| Popis: |
Free radical chain autoxidation is the primary oxidation mechanism for many polymers, but it is not the only way that organic materials can react with oxygen. Organic chemists have identified several ways that molecular oxygen can react directly with molecules despite the spin-forbidden nature of the reaction or apparently high energy barriers. These reactions tend to be very slow or to occur rapidly and cleanly only under special conditions, so they are very difficult to study. Several of these mechanisms are briefly reviewed, and two recently reported examples from this laboratory are discussed in more detail. One example is the photooxidation of the methyl groups of an aryl ether model compound that seems to involve oxygen directly abstracting a hydrogen atom from the methyl group. The intermediate state can be trapped by a solvent bearing secondary or tertiary hydrogen atoms. The second example is the thermal oxidation of fully aromatic triaryloxazoles that seem to add molecular oxygen in a spin-forbidden 4 + 2 cycloaddition reaction. |
