On the mechanism of oxidation process initiation by the N-hydroxyphthalimide-cobalt (II) acetate system

Abstract

The effect of the structure of radical catalysts, N hydroxyphthalimides (NHPI), on the oxida tion process initiation in the presence of cobalt (II) acetate is studied. It is shown that the magnitude of the synergic effect of the system NHPI-Co(OAc) 2 depends on the structure of NHPI molecule. The proposed mechanism is confirmed according to which of the NHPI molecules in the inner sphere of the metal are catalytically active.

Kinetics of N-oxyl Radicals’ Decay

“…The conversion of the substrate was only 10% with 5% acetophenone yield. Earlier we have shown that NHPI is much more effective than 4-HOOC–NHPI with an electron-withdrawing substituent in the cumene oxidation when using cocatalysts CuCl, CuBr, and Co­(OAc) 2 . , Li et al successfully used 4-HOOC–NHPI in combination with NHQI for the aerobic oxidation of ethylbenzene, but it was shown that 4-HOOC–NHPI alone is an ineffective catalyst in the allylic oxidation of cholesteryl acetate . Thus, the high reactivity of N -oxyl radicals with electron-withdrawing substituents in H-abstraction does not always correlate with the overall catalytic activity.…”

Selective oxidation of cellulose catalyzed by NHPI/Co(OAc)2 using air as oxidant

“…According to the above results and the relevant literature (Coseri 2009a, b;Recupero and Punta 2007;Bailey et al 2007;Opeida et al 2012;Coseri et al 2009), a possible mechanism of cellulose oxidation with air as oxidant in the presence of NHPI-Co(OAc) 2 in acetic acid complex. Then, the bivalent cobalt species were oxidized to form superoxocobalt species under the participation of oxygen, which subsequently decomposed to form the key species of phthalimide-N-oxy radical (PINO) for oxidation of cellulose.…”

Chemo- and regioselective oxygenation of C(sp3)–H bonds in aliphatic alcohols using a covalently bound directing activator and atmospheric oxygen

“…The initiation step must be the one-electron oxidation of the N -hydroxy group of 1 by Co( iii ) species, which are generated through the reaction between Co( ii ) and O 2 . 25 The thus-generated N -oxyl radical 5 abstracts a hydrogen atom of a C–H bond at a proximate position, generating carbon radical species 6 . Trapping 6 with molecular oxygen, the resulting alkyl peroxy radical 7 is quenched by a hydroperoxy radical generated in the initiation step to produce alkyl peroxide 8 , or through intramolecular hydrogen abstraction from DA, generating 9 .…”