2679-89-2Relevant academic research and scientific papers
Catalytic etherification of alcohols in Shilov system: C[sbnd]O versus C[sbnd]H bond activation
Khazipov, Oleg V.,Nykytenko, Denys V.,Krasnyakova, Tatyana V.,Vdovichenko, Alexander N.,Fuentes Frias, Dario A.,Mitchenko, Serge A.
, p. 490 - 498 (2016/12/16)
A novel catalytic reaction of alcohol etherification in the system ROH ? PtCl42? ‐ PtCl62? was found. Methanol easily transforms into dimethyl ether in the presence of catalytic amounts of PtII chloro complexes at 70?°C. Under the same conditions reaction of ethanol affords diethyl ether (catalytic) and π-ethylene PtII complex (stoichiometric). The reactions are accompanied by multiple H/D exchange, which is indicative of intermediacy of corresponding alkyl platinum derivatives. The plausible reaction mechanism involves oxidative addition of alcohol forming intermediate alkyl platinum(IV) derivative followed by decomposition of it via reductive elimination step under the action of alcohol giving the ether and regenerating catalyst. In the case of ethyl alcohol reaction, β-hydrogen abstraction from the intermediate Pt-ethyl species yields π-ethylene platinum(II) complex. Although it seems that the reaction does not involve the initial breaking of C[sbnd]H bonds of an alcohol, this system can be regarded as a model for studying of some peculiarities of Shilov chemistry, in particular, of isotope scrambling mechanisms in Shilov alkane activation. In contrast to reactions of dimethyl and diethyl ethers formation, tert-butyl ethers formation in CD3OH/t-BuOH medium is catalyzed by PtIV chloro complexes also and is not accompanied by isotope scrambling. These observations argue against intermediacy of alkyl platinum derivatives suggesting that acid-catalyzed mechanism operates in tert-butyl alcohol etherification.
Kinetics and mechanism of ethanol dehydration on γ-Al 2O3: The critical role of dimer inhibition
DeWilde, Joseph F.,Chiang, Hsu,Hickman, Daniel A.,Ho, Christopher R.,Bhan, Aditya
, p. 798 - 807 (2013/05/21)
Steady state, isotopic, and chemical transient studies of ethanol dehydration on γ-alumina show unimolecular and bimolecular dehydration reactions of ethanol are reversibly inhibited by the formation of ethanol-water dimers at 488 K. Measured rates of ethylene synthesis are independent of ethanol pressure (1.9-7.0 kPa) but decrease with increasing water pressure (0.4-2.2 kPa), reflecting the competitive adsorption of ethanol-water dimers with ethanol monomers; while diethyl ether formation rates have a positive, less than first order dependence on ethanol pressure (0.9-4.7 kPa) and also decrease with water pressure (0.6-2.2 kPa), signifying a competition for active sites between ethanol-water dimers and ethanol dimers. Pyridine inhibits the rate of ethylene and diethyl ether formation to different extents verifying the existence of acidic and nonequivalent active sites for the dehydration reactions. A primary kinetic isotope effect does not occur for diethyl ether synthesis from deuterated ethanol and only occurs for ethylene synthesis when the β-proton is deuterated; demonstrating olefin synthesis is kinetically limited by either the cleavage of a Cβ-H bond or the desorption of water on the γ-alumina surface and ether synthesis is limited by the cleavage of either the C-O bond of the alcohol molecule or the Al-O bond of a surface bound ethoxide species. These observations are consistent with a mechanism inhibited by the formation of dimer species. The proposed model rigorously describes the observed kinetics at this temperature and highlights the fundamental differences between the Lewis acidic γ-alumina and Bronsted acidic zeolite catalysts.
Alkyl groups as synthetic vehicles in gold-mediated oxidative coupling reactions
Xu, Bingjun,Madix, Robert J.,Friend, Cynthia M.
, p. 3179 - 3185 (2013/05/08)
The use of surface-bound alkyl and phenyl groups as synthetic vehicles in coupling reactions on oxygen-activated Au(111) is demonstrated by the formation of ethers via alkyl and phenyl iodides. Ethers are formed by successive additions of surface-bound alkyl groups to adsorbed atomic oxygen to form first the alkoxy and then the ether. The addition of the ethyl group to adsorbed oxygen on Au(111) is the rate-limiting step leading to diethyl ether formation. Alkyl groups also add to adsorbed alkoxy groups formed from alcohols. An unusual feature of the alkyl iodide reactions on Au is that oxygen is not required for the activation step; hence, opening new potential reactive pathways on metallic Au. This journal is
An Air/water-stable tridentate N-heterocyclic carbene-palladium(II) Complex: Catalytic C-H activation of hydrocarbons via hydrogen/deuterium exchange process in deuterium oxide
Lee, Joo Ho,Yoo, Kyung Soo,Park, Chan Pil,Olsen, Janet M.,Sakaguchi, Satoshi,Prakash, G. K. Surya,Mathew, Thomas,Jung, Kyung Woon
experimental part, p. 563 - 568 (2009/11/30)
While developing novel catalysts for carbon-carbon or carbon-heteroatom coupling (nitrogen, oxygen, or fluorine), we were able to introduce tridentate N-heterocyclic carbene (NHC)-amidate-alkoxide palladium(II) complexes. In aqueous solution, these NHC-Pd(II) complexes showed high ability for C-H activation of various hydrocarbons (cyclohexane, cyclopentane, dimethyl ether, tetrahydrofuran, acetone, and toluene) under mild conditions.
