Abstract
Photooxidation of cyclooctene by molecular oxygen in the presence of tetraphenyl porphyrin (H2TPP), tetramesityle porphyrin (H2TMP), tetrakis dichlorophenyl porphyrin (H2TDCPP) and ClFeTMP, ClFeTPP, tetrakis pentaflouro phenyl porphyrin iron chloride (ClFeTPFPP), ClFeTDCPP, ClMnTPP, ClMnTPFPP, ZnTDCPP, ClMnTDCPP, ClCoTDCPP, ClCoTPP and ZnTPP as sensitizers has been studied. 98% cyclooctene conversion with 97% selectivity toward cyclooctene oxide was obtained by H2TDCPP and ZnTDCPP sensitizers. The effect of electron-donating and withdrawing groups on the porphyrin macrocycle ring showed that non-metalled porphyrins with electron-withdrawing groups have higher reactivity (H2TDCPP > H2TPP > H2TMP). The order of reactivity for metalloporphyrins is Zn > Mn > Fe > Co for the same porphyrin ligand. A turnover number (TON) up to 6,000 with selectivity up to 95% was obtained by ClMnTDCPP. In free-base porphyrins and Zn porphyrins, singlet oxygen production is the major route for oxidation, whereas in Mn and Fe porphyrins, two parallel pathways for oxidation products is proposed.
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