Gas-phase preparation of carbonic acid and its monomethyl ester.

Angewandte Chemie (International ed. in English) (2014-09-10)
Hans Peter Reisenauer, J Philipp Wagner, Peter R Schreiner
ABSTRACT

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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Di-tert-butyl dicarbonate, ReagentPlus®, 99%
Sigma-Aldrich
Di-tert-butyl dicarbonate, ≥98.0% (GC)
Sigma-Aldrich
Di-tert-butyl dicarbonate, ReagentPlus®, ≥99%
Sigma-Aldrich
Di-tert-butyl dicarbonate solution, 1.0 M in THF
Sigma-Aldrich
Di-tert-butyl dicarbonate solution, 2 M in methylene chloride
Sigma-Aldrich
Di-tert-butyl dicarbonate solution, 2 M in THF