13425-80-4Relevant articles and documents
How the sustainable solvent water unleashes the photoredox catalytic potential of ruthenium polypyridyl complexes for pinacol couplings
Naumann, Robert,Goez, Martin
supporting information, p. 4470 - 4474 (2019/08/21)
By complementing laser flash photolysis with product studies in visible-LED driven syntheses, we show that the one-electron reduced forms OER of tris(2,2′-bipyridine)ruthenium(ii) and its more reactive derivative with 4,4′-dimethylated ligands exhibit a reductive power greater by 0.2 eV in water than in acetonitrile; and that this difference allows the reduction of carbonyl compounds, and thus pinacol couplings, in aqueous medium via ruthenium-based photoredox catalysis as an alternative to using more expensive and less photostable higher-energy complexes (e.g., of iridium). Ascorbate serves as sacrificial donor to access OER. SDS micelles or cyclodextrins as carriers help overcome solubility problems of less hydrophilic substrates, and more reactive water-soluble substrates can even be coupled at neutral pH, such that the mild conditions make the process fully sustainable.
Structure-Activity Relationships in the Esterase-catalysed Hydrolysis and Transesterification of Esters and Lactones
Barton, Patrick,Laws, Andrew P.,Page, Michael I.
, p. 2021 - 2030 (2007/10/02)
The Broensted exponents for the alkaline hydrolysis of alkyl esters are 1.3 and 0.4 for substitution in the acyl and alcohol portions, respectively, which is indicative of a transition state which resembles the anionic tetrahedral intermediate with a localised negative charge.By contrast, the rate of the pig liver esterase (PLE)-catalysed hydrolysis shows little dependence upon the electron-withdrawing power of substituents.The values of kcat are independent of the pKa of the leaving group alcohol suggesting rate-limiting deacylation.There is a small steric effect of α-substitution in both the alcohol and carboxylic acid residues for the enzyme-catalysed reactions but the enzyme rate enhancement factor remains high for most esters.There is no substantial ee observed for the hydrolysis of racemic esters although the kinetic data can be used for determining the regioselective hydrolysis of diesters.Unsubstituted lactones are poor substrates for PLE but derivatives with hydrophobic substituents show kcat/Km values similar to those for acyclic esters.Dihydrocoumarin undergoes transesterification catalysed by PLE, kcat increases with increasing alcohol concentration indicative of rate-limiting deacylation.There is enantioselectivity in the PLE-catalysed hydrolysis of some racemic lactones but little or none in the transesterification of racemic alcohols with dihydrocoumarin.
Proton transfers among oxygen and nitrogen acids and bases in DMSO solution
Ritchie, Calvin D.,Lu, Shanzheng
, p. 7748 - 7756 (2007/10/02)
Rate constants for the proton-transfer reactions between conjugate acids and bases of several amines, phenols, carboxylic acids, and the solvated proton in DMSO-d6 at 20 °C have been determined by the use of NMR line-shape analysis. Equilibrium constants for the same reactions are obtained from the pKa's of the acids in dimethyl sulfoxide, some of which have been reported in earlier work and the rest obtained in the present work by use of Bordwell's indicator techniques. All of the reactions have rale constants considerably below expected diffusion-controlled limits for the proton transfers in the thermodynamically favorable direction, and several of the reactions, including the identity reactions of carboxylic acids, have kinetic deuterium isotope effects, kH/kD, between 0.8 and 1.3. For reactions of N,N-dimethylbenzylammonium ion with several phenoxides, carboxylates, and solvent, the rate constants for transfers in the unfavorable directions show a reasonable Bronsted correlation with β ≈ 1 and a reasonably constant reverse rate constant of ≈3 × 106 M-1 s-1. The data clearly indicate that the proton-transfer step is not rate-limiting in these reactions. Most likely, desolvation is involved in the rate-limiting steps, but the rate constants are not simple functions of acidities as might have been expected if hydrogen bonding of acid to solvent were the major factor involved in the solvation Other factors, particularly dispersion interactions of solvent with solutes, are discussed. We suggest that the formation of an acid-base complex with proper orientation to allow contact between the proton and the basic site is rate-determining and involves desolvation along with detailed steric interactions of the acid-base pair.
