666-52-4Relevant articles and documents
Mechanisms of Oxidation of 2-Propanol by Polypyridyl Complexes of Ruthenium(III) and Ruthenium (IV)
Thompson, Mark S.,Meyer, Thomas J.
, p. 4106 - 4115 (1982)
Kinetic and mechanistic studies have been carried out on the oxidation of 2-propanol to acetone in water by RuIV(trpy)(bpy)O2+ (trpy is 2,2',2''-terpyridine; bpy is 2,2'-bipyridine) and in acetonitrile by RuIV(bpy)2(py)O2+ (py is pyridine).The reactions proceed by oxidation of 2-propanol by Ru(IV) followed by a slower oxidation by the Ru(III) complexes Ru(trpy)(bpy)OH2+ or Ru(bpy)2(py)OH2+.For the reactions: in water, kIV(25 deg C) = 6.7 * 10-2 M-1 s-1, ΔH = 9 +/- kcal/mol, ΔS = -34 +/- 4 eu, kH/kD = 18 +/- 3; in , kIII(25 deg C) = 6 * 10-5 M-1 s-1, ΔH = 19 +/- 2 kcal/mol, ΔS = -12 +/- 6 eu, kH/kD = 2.7 +/- 1.4.An 18O-labeling experiment in 2-propanol and a spectral experiment in CH3CN show that oxo transfer from the oxidant to the substrate does not occur.It is concluded that the most likely mechanism of oxidation for Ru(IV) is a concerted, two-electron hydride transfer from the α-C-H bond to RuIV=O with the oxo group acting as a lead-in atom to the Ru(IV) acceptor site.The Ru(III) reaction in water appears to occur by an initial one-electron, outer-sphere electron transfer.In acetonitrile there appears to be a change in mechanism for this reaction, apparently to a H-atom transfer, once again involving the α-C-H group.For this path: k(25 deg C) = (8+/- 2) * 10 -4 M-1 s-1, ΔH = 10 +/- 2 kcal/mol, ΔS = -38 +/- 7 eu, kH/kD 8.
BASE CATALYZED ENOLIZATION AND HYDROGEN EXCHANGE OF TRIFLUOROACETONE. A COMPARISON TO ACETONE
Jansen, Michael P.,Tidwell, Thomas T.
, p. 791 - 802 (1982)
The kinetics of the pyridine catalyzed hydrogen exchange of 1,1,1-trifluoroacetone in 50percent D2O-dioxane have been measured using 1H-NMR.Rates of hydrogen exchange of acetone were also measured under comparable conditions and the rate of deuterium uptake by trifluoroacetone was found to exceed that of acetone by a factor of 1700 at 25 deg C.However trifluoroacetone is known to be extensively hydrated under these conditions.The hydrogen exchange of trifluoroacetone is interpreted as most probably proceeding through proton abstraction by pyridine from the free ketone to form the enolate followed by deuteration on carbon, with the rate of proton abstraction from trifluoroacetone exceeding that of acetone by a factor of 105 to 106.Other possibilities are also considered.
Oxidation of 2-Propanol to Acetone by Dioxygen on a Platinized Electrode under Open-Circuit Conditions
DiCosimo, Robert,Whitesides, George M.
, p. 768 - 775 (1989)
This paper examines the catalytic oxidation of 2-propanol by dioxygen on a platinized platinum gauze electrode.Under open-circuit conditions, the rate of reaction was limited by mass transport of dioxygen to the catalyst surface and obeyed the rate law -d/dt = k0s>1PO21.The rate of reaction depended on the rate of stirring of the system.No kinetic deuterium isotope effect was observed upon substitution of 2-propanol-d7 for 2-propanol-d0.Under the reaction conditions employed, the open-circuit potential of the catalyst during the catalytic oxidation of 2-propanol indicated that the platinum surface was covered predominately with platinum hydride and not with platinum oxide.No catalyst deactivation due to reaction of dioxygen with surface platinum atoms were obserevd, and hydrogen peroxide could be substituted for dioxygen as the oxidizing agent in the reaction.The reaction is proposed to proceed by the formation of an intermediate surface alkoxide that dehydrogenates and produces acetone and surface hydrides.These surface hydrides then react with dioxygen, hydrogen peroxide, platinum oxide, or some other oxidizing species and yield (ultimately) water, possibly by an electrochemical local cell mechanism.
Heterolytic Oxidative Addition of sp2and sp3C-H Bonds by Metal-Ligand Cooperation with an Electron-Deficient Cyclopentadienone Iridium Complex
Higashi, Takuya,Kusumoto, Shuhei,Nozaki, Kyoko
supporting information, p. 12999 - 13004 (2021/08/16)
Oxidative addition reactions of C-H bonds that generate metal-carbon-bond-containing reactive intermediates have played essential roles in the field of organometallic chemistry. Herein, we prepared a cyclopentadienone iridium(I) complex 1 designed for oxidative C-H bond additions. The complex cleaves the various sp2 and sp3 C-H bonds including those in hexane and methane as inferred from their H/D exchange reactions. The hydroxycyclopentadienyl(nitromethyl)iridium(III) complex 2 was formed when the complex was treated with nitromethane, which highlights this elementary metal-ligand cooperative C-H bond oxidative addition reaction. Mechanistic investigations suggested the C-H bond cleavage is mediated by polar functional groups in substrates or another iridium complex. We found that ligands that are more electron-deficient lead to more favorable reactions, in sharp contrast to classical metal-centered oxidative additions. This trend is in good agreement with the proposed mechanism, in which C-H bond cleavage is accompanied by two-electron transfer from the metal center to the cyclopentadienone ligand. The complex was further applied to catalytic transfer-dehydrogenation of tetrahydrofuran (THF).
Phosphonium Phenolate Zwitterion vs Phosphonium Ylide: Synthesis, Characterization and Reactivity Study of a Trimethylphosphonium Phenolate Zwitterion
Xiao, Jing,Li, Qiang,Shen, Ruwei,Shimada, Shigeru,Han, Li-Biao
supporting information, p. 5715 - 5720 (2019/11/22)
4-Methoxy-3-(trimethylphosphonio)phenolate was obtained from a regioselective addition of PMe3 to p-quinone monoacetal. This compound undergoes hydrogen isotope exchange with D2O or CD3CN, and is capable of catalyzing H/D exchange of CD3CN with substrates bearing weakly acidic hydrogens. It exhibits similar reactivity to phosphorus ylides for olefinations of aldehydes. A possible tautomerization between the phosphonium phenolate zwitterion and phosphonium ylide is proposed for the first time to rationalize the unique reactivity.
Pd-Catalyzed Aerobic Oxidation Reactions: Strategies to Increase Catalyst Lifetimes
Ho, Wilson C.,Chung, Kevin,Ingram, Andrew J.,Waymouth, Robert M.
supporting information, p. 748 - 757 (2018/01/26)
The palladium complex [(neocuproine)Pd(μ-OAc)]2[OTf]2 (1, neocuproine = 2,9-dimethyl-1,10-phenanthroline) is an effective catalyst precursor for the selective oxidation of primary and secondary alcohols, vicinal diols, polyols, and carbohydrates. Both air and benzoquinone can be used as terminal oxidants, but aerobic oxidations are accompanied by oxidative degradation of the neocuproine ligand, thus necessitating high Pd loadings. Several strategies to improve aerobic catalyst lifetimes were devised, guided by mechanistic studies of catalyst deactivation. These studies implicate a radical autoxidation mechanism initiated by H atom abstraction from the neocuproine ligand. Ligand modifications designed to retard H atom abstractions as well as the addition of sacrificial H atom donors increase catalyst lifetimes and lead to higher turnover numbers (TON) under aerobic conditions. Additional investigations revealed that the addition of benzylic hydroperoxides or styrene leads to significant increases in TON as well. Mechanistic studies suggest that benzylic hydroperoxides function as H atom donors and that styrene is effective at intercepting Pd hydrides. These strategies enabled the selective aerobic oxidation of polyols on preparative scales using as little as 0.25 mol % of Pd, a major improvement over previous work.
Organocatalytic Imidazolium Ionic Liquids H/D Exchange Catalysts
Zanatta, Marcileia,Dos Santos, Francisco P.,Biehl, Cristina,Marin, Graciane,Ebeling, Gunter,Netz, Paulo A.,Dupont, Jairton
supporting information, p. 2622 - 2629 (2017/03/14)
Simple 1,2,3-trialkylimidazolium cation associated with basic anions, such as hydrogen carbonate, prolinate, and imidazolate, is an active catalyst for the H/D exchange reaction of various substrates using CDCl3 as D source, without the addition of any extra bases or metal. High deuterium incorporation (up to 49%) in acidic C-H bonds of ketone and alkyne substrates (pKa from 18.7 to 28.8) was found at room temperature. The reaction proceeds through the fast and reversible deuteration of the 2-methyl H of the imidazolium cation followed by D transfer to the substrate. The IL acts as a neutral base catalyst in which the contact ion pair is maintained in the course of the reaction. The basic active site is due to the presence of a remote basic site in the anion namely, OH of bicarbonate, NH of prolinate, and activated water in the imidazolate anion. Detailed kinetic experiments demonstrate that the reaction is first order on the substrate and pseudozero order relative to the ionic liquid, due to the fast reversible reaction involving the deuteration of the ionic liquid by the solvent.
Electrocatalytic alcohol oxidation with ruthenium transfer hydrogenation catalysts
Waldie, Kate M.,Flajslik, Kristen R.,McLoughlin, Elizabeth,Chidsey, Christopher E.D.,Waymouth, Robert M.
, p. 738 - 748 (2017/05/16)
Octahedral ruthenium complexes [RuX-(CNN)(dppb)] (1, X = CI; 2, X = H; CNN = 2-aminomethyl-6-tolylpyridine, dppb = 1, 4-bis-(diphenylphosphino)butane) are highly active for the transfer hydrogenation of ketones with isopropanol under ambient conditions. Turnover frequencies of 0.88 and 0.89 s-I are achieved at 25 °C using 0.1 mol % of 1 or 2, respectively, in the presence of 20 equiv of potassium t-butoxide relative to ' catalyst. Electrochemical studies reveal that the Ru-hydride 2 is oxidized at low potential (-0.80 V versus ferrocene/, ferrocenium, Fc0/+) via a chemically irreversible process with concomitant formation of dihydrogen. Complexes 1 and 2 are active for the electrooxidation of isopropanol in the presence of strong base (potassium r-butoxide) with an onset potential near -IV versus Fc. By cyclic voltammetry, fast turnover frequencies of 3.2 and 4.8 s-I for isopropanol oxidation are achieved with 1 and 2, respectively. Controlled potential electrolysis studies confirm that the product of isopropanol electrooxidation is acetone, generated with a Faradaic efficiency of 94 ± 5%.
Experimental and theoretical assessment of the mechanism and site requirements for ketonization of carboxylic acids on oxides
Wang, Shuai,Iglesia, Enrique
, p. 183 - 206 (2016/12/16)
Ketonization of carboxylic acids removes O-atoms and forms new CC bonds, thus providing routes from sustainable carbon feedstocks to fuels and chemicals. The elementary steps involved and their kinetic relevance, as well as the number and nature of the active sites on active TiO2 and ZrO2 catalysts, remain matters of active discourse. Here, site titrations demonstrate the requirement for coordinatively-unsaturated M-O-M sites (M?=?Ti, Zr) with specific geometry and intermediate acid-base strength. The measured site densities allow rigorous reactivity comparisons among catalysts based on turnover rates and activation free energies, as well as the benchmarking of mechanistic proposals against theoretical assessments. Kinetic, isotopic, spectroscopic, and theoretical methods show that C2C4 acids react on anatase TiO2 via kinetically-relevant CC coupling between 1-hydroxy enolate species and coadsorbed acids bound at vicinal acid-base pairs saturated with active monodentate carboxylates. Smaller TiTi distances on rutile TiO2 lead to the prevalence of unreactive bidentate carboxylates and lead to its much lower ketonization reactivity than anatase. The prevalent dense monolayers of chemisorbed acid reactants reflect their strong binding at acid-base pairs and their stabilization by H-bonding interactions with surface OH groups derived from the dissociation of the carboxylic acids or the formation of 1-hydroxy enolates; these interactions also stabilize CC coupling transition states preferentially over their carboxylate precursors; high coverages favor sequential dehydration routes of the α-hydroxy-γ-carboxy-alkoxide CC coupling products over previously unrecognized concerted six-membered-ring transition states. Infrared spectra show that ubiquitous deactivation, which has precluded broader deployment of ketonization in practice and unequivocal mechanistic inquiries, reflects the gradual formation of inactive bidentate carboxylates. Their dehydration to ketene-like gaseous species is faster on anatase TiO2 than on ZrO2 and allows the effective scavenging of bidentate carboxylates via ketene hydrogenation to alkanals/alkanols on a Cu function present within diffusion distances. These strategies make anatase TiO2, a more effective catalyst than ZrO2, in spite of its slightly lower initial turnover rates. This study provides details about the mechanism of ketonization of C2C4 carboxylic acids on TiO2 and a rigorous analysis of the sites required and of active and inactive bound species on TiO2 and ZrO2. The preference for specific distances and for intermediate acid-base strength in M-O-M species is consistent with the structure and energy of the proposed transition states and intermediates; their relative stabilities illustrate how densely-covered surfaces, prevalent during ketonization catalysis, represent an essential requirement for the achievement of practical turnover rates.
Steric Effects on the Primary Isotope Dependence of Secondary Kinetic Isotope Effects in Hydride Transfer Reactions in Solution: Caused by the Isotopically Different Tunneling Ready State Conformations?
Maharjan, Binita,Raghibi Boroujeni, Mahdi,Lefton, Jonathan,White, Ormacinda R.,Razzaghi, Mortezaali,Hammann, Blake A.,Derakhshani-Molayousefi, Mortaza,Eilers, James E.,Lu, Yun
supporting information, p. 6653 - 6661 (2015/06/08)
The observed 1° isotope effect on 2° KIEs in H-transfer reactions has recently been explained on the basis of a H-tunneling mechanism that uses the concept that the tunneling of a heavier isotope requires a shorter donor-acceptor distance (DAD) than that of a lighter isotope. The shorter DAD in D-tunneling, as compared to H-tunneling, could bring about significant spatial crowding effect that stiffens the 2° H/D vibrations, thus decreasing the 2° KIE. This leads to a new physical organic research direction that examines how structure affects the 1° isotope dependence of 2° KIEs and how this dependence provides information about the structure of the tunneling ready states (TRSs). The hypothesis is that H- and D-tunneling have TRS structures which have different DADs, and pronounced 1° isotope effect on 2° KIEs should be observed in tunneling systems that are sterically hindered. This paper investigates the hypothesis by determining the 1° isotope effect on α- and β-2° KIEs for hydride transfer reactions from various hydride donors to different carbocationic hydride acceptors in solution. The systems were designed to include the interactions of the steric groups and the targeted 2° H/D's in the TRSs. The results substantiate our hypothesis, and they are not consistent with the traditional model of H-tunneling and 1° /2° H coupled motions that has been widely used to explain the 1° isotope dependence of 2° KIEs in the enzyme-catalyzed H-transfer reactions. The behaviors of the 1° isotope dependence of 2° KIEs in solution are compared to those with alcohol dehydrogenases, and sources of the observed "puzzling" 2° KIE behaviors in these enzymes are discussed using the concept of the isotopically different TRS conformations. (Figure Presented).
