High-speed C-H chlorination of ethylene carbonate using a new photoflow setup.

We report the high-speed C-H chlorination of ethylene carbonate, which gives chloroethylene carbonate, a precursor to vinylene carbonate. A novel photoflow setup designed for a gas-liquid biphasic reaction turned out to be useful for the direct use of chlorine gas. The setup employed sloped channels so as to make the liquid phase thinner, ensuring a high surface-to-volume ratio. When ethylene carbonate was introduced to the reactor, the residence time was measured to be 15 or 30 s, depending on the slope of the reactor set at 15 or 5°, respectively. Such short time of exposition sufficed the photo C-H chlorination. The partial irradiation of the flow channels also sufficed for the C-H chlorination, which is consistent with the requirement of photoirradiation for the purpose of radical initiation. Near-complete selectivity for single chlorination required the low conversion of ethylene carbonate such as 9%, which was controlled by limited introduction of chlorine gas. At a higher conversion of ethylene carbonate such as 61%, the selectivity for monochlorinated ethylene carbonate over dichlorinated ethylene carbonate was 86%. We found that the substrate contamination with water negatively influenced the performance of the C-H chlorination.