99845-94-0Relevant articles and documents
Selective Solvent-Free and Additive-Free Oxidation of Primary Benzylic C–H Bonds with O2 Catalyzed by the Combination of Metalloporphyrin with N-Hydroxyphthalimide
Shen, Hai-Min,Qi, Bei,Hu, Meng-Yun,Liu, Lei,Ye, Hong-Liang,She, Yuan-Bin
, p. 3096 - 3111 (2020/04/29)
Abstract: A protocol for solvent-free and additive-free oxidation of primary benzylic C–H bonds with O2 was presented through adjusting the combination of metalloporphyrins and NHPI as binary catalysts to overcome the deficiencies encountered in current oxidation systems. The effects of reaction temperature, porphyrin structure, central metal, catalyst loading and O2 pressure were investigated systematically. For the optimized combination of T(2-OCH3)PPCo and NHPI, all the primary benzylic C–H bonds could be functionalized efficiently and selectively at 120 °C and 1.0?MPa O2 with aromatic acids as the primary products. The selectivity towards aromatic acids could reach up to 70–95% in the conversion of more than 30% for most of the substrates possessing primary benzylic C–H bonds in the metalloporphyrin loading of 0.012% (mol/mol). And the superior performance of T(2-OCH3)PPCo among the metalloporphyrins investigated was mainly attributed to its high efficiency in charge transfer and fewer positive charges around central metal Co (II) which favored the adduction of O2 to cobalt (II) forming the high-valence metal-oxo complex followed by the production of phthalimide N-oxyl radical (PINO) and the initiation of the catalytic oxidation cycle. This work would provide not only an efficient protocol in utilization of hydrocarbons containing primary benzylic C–H bonds, but also a significant reference in the construction of more efficient C–H bonds oxidation systems. Graphic Abstract: The solvent-free and additive-free oxidation of primary benzylic C–H bonds with O2 was presented through adjusting the combination of metalloporphyrins and NHPI as binary catalysts, and the highest selectivity towards aromatic acid reached up to 95.1% with the conversion of 88.5% in the optimized combination of T(2-OCH3)PPCo and NHPI.[Figure not available: see fulltext.].
Autoxidation of alkylnaphthalenes. 2. Inhibition of the autoxidation of n-hexadecane at 160 °C
Igarashi,Jensen,Lusztyk,Korcek,Ingold
, p. 7727 - 7736 (2007/10/02)
The rate of the self-initiated autoxidation of hexadecane at 160 °C under 760 Torr of O2 is reduced by the addition of submolar concentrations of naphthalene or alkylnaphthalene. The kinetics of these (alkyl)naphthalene-modulated, self-initiated hexadecane autoxidations have been examined by monitoring hydroperoxide concentrations. Under similar conditions, the extent of the rate retardation is essentially identical for equal concentrations of naphthalene and 1- and 2-methylnaphthalene (and 2-sec-butylnaphthalene), which proves that retardation is due to chemistry associated with the naphthalene moiety. It is shown that the (alkyl)naphthalene produces both an increase in the rate constant for a bimolecular, peroxyl + peroxyl chain-termination process and a kinetically-first-order chain-termination reaction. Both of these termination processes are attributed to an initial addition of hexadecylperoxyl radicals to the naphthalene ring. Reaction of the resultant peroxycydohexadienyl radical with O2 produces the HOO? radical which is responsible for the increase in the rate constant for bimolecular termination. Unimolecular decomposition of the peroxycyclohexadienyl radical yields hexadecanol and an (alkyl)naphthoxyl radical, the latter being responsible for the kinetically-first-order termination process. A simplified scheme of 17 elementary reactions yields a kinetic expression which, via computer modeling, is shown to give a very satisfactory agreement between calculated and measured hydroperoxide yields under all experimental conditions surveyed. This simulation yields a rate constant k19 of ～70 M-1 s-1 for the addition of hexadecylperoxyl radicals to (alkyl)naphthalenes at 160 °C, a value which may be compared with the estimated rate constant for hydrogen abstraction from 1- or 2-methylnaphthalene under similar conditions, viz., k15 = 34 M-1 s-1. The simulation also gives a satisfactory agreement between calculated and measured yields of organic hydroperoxides and hydrogen peroxide. That the naphthalene ring was oxidatively cleaved under the experimental conditions was demonstrated by the identification of phthalic acid and phthalic anhydride following the addition of naphthalene or a methylnaphthalene to autoxidizing hexadecane. Both 1- and 2-methylnaphthalene also yielded 2-acetylbenzoic acid. The possible mechanisms by which these naphthalene ring-cleaved products are formed are discussed.
