2,6-Di-tert-butylpyridine is a weak base used in the preparation of 2, 6-di-tert-butylpyridine hydrotriflate. It is used as a proton scavenger to check the progress of the living polymerization of isobutylene. It is associated with cerric ammonium nitrate and used in the alfa-enolation of aldehydes. It is involved in the preparation of vinyl triflate using polymer-bound 2,6-di-tert-butylpyridine. Since it was first synthesized by Brown and Kanner[1], 2,6-di-tert-butylpyridine has attracted the interest of many researchers because of its unusually low basicity: with its two-alkyl substituents, DTBP is nevertheless a weaker base than unsubstituted pyridine in aqueous solution. Brown and Kanner[1] and others[2] proposed that the abnormally low basicity of DTBP was caused by steric hindrance to hydration of DTBPH+. Recent determinations of gas-phase proton affinities of DTBP and other alkyl-substituted pyridines showed that the basicity of DTBP in the gas phase was normal[2, 3], which confirmed that its weak basicity in water was due to solvent effects on DTBP and (or) DTBPH+. A complete analysis of the thermodynamic cycles linking the protonation processes of DTBP and other pyridines in the gas phase and in aqueous solution led Arnett and Chawla[2] to conclude that there was indeed some hindrance to the hydration of DTBPH+ as reflected in its abnormally low enthalpy of hydration. However, more recently Hopkins et al.[3], after investigating the protonation of additional tertbutylpyridines and repeating the thermodynamic determinations of Amett and Chawla[2] of DTBP, concluded from their new data that the hydration enthalpy of DTBPH+ was normal but that the corresponding entropy was abnormal; they suggested that the rotation of the water molecule attached to DTBPH+ and of -CMe3 was restricted. These results and conclusions were in agreement with the gas phase studies of Moet-Ner and Sieck[4] on the attachment of one water molecule to a series of pyridinium cations including DTBPH+.
