Propiolic and acrylic acids are shown to react with SO3 in a supersonic jet to produce propiolic sulfuric anhydride (HC≡CCOOSO2OH) and acrylic sulfuric anhydride (H2C=CHCOOSO2OH), respectively. The products are characterized by microwave spectroscopy and theoretical calculations. In the case of acrylic acid, two species corresponding to the s-cis and s-trans conformers of the acrylic acid monomer are observed. The calculations indicate that both acids react with SO3 via a barrierless cycloaddition reaction. Interestingly, the s-cis monomer leads to the s-trans anhydride and vice versa. This apparent reversal, however, does not arise from rotation about a carbon-carbon bond, but rather is due to migration of a C=O double bond from one oxygen of the carboxyl group to the other during the cycloaddition. Estimates of the equilibrium constants for the anhydride formation are presented, and the energetics are compared with those of related carboxylic sulfuric anhydrides. Possible implications for atmospheric science are noted.

Acrylic and propiolic sulfuric anhydrides: Formation, microwave characterization, and theoretical calculations

255th National Meeting (2018)

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