T:Toxic;526-75-0Relevant articles and documents
Active Site Dynamics of Xylene Hydroxylation by Cytochrome P-450 As Revealed by Kinetic Deuterium Isotope Effects
Hanzlik, Robert P.,Ling, Kah-Hiing John
, p. 9363 - 9370 (1993)
The cytochrome P-450 catalyzed hydroxylation of o- and p-xylene and five deuterated derivatives of each has been investigated using phenobarbital-induced rat liver microsomes.All possible monohydroxylation products were observed but benzylic hydroxylation predominated strongly (88-96percent).H/D discrimination was strongest when both isotopes were located on the same methyl gorup, less when they were located in different methyl groups on the same xylene molecule, and least when they were located in methyl groups on different molecules.Benzylic hydroxylation is subject to a large intrinsic (intramolecular) deuterium isotope effect (CH3/CD3=7.5-9.5), comprised of a large primary component (5.3-7.8) and a large normal α-secondary component (1.09-1.19).These isotope effects suggest a transition state for benzylic H-abstraction that is linear and symmetrical with substantial rehybridization toward planarity at the benzylic carbon and little residual C-H bond order remaining.In contrast aromatic hydroxylation of o- and p-xylene shows a small inverse α-secondary isotope effect (0.83-0.94).The D(V/K) isotope effect observed for benzylic hydroxylation in intermolecular competitions (ca. 1.9-2.3 for d0/d6 substrate mixtures) is substantially reduced by commitment to catalysis, with Cf=(kH+kr)k-1=3.6 for p-xylene and 5.9 for o-xylene.These results suggest a dynamic picture of catalysis with the following relative rates: methyl group rotation > substrate-orientation within the Michaelis complex (i.e. isotopically sensitive branching to different products) > product formation (i.e. commitment to catalysis) > substrate dissociation prior to hydroxylation.
Reaction of hydroxyl radical with arenes in solution—On the importance of benzylic hydrogen abstraction
Waggoner, Abygail R.,Abdulrahman, Yahya,Iverson, Alexis J.,Gibson, Ethan P.,Buckles, Mark A.,Poole, James S.
, (2021/08/27)
The regioselectivity of hydroxyl radical reactions with alkylarenes was investigated using a nuclear magnetic resonance (NMR)-based methodology capable of trapping and quantifying addition and hydrogen abstraction products of the initial elementary step of the oxidation process. Abstraction products are relatively minor components of the product mixtures (15–30 mol%), depending on the magnitude of the overall rate coefficient and the number of available hydrogens. The relative reactivity of addition at a given position on the ring depends on its relation to the methyl substituents on the hydrocarbons under study. The reactivity enhancements for disubstituted and trisubstituted rings are approximately additive under the conditions of this study.
REARRANGEMENT OF DIMETHYLPHENYLACYLATES USING ZEOLITES
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Page/Page column 9-11, (2021/08/14)
The present invention relates to a Fries rearrangement of specific dimethylphenylacylates to form the desired respective hydroxyaryl ketones having two methyl groups bound to the aromatic ring. It has been found that the process is surprisingly very specific in view of the number and position of the methyl group(s) bound to the aromatic ring.
A scalable and green one-minute synthesis of substituted phenols
Elumalai, Vijayaragavan,Hansen, J?rn H.
, p. 40582 - 40587 (2020/11/18)
A mild, green and highly efficient protocol was developed for the synthesis of substituted phenols via ipso-hydroxylation of arylboronic acids in ethanol. The method utilizes the combination of aqueous hydrogen peroxide as the oxidant and H2O2/HBr as the reagent under unprecedentedly simple and convenient conditions. A wide range of arylboronic acids were smoothly transformed into substituted phenols in very good to excellent yields without chromatographic purification. The reaction is scalable up to at least 5 grams at room temperature with one-minute reaction time and can be combined in a one-pot sequence with bromination and Pd-catalyzed cross-coupling to generate more diverse, highly substituted phenols.
