SINGLET OXYGEN REACTIONS WITH 2,7-DIMETHYL-2,6-OCTADIENE

Abstract— Results concerning Rose Bengal sensitized photoxidation of 2,7-dimethyl-2,6-octadiene (A) are discussed. This diolefin may be considered as a model molecule of polyisoprene of polymerization number two with 1,4-4,1 addition mode.
All the mono- and dihydroperoxides apt to occur are actually obtained. One of the occurring hydroperoxides, 2,7-dimethyl-dihydroperoxy-3,5-octadiene, which has the structure of a conjugated diene, does not lead to an endoperoxide. This is contrary to Kaplan and Kelleher's hypothesis. On the other hand, no trihydroperoxide forms as a result of further addition of singlet oxygen (¹O₂).
A complete kinetic study has allowed us to determine the rate constants of all the reactions which take place. The reactivity of (A) is twice that of 2-methyl-2-pentene and the addition of ¹O₂ to one of the double bonds of (A) induces deactivation of the remaining double bond.     

Sensitized photo-oxidation of polyisoprene: effect of the presence of hydroxy and hydroperoxy groups

The effect of a hydroxy group on the reaction of singlet oxygen with an unsaturated group has been studied for linalol and geraniol, model molecules for hydroxylated polyisoprene. Only some of all the possible reactions actually occur. A hydroxy group in a unit strongly deactivates this unit but has little influence on the reactivity of an adjacent unit.     

Singlet oxygen reactions with model compounds of cis- and trans-polyisoprene containing one unit. Kinetic aspects

We have studied the rose bengal-sensitized photooxygenation of cis- and trans-polyisoprene model compounds that contain one unit in methanolic solution, characterized the resulting monohydroperoxides, and determined their yield. We have also demonstrated the possibility of a second addition of singlet oxygen on the same unit and have undertaken a kinetic study to determine the rate constants of all the reactions of 4-methyl-4-octene.