Threshold catalyst strength

Together with the well-accepted threshold DPE value for superacidity (250 kcal/mol) [18], it is noteworthy that only marginal variation in was observed for the TMPH" " adduct as DPE decreases from ca. 320 (weak acidic strength) to 250 kcal/mol (super strong acidic strength) [18]. As such, it is obvious that the P-TMP NMR approach is inferior for differentiating Bronsted acidic strengths in soHd acid catalysts. 

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