Hydride Transfer Process Research Articles

The reduction of aryl trifluoromethyl ketones by sodium borohydride. The hydride transfer process

The rates of reduction of 17 aryl trifluoromethyl ketones by sodium borohydride in 2-propanol have been measured. The rho (ρ) value is +3.12, excluding the 4-amino and 4-dimethylamino groups, which both lower the rate to a greater extent than their σ values predict. The close correspondence between substituent effects for hydride addition in the methyl and trifluoromethyl series (excluding the amino groups) suggests that normal substituent effects are to be expected for oxidation processes involving hydride removal in trifluoromethyl compounds. The present results are consistent with the oxidation of aryl trifluoromethyl carbinols by permanganate taking place by hydrogen atom abstraction. The effect of substituents on the rate of reduction of the trifluoromethyl ketones is almost identical to that on the equilibrium constant for formation of the ketone hydrates. The application of the reactivity–selectivity principle to the reduction reaction is also considered. Reduction of the 4-ethyl compound has ΔH≠ = 2.7 kcal mol−1 and ΔS≠ = −38 cal deg−1 mol−1

Stereochemical studies of 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from Methanococcus vannielii.

The purified 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from Methanococcus vannielii catalyzes an oxidation-reduction reaction between a novel 8-hydroxy-5-deazaflavin cofactor and nicotinamide adenine dinucleotide phosphate. The reaction was shown to be a direct hydride transfer process. Using stereospecifically 3H-labeled substrates, the steric course of this process was established to be S-specific with respect to the nicotinamide nucleotide. The 8-hydroxy-5-deazaflavin-dependent NADP+ reductase from M. vannielii and the hydrogenase system in the cell-free extracts of Methanobacterium thermoautotrophicum recognize the same side, designated as A side, with respect to the prochiral center at C-5 of the dihydro-8-hydroxy-5-deazaflavin cofactor.

Primary hydrogen–deuterium kinetic isotope effects in the reduction of triarylcarbonium ions by formate anion

The rates of reduction of 16 triarylcarbonium ions to the corresponding triarylmethanes by HCO2Na and DCO2Na have been measured in 71.0% aqueous trifluoroacetic acid containing 2.50M-formate. Bronsted plots of log kH and log kD against pKR+ of the carbonium ion are slightly curved with the curvature of the former being the more pronounced. The kinetic isotope effect kH/kD varies between 1.8 and 3.2 and shows a maximum near pKR+ of –4, the first such maximum observed for a hydride transfer process.

ChemInform Abstract: ION‐MOLECULE REACTIONS IN THE SYSTEMS CF4‐CH4 AND CF4‐C2H6

A mass spectrometric study of ionic reactions in CH4−CF4 and C2H6−CF4 mixtures was undertaken at pressures as high as 0.52 torr. It was found that CF3+ ions react in a hydride transfer process with ethane with a rate constant of 3.3×10−10 cm3 molecule−1⋅s−1. A rate constant of 1.6×10−10 cm3 molecule−1⋅s−1 was determined for the reaction of C2H5+ ions with C2H6. In mixtures of CH4 and CF4, both CH3+ and CH5+ react with CF4, apparently by fluoride ion transfer, for which we calculated rate constants of 8.6×10−10 and 2.3×10−10 cm3 molecule−1⋅s−1, respectively. CF3+ ions do not attack molecular methane. There is good agreement with published rate constants for the disappearance of CH2+, CH3+, and CH4+ ions in pure methane. However we observed a decreasing CH5+ yield above 0.1 torr which may be due either to impurities or to excess energy in CH5+ ions as a result of a relatively high repeller field strength within the ion source in our experiments.

Ion–molecule reactions in the systems CF4–CH4 and CF4–C2H6

A mass spectrometric study of ionic reactions in CH4−CF4 and C2H6−CF4 mixtures was undertaken at pressures as high as 0.52 torr. It was found that CF3+ ions react in a hydride transfer process with ethane with a rate constant of 3.3×10−10 cm3 molecule−1⋅s−1. A rate constant of 1.6×10−10 cm3 molecule−1⋅s−1 was determined for the reaction of C2H5+ ions with C2H6. In mixtures of CH4 and CF4, both CH3+ and CH5+ react with CF4, apparently by fluoride ion transfer, for which we calculated rate constants of 8.6×10−10 and 2.3×10−10 cm3 molecule−1⋅s−1, respectively. CF3+ ions do not attack molecular methane. There is good agreement with published rate constants for the disappearance of CH2+, CH3+, and CH4+ ions in pure methane. However we observed a decreasing CH5+ yield above 0.1 torr which may be due either to impurities or to excess energy in CH5+ ions as a result of a relatively high repeller field strength within the ion source in our experiments.

Steric effects in proton and hydride transfer processes in strongly acidic solvents

The formation of proton complexes of aromatic hydrocarbons in HSO 3FSbF 5 has been investigated at low temperature. In the case of steric hindered positions as occur in biphenyl and phenanthrene another position in the molecule is protonated as in HFBF 3. This contradiction can be explained by the bulk of the electrophilic attacking agent. A similar result was obtained by transfer of an hydride ion to the divalent positive ion of 1,2-benzanthracene. Our results are supported by quantum chemical calculations according to the method of Pariser, Parr and Pople.

Radiolysis of Propane-d8 in the Presence of Organic Compounds Other Than Hydrocarbons

The gas phase radiolysis of propane-d8 has been investigated in the presence of dimethylmercury, azomethane, acetone, methyliodide, methanol, nitromethane, and methylamine. The cross section of the hydride-transfer reactionC2D5++RH→C2D5H+R+is, in all cases, at least 10 times smaller than that of the reactionC2D5++C3D8→C2D6+C3D7+.Evidence for the occurrence of the proton-transfer reactionC2D5++RH→C2D4+RHD+has been obtained. For the mixtures containing methanol, the cross section of this proton-transfer reaction is about 50 times that of the hydride-transfer process. Approximate values of G (CH3+) have been determined for most of the additives.