Gas phase preparation of carbonic acid and its monomethyl ester.

Hans Peter Reisenauer, Jan Philipp Wagner, Peter R. Schreiner 

Angew. Chem. Int. Ed. 2014, 53, 11766–11771 (“hot paper”), DOI: 10.1002/anie.201406969.

Highlights:

a) Front cover of this issue;

b) Perspective: Götz Bucher and Wolfram Sander Science 2014, 346, 544–545; c) Feature: Carbonic Acid Crystal Forms Identified. Jyllian N. Kemsley C & EN News 2014, 92 (41), 28–29;

d) ChemistryViews: Carbonic Acid – And Yet It Exists!;

e) Innovations Report: Carbonic Acid—And Yet It Exists!;

f) Physorg.com: Preparation and characterization of gas-phase carbonic acid and its monomethyl ester.

Carbonic acid (H₂CO₃), an essential molecule of life (e.g., as bicarbonate buffer), has been well characterized in solution and in the solid state, but for a long time, it has eluded its spectral characterization in the gas phase owing to a lack of convenient preparation methods; microwave spectra were recorded only recently. Here we present a novel and general method for the preparation of H₂CO₃ and its monomethyl ester (CH₃OCO₂H) through the gas-phase pyrolysis of di-tert-butyl and tert-butyl methyl carbonate, respectively. H₂CO₃ and CH₃OCO₂H were trapped in noble-gas matrices at 8 K, and their infrared spectra match those computed at high levels of theory [focal point analysis beyond CCSD(T)/cc-pVQZ] very well. Whereas the spectra also perfectly agree with those of the vapor phase above the β-polymorph of H₂CO₃, this is not true for the previously reported α-polymorph. Instead, the vapor phase above α-H₂CO₃ corresponds to CH₃OCO₂H, which sheds new light on the research that has been conducted on molecular H₂CO₃ over the last decades.