Evidence for Oxonium Ions in Ethereal “Hydrogen Chloride”

Abstract

Although solutions of hydrogen chloride in ethereal solvents like diethyl ether or dioxane are commonly employed in the laboratory, the solution structure of these reagents has yet to be firmly established. Here, we analyze solutions of ethereal hydrogen chloride or deuterium chloride in toluene, in dichloromethane, or in the absence of a co-solvent by in situ infrared spectroscopy. The resulting spectra are inconsistent with free HCl or often-proposed 1:1 HCl–ether complexes but closely match the predicted spectra of oxonium ions generated via protonation of diethyl ether. Molecular dynamics simulation of the oxonium chloride complexes provides evidence for an outer-sphere contact ion pair. These results suggest new approaches for tuning the acidity of strong Brønsted acids in organic solvents and demonstrate the importance of conducting spectroscopic measurements under reaction-relevant conditions.

Advancements in hydrochlorination of alkenes

“…It is crucial to emphasize the distinction between hydrochloric acid and HCl (gas) or HCl solutions in apolar solvents, as HCl molecules in hydrochloric acid are predominantly dissociated into H 3 O + and Cl − . Recent studies by Jacobsen suggest a similar dissociation of HCl for ethereal HCl solutions, which are better described as HEt 2 O + and Cl − [ 34 ].…”

Carboxonium derivatives based on closo-dodecaborate anions [1,2-B12H10O2CR]−: synthesis and molecular orbital analysis

“…Interest in such systems is driven by the fact that they can act as key intermediates in acidcatalysed reactions. [4][5][6][7] For their generation, strong acids such as FSO 3 H and CF 3 SO 3 H are used in mixtures with SbF 5 and SO 2 . 8,9 Another approach for generating carboxonium ions involves the interaction of acids or esters with trimethylsilyl chloride (CH 3 ) 3 SiCl.…”