THE ACTIVATION PROCESS IN SOLVOLYSIS

1964 ◽  
Vol 42 (7) ◽  
pp. 1707-1711 ◽  
Author(s):  
R. E. Robertson
Keyword(s):  
Activation Energy ◽  
Heat Capacity ◽  
Transition State ◽  
Isotope Effect ◽  
Activation Process ◽  
Solvent Isotope Effect ◽  
Apparent Heat Capacity ◽  
Structural Nature ◽  
Solvent Isotope

The structural nature of water is a major factor in determining the solvent isotope effect and the apparent heat capacity of activation for solvolysis. The consequences of this assumption are examined for the SN2 mechanism in terms of solvation changes at the transition state and the probable make-up of the activation energy.

Solvolysis of sulphonyl halides. V. Hydrolysis and deuterolysis of methanesulphonyl chloride

1970 ◽  
Vol 23 (12) ◽  
pp. 2427
Author(s):  
ML Tonnet ◽  
AN Hambly
Keyword(s):  
Transition State ◽  
Thermodynamic Parameters ◽  
Isotope Effect ◽  
Large Reduction ◽  
Butyl Chloride ◽  
Solvent Isotope Effect ◽  
Initial State ◽  
Solvent Isotope ◽  
Hydrolysis Of

The values of the thermodynamic parameters of activation have been determined for the solvolysis of methanesulphonyl chloride in H2O and D2O and their mixtures with moderate amounts of dioxan. Some of the data are not in agreement with the postulate that the kinetic solvent isotope effect and the maximum in the rate of solvolysis produced by the addition of dioxan are due to changes in the initial state of the reacting system rather than to changes in the transition state. The addition of dioxan does not produce a large reduction in the solvent isotope effect as reported for the hydrolysis of t-butyl chloride and predicted to be general. The relative rates of solvolysis in mixtures of H2O and D2O are not in agreement with the analysis of such reactions by Swain and Thornton.

Kinetic solvent isotope effect, solvent reorganization, and the SN1–SN2 mechanism

1969 ◽  
Vol 47 (18) ◽  
pp. 3397-3404 ◽  
Author(s):  
L. Treindl ◽  
R. E. Robertson ◽  
S. E. Sugamori
Keyword(s):  
Heat Capacity ◽  
Probable Mechanism ◽  
Activation Process ◽  
Solvent Structure ◽  
Butyl Chloride ◽  
Solvent Isotope Effect ◽  
Mechanism Of Reaction ◽  
Wide Range ◽  
Two Temperatures ◽  
Solvent Isotope

The temperature dependence of the rates of solvolysis have been determined in D2O for t-butyl chloride, 2,2-dibromopropane, 2-bromo-2-chloropropane, and 2-chloro-2-methyl propyl methyl ether, and corresponding values of ΔH≠, ΔS≠, and ΔCp≠ are derived. Values of ΔH≠ and ΔS≠ from the solvolysis of seven other halides and two benzenesulfonates have been estimated from rate determinations at two temperatures in D2O.A comparison of these values with terms from corresponding experiments in H2O provides values of δIΔG≠, δIΔH≠, and δIΔS≠ characterizing the kinetic solvent isotope effect.While δIΔG≠ appears to have about the same value for a wide range of halides of different structure irrespective of the probable mechanism of reaction, systematic differences in δIΔH≠ and δIΔS≠ differentiate those reacting by an SN2 mechanism from those reacting by an SN1 mechanism. This difference is in the direction suggesting a loosening of solvent structure in the activation process in agreement with indications obtained from the corresponding values of the heat capacity of activation.

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.

Solvent reorganization for hydrolysis with hydrogen participation

1969 ◽  
Vol 47 (24) ◽  
pp. 4599-4605 ◽  
Author(s):  
Y. Inomoto ◽  
R. E. Robertson ◽  
G. Sarkis
Keyword(s):  
Acetic Acid ◽  
Isotope Effect ◽  
Activation Process ◽  
Solvent Isotope Effect ◽  
Butyl Bromide ◽  
Rate Of Hydrolysis ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Reaction In Water

A study of the rates of hydrolysis of 3-Me-2-butyl bromide and methanesulfonate in water leads to values of ΔCp≠ of −80 and −40 cal deg−1 mole−1, respectively. The product was about 85–95 % t-pentanol, the remainder being olefin. The value of ΔCp≠ for the solvolysis of the methanesulfonate in D2O was −44 cal deg−1 mole−1. The kinetic solvent isotope effect (k.s.i.e.) for the latter was unusually low (k.s.i.e. = 1.047 at 5 °C and 1.025 at 25 °C). Deuteration at C-3 led to a reduction in the rate of hydrolysis by a factor of about 2.25. This is consistent with an activation process involving "hydrogen participation" as previously reported by Winstein and Takahashi for solvolysis of the corresponding tosylate in acetic acid. In contrast to the latter work, the reaction in water appears to be uncomplicated.

Sulfonyl Chloride Kinetics. Part III. Nucleophilic Interaction on the Transition State for 4-X-Benzenesulfonyl Chloride Solvolyses

1971 ◽  
Vol 49 (9) ◽  
pp. 1451-1455 ◽  
Author(s):  
B. Rossall ◽  
R. E. Robertson
Keyword(s):  
Carbon Atom ◽  
Transition State ◽  
Isotope Effect ◽  
Structural Changes ◽  
Sulfonyl Chloride ◽  
Solvent Isotope Effect ◽  
Benzenesulfonyl Chloride ◽  
Solvent Isotope ◽  
Linear Correlations ◽  
Saturated Carbon Atom

The kinetic solvent isotope effect [Formula: see text], was measured for 4-X-benzenesulfonyl chlorides (where X = MeO, Me, H, Br, and NO2) and shown to vary systematically, giving linear correlations with Hammett σ values and with [Formula: see text] ratios. These results contrast with the lack of sensitivity in k.s.i.e. to structural changes for displacement from a saturated carbon atom. This behavior is attributed to a greater degree of bond making required to achieve a critical charge on the chloride of the sulfonyl chloride at the transition state.

Zur Theorie des kinetischen Lösungsmittel-Isotopeneffektes auf säurekatalytische organische Reaktionen II

1964 ◽  
Vol 19 (6) ◽  
pp. 461-467 ◽  
Author(s):  
Alfred V. Willi
Keyword(s):  
Partition Function ◽  
Transition State ◽  
Isotope Effect ◽  
Acid Catalysis ◽  
Free Energies ◽  
Solvent Isotope Effect ◽  
General Acid ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Limiting Value

From the known difference of free energies of liquid H2O and D2O at 25°, the following partition function ratio may be calculated: QD2O/QH2O = 1416. By combination with the constant L=11.0 for the equilibrium 2 D3O⊕ +3 H2O ⇆ 2H3O⊕ + 3D2O, one obtains QD3O/QH3O = 16100. The partition function ratio of an organic acid ROH is approximated by QROD/QROH ≈ (QD2O/QH2O)½. KH/KD≈ 3.3 is calculated for the solvent isotope effect on the acidity of ROH. Correspondingly, the approximation QSD/QSH ≈ (QD3O/QΗ3O)⅓ is introduced for conjugate acids (SH®) of ethers and carbonyl compounds, leading to the solvent isotope effect: KH/KD ≈ 2.2. - In the acid-catalysed hydrolysis of acetals, the formation of the transition state involves the complete transformation from the H3O⊕ to the H2O state of 2 OH bonds and the partial transformation of one more OH bond. Consequently, the limits 1/3.3 < kH/kD < 1/2.2 are calculated for the kinetic solvent isotope effect. The following equation is valid for the general acid catalysis by HA of the enolisation of acetone: kHA/kDA = (KHA/KDA) / (KSH/KSD). Theoretical values are calculated which agree well with experimental data. - On the basis of a simple model for the transition state, the solvent isotope effect on rate determining H® transfer from acetic acid to a substrate (general acid catalysis) may be calculated. (kHA/kDA) min = 5.7 is obtained as a limiting value.

Neutral Solvolysis of Acyl Carbon and the Temperature Dependence of the Kinetic Solvent Isotope Effect

1975 ◽  
Vol 53 (6) ◽  
pp. 869-877 ◽  
Author(s):  
B. Rossall ◽  
R. E. Robertson
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Solvent Isotope Effect ◽  
Acyl Carbon ◽  
Rate Of Hydrolysis ◽  
Solvent Isotope ◽  
Neutral Conditions ◽  
Hydrolysis Of

The temperature dependence of the rate of hydrolysis of benzoic, phthalic, and succinic anhydrides have been determined in H2O and D2O under "neutral" conditions. Corresponding data have been obtained for methyl trifluoroacetate. While both series supposedly react by the same BAc2 mechanism, remarkable differences are made obvious by this investigation. Possible sources of such differences are proposed.

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