5380-80-3Relevant articles and documents
Earth-Abundant Mixed-Metal Catalysts for Hydrocarbon Oxygenation
Pankhurst, James R.,Curcio, Massimiliano,Sproules, Stephen,Lloyd-Jones, Guy C.,Love, Jason B.
supporting information, p. 5915 - 5928 (2018/05/28)
The oxygenation of aliphatic and aromatic hydrocarbons using earth-abundant Fe and Cu catalysts and "green" oxidants such as hydrogen peroxide is becoming increasingly important to atom-economical chemical processing. In light of this, we describe that dinuclear CuII complexes of pyrrolic Schiff-base macrocycles, in combination with ferric chloride (FeCl3), catalyze the oxygenation of π-activated benzylic substrates with hydroperoxide oxidants at room temperature and low loadings, representing a novel design in oxidation catalysis. Mass spectrometry and extended X-ray absorption fine structure analysis indicate that a cooperative action between CuII and FeIII occurs, most likely because of the interaction of FeCl3 or FeCl4- with the dinuclear CuII macrocycle. Voltammetric measurements highlight a modulation of both CuII and FeIII redox potentials in this adduct, but electron paramagnetic resonance spectroscopy indicates that any Cu-Fe intermetallic interaction is weak. High ketone/alcohol product ratios, a small reaction constant (Hammett analysis), and small kinetic isotope effect for H-atom abstraction point toward a free-radical reaction. However, the lack of reactivity with cyclohexane, oxidation of 9,10-dihydroanthracene, oxygenation by the hydroperoxide MPPH (radical mechanistic probe), and oxygenation in dinitrogen-purge experiments indicate a metal-based reaction. Through detailed reaction monitoring and associated kinetic modeling, a network of oxidation pathways is proposed that includes "well-disguised" radical chemistry via the formation of metal-associated radical intermediates.
ACID-CATALYSED DEHYDRATION OF HETEROCYCLIC RING HYDRATES OF BENZOFURAN, BENZOTHIOPHENE, CHROMENE AND THIOCHROMENE
Kelly, Sandra C.,McDonnell, Claire A.,O'Ferrall, Rory A. More,Rao, S. Nagaraja,Boyd, Derek R.,et al.
, p. 747 - 754 (2007/10/03)
Rate constants and equilibrium constants have been measured for acid-catalysed dehydration of benzo-fused five- and six-membered heterocyclic and carbocyclic rings.Substrates studied include 2- and 3-hydroxy-2,3-dihydrobenzofuran, 3-hydroxy-2,3-dihydrobenzothiophene, 1-indanol, 4-chromanol, 4-thiochromanol and 1-tetralol.For the benzofuran-3-hydrate (3-hydroxy-2,3-dihydrobenzofuran), 1-indanol and 1-tetralol rate constants have also been measured for the acid-catalysed racemisation of optically active substrates.These are believed to represent carbocation formation, and this supposition is confirmed by measurements of product partitioning between benzofuran and benzofuran hydrate products from solvolysis of the chloroacetate ester of the 3-hydrate.A surprising observation is that, in the five-membered ring series, heterocyclic oxygen and sulphur atoms have very small accelerating effects on rates of carbocation formation (1.3 and 2.5-fold, respectively, relative to indanol) despite the possibility of direct resonance between the heteroatom and carbocation centre.For dehydration of the corresponding six-membered rings indeed the heteroatoms slow the reaction: in the case of oxygen (4-chromanol) by 100-fold.The possibility that this behavior arises from adverse inductive or stereoelectronic effects is discussed.
