1402410-52-9Relevant articles and documents
Synthesis and application of strong Bronsted acids generated from the Lewis acid Al(ORF)3 and an alcohol
Kraft, Anne,Beck, Jennifer,Scherer, Harald,Himmel, Daniel,Krossing, Ingo,Steinfeld, Gunther
, p. 7485 - 7491,7 (2012)
The strong neutral Bronsted acids [(R)OH→Al(OC(CF 3)3)3] (R = -C(CF3)3 (1), -C6F5 (2), (-)-menthyl (3)) were synthesized by complexation of perfluoro tert-butyl alcohol, pentafluorophenol, and (-)-menthol with the Lewis superacid Al(OC(CF3)3)3. The 1:1 composition of the compounds was proven by NMR (except for compound 2), IR, and partially Raman spectroscopy and X-ray crystallography. Of the structures, 2 crystallized with a coordinated toluene molecule, which might be seen as a frozen intermediate or prestep to form the classical Wheland complex of protonated toluene. This interaction was calculated to be exothermic by 32 (no dispersion) or 88 kJ mol-1 (Grimmes D3 dispersion correction included ? RI-BP86/SV(P)). 1 proved suitable to protonate mesitylene and Et 2O, giving the acidic cationic Bronsted acids [H(C 6H3(CH3)3)]+ (4b) and [H(OEt2)2]+ (5) with the respective weakly coordinating anion [Al(OC(CF3)3)4]-. In dichloromethane solution 4b decomposes at room temperature, leaving the room-temperature-stable salt [H(C6H3(CH3) 3)]+[((CF3)3CO)3Al-F- Al(OC(CF3)3)3]- (4a; XRD). The acidities reached with 4 and 5 are discussed in terms of our recently introduced absolute Bronsted acidity scale. The absolute chemical potentials of a 0.001 M solution of protonated mesitylene and Et2O amount to -944 and -1015 kJ mol-1 or-in terms of absolute pHabs values-to 165 and 178 and thus are at the threshold of superacidity of -975 kJ mol -1 or pHabs of 171.
