Pokutsa Alexander, Tkach Sergiy, Zaborovsky Andriy, Bloniarz Pawel, Paczeŝniak Tomasz, Muzart Jacques
Department of Physical Chemistry of Fuel Fossils NAS of Ukraine, Institute of Physical Organic Chemistry and Chemistry of Coal NAS of Ukraine, Naukova Str., 3A, Lviv 79060, Ukraine.
Yuriya-Farm Corp., Narodnogo Opolchennya Str., 19, Kyiv 03151, Ukraine.
ACS Omega. 2020 Mar 30;5(13):7613-7626. doi: 10.1021/acsomega.0c00447. eCollection 2020 Apr 7.
The oxygenation of cyclohexane and toluene by O and HO catalyzed by VO(acac) and Co(acac) 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 (H) or -hydroxyphthalimide (NHPI). The revealed effect of H on HO-piloted oxidation is closely associated with the nature of the catalyst cation and boosted by VO(acac). Whereas the effectiveness of Co(acac)-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 HO for the NHPI-promoted process leads to the decisively lower (5-7 times) yield in comparison to the O-driven reaction. Similarly, for the O-operated protocol, the yield cannot be improved by addition of OxalH either to VO(acac) + NHPI or to Co(acac) + NHPI mixture. By contrast, the combination of NHPI with VO(acac) or Co(acac) and particularly with the above two mixtures in O-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)- or Co(acac)-catalyzed toluene oxidation, while cyclohexane oxidation yields cyclohexylhydroperoxide in line with cyclohexanol and cyclohexanone. The putative mechanism of investigated processes is highlighted and discussed.
研究了在40 - 100°C和1 - 10个大气压下，由VO(acac)₂和Co(acac)₂催化的O₂和HO₂对环己烷和甲苯的氧化作用。在这些条件下，草酸（H₂C₂O₄）或N - 羟基邻苯二甲酰亚胺（NHPI）的微量（6 - 15 mM）添加剂可显著（30倍）增强该过程。所揭示的H₂C₂O₄对HO₂引发氧化的影响与催化剂阳离子的性质密切相关，并由VO(acac)₂促进。而基于Co(acac)₂的体系的有效性因加入草酸而受到抑制，且仍远低于前一体系所表现出的有效性。观察到的活性显著差异归因于原位形成的VO(IV)草酸盐的溶解度远高于Co(II)草酸盐。对NHPI促进过程中HO₂的探索导致与O₂驱动反应相比产率显著降低（5 - 7倍）。同样，对于O₂操作方案，向VO(acac)₂ + NHPI或Co(acac)₂ + NHPI混合物中加入草酸也不能提高产率。相比之下，在O₂引发的氧化中，NHPI与VO(acac)₂或Co(acac)₂的组合，特别是与上述两种混合物的组合，无论使用何种底物，均可将目标产物的产率提高3 - 6倍。所揭示的钴 + 氧钒双组分催化剂显著的协同效应归因于其每个部分参与了过程机理的不同阶段。在VO(acac)₂或Co(acac)₂催化的甲苯氧化中仅鉴定出苯甲醇和苯甲醛，而环己烷氧化生成环己基过氧化氢以及环己醇和环己酮。突出并讨论了所研究过程的推定机理。
