The Proline Enamine Formation Pathway Revisited in Dimethyl Sulfoxide: Rate Constants Determined via NMR

2015 ◽  
Vol 137 (40) ◽  
pp. 12835-12842 ◽  
Author(s):  
Michael H. Haindl ◽  
Johnny Hioe ◽  
Ruth M. Gschwind
Keyword(s):  
Dimethyl Sulfoxide ◽  
Rate Constants ◽  
Formation Pathway ◽  
Enamine Formation

Dynamics of the Bis-Tris and High Spin-Low Spin Equilibria of 2-(2′-Pyridyl)imidazoleiron(II) Complexes in Dimethyl Sulfoxide Solutions

1988 ◽  
Vol 41 (9) ◽  
pp. 1315 ◽  
Author(s):  
JK Beattie ◽  
KJ Mcmahon
Keyword(s):  
Relaxation Time ◽  
Dimethyl Sulfoxide ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Temperature Jump ◽  
Free Ligand ◽  
Relaxation Curve ◽  
Dissociation Equilibrium ◽  
Laser Temperature Jump ◽  
Equilibrium Transition

Ultrasonic and temperature-jump relaxation kinetics have been used to observe, respectively, the spin equilibrium and tris-bis ligand dissociation equilibrium of the 2-(2′-pyridyl) imidazoleiron (II) complexes in dimethyl sulfoxide solutions. In the ultrasonic experiments a single relaxation curve describes the excess sound absorption with a relaxation time of 73�3 ns. This was identified as perturbation of the singlet-quintet spin equilibrium by comparison with previous laser temperature-jump measurements in other solvents and by the temperature dependence of the relaxation amplitude. The equilibrium constant for the singlet-quintet transition was determined by the Evans n.m.r . method to be 0.48 at 298 K. From the relaxation time and the equilibrium constant the rate constants for the spin-equilibrium transition can be calculated to be k15 of 4.5×106 s-1 and k51 of 9.4×106s-1. In the temperature-jump experiments a millisecond relaxation time was observed. The dependence of the relaxation time on the concentration of the free ligand is of the form kobs = a + b[L]. From the ratio b/a an equilibrium constant for the perturbed process can be calculated. An independent measure of this equilibrium constant was obtained from spectrophotometric measurements. The rate constants for the formation and dissociation of the tris complex are calculated to be 2.8 × 104 dm3 mol-1 s-1 and 2.1 × 102 s-1, respectively, at 298 K.

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.

Aromatic Substitutions with Carbanion Nucleophiles. II. The Kinetics and Mechanism of the Reaction of 1-Fluoro-2,4-dinitrobenzene with the Diethyl Malonate Anion

1973 ◽  
Vol 51 (10) ◽  
pp. 1659-1664 ◽  
Author(s):  
Kenneth T. Leffek ◽  
Paul H. Tremaine
Keyword(s):  
Dimethyl Sulfoxide ◽  
Sodium Salt ◽  
Rate Constants ◽  
Activation Parameters ◽  
Diethyl Malonate ◽  
Kinetics And Mechanism ◽  
Reaction Solution ◽  
Red Color ◽  
Unstable Intermediate ◽  
Mechanism Of The Reaction

The reaction of fluoro-2,4-dinitrobenzene with the sodium salt of diethyl malonate to form diethyl (2,4-dinitrophenyl)malonate is fast in dimethyl sulfoxide solvent. The stable red color of the reaction solution is due to the anion of the product, although the initially formed unstable intermediate between the substrate and the anion nucleophile is also red and can be observed at times less than 200 ms after mixing.The rate constants for all the steps in the reaction have been measured and the activation parameters for the three processes involved in the nucleophile substitution have been calculated.

Reactivity of nucleophiles in dimethyl sulfoxide and its comparison with nucleophilic reactivity in protic medium

1989 ◽  
Vol 54 (10) ◽  
pp. 2715-2720 ◽  
Author(s):  
Vítězslav Zima ◽  
Oldřich Pytela ◽  
Jaromír Kaválek ◽  
Miroslav Večeřa
Keyword(s):  
Dimethyl Sulfoxide ◽  
Electrostatic Interaction ◽  
Rate Constants ◽  
Reaction Medium ◽  
Correlation Equation ◽  
Regression Coefficients ◽  
Aprotic Solvents ◽  
Protic Solvents ◽  
Nucleophilic Reactivity

Reactions of 2,4-dinitrophenyl acetate and 2,4-dinitrofluorobenzene as model substrates with 12 nucleophiles have been studied in dimethyl sulfoxide. The rate constants obtained have been discussed with regard to the nucleophilic reactivity differences in dimethyl sulfoxide and protic solvents inclusive of the different manifestation of the charge of nucleophiles. The applicability of an earlier-suggested correlation equation to the data obtained has been verified. The reaction medium markedly affects the reactivity of nucleophiles, the effect of charge being substantially greater in aprotic solvents (electrostatic interaction) than in protic ones (solvation). In spite of these differences the correlation with application of an empirical nucleophilicity scale suggested earlier is satisfactory, the regression coefficients obtained reflect changes in the nature of medium.

Rates of Reaction of Nickel (II) with Terpyridine in Dimethyl Sulfoxide

1972 ◽  
Vol 50 (3) ◽  
pp. 402-411 ◽  
Author(s):  
Patricia A. Cock ◽  
C. E. Cottrell ◽  
R. K. Boyd
Keyword(s):  
Dimethyl Sulfoxide ◽  
Rate Constants ◽  
Second Order ◽  
Dmso Solution ◽  
Substitution Reactions ◽  
Order Rate ◽  
Nickel Species

The rates at which 2,2′,2″-terpyridine reacts with nickel(II) ion to form the monoligand–nickel(II) and the bisligand–nickel(II) complexes were determined in DMSO solution. Ni(terpy)Cl2 was isolated, and used to study the rate of formation of bis complex. The second-order rate constants were found to parallel the rates of DMSO exchange, determined using n.m.r. techniques, from the respective paramagnetic nickel species. Attempts were made to relate the results to the generally accepted "dissociative" pathways for this class of substitution reactions.

The kinetics and mechanism of the reaction between nickel(II) and dithiocarbamate ions in dimethyl sulfoxide. Evidence for the ID mechanism for a bidentate uninegative ligand

1978 ◽  
Vol 31 (12) ◽  
pp. 2581 ◽  
Author(s):  
PJ Nichols ◽  
MW Grant
Keyword(s):  
Fourier Transform ◽  
Ionic Strength ◽  
Dimethyl Sulfoxide ◽  
Excellent Agreement ◽  
Rate Constants ◽  
Second Order ◽  
Kinetics And Mechanism ◽  
First Order ◽  
Temperature Dependences ◽  
Mechanism Of The Reaction

13C Fourier-transform N.M.R. has been used to measure the rate of exchange of dimethyl sulfoxide with hexakis(dimethyl sulfoxide)nickel(II) cation. The parameters obtained, kex(25°C)(9.8�4.6) × 103 s-1, ΔH‡ 50�2 kJ mol-1 and ΔS‡ 0�4 J K-1 mol-1, are in excellent agreement with those of the most recent 1H N.M.R. study. The reaction between Ni(Me2SO)62+ and diethyldithiocarbamate (dtc-) gives only Ni(dtc)2. When dtc- is in excess, the rate of formation of Ni(dtc)2 is first order in Ni2+ and dtc-. The ionic-strength and temperature dependences of the second-order rate constants are consistent with the rate-determining formation of an unstable Ni(dtc)+ complex by an ID mechanism.

ELECTRONIC EFFECTS IN E2 REACTIONS: II. t-BUTOXIDE-INDUCED ELIMINATIONS OF 2-METHYL-3-PENTYL ARENESULFONATES

1965 ◽  
Vol 43 (5) ◽  
pp. 1282-1292 ◽  
Author(s):  
Allan K. Colter ◽  
Donald R. McKelvey
Keyword(s):  
Transition State ◽  
Dimethyl Sulfoxide ◽  
Vapor Phase ◽  
Rate Constants ◽  
Equilibrium Mixture ◽  
Second Order ◽  
Electronic Effects ◽  
Electronic Nature ◽  
Leaving Group ◽  
Electron Withdrawal

As part of a study of the influence of electronic effects imposed by the leaving group on orientation in E2 reactions, a study of elimination in a series of 2-methyl-3-pentyl arenesulfonates (I) has been carried out. The compositions of the olefin mixtures resulting from reaction of selected members of this series with potassium t-butoxide in t-butanol (1a, Id), 50% (by volume) t-butanol – dioxane (Ia–Ig), 25% (by volume) t-butanol – dioxane (Id–If), and 25% (by volume) t-butanol – dimethyl sulfoxide (Ia, Id, If, Ig), at 50 °C, have been determined using vapor phase chromatography. Second-order rate constants were measured for these reactions in t-butanol (Ie), and 50% t-butanol – dioxane (Ia, Ic–Ig) at 50 °C and in 25% t-butanol – dimethyl sulfoxide (Ia, Id, Ie) at 25 °C.The compositions of the olefin mixtures vary in a fairly regular way with changes in the electronic nature of the leaving group, the fraction of 2-methyl-2-pentene and ratio of trans-to cis-4-methyl-2-pentene for the most part increasing with increasing electron withdrawal. The E2 reactions in 25% t-butanol – dimethyl sulfoxide produce trans- and cis-4-methyl-2-pentene in ratios (20 to 35) considerably higher than those in an equilibrium mixture (ca. 6).The results are discussed in terms of recent views on the E2 transition state.

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