Evaluation of Aliphatic Alcohols for CO₂ Capture Using the Characteristic Carbonate Frequency

Control over CO₂ capture and utilization are important scientific and technological challenges. Although a variety of amine absorbents are used for capture, releasing the captured CO₂ is often difficult and limits their recyclability. Therefore, it is crucial to control the strength of the CO₂ bond with the absorbent. Furthermore, it is desirable to use a method that can conveniently report the strength of this bond. This motivates exploring adducts of CO₂ with alcohols in the presence of a base, using vibrational spectroscopy to report on the bond strength. Although reactions of alcohols with CO₂ to form alkyl carbonates are known, a systematic study of these adducts has not been conducted. Here we show formation of alkyl carbonates by a series of alcohols spanning the pK_a range 9.5 to 16.8. We show experimental and computational results for the frequency of the characteristic asymmetric stretch of the carbonate and demonstrate that it correlates inversely with the pK_a of the alcohol. Based on computations of the bond lengths and previous work, we propose that this frequency also correlates inversely with the adduct strength. This work extends the scope of CO₂ capture reagents and inspires further research in tuning alcohols as reversible absorbents.