Caged CO2 for the Direct Observation of CO2-Consuming Reactions

CO2‐consuming reactions, in particular carboxylations, play important roles in technical processes and in nature. Their kinetic behavior and the reaction mechanisms of carboxylating enzymes are difficult to study because CO2 is inconvenient to handle as a gas, exists in equilibrium with bicarbonate in aqueous solution, and typically yields products that show no significant spectroscopic differences from the reactants in the UV/Vis range. Here we demonstrate the utility of 3‐nitrophenylacetic acid and related compounds (caged CO2) in conjunction with infrared spectroscopy as widely applicable tools for the investigation of such reactions, permitting convenient measurement of the kinetics of CO2 consumption. The use of isotopically labeled caged CO2 provides a tool for the assignment of infrared absorption bands, thus aiding insight into reaction intermediates and mechanisms. How to see CO2 too: Photodecarboxylation of 3‐nitrophenyl acetic acid has been used to release CO2 in aqueous thin‐layer samples. CO2 and its reactions can then be measured directly and conveniently by time‐resolved infrared spectroscopy.