A simple Norrish Type II actinometer for flow photoreactions.

Abstract

This contribution addresses a frequent problem in flow photochemistry, where methodologies to determine the quantum efficiency of photoreactions are totally lacking. In spite of numerous studies being available in the literature, product reaction yields are never accompanied by measurements to determine their quantum yields. Basically, the key reagent in the reaction, light, is not measured under the experimental conditions of exposure. We report here a flow actinometer based on the photochemistry of valerophenone that can be readily implemented in the organic laboratory for irradiations in the UV region. For example for UVB lamps used in our work, the irradiance was measured as 1.1 × 10-4 einstein l-1s-1. Our photoreactor design involves wrapping low-pressure lamps with Teflon tubbing, where the photochemistry takes place. Similar strategies could be implemented with other geometries or with lamps (e.g. LED) and actinometers with sensitivity in other spectral regions.