The Research Of Interaction Of Metalloporphyrins With Organic Hydroperoxides

Hydroperoxides are very important intermediates in the metalloporphyrin catalyzed hydrocarbon oxidation with air, the study of the interaction of hydroperoxide with metalloporphyrin is of great value to understand the exact nature of metalloporphyrin catalyzed biomimetic catalysis.The interaction of metalloporphyrins with organic hydroperoxides was studied by EPR, UV-Vis spectroscopies and chemical analysis in this paper. We have investigated the effects of reaction temperature, the concentration of metalloporphyrins and organic peroxides on the catalytic decomposition reaction. And the decomposition reaction mechanism was also studied.The results showed that the main products of the decomposition of cumene hydroperoxide were 2-phenyl-2-propanol and acetophenone under a nitrogen atmosphere.And cumene hydroperoxide decomposition reaction occurred mainly in the initial 5 min and at the same time, some of T(p-Cl)PPMnCl was destroyed by CHP.Though the 2-phenyl-2-propanol generated in the reaction may protect the metalloporphyrin against the destruction by CHP, it also inhibited the catalytic activity of metalloporphyrin thus slowed the decomposition rate of CHP. Solvents had important effect on the catalytic decomposition reaction, which was significantly inhibited using benzene and alcohol solvents. In the reaction system of the catalytic decomposition of p-menthane hydroperoxide(PMHP) by T(p-Cl)PPCoCl, the decomposition was similar to the CHP decomposition. The O-O bond of organic hydroperoxides containing electron-donating substituents required higher catalytic decomposition temperature, whereas electron-withdrawing substituents facilitated to be catalytic decomposition by metalloporphyrins.5,5-dimethyl-1-pyrroline N-oxide(DMPO) was used as spin trap and only cumoxyl radical adduct was detected at the initial reaction time in the reaction of T(p-Cl)PPMnCl with low CHP concentration solution at 25℃. It indicated the CHP decomposition started from the homolytic O-O bond cleavage under catalysis of T(p-Cl)PPMnCl and generated cumoxyl radicals. The cumylperoxyl radicals were formed from the subsequent reaction of cumoxyl radicals with CHP when increasing the CHP concentration. In the decomposition reactions of tert-butyl hydroperoxide and p-methane hydroperoxide by different metalloporphyrins, also only alkoxyls were detected at the initial reaction time. It showed the O-O bond of hydroperoxides cleaved homolytically forming alkoxyl radicals by metalloporphyrins. Alcohols generated more than ketones by the hemolytic scission of the O-O bond in the metalloporphyrin catalyzed hydrocarbon oxidation system.T(p-Cl)PPCoCl and T(p-Cl)PPMnCl had stronger ability to decompose CHP and PMHP while T(p-Cl)PPFeCl was less efficient producing low free radicals concentration, whereas PMHP was relatively stable by T(p-Cl)PPFeCl,T(p-Cl)PPCoCl and T(p-Cl)PPMnCl catalytic decopmsition. Formation of higher alkoxyl radical concentration required higher temperature and concentration.In the process of the interaction of different metalloporphyrins with organic hydroperoxides, the order of anti-destroyed ability of different metalloporphyrins was:T(p-Cl)PPMnCl > T(p-Cl)PPCoCl.