55631-08-8Relevant academic research and scientific papers
Multiple Mechanisms Mapped in Aryl Alkyl Ether Cleavage via Aqueous Electrocatalytic Hydrogenation over Skeletal Nickel
Hegg, Eric L.,Jackson, James E.,Klinger, Grace E.,Saffron, Christopher M.,Zhou, Yuting
supporting information, p. 4037 - 4050 (2020/03/10)
We present here detailed mechanistic studies of electrocatalytic hydrogenation (ECH) in aqueous solution over skeletal nickel cathodes to probe the various paths of reductive catalytic C-O bond cleavage among functionalized aryl ethers relevant to energy science. Heterogeneous catalytic hydrogenolysis of aryl ethers is important both in hydrodeoxygenation of fossil fuels and in upgrading of lignin from biomass. The presence or absence of simple functionalities such as carbonyl, hydroxyl, methyl, or methoxyl groups is known to cause dramatic shifts in reactivity and cleavage selectivity between sp3 C-O and sp2 C-O bonds. Specifically, reported hydrogenolysis studies with Ni and other catalysts have hinted at different cleavage mechanisms for the C-O ether bonds in α-keto and α-hydroxy β-O-4 type aryl ether linkages of lignin. Our new rate, selectivity, and isotopic labeling results from ECH reactions confirm that these aryl ethers undergo C-O cleavage via distinct paths. For the simple 2-phenoxy-1-phenylethane or its alcohol congener, 2-phenoxy-1-phenylethanol, the benzylic site is activated via Ni C-H insertion, followed by beta elimination of the phenoxide leaving group. But in the case of the ketone, 2-phenoxyacetophenone, the polarized carbonyl πsystem apparently binds directly with the electron rich Ni cathode surface without breaking the aromaticity of the neighboring phenyl ring, leading to rapid cleavage. Substituent steric and electronic perturbations across a broad range of β-O-4 type ethers create a hierarchy of cleavage rates that supports these mechanistic ideas while offering guidance to allow rational design of the catalytic method. On the basis of the new insights, the usage of cosolvent acetone is shown to enable control of product selectivity.
Catalytic aerobic synthesis of aromatic ethers from non-aromatic precursors
Simon, Marc-Olivier,Girard, Simon A.,Li, Chao-Jun
supporting information; experimental part, p. 7537 - 7540 (2012/09/10)
Only little waste: Aryl ether formation is accomplished by oxidative condensation of alcohols and 2-cyclohexenones. The reaction complements the existing methods used by synthetic chemists to obtain aryl ethers, and allows a straightforward access to a wide range of functionalized products. In addition, the catalytic reaction with O2 as the oxidant generates water as the only by-product and provides a greener approach to aryl ethers. Copyright
Absolute Rate Constants for the β-Scission Reaction of the 1-Phenyl-2-phenoxypropyl Radical: A Model for Radical Reactions of Lignin
Autrey, Thomas S.,Almajjar, Mikhail S.,Nelson, David A.,Franz, James A.
, p. 2197 - 2202 (2007/10/02)
Absolute rate expressions for β-scission of the phenoxy radical from the 1-phenyl-2-phenoxypropyl radical, forming cis- and trans-β-methylstyrene, were determined by competition of β-scission (kβ) with abstraction of hydrogen from trimethylstannane (kabs).Relative rates (kβ/kabs) were converted to absolute rates (kβ) by using a rate expression determined for abstraction of hydrogen atom from tributylstannane by the phenylethyl radical: log abs/(M-1s-1)> = (9.31 +/- 0.30) - (7.11 +/- 0.49)/θ, where θ = 3.303RT kcal/mol (errors are 2?).The resulting expressions for β-scission are log (kβ,trans/s-1) = (13.45 +/- 0.26) - (16.94 +/- 0.52)/θ and log (kβ,cis/s-1) = (13.41 +/- 0.3) - (19.3 +/- 0.75)/θ.The basis rate expression for abstraction of hydogen from tributylstannane by the phenylethylradical was determined in a competition of abstraction (kabs) with self-termination (kt), using the Smoluchowski expression for self-reaction of phenylethyl radical: log t/(M-1s-1)> = 11.93 - 3.112/θ.Combining the Arrhenius parameters with the enthalpy change for β-scission leads to activation barriers for addition of phenoxyradical to trans- and cis-β-methylstyrene of 5.2 and 6.6 kcal/mol, respectively.
