NHPI and ferric nitrate: a mild and selective system for aerobic oxidation of benzylic methylenes

Abstract

A mild and selective system comprising N-hydroxyphthalimide (NHPI) and FeIJNO 3 ) 3 ·9H 2 O was developed for the oxidation of benzylic methylenes with an atmospheric pressure of molecular oxygen at 25°C. The influences of reaction conditions such as solvent, different metal catalysts and catalyst loading were studied, as well as the kinetics of the oxidation reaction. Various benzylic methylene substrates could be oxidized to the corresponding carbonyl compounds in satisfactory yields with this catalytic system. Hammett analysis suggested that the substrates with electron-donating groups would have higher oxidation rates. Isotopic ( 18 O) labeling experiments provided evidence of the participation of the nitrate anion in the catalytic cycle. In addition, a possible radical mechanism involving hydrogen atom abstraction by PINO (phthalimide-N-oxyl) and nitrate participation for the oxidation of benzylic methylenes in the FeIJNO 3 ) 3 ·9H 2 O/NHPI/O 2 system was proposed.Catal. Sci. Technol. This journal is

Solvent‐Free Aerobic Oxidation of Ethylbenzene Promoted by NHPI/Co(II) Catalytic System: The Key Role of Ionic Liquids

“…[7] NHPI-catalyzed oxidation reactions are most often carried out in polar solvents, such as acetic acid, acetonitrile (MeCN), and benzonitrile (PhCN), due to its poor solubility in non-polar hydrocarbons. [7][8][9][10] The complete solubilization of NHPI catalyst is essential, as NHPI can exploit its hydrogen atom donating action in the HAT processes shown in Figure 1 only provided it is under homogeneous conditions. However, the use of polar solvents limits the implementation of the catalytic system in real oxidative processes.…”

Aerobic Oxygenation of Alkylarenes over Ultrafine Transition‐Metal‐Containing Manganese‐Based Oxides

“…To date, several efficient homogeneous catalytic systems have been reported for aerobic alkylarene oxygenation (Table S1). [6][7][8][9][10][11][12][13][14][15] However,h omogeneous catalysts have severald rawbacks, for example, the use of various additivesa nd the difficulty in catalyst/product separation in exchange for their high catalytic activities. Therefore, the development of efficient heterogeneousc atalysts is desirable, and to date, many research groups have focused on the development of heterogeneous catalysts fora lkylarene oxygenationutilizing O 2 as the oxidant (Tables S2 and S3).…”

Synergistic Catalytic Oxidation of Ethylbenzene to Acetophenone by Metallophthalocyanine Intercalated Layered Double Hydroxide with Oxygen

“…On the basis of the results presented in the previous sections and some literatures,,,,, a probable mechanism is proposed (Scheme ). PINO was first generated from NHPI under the catalysis of the CoPcTs‐Zn 2 Al‐LDH or through autoxidation, and promoted radical transfer and chain rupture of the benzylic hydrogen atom of ethylbenzene.…”

“…When the log(k X /k H ) values determined for each p ‐substituted ethylbenzene were plotted against the substituent constants σ, Hammett correlations were obtained (Figure ). A negative slope of the Hammett plot ( ρ ≈ −0.62) indicates that an electron‐demanding transition state involved in the oxidation, demonstrating the more electron‐rich substrates with higher oxidation rates . The observed ρ value is somewhat lower than the ones catalyzed by metalloporphyrin analogues, such as (TMP) +• Fe IV (O)(ClO 4 ) ( ρ= −1.96), (PPh 3 ) 3 RuCl 2 / t ‐BuOOH ( ρ= −1.39) and [(pymox‐Me 2 )RuCl 2 ] + BF 4 – ( ρ= −1.1), but comparable to the ones under the Mn(TMP)Cl‐ Ph 4 PHSO 5 ( ρ= −0.78), (TMP)Fe V (O)(ClO 4 ) ( ρ= −0.72) and (OEP)Fe V (O)(ClO 4 ) ( ρ= −0.52) .…”