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.
Paulsen,Cooke
, p. 1560 (1963)
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.
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.
