Carboxylic Sulfuric Anhydrides

Abstract

Carboxylic acids react with sulfur trioxide to form carboxylic sulfuric anhydrides, RCOOSO 2 OH. In this article, new supersonic jet microwave spectra are presented for the anhydride derived from propiolic acid (HCCCOOH), and recent work on a series of carboxylic sulfuric anhydrides is reviewed. For the propiolic acid derivative, computed minimumenergy structures are reported for both the anhydride ( H C C C O O S O 2 O H ) a n d i t s p r e c u r s o r c o m p l e x (HCCCOOH−SO 3 ), and additional CCSD(T)/CBS(D-T)// M06-2X/6-311++G(3df,3pd) calculations indicate that, after zero-point energy corrections, the barrier to anhydride formation is effectively zero. These results are similar to those for other carboxylic sulfuric anhydrides studied and are consistent with their rapid production under supersonic jet conditions. Carboxylic sulfuric anhydrides, as a class, have not been widely characterized in the chemical literature and thus their study represents a new feature of the chemistry of sulfur oxides and oxyacids. As such, structural and energetic features of the carboxylic sulfuric anhydrides derived from formic, acetic, acrylic, trifluoroacetic, propiolic, pinic, and benzoic acids are compared. Computed vibrational frequencies are provided as Supporting Information and should be useful for possible future observation by infrared and/or Raman spectroscopy. Statistical thermodynamics is used to estimate the equilibrium constants for the formation reactions at a series of temperatures, and the results indicate values ranging from ∼10 4 atm −1 for formic acid at 288 K to over 10 11 atm −1 for benzoic acid at 217 K. We speculate that carboxylic sulfuric anhydrides could be active species in the Earth's atmosphere and atmospheric concentrations have, therefore, been estimated assuming an equilibrium state. These estimates are subject to significant uncertainties in the atmospheric SO 3 and carboxylic acid concentrations but may be as high as 10 7 molecules/cm 3 in some locations. Related calculations suggest that equilibrium anhydride concentrations may exceed those of the sulfuric acid precursors SO 3 −H 2 O and SO 3 −(H 2 O) 2 by several orders of magnitude. Kinetic modeling will ultimately be necessary to fully assess the role, if any, of carboxylic sulfuric anhydrides in atmospheric processes.

New Mechanistic Pathways for the Reactions of Formaldehyde with Formic Acid Catalyzed by Sulfuric Acid and Formaldehyde with Sulfuric Acid Catalyzed by Formic Acid: Formation of Potential Secondary Organic Aerosol Precursors

“…The reaction of formaldehyde with formic acid is depicted in Figure , where the product P1 (H 2 C­(OH)­OCOH) is formed by the transition state TS1 after the prereactive complex C1. With regard to the reaction mechanism of HCHO + HCOOH, the hydrogen atom of the hydroxyl group in formic acid is transferred to the oxygen atom of the carbonyl group in formaldehyde, while the oxygen atom of the CO group in formic acid simultaneously adds to the central carbon atom of formaldehyde, leading to the formation of the carboxylic acid ester; this mechanism is similar to the reactions of sulfur trioxide with atmospheric acids. , …”

Molecular-Scale Mechanism of Sequential Reaction of Oxalic Acid with SO3: Potential Participator in Atmospheric Aerosol Nucleation

“…In addition, the atmospheric concentration of SO 3 is appreciable at a high altitude (with low temperature), and the energy barriers of six studied reaction processes drop with the decrease of temperature as shown in Table S13. The equilibrium constants increase as the temperature decreases implying the significant atmospheric concentration of OSA and ODSA at a low temperature.…”

“…Recent experimental research on the hydrolysis of sulfur trioxide (SO 3 ) catalyzed by formic acid has shown that formic acid can react with SO 3 forming sulfuric anhydride via introducing a new functional group −OSO 3 H barrierlessly . According to the statistical thermodynamic calculations, the estimated equilibrium concentration of carboxylic sulfuric anhydrides deriving from different original carboxylic acid is in the range from 10 3 to 10 7 molecules cm –3 . It is also found that −OSO 3 H has a stronger binding ability than the original −COOH resulting from more stable clusters involving carboxylic sulfuric anhydrides than those involving corresponding carboxylic acids through comparing the Gibbs free energy of formation and hydrogen bond energy.…”

“…It seems that the nucleation ability of carboxylic acid could be improved by the reaction with SO 3 , and the corresponding product carboxylic sulfuric anhydride is speculated to participate in NPF . The subsequent theoretical calculation on monocarboxylic acids suggested that different types of substituents such as −CHCH 2 , −CCH, −CF 3 , and the aldehyde group have little effect on the reaction energy barrier, ,, while for polycarboxylic acids, the energy barriers of reactions between one SO 3 and −COOH at different sites are all low enough for these reactions to take place in the gas phase . However, the kinetics of the sequential reaction of multiple −COOH with multiple SO 3 and their influence on NPF are still unclear.…”

Microwave and Computational Study of Pivalic Sulfuric Anhydride and the Pivalic Acid Monomer: Mechanistic Insights into the RCOOH + SO3 Reaction

“…Previous work in our laboratory has shown that carboxylic sulfuric anhydrides (CSAs) can be readily formed through a low-to-no barrier pericyclic reaction between a carboxylic acid (RCOOH) and SO 3 , − viz., In cases where the R group of the carboxylic acid is a 3-fold rotor such as in acetic or trifluoroacetic acid (R = CH 3 , CF 3 ), the orientation of the rotor relative to the carboxyl moiety differs between that in the complex and that in the product. Thus, reaction for these species is accompanied by an additional 60° rotation of the R group.…”