In Situ Formation of Alkylcarbonic Acids with CO₂

The mutual solubility of carbon dioxide and alcohols over a wide range of temperature and pressure provides a useful and tunable medium for reactions and separations. For many years, researchers have used alcohols as cosolvents in supercritical CO 2, and recently CO 2 -swollen alcohols have been used for antisolvent crystallization and as mobile phases for chromatography. However, little consideration has been given to chemical interaction between the alcohols and CO 2 . We have confirmed that such an interaction does exist and can create an acidic environment. By isolating reaction products we have demonstrated that alcohol−CO 2 complexes react similarly to carboxylic acids with diazodiphenylmethane, a compound typically used to evaluate acid strengths. Our evidence indicates that the behavior of CO 2 −alcohol systems is comparable to that of CO 2 −water systems, where carbonic acid is formed.