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Generation of Phosphonium Sites on Sulfated Zirconium Oxide: Relationship to Brønsted Acid Strength of Surface −OH Sites
- Rodriguez, Jessica, Culver, Damien B., Conley, Matthew P.
- Journal of the American Chemical Society 2019 v.141 no.4 pp. 1484-1488
- Bronsted acids, zirconium oxide
- The reaction of (ᵗBu)₂ArP (1a–h), where the para position of the Ar group contains electron-donating or electron-withdrawing groups, with sulfated zirconium oxide partially dehydroxylated at 300 °C (SZO₃₀₀) forms [(ᵗBu)₂ArPH][SZO₃₀₀] (2a–h). The equilibrium binding constants of 1a–h to SZO₃₀₀ are related to the pKₐ of [(ᵗBu)₂ArPH]; R₃P that form less acidic phosphoniums (high pKₐ values) bind stronger to SZO₃₀₀ than R₃P that form more acidic phosphoniums (low pKₐ values). These studies show that Brønsted acid sites on the surface of SZO₃₀₀ are not superacidic.