A Perfluorinated Carboxylic Sulfuric Anhydride: Microwave and Computational Studies of CF₃COOSO₂OH

Abstract

Trifluoroacetic sulfuric anhydride (CF 3 COOSO 2 OH, TFASA) and its deuterated isotopologue have been observed by pulsed-nozzle Fourier transform microwave spectroscopy. TFASA was generated in situ in a supersonic expansion from the reaction of CF 3 COOH or CF 3 COOD with SO 3 . The spectrum, which was notably weaker than those of previously studied carboxylic sulfuric anhydrides, is that of a simple asymmetric rotor with no evidence of internal rotation of the CF 3 group. Calculations at the M06-2X/6-311+ +G(3df,3pd) level indicate that the title compound is produced via a mechanism involving a concerted cycloaddition, analogous to that found for other carboxylic sulfuric anhydrides. The calculations further show that the equilibrium orientation of CF 3 relative to the CO bond changes upon formation of the anhydride, indicating that any path connecting the equilibrium structures of CF 3 COOH and CF 3 COOSO 2 OH necessarily includes both cycloaddition and internal rotation. CCSD(T)/complete basis set with double and triple extrapolation [CBS(D-T)] single-point energy calculations at key points on the potential surface indicate that the barrier to form TFASA from a putative CF 3 COOH•••SO 3 complex is about 1.2 kcal/mol after zero-point energy corrections. This value is significantly larger than the near-zero or slightly negative barriers previously reported for the reactions of SO 3 with nonfluorinated carboxylic acids and likely accounts, at least in part, for the reduced spectral intensity. Thus, TFASA is a somewhat unique addition to the series of carboxylic sulfuric anhydrides studied to date. Theoretical values of certain structural parameters, atomic charges, and vibrational frequencies also support this point of view. Despite the differences, however, this work clearly demonstrates that the reaction RCOOH + SO 3 → RCOOSO 2 OH readily occurs in the gas phase and is not restricted to acids with hydrocarbon R groups.

Carboxylic Sulfuric Anhydrides

“…However, with the inclusion of ZPE, the calculations indicate a barrierless process, with a zero-point corrected activation energy of only 0.01 kcal/mol. The imaginary frequency found at the transition state corresponds to the concerted π 2 + π 2 + σ 2 cycloaddition mechanism, as previously proposed. − A diagram summarizing the relative energies at key points on the potential energy surface is given in Figure and numerical values are provided in Table .…”

“…Energy diagram depicting key points on the intermolecular potential surface for the formation of carboxylic sulfuric anhydrides that do not involve internal rotation. For the reaction with CH 3 COOH and CF 3 COOH, see refs and , respectively, for a more complete representation including internal rotation. Electronic energies are calculated at the CCSD­(T)/CBS­(D-T)//M06-2X/6-311++G­(3df,3pd) level of theory with zero-point corrections from M06-2X frequencies.…”

“… a Derived from optimized M06-2X/6-311++G­(3df,3pd) geometries. b Atomic numbering of Figure . c Reference . d Values taken from the calculations of ref . e This work. f Reference . g Reference . h Pinic acid derivative. …”

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

“…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.…”

Studying the Chemical Reactivity Properties of Cytosine and its Antiviral Analogues: Zebularine, 5-Aza-Cytosine And 5-Aza-5,6-Dihydro-Cytosine through Density Functional Theory

“…Hybrid meta-GGA functional M06-2X has been performed to study the different reactivity descriptors concerning IP, electronic a nity, hardness. This method has been proved to give the best correlation with experimental data [26,27]. The split-valence 6-311++G(2d, 2p) has been employed in this study.…”