The human bloodstream has a slightly basic pH of 7.4 and even minimal deviations from this number can result in detrimental health conditions such as acidosis, which can lead to coma and death. Carbonic acid (H2CO3) is one of the primary buffer components in the human bloodstream where it helps to regulate blood pH. Despite its physiological importance, many of the specific kinetic properties of aqueous H2CO3 are incompletely understood due to a rapid, bidirectional equilibrium where H2CO3 simultaneous decomposes to form 1) bicarbonate (HCO3-) and an acidic proton (H+), and 2) water (H2O) and carbon dioxide (CO2). This study aims to describe the kinetics specific to the latter decomposition pathway. Because H2CO3 is so short-lived in aqueous solution, past studies have been limited to computational approaches or indirect experimental probes. This study couples high resolution Raman scattering spectroscopy with a high-speed liquid mixing system wherein H2CO3 is generated in situ, allowing us to probe the carbonic acid molecule directly, and quantitatively measure its rate of decomposition. We have experimentally determined the rate constant for the dissociation of aqueous H2CO3 into H2O and CO2. This decomposition proceeds according to first order kinetics with a rate constant of 0.027 ms–1. Future studies will be conducted to shed light on the decomposition of H2CO3 under physiological conditions, specifically using a phosphate buffer system that more closely mimics the human bloodstream.

Kinetic investigations of the decomposition of aqueous carbonic acid

ACS Spring 2022

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