Hydrogen atom abstraction

About: Hydrogen atom abstraction is a research topic. Over the lifetime, 7059 publications have been published within this topic receiving 151781 citations.

Aerobic oxidation of N-alkylamides catalyzed by N-hydroxyphthalimide under mild conditions. Polar and enthalpic effects.

Abstract: The oxidation of N-alkylamides by O2, catalyzed by N-hydroxyphthalimide (NHPI) and Co(II) salt, leads under mild conditions to carbonyl derivatives (aldehydes, ketones, carboxylic acids, imides) whose distribution depends on the nature of the alkyl group and on the reaction conditions. Primary N-benzylamides lead to imides and aromatic aldehydes at room temperature without any appreciable amount of carboxylic acids, while under the same conditions nonbenzylic derivatives give carboxylic acids and imides with no trace of aldehydes, even at very low conversion. These results are explained through hydrogen abstraction by the phthalimide-N-oxyl (PINO) radical, whose reactivity with benzyl derivatives is governed by polar effects, so that benzylamides are much more reactive than the corresponding aldehydes. The enthalpic effect is, however, dominant with nonbenzylic amides, making the corresponding aldehydes much more reactive than the starting amides. The importance of the bond dissociation energy (BDE) of th...

Oxygen activation by metal complexes and alkyl hydroperoxides. Applications of mechanistic probes to explore the role of alkoxyl radicals in alkane functionalization

Abstract: The mechanism of the oxidation of cycloalkanes by tertiary alkyl hydroperoxides catalysed by iron(III) dichlorotris(2-pyridylmethyl)amine [FeIIICl2(TPA)]+ and by the acetate bridged (µ-oxo) di-iron complex [Fe2III(TPA)2O(OAc)]3+ has been investigated. Product studies do not support oxidation via a high valent iron–oxo intermediate (formally FeVO), but are consistent with a mechanism involving hydrogen atom abstraction from the alkane by alkoxyl radicals derived from the hydroperoxide. In the presence of a large excess of tert-butyl hydroperoxide, the oxidation of cyclohexane yields cyclohexanone, cyclohexanol and tert-butylcyclohexyl peroxide in more than stoichiometric amounts and, in the case of the mono-iron catalyst, one equivalent of cyclohexyl chloride. Replacement of Me3COOH by hydroperoxides, which could yield tert-alkoxyl radicals having much shorter lifetimes than the tert-butoxyl radical prevents oxidation of the cycloalkane. The products obtained with these hydroperoxide mechanistic probes are those derived from the fast unimolecular reactions (generally β-scissions) of the corresponding alkoxyl radicals. The inapplicability of dimethyl sulfide as a mechanistically diagnostic trap for the putative FeVO intermediate and the value of di-tert-butyl hyponitrite as a non-iron-based source of tert-butoxyl radicals are discussed.

ICR studies of some hydrogen atom abstraction reactions: X+ + H2 → XH+ + H

Abstract: Ion cyclotron resonance methods are used to identify and to measure the rate constants for the abstraction of a hydrogen atom from H2 by CH+, CH2 +, CH4 +, N+, NH+, NH2 +, NH3 +, O+, OH+, H2O+, CO+, N2 +, C2 +, and C2H+ ions. Although in most cases hydrogen atom abstraction is the only available exothermic pathway for these reactions at thermal energies, the rate constants measured show that except for O+, CO+, and N2 +, a large fraction of collisions between these ions and H2 are not reactive. The rate constants measured range from a low of (3±1) × 10−13 cm3/sec for the NH3 +−H2reaction to (1.73±0.04) × 10−9 cm3/sec for the N2 +−H2reaction. These values compare to the Langevin value of about 1.5 × 10−9 cm3/sec for collisions between these ions and H2. An examination was also made for possible thermoneutral hydrogen atom exchange reactions for those ions which do not react with H2 (CH5 +, CH3 +, NH4 +, H3O+, H2S+, H3S+). The only exchange reaction observed was for collisions between CD3 + ions and H2, for which a rate constant of (5.1±0.5) × 10−10 cm3/sec was measured.

Synthesis of partially hydrogenated graphene and brominated graphene

Abstract: Partially hydrogenated graphene was readily prepared by an interesting reaction between graphene oxide and phenylboronic acid. This partially hydrogenated graphene was employed to synthesize brominated graphene through subsequent radical hydrogen abstraction.