scholarly journals Alcohol-assisted base-free hydrogenation of acetophenone catalyzed by OsH(NHCMe2CMe2NH2)(PPh3)2

2014 ◽  
Vol 92 (8) ◽  
pp. 731-738 ◽  
Author(s):  
Sean E. Clapham ◽  
Marco Zimmer-De Iuliis ◽  
Katharina Mack ◽  
Demyan E. Prokopchuk ◽  
Robert H. Morris
Keyword(s):  
Reaction Rate ◽  
Catalyst Concentration ◽  
Initial Conditions ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Alcohol Concentration ◽  
Transfer Hydrogenation ◽  
Kinetic Isotope ◽  
Constant Rate

The hydrido–amido complex OsH(NHCMe2CMe2NH2)(PPh3)2 (1) catalyzes the base-free hydrogenation of ketones in benzene. Kinetic studies using acetophenone revealed that the system has an induction period, after which the rate of the reaction increases. A constant rate was observed when a critical amount of the product alcohol was added, indicating that the reaction is autocatalytic in 1-phenylethanol. Varying the initial conditions showed that the reaction rate is dependent on hydrogen and catalyst concentration and independent of ketone concentration. Above the critical concentrations of 1-phenylethanol, the reaction rate is independent of alcohol concentration. The rate law for pressures up to 5 atm was found to be rate = d[alcohol]/dt = −d[ketone]/dt = k[Os][H2], with k = 30 mol L−1 s−1 at 293 K and the temperature dependence provided energy of activation parameters. Therefore, the heterolytic splitting of dihydrogen is rate determining under these conditions. Only small kinetic isotope effects were measured in contrast with the analogous ruthenium system. Complex 1 reacts with the product alcohol 1-phenylethanol and is partially converted into the dihydride complex trans-OsH2(NH2CMe2CMe2NH2)(PPh3)2 and acetophenone; with excess alcohol, an osmium alkoxide is observed at low temperature. As expected from these results, 1 is a ketone transfer hydrogenation catalyst in isopropanol.

Isotope effects in nucleophilic substitution reactions. IV. The effect of changing a substituent at the α carbon on the structure of SN2 transition states

1982 ◽  
Vol 60 (19) ◽  
pp. 2500-2520 ◽  
Author(s):  
Kenneth Charles Westaway ◽  
Zbigniew Waszczylo
Keyword(s):  
Nucleophilic Substitution ◽  
Isotope Effects ◽  
Transition States ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Kinetic Isotope Effects ◽  
Substitution Reactions ◽  
Nucleophilic Substitution Reactions ◽  
Kinetic Isotope ◽  
Benzyl Chlorides

Kinetic studies, secondary α-deuterium kinetic isotope effects, primary chlorine kinetic isotope effects (1), Hammett ρ values determined by changing the substituent in the nucleophile, and activation parameters have been used to determine the detailed (relative) structures of the transition states for the SN2 reactions between para-substituted benzyl chlorides and thiophenoxide ion. A rationale for the U-shaped Hammett ρ plots observed when para-substituted benzyl compounds react with negatively charged nucleophiles is also presented.

Kinetics and mechanism of redox reactions of U(III) ions with monochloroacetic and dichloroacetic acids

1979 ◽  
Vol 44 (2) ◽  
pp. 401-405 ◽  
Author(s):  
Ľubica Adamčíková ◽  
Ľudovít Treindl
Keyword(s):  
Redox Reactions ◽  
Reaction Rate ◽  
Activation Parameters ◽  
Outer Sphere ◽  
Alcohol Concentration ◽  
Kinetics And Mechanism ◽  
Solvent Structure ◽  
Influence Of Ph ◽  
Sphere Mechanism

The kinetics and mechanism of the redox reactions of U3+ ions with mono- and dichloroacetic acids were studied. The influence of pH was observed mainly in the second case and led to the determination of the rate constants and activation parameters corresponding to two parallel steps, namely oxidation of U3+ with CHCl2COO- ions and oxidation of U3+ with CHCl2.COOH molecules. The influence of binary mixtures of water with methanol, ethanol, isopropanol, or tert-butenol on the reaction rate was followed. Increasing alcohol concentration influences the rate constant not only through changing dielectric constant and solvation of the reactants but also through a change of the solvent structure which plays a role in reactions with an outer sphere mechanism of the electron transfer.

Direct dynamics calculations of reaction rate and kinetic isotope effects in enzyme catalysed reactions

2002 ◽  
Vol 122 ◽  
pp. 223-242 ◽  
Author(s):  
Gary Tresadern ◽  
Sara Nunez ◽  
Paul F. Faulder ◽  
Hong Wang ◽  
Ian H. Hillier ◽  
...  
Keyword(s):  
Reaction Rate ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Direct Dynamics ◽  
Kinetic Isotope

The reaction between 2,2-di(4-nitrophenyl)1,1,1-trifluoroethane and tert-butoxide ion in tert-butyl alcohol solvent

1980 ◽  
Vol 58 (18) ◽  
pp. 1979-1982 ◽  
Author(s):  
Arnold Jarczewski ◽  
Kenneth T. Leffek
Keyword(s):  
Isotope Effects ◽  
Activation Parameters ◽  
Butyl Alcohol ◽  
Blue Colour ◽  
Butyl Ether ◽  
Tert Butyl ◽  
Kinetic Isotope ◽  
Tert Butyl Alcohol ◽  
Reaction Proceeds ◽  
Alcohol Solvent

The reaction between 2,2-di(4-nitrophenyl) 1,1,1-trifluoroethane and excess sodium tert-butoxide in tert-butyl alcohol takes place rapidly to yield first the olefin, by elimination of HF. This is followed by a slower addition of tert-butoxide to the olefin, which upon reaction with the solvent gives the tert-butyl ether as the final product. The blue anions involved in each of these reactions are observed.Rate constants, the primary deuterium kinetic isotope effects, and the activation parameters have been measured for the appearance of the initial blue colour and also for the formation of the olefin. It is concluded that the reaction proceeds by a reversible ElcB mechanism.

The kinetics of proton and deuteron transfer from 1-(4-nitrophenyl)-1-nitroethane to1,8-diazabicyclo[5.4.0]undec-7-ene in aprotic solvents

1982 ◽  
Vol 60 (13) ◽  
pp. 1692-1695 ◽  
Author(s):  
Kenneth T. Leffek ◽  
Przemyslaw Pruszynski
Keyword(s):  
Energy Barrier ◽  
Reaction Rate ◽  
Significant Contribution ◽  
Transfer Reaction ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Proton Transfer Reaction ◽  
Potential Energy Barrier ◽  
Deuteron Transfer ◽  
Kinetics Of

1-(4-Nitrophenyl)-1-nitroethane reacts with the base1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in both acetonitrile and toluene solvents in a normal second-order proton-transfer reaction, in contrast to its behaviour with the base 2,7-dimethoxy-1,8-bis(dimethylamino)naphthalene in acetonitrile.The primary isotope effect, kHlkD = 12.0 at 25° in toluene is very similar to that observed by other workers for the reaction of 4-nitrophenylnitromethane with DBU under the same conditions. In acetonitrile solvent a kHlkD ratio of 7.8 was found at 25 °C. The isotope effects on the activation parameters for the reaction in both solvents indicate that tunnelling of the proton through the potential energy barrier makes a significant contribution to the reaction rate.

Isotope effects in solution: contrasts between muonium and hydrogen in reactions with acetone

1990 ◽  
Vol 68 (10) ◽  
pp. 1719-1724 ◽  
Author(s):  
David C. Walker
Keyword(s):  
Free Radicals ◽  
Physical Properties ◽  
Rate Constants ◽  
Nuclear Physics ◽  
Reaction Rate ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Reaction Rate Constants ◽  
Thiyl Radicals ◽  
Kinetic Isotope

Munonium atoms are hydrogen isotopes with positive muons rather than protons, deuterons, or tritons as nuclei. Thus, they have one ninth the mass of 1H, and microsecond lifetimes. By using nuclear physics counting techniques, muonium can be studied in a wide variety of media and its chemical and physical properties used to appraise hydrogen. Results are described for the interaction of muonium with acetone, showing two types of kinetic isotope effects, formation of free radicals, evidence for intermolecular "muonium bonding", and micelle-induced enhancements of reaction rate constants. Keywords: isotope effects, muonium atoms, muonium bonding, thiyl radicals, micelles.

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