四(五氟化苯基)卟啉氯化铁选择催化氧化超临界丙烷的反应机理

Reaction Mechanism of Selective Oxidation of Supercritical Propane Catalyzed by Tetrakis(pentafluorophenyl)-Porphyrin-Ferric Chloride

以BHT为自由基捕捉剂 ,研究了四 (五氟化苯基 )卟啉氯化铁 (Ⅲ )将超临界丙烷高选择性催化氧化为丙醇的反应机理 .通过GC MS分析发现 ,反应产物中有PBHT ,故可认为在超临界丙烷氧化反应过程中有丙基自由基存在 ,初步推断反应涉及自由基机理 .同时发现高浓度BHT抑制反应 ,低浓度BHT促进反应的现象 ,而以戊烷为底物时没有促进作用 .这是由于BHT的位阻效应所致 .并对BHT存在时超临界丙烷氧化反应机理进行了初步的推断 .

It is a great illumination to use the porphyrin, a substance originated in organism, as the catalyst to convert directly the saturated hydrocarbon to alcohol. But the expensive cost and the catalyst decomposition during reaction block its commercial application. Up to date, there are two mechanisms of selective oxidation of hydrocarbon, one is concerned with high valence Fe(Ⅳ), other is concerned with chain radical auto-oxidation, but they are not very satisfied. The reaction mechanism of selective oxidation of supercritical propane to propanol in air catalyzed by tetrakis(pentafluorophenyl)-porphyrin-ferric chloride (TPFPPFeCl) was investigated by using the radical trap butylated hydroxyl-toluene (BHT). It was found that larger amount of BHT( n(BHT)/ n(TPFPPFeCl)=5) retarded the oxidation of supercritical propane, but smaller amount of BHT( n(BHT)/ n(TPFPPFeCl)=3) promoted the reaction significantly. By GC-MS, the propyl radical was trapped by BHT to form PBHT. It could be regarded that high concentration of radical, especially isopropyl radical, did exist in the reaction system. The same promotion effect was not found in pentane oxidation, so it could be attributed to the steric effect of BHT radical. The reaction characteristics consisted with chain radical auto-oxidation mechanism, so the reasonable mechanism of oxidation of supercritical propane was advanced.