Hydrolysis of substituted .alpha.-nitrostilbenes: dissection of rate coefficients for individual steps in the four-step mechanism. Estimates of intrinsic rate constants and transition-state imbalances

1994 ◽  
Vol 116 (2) ◽  
pp. 514-522 ◽  
Author(s):  
Claude F. Bernasconi ◽  
Julianne Fassberg
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Intrinsic Rate ◽  
Rate Coefficients ◽  
Hydrolysis Of ◽  
Step Mechanism

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.

The Hydrolysis of Bis(2-chloroethyl) Sulfide (Sulfur Mustard) in Aqueous Mixtures of Ethanol, Acetone and Dimethyl Sulfoxide

1993 ◽  
Vol 46 (3) ◽  
pp. 293 ◽  
Author(s):  
RI Tilley
Keyword(s):  
Transition State ◽  
Dimethyl Sulfoxide ◽  
Rate Constants ◽  
Charge Separation ◽  
Sulfur Mustard ◽  
Transition States ◽  
Aqueous Mixtures ◽  
Sulfide Sulfur ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

The rate of hydrolysis of bis (2-chloroethyl) sulfide (sulfur mustard) in aqueous mixtures of ethanol, acetone and dimethyl sulfoxide has been measured and compared with previously reported values. Rate constants in water at 25°C for the two consecutive hydrolysis reactions undergone by sulfur mustard were estimated to be (2.93�0.15)×10-3 and (3.87�0.14)×10-3 s-1. Charge separation of 0.42 in the transition states was indicated together with significant solvation of the positive end of the transition state dipoles.

Microcanonical Transition State Theory Rate Coefficients from Thermal Rate Constants via Inverse Laplace Transformation

1998 ◽  
Vol 102 (42) ◽  
pp. 8104-8115 ◽  
Author(s):  
Prasana K. Venkatesh ◽  
Robert W. Carr ◽  
Morrel H. Cohen ◽  
Anthony M. Dean
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Laplace Transformation ◽  
Transition State Theory ◽  
State Theory ◽  
Rate Coefficients ◽  
Inverse Laplace Transformation ◽  
Thermal Rate Constants

Kinetics and mechanism of the hydrolysis of a (5,6)-spirophosphorane. Thermodynamics of the hydrolysis of cyclic five-membered and six-membered phosphonium ions

1991 ◽  
Vol 69 (12) ◽  
pp. 2064-2074 ◽  
Author(s):  
Glenn H. McGall ◽  
Robert A. McClelland
Keyword(s):  
Free Energy ◽  
Transition State ◽  
Rate Constants ◽  
Strong Acid ◽  
Membered Ring ◽  
Phosphate Esters ◽  
Hydrolysis Rate ◽  
Activation Free Energy ◽  
Stabilizing Effect ◽  
Hydrolysis Of

The cyclic five-membered phosphonium ion 2b (2-(2′-hydroxyethoxy)-2-phenyl-1,3,2-dioxaphospholan-2-ylium) derived from ring-opening of the (5,5)-spirophosphorane 1b (5-phenyl-1,4,6,9-tetraoxa-5-phosphaspiro[4,4]nonane) has been observed in neat CF3SO3H and at >85% H2SO4. The cation undergoes hydrolysis in the latter solutions, and an extrapolation has been carried out to obtain an estimate for reactivity in 100% water. Hydrolysis rate constants for phenyltrialkoxyphosphonium ions in water are 107, 100, and 5 × 10−3 s−1 for cyclic five-membered, cyclic six-membered, and acyclic derivatives respectively; these show an excellent correlation with rate constants for a similar series of phosphate esters. An investigation of the hydrolysis of the (5,6)-spirophosphorane 5 (5-phenyl-8,8-dimethyl-1,4,6,10-tetraoxa-5-phosphaspiro[4,5]decane) provides a clue as to the origins of these rate differences. This phosphorane can in principle hydrolyze via two isomeric cyclic phosphonium ions, the six-membered 14 and the five-membered 15. The former is thermodynamically more stable, being the only cation observed under equilibrating conditions of strong acid. However, the hydrolysis of the spirophosphorane, as well as the hydrolysis of fully formed 14, channels through the cyclic five-membered 15. A thermodynamic breakdown reveals that the 9.5 kcal mol−1 difference in activation free energy for the hydrolysis of five- and six-membered cyclic phosphonium ions is due to a combination of a higher free energy (2.5–4.5 kcal mol−1) for the five-membered cation, and a lower free energy (7–5 kcal mol−1) for the pentacoordinate transition state with the five-membered ring. This analysis also shows that a (5,6)-spirophosphorane is 6–8 kcal mol−1 more stable than a (6,6)-spirophosphorane. Thus, a five-membered ring has a significant stabilizing effect on a pentacoordinated phosphorus structure. The accelerated hydrolysis of cyclic phosphonium ions and phosphate esters with five-membered rings is caused by a combination of this stabilizing effect in the transition state and a destabilizing effect in the ground state associated with ring strain. Key words: phosphorane, hydrolysis, phosphate, phosphonium.

scholarly journals Path sampling for atmospheric reactions: formic acid catalysed conversion of SO3 + H2O to H2SO4

2020 ◽  
Vol 2 ◽  
pp. e7 ◽  
Author(s):  
Christopher D. Daub ◽  
Enrico Riccardi ◽  
Vesa Hänninen ◽  
Lauri Halonen
Keyword(s):  
Transition State ◽  
Formic Acid ◽  
Exploratory Study ◽  
Path Space ◽  
Rate Coefficients ◽  
Sampling Techniques ◽  
Path Sampling ◽  
Atmospheric Reactions ◽  
Computational Resources ◽  
Hydrolysis Of

Atmospheric reactions, hitherto studied computationally mainly with static computations in conjunction with transition state theories, can be further described via path sampling calculations. Here we report on an exploratory study of the formic acid catalysed hydrolysis of SO3 to produce H2SO4. We demonstrate that precise measurements of rate coefficients can be obtained in principle for such reactions with an acceptable expenditure of computational resources, and that new insights into the reaction can be obtained by the analysis of the path space explored via path sampling techniques.

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