The problems encountered in the normal method used to determine β values (rate of decay of singlet oxygen divided by the rate of its reaction with an organic compound) are discussed. The use of dilute solutions of organic acceptors for our measurements was found to give more reproducible values and simplified kinetics. These β values were used to obtain relative rate constants for a variety of substituted furans. Hammett plots were made to quantitate the substituent effects in order to explore the nature of singlet oxygen in the dye-sensitized photooxidation reactions of these furans. The calculated ρ values were compared with other photooxidation and Diels–Alder reactions. Hammett ρ values in a series of solvents were also calculated for the reaction of singlet oxygen with 2-arylfurans and increasing ρ values were correlated with decreasing solvent polarity.
Synthesis of Some Substituted Furans and Endoperoxides Via Singlet Oxygen Reactions
