Sustainable Oxidation of Cyclohexane and Toluene in the Presence of Affordable Catalysts: Impact of the Tandem of Promoter/Oxidant on Process Efficiency

Abstract

The oxygenation of cyclohexane and toluene by O2 and H2O2 catalyzed by VO­(acac)2 and Co­(acac)2 was studied at 40–100 °C and 1–10 atm. Upon such conditions, the process can be remarkably (30× times) enhanced by the minute (6–15 mM) additives of oxalic acid (OxalH) or N-hydroxyphthalimide (NHPI). The revealed effect of OxalH on H2O2-piloted oxidation is closely associated with the nature of the catalyst cation and boosted by VO­(acac)2. Whereas the effectiveness of Co­(acac)2-based systems was curbed by the addition of OxalH and remained much below the one displayed with the previous system. The observed conspicuous difference in activity was attributed to the substantially higher solubility of in situ formed VO­(IV)­oxalate compared to that of Co­(II)­oxalate. The exploration of H2O2 for the NHPI-promoted process leads to the decisively lower (5–7 times) yield in comparison to the O2-driven reaction. Similarly, for the O2-operated protocol, the yield cannot be improved by addition of OxalH either to VO­(acac)2 + NHPI or to Co­(acac)2 + NHPI mixture. By contrast, the combination of NHPI with VO­(acac)2 or Co­(acac)2 and particularly with the above two mixtures in O2-piloted oxidation enhances the yield of the aimed products 3–6 times regardless of the substrate used. The revealed significant synergetic effect of the cobalt + vanadyl bicomponent catalyst was due to the participation of each of its moiety in the different stages of the process mechanism. Only benzyl alcohol and benzaldehyde were identified in VO­(acac)2- or Co­(acac)2-catalyzed toluene oxidation, while cyclohexane oxidation yields cyclohexylhydroperoxide in line with cyclohexanol and cyclohexanone. The putative mechanism of investigated processes is highlighted and discussed.

Recyclable Mesoporous Graphitic Carbon Nitride Catalysts for the Sustainable Photoredox Catalyzed Synthesis of Carbonyl Compounds

“…Nevertheless, oxygenation of hydrocarbons is widely applied in the pharmaceutical and fine chemical industries . Most reported procedures use toxic reagents and harsher reaction conditions, often involving transition metals, to functionalize benzylic C–H bonds. , Unlike other reported methods, , upon excitation with visible light, mpg-CN acts as a direct hydrogen atom transfer catalyst (HAT) without the need to use an additive or a base (Figure ). , Alkyl arenes, both acyclic and cyclic, were selectively oxidized to yield the desired products in up to 93% yield (Figure ).…”

UV‐induced oxygenation of toluene enhanced by Co (acac)2/9‐mesityl‐10‐methylacridinium ion/N‐hydroxyphthalimide tandem

“…A detailed CV, UV-vis, GLC, and iodometry descriptions are brought in the literature. 18,19 Thin-liquid chromatography (TLC) was used for semiquantitative detection of peroxide-like compounds (TLC plates Silufol UV 254, Kavalier, Czechoslovakia, eluent toluene + ethyl acetate mixture (1/1), developer-saturated solution of NaI in acetone).…”

“…More information concerning the construction of the oxidation unit is presented in Schemes S1 and S2 and literature. 18…”

“…17 Consequently, these radicals initialize the forthcoming reactions of the stable primary C-H bond cleavage. 18 Inspired by these studies, we determined the impact of NHPI on the photoinitiated oxidation of toluene by O 2 in the presence of an inexpensive and unsophisticated dmetal catalyst (Co (acac) 2 (acac = acetylacetonate) and photocatalyst (Me 2 Acr + -Mes), which is different from g-C 3 N 4 . We hypothesized that the inclusion of NHPI in the above oxidation protocol would be beneficial for yield.…”

Greenhouse gas emissions reduction by process intensification: Reactive distillation column with side decanter

“…metal oxodiperoxo complexes, 9 O 3 in liquid CO, 10 tert-butyl hydroperoxide 11 or H 2 O 2 . 12 Although process promoters increase the yield, 13 low yields are achieved compared with O 2 . 14 Some catalysts with higher conversion rates produce lower selectivity towards cyclohexanol.…”