Bopp et al. On the basis of these hydrogen and oxygen isotope effects it is concluded that H218O is enriched in the water molecules coordinated to Li+ ions and HD16O is enriched in the free water molecules of the solution. The observed deviation from linearity for concentrations higher than ca. 12m is interpreted in terms of structural changes in the hydration sphere of the Li+ ions.

The kinetics of proton and deuteron transfer from 4-nitrophenylnitromethane and l-(4-nitrophenyl)-l-nitroethane to 2,7-dimethoxy-l,8-bis(dimethylamino)naphthalene in acetonitrile solvent

1981 ◽  
Vol 59 (21) ◽  
pp. 3034-3038 ◽  
Author(s):  
Kenneth T. Leffek ◽  
Przemyslaw Pruszynski
Keyword(s):  
Isotope Effect ◽  
Reaction Rate ◽  
Significant Contribution ◽  
Reaction Parameters ◽  
Deuterium Isotope Effect ◽  
First Order ◽  
Enthalpy Of Activation ◽  
Deuteron Transfer ◽  
Slow Dissociation ◽  
Kinetics Of

4-Nitrophenylnitromethane reacts with 2,7-dimethoxy-1,8-bis(dimethylamino)naphthalene in acetonitrile in a bimolecular proton transfer, which shows a primary deuterium isotope effect, kH/kD = 12.2 at 25 °C. The large isotope effect on the enthalpy of activation, (ΔHD≠ – ΔHH≠) = 4.6 ± 0.3 kcal mol−1 is consistent with a significant contribution of proton tunnelling to the reaction rate of the protium substrate.The analogous reaction of 1-(4-nitrophenyl)-1-nitroethane with the same base in acetonitrile gives contrasting kinetics and reaction parameters. The reaction is first order, showing no dependence on base concentration. While the isotope effect kH/kD = 9.3 at 25 °C, the enthalpy of activation difference (ΔHD≠ – ΔHH≠) is only 0.5 ± 0.1 kcal mol−1. It is concluded that the 1-(4-nitrophenyl)-1-nitroethane undergoes a slow dissociation, with a very small dissociation constant, followed by a fast association with the base to yield the carbanion ion-pair.

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