Ring Opening and Closure Reactions of β-Propiolactone in the Superacids HF/MF5 (M=Sb, As)

Transformations of beta-propiolactone in the binary superacidic systems HF/MF5 (M = Sb, As) were investigated at different temperatures. Salts of monoprotonated 3-hydroxypropanoyl fluoride [H2O(CH2)(2)C(O)F][SbF6] (1) and [H2O(CH2)(2)C(O)F][AsF6] (2) were obtained by performing the reactions at temperatures lower than -40 degrees C. In contrast, temperatures higher than -40 degrees C yield the respective salts [C9H15O6][SbF6](3) (3) and [C9H15O6][AsF6](3) (4) containing a cyclic trication. The protonated species of beta-propiolactone was not observed. All salts were characterized by low temperature Raman and IR spectroscopy. In addition, single-crystal X-ray analyses were performed for (1) and (3). For both cations the existence of a cationic acyl species as a reactive intermediate in the form of [HO(CH2)(2)CO][MF6] is assumed. The formation of the acyl cation, based on protonated beta-propiolactone, was investigated by quantum chemical calculations on the MP2/aug-cc-pVTZ level of theory.

Automated summary

In binary superacidic systems HF/MF5 (M = Sb, As), transformations of beta-propiolactone were studied at various temperatures. Different salts were obtained depending on the reaction temperature, with monoprotonated products at lower temperatures and cyclic trications at higher temperatures. Protonated species of beta-propiolactone was not observed. The salts were characterized by low temperature Raman and IR spectroscopy, and single-crystal X-ray analyses were performed for selected samples. The formation of acyl cation as a reactive intermediate was proposed based on quantum chemical calculations.