Add time:09/05/2019         Source:sciencedirect.com

The kinetics of the photochemical reaction of tert-butylguaiacyl-carbinol sensitized by p-methoxypropiophenone in aerated dimethoxyethane solution were measured experimentally. In contrast with the same model system in oxygen-free solution, the concentration of the sensitizer in the presence of oxygen remained constant within the experimental error limits. This implies that a regenerative loop exists for the sensitizer which operates efficiently if oxygen is present. The efficiency of this regenerative loop seems to depend on the substrate concentration. The rate of substrate consumption was found to be considerably faster than the rate obtained previously for the oxygen-free system.The kinetics of substrate and sensitizer consumption and product formation were also studied by computer modelling, employing a reaction set consisting of 91 elementary reactions and 58 different species. Using this reaction set the kinetics of the substrate consumption were simulated for 4 h with good agreement with the experimental results. The calculated yields of the various reaction products were in fairly good agreement with previous experimental results for a similar model system. For the sensitizer, however, a small disagreement with the experimental results still remains, implying that in our simulation the regenerative loop does not operate with sufficient efficiency. The most important pathways for substrate reaction are the different singlet oxygen channels and the hydrogen abstraction mode of reaction. The relative importance of these two pathways could not be determined quantitatively.

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