A density functional theory study on the superacidity of sulfuric, fluorosulfuric, and triflic acid derivatives with two cyclopentadiene rings: ion pairs formation in the gas phase

Abstract

The gas phase acidity of organosulfuric acid derivatives with two cyclopentadiene rings replacing the doubly‐bonded oxygen atoms was computationally assessed using the B3LYP DFT functional and 6–311++G(d,p) basis set. Introduced five‐membered rings increased the acidity through the delocalization of the excess negative charge in conjugates bases and by providing positions to accommodate electron withdrawing substituents such as F and CN. The calculated enthalpies of deprotonation (∆Hacid) of polycyanated systems were as low as 227.8 to 263.2 kcal mol–1 indicating exceptional superacidity. Substitution of one OH moiety by F or CF3 groups offered additional acidifying effect by preventing prototropic tautomerism in the neutral acids that acts towards lowering the acidity. The designed systems spontaneously protonated H2O and NH3 in the gas phase and produced stable ion pair clusters.

Caralumane Superacids of Lewis and Brønsted Character

“…120 kcal/mol) . The acidity of Brønsted acids is commonly expressed as the value of the gas-phase Gibbs free energy of deprotonation at T = 298.15 K (denoted Δ G a 298 ), , and the Δ G a 298 of 303 kcal/mol for anhydrous H 2 SO 4 is usually considered the threshold separating regular Brønsted acids from superacids. In this work, we demonstrate that our Brønsted acids have Δ G a 298 values below 303 kcal/mol and the corresponding Lewis acids have FIA values in excess of 120 kcal/mol.…”

The Effect of Intramolecular Hydrogen Bond Type on the Gas-Phase Deprotonation of ortho-Substituted Benzenesulfonic Acids. A Density Functional Theory Study

“…Compounds with increased acidic properties have attracted the attention of researchers [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. Among them, a special place was occupied by substituted arenesulfonic acids (ASA), which have found application in homogeneous catalysis [ 9 , 10 , 11 , 12 ], electrochemical technologies [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ], and as components of ionic liquids [ 23 , 24 , 25 ].…”

“…It has been shown in [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ] that the Gibbs free energy Δ r G 0 298 of gas-phase deprotonation (GD), can be used as a criterion for the proton-donating ability of organic acids. The value Δ r G 0 298 GD is used to build the scales of molecular acidity and to identify compounds with superacidic properties.…”

Design of new organic superacids with fused and isolated pyrrole and cyclopentadiene rings and assessment of effect of –BX2(X = H, F, Cl, CN) substituents on the acidity enhancement: A DFT analysis

“…The reported ∆ H acid value for C 5 (CN) 5 H is 263.5 kcal mol −1 , indicating superacidity of this simple organic compound. Because of important role of the proton donor site on the acidity, recently, organic acids using incorporation of sulfate and phosphate moieties as proton donor with cyclopentadiene rings have been reported …”