Ja. Koehler et al., Selective adsorption of sterically hindered phenols through a single-pointbinding mechanism, IND ENG RES, 38(8), 1999, pp. 3076-3082
There are growing demands for improved selectivity in industrial separation
s. Although preorganized three-point binding systems can achieve these sele
ctivities, supramolecular systems are seldom economical for the bulk separa
tions of low-valued chemicals. In this study, we examined the potential of
a one-point hydrogen-bonding mechanism to confer selectivity to the adsorpt
ion of phenolic species encountered in the industrial synthesis of the anti
oxidant, 2,6-di-tert-butyl-p-cresol (butylated hydroxytoluene, BHT). The ad
sorption of 2,6-di-tert-butyl-p-cresol from hexanes onto an acrylic ester s
orbent was observed to have a 270-fold lower affinity and a 2.4 kcal/mol le
ss favorable adsorption enthalpy compared to adsorption of the unbutylated
species p-cresol. To provide mechanistic explanations for the observed adso
rption behavior, we performed infrared spectroscopic and molecular-modeling
studies with a small molecule analogue of the acrylic ester sorbent. These
small molecule binding studies indicate that the phenolic hydroxyl of p-cr
esol forms a strong hydrogen bond with an appropriate accepting site, while
the bulky tert-butyl groups sterically hinder hydrogen bonding for 2,6-di-
tert-butyl-p-cresol.