Issue 20, 2014

CO2 incorporation in hydroxide and hydroperoxide containing water clusters—a unifying mechanism for hydrolysis and protolysis

Abstract

The reactions of CO2 with anionic water clusters containing hydroxide, OH(H2O)n, and hydroperoxide, HO2(H2O)n, have been studied in the isolated state using a mass spectrometric technique. The OH(H2O)n clusters were found to react faster for n = 2,3, while for n >3 the HO2(H2O)n clusters are more reactive. Insights from quantum chemical calculations revealed a common mechanism in which the decisive bicarbonate-forming step starts from a pre-reaction complex where OH and CO2 are separated by one water molecule. Proton transfer from the water molecule to OH then effectively moves the hydroxide ion motif next to the CO2 molecule. A new covalent bond is formed between CO2 and the emerging OH in concert with the proton transfer. For larger clusters, successive proton transfers from H2O molecules to neighbouring OH are required to effectively bring about the formation of the pre-reaction complex, upon which bicarbonate formation is accomplished according to the concerted mechanism. In this manner, a general mechanism is suggested, also applicable to bulk water and thereby to CO2 uptake in oceans. Furthermore, this mechanism avoids the intermediate H2CO3 by combining the CO2 hydrolysis step and the protolysis step into one. The general mechanistic picture is consistent with low enthalpy barriers and that the limiting factors are largely of entropic nature.

Graphical abstract: CO2 incorporation in hydroxide and hydroperoxide containing water clusters—a unifying mechanism for hydrolysis and protolysis

Supplementary files

Article information

Article type
Paper
Submitted
09 Jan 2014
Accepted
24 Mar 2014
First published
24 Mar 2014
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2014,16, 9371-9382

Author version available

CO2 incorporation in hydroxide and hydroperoxide containing water clusters—a unifying mechanism for hydrolysis and protolysis

M. J. Ryding and E. Uggerud, Phys. Chem. Chem. Phys., 2014, 16, 9371 DOI: 10.1039/C4CP00100A

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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