SOLVOLYSIS IN HYDROGEN AND DEUTERIUM OXIDE: III. ALKYL HALIDES

1959 ◽  
Vol 37 (9) ◽  
pp. 1491-1497 ◽  
Author(s):  
P. M. Laughton ◽  
R. E. Robertson
Keyword(s):  
Isotope Effect ◽  
Relative Stability ◽  
Rate Ratio ◽  
Deuterium Oxide ◽  
Pure Water ◽  
Relative Viscosity ◽  
Solvation Shell ◽  
Alkyl Halides ◽  
Kinetic Isotope ◽  
Hydrolysis Of

Rate data for the hydrolysis of a series of α- and β-methylated allyl, benzyl, and cycloalkyl halides in light and heavy water are compared. The major factor determining the rate ratio [Formula: see text] appears to be the relative stability of the initial solvation shell. When the relative viscosity of H2O and D2O is used as a measure of the relative stability of structure in bulk solvent, the observed kinetic isotope effect and the temperature dependence of the isotope effect can be rationalized in terms of accepted properties of aqueous solutions.Attention is drawn to the anomalous rate ratio kRBr/kRI > 1 which appears to be characteristic of solvolysis of these alkyl halides in pure water in contrast to other media.

SOME DEUTERIUM KINETIC ISOTOPE EFFECTS: IV. β-DEUTERIUM EFFECTS IN WATER SOLVOLYSIS OF ETHYL, ISOPROPYL, AND tert-BUTYL COMPOUNDS

1960 ◽  
Vol 38 (11) ◽  
pp. 2171-2177 ◽  
Author(s):  
K. T. Leffek ◽  
J. A. Llewellyn ◽  
R. E. Robertson
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Alkyl Halides ◽  
Tert Butyl ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
Intramolecular Forces

The secondary β-deuterium isotope effects have been measured in the water solvolytic reaction of alkyl halides and sulphonates for primary, secondary, and tertiary species. In every case the kinetic isotope effect was greater than unity (kH/kD > 1). This isotope effect may be associated with varying degrees of hyperconjugation or altered non-bonding intramolecular forces. The experiments make it difficult to decide which effect is most important.

Solvent isotope effects in the oxidation of dipeptides by aqueous chlorine

1999 ◽  
Vol 77 (5-6) ◽  
pp. 997-1004 ◽  
Author(s):  
X L Armesto ◽  
M Canle L. ◽  
V García ◽  
J A Santaballa
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Second Step ◽  
Solvent Isotope Effect ◽  
General Base ◽  
Peptide Oxidation ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

A kinetic study of the mechanism of oxidation of Ala-Gly and Pro-Gly by aqueous chlorine has been carried out. Among other experimental facts, the deuterium solvent isotope effects were used to clarify the mechanisms involved. In a first stage, N-chlorination takes place, and then the (N-Cl)-dipeptide decomposes through two possible mechanisms, depending on the acidity of the medium. The initial chlorination step shows a small isotope effect. In alkaline medium, two consecutive processes take place: first, the general base-catalyzed formation of an azomethine (β ca. 0.27), which has an inverse deuterium solvent isotope effect (kOH-/kOD- ~ 0.8). In a second step, the hydrolysis of the azomethine intermediate takes place, which is also general base-catalyzed, without deuterium solvent isotope effect, the corresponding uncatalyzed process having a normal deuterium solvent isotope effect (kH2O/kD2O ~ 2). In acid medium, the (N-Cl)-dipeptide undergoes disproportionation to a (N,N)-di-Cl-dipeptide, the very fast decomposition of the latter in deuterium oxide preventing a reliable estimation of the solvent isotope effect.Key words: chlorination, deuterium isotope effects, fractionation factors, peptide oxidation, water treatment.

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.

Aspects of the hydrolysis of formamide: revisitation of the water reaction and determination of the solvent deuterium kinetic isotope effect in base

2002 ◽  
Vol 80 (10) ◽  
pp. 1343-1350 ◽  
Author(s):  
H Slebocka-Tilk ◽  
F Sauriol ◽  
Martine Monette ◽  
R S Brown
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Base Hydrolysis ◽  
Kinetic Isotope ◽  
Acid And Base ◽  
Acid Reaction ◽  
Ph Range ◽  
Hydrolysis Of

A study of the hydrolysis of formamide is reported with the aims of isolating the water reaction for hydrolysis from the acid and base hydrolysis terms and determining the solvent deuterium kinetic isotope effect (dkie) on base-catalyzed hydrolysis. Respective activation parameters (ΔH‡ and ΔS‡) of (17.0 ± 0.4) kcal mol–1 and (–18.8 ± 1.3) cal mol–1 K–1 for the acid reaction and (17.9 ± 0.2) kcal mol–1 and (–11.1 ± 0.5) cal mol–1 K–1 for the base reaction were determined from Eyring plots of the second-order rate constants over the range of 27–120°C. Kinetic studies at the minima of the pH/rate profiles in the pH range from 5.6 to 6.2 in MES buffers at 56°C, and in the pH range of 4.25–6.87 in acetate and phosphate buffers at 120°C are reported. At 56°C the available data fit the expression k56obs = 0.00303[H3O+] + 0.032[HO–] + (3.6 ± 0.1) × 10–9, while at 120°C the data fit k120obs = (0.15 ± 0.02)[H3O+] + (3.20 ± 0.24)[HO–] + (1.09 ± 0.29) × 10–6. Preliminary experimental estimates of Ea (ln A) of 22.5 kcal mol–1 (15.03) for the water rate constant (kw) are calculated from an Arrhenius plot of the 56 and 120°C data giving an estimated kw of 1.1 × 10–10 s–1 (t1/2 = 199 years) at 25°C. Solvent dkie values of kOH/kOD = 1.15 and 0.77 ± 0.06 were determined at [OL–] = 0.075 and 1.47 M, respectively. The inverse value is determined under conditions where the the first step of the reaction dominates and is analyzed in terms of a rate-limiting attack of OL–.Key words: formamide, activation parameters, water reaction, acid and base hydrolysis, solvent kinetic isotope effect.

Solvent Isotope Effect on the Reaction Catalysed by the Pyruvate Dehydrogenase Complex from Escherichia coli

2003 ◽  
Vol 384 (4) ◽  
pp. 673-679 ◽  
Author(s):  
X. Liu ◽  
H. Bisswanger
Keyword(s):  
Escherichia Coli ◽  
Isotope Effect ◽  
Pyruvate Dehydrogenase ◽  
Deuterium Oxide ◽  
Pyruvate Dehydrogenase Complex ◽  
Pyrimidine Ring ◽  
Ph Profile ◽  
Kinetic Isotope ◽  
Michaelis Constants ◽  
Solvent Isotope

Abstract The pyruvate dehydrogenase from Escherichia coli showed a primary kinetic isotope effect when its overall reaction or the partial reaction of the pyruvate dehydrogenase component were tested in deuterium oxide. The Michaelis constants for pyruvate were nearly unchanged, but the maximum velocities in water and deuterium oxide differed, their ratio being DV = 1.7 for the overall reaction and DV = 2.1 for the E1p reaction. The pH profile and, accordingly, the δpK1 and δpK2 values were shifted by 0.6 units to higher pL values. A linear proton inventory curve was obtained when varying the atom fractions of protons relative to deuterons from 100 to 0%. This is an indication for a single proton transfer. It is proposed that this relatively weak primary isotope effect may be caused by the protonation of the N1 nitrogen at the pyrimidine ring of the cofactor by an adjacent glutamate residue. The proton of its carboxylic group exchanges very fast with deuterons of the solvent.

The Mechanism for Hydrolysis of Primary Alkyl Chlorosulfates in Water. The Kinetic Solvent Isotope Effect and the Secondary Deuterium Isotope Effect

1972 ◽  
Vol 50 (3) ◽  
pp. 434-437 ◽  
Author(s):  
E. C. F. Ko ◽  
R. E. Robertson
Keyword(s):  
Isotope Effect ◽  
Sulfonyl Chloride ◽  
Alkyl Halides ◽  
Activation Process ◽  
Deuterium Isotope Effect ◽  
Solvent Isotope Effect ◽  
Temperature Coefficients ◽  
Enthalpy Of Activation ◽  
Solvent Isotope ◽  
Hydrolysis Of

The temperature coefficients of the enthalpy of activation [Formula: see text] for the hydrolysis of the three chlorosulfates, methyl, ethyl, and β-chloro, are shown to have values of −50,−55, and −60 cal deg−1 mol−1; values in the same range as previously reported for the hydrolysis of the sulfonyl chlorides. The corresponding value for the β-methoxy isomer was −40 cal deg−1 mol−1, about the same as found for the p-methoxybenzenesulfonyl chloride. The kinetic solvent isotope effect, however, was significantly lower than reported for the sulfonyl chloride series, being about the same as found for the hydrolysis of the alkyl halides. While some degree of nucleophilic overlap is probably required in the activation process, the requirement here is reduced to about the same level as that for the primary halides, and there is no need to postulate a different mechanism on passing from the methyl to the ethyl member of the series, confirming the earlier conclusion of Buncel and Millington.

Mechanistic implications of the solvent kinetic isotope effect in the hydrolysis of NaBH4

2021 ◽  
Author(s):  
Alina Sermiagin ◽  
Dan Meyerstein ◽  
Gifty Sara Rolly ◽  
Totan Mondal ◽  
Haya Kornweitz ◽  
...  
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Kinetic Isotope ◽  
Hydrolysis Of ◽  
Hydrolysis Of Nabh4

Studies in Solvolysis. Part IV. Substituent and Solvent Isotope Effects in the Solvolysis of a Series of Benzyl Trifluoroacetates

1972 ◽  
Vol 50 (12) ◽  
pp. 1886-1890 ◽  
Author(s):  
June G. Winter ◽  
J. M. W. Scott
Keyword(s):  
Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
The Other ◽  
Solvent Isotope Effect ◽  
Other Hand ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Solvent Isotope Effects

The rates of neutral hydrolysis of a series of 4-substituted benzyl trifluoroacetates 4-X-C6H4CH2OCOCF3, X = NO2, Cl, H, CH3, and OCH3 have been studied in water and deuterium oxide, both solvents containing 0.012 mol fraction of acetone. The alteration of the rates with the nature of the 4-substituent and the kinetic solvent isotope effect (k(H2O)/k(D2O)) are consistent with the proposal that the esters with X = NO2, Cl, H, and CH3 all react by an acyl–oxygen BAc2 mechanism. On the other hand, the same mechanistic criteria indicate that the 4-methoxybenzyl ester reacts by both the BAc2 and the SN1 alkyl–oxygen fission paths in equal amounts.

Sign in / Sign up

Export Citation Format

Share Document