Monitoring the Progress of a Photochemical Reaction Performed in Supercritical Fluid Carbon Dioxide Using a Continuously Stirred Reaction Cell Interfaced to On-Line SFC

A high-pressure photochemical reaction cell operated with a magnetic stir drive has been directly interfaced on-line with either SFC or HPLC. The interface consisted of an oven housing a recirculation pump directly connected to a sample injection valve. The inlet of the recirculation pump and the outlet from the sample injection valve were connected to the stirred reaction cell such that a return flow circuit was established. With this arrangement, a continuous flow of fresh supercritical fluid photochemical reaction mixture was maintained through the sample injection valve. This enabled samples of reaction mixture to be conveniently analyzed at regular intervals to monitor reaction progress using either on-line SFC or HPLC. The photoreduction of benzophenone in the presence of propan-2-ol to produce 1,1,2,2-tetraphenylethane-1,2-diol and 2-methyl-1,1-diphenylpropan-1,2-diol was studied. For this reaction, on-line SFC provided significantly better performance than on-line HPLC and was therefore used to monitor overall reaction progress and the different product yields. Quantitative results for this study demonstrate that highly efficient photochemical reactions proceeded in supercritical fluid carbon dioxide at 13 and 20 MPa.