Bestimmung von Säure-Dissoziationskonstanten in Eisessig aus ¹H-NMR-Messungen

Trimethylsilyl Pentafluorophenylbis(trifluoromethanesulfonyl)methide as a Super Lewis Acid Catalyst for the Condensation of Trimethylhydroquinone with Isophytol

“…Recently, Ghosez and co‐workers demonstrated that a surprising reversal of relative acidity on going from Brønsted acids to trimethylsilyl derivatives thereof could result from the difference in size between the trifluoromethanesulfonate anion (TfO − ) and the trifluoromethanesulfonimide anion (Tf 2 N − ) 1. The order of Brønsted acidity is HOTf (p K a =−0.96 in HOAc (Ac=acetyl)2, 3)>HNTf 2 (p K a =0.67 in HOAc 2, 3),4 whereas the order of Lewis acidity is Me 3 SiNTf 2 >Me 3 SiOTf. Me 3 SiNTf 2 is a highly efficient Lewis acid catalyst for various carbon–carbon bond‐forming reactions 1.…”

Unusual Rate Acceleration in Brønsted Acid Catalyzed Dehydration Reactions: Local Hydrophobic Environment in Aggregated N‐(2,6‐diphenylphenyl)‐N‐mesitylammonium Pentafluorobenzenesulfonates

“…TsOH (p K a =8.5 in CD 3 CO 2 D) is a stronger acid than C 6 F 5 SO 3 H (p K a =11.1 in CD 3 CO 2 D) 2. 7, 8 As a result of its weaker acidity and slight hydrophobicity, diphenylammonium pentafluorobenzenesulfonate ([Ph 2 NH 2 ] + [O 3 SC 6 F 5 ] − , black line) showed lower catalytic activity than C 6 F 5 SO 3 H (red line), whereas 1 a (green line) and dimesitylammonium pentafluorobenzenesulfonate ([Mes 2 NH 2 ] + [O 3 SC 6 F 5 ] − , blue line) exhibited significantly higher catalytic activities than that of C 6 F 5 SO 3 H. In particular, the bulkiest catalyst, 1 a , had the highest catalytic activity because of its efficient creation of a local hydrophobic environment. Interestingly, 1 a exhibited higher catalytic activity than TsOH despite the much weaker acidity of 1 a (red line, Figure 3 a vs.…”

A Fluorous Super Brønsted Acid Catalyst: Application to Fluorous Catalysis without Fluorous Solvents

“…Fluorous solid catalyst 3d was also used in the Mukaiyama aldol reaction (Equation 6) and Sakurai-Hosomi allylation reaction (Equation 7). These reactions were performed at -78 °C and r.t., respectively, under heterogeneous conditions.…”