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Acid catalyzed alkylation of phenols with cyclohexene: Comparison between homogeneous and heterogeneous catalysis, influence of cyclohexyl phenyl ether equilibrium and of the substituent on reaction rate and selectivity

“…The general trend observed in this case is similar for all phenols, thus suggesting the involvement of a same reaction path. In agreement with that observed for the phenol the activity of the Amberlyst 15 is, in any case, higher than that of CH 3 SO 3 H (Table 3), which is likely due to the superior protonation ability of the solid acid with respect to the liquid one [34,35]. The activity of 3,5-dimethyl phenol and 2,6-dimethyl phenol are lower than that of neat phenol (Table 1), the phenomenon may be ascribed to the steric hindrance of the substituents, which slow down the electrophilic attack [37,38].…”

“…In fact, the activities of the two catalysts are quite similar considering the initial turnover frequency referred to the whole H + sites (Table 1). CH 3 SO 3 H (in homogeneous phase) is the least active catalyst and its TOF is 20 times lower than that of the sulfonic resins, likely due to the higher acidity of the latter [34]. As a matter of fact, by considering p-toluensulfonic acid as simplified model for the sulfonic resins, the pK a of the p-toluensulfonic acids is 2.7 pK a units lower than that of methanesulfonic acid (−4.7 and −2, respectively) [35].…”

The Influence of Solvent on the Acidity and Activity of Supported Sulfonic Acid Catalysts

“…On the basis that p-TsOH is a good monomeric analogue of sulfonated polystyrene, this suggests that it is not simply the high concentration of acid in solution in the swollen resin gel that is responsible for the elevated acid strengths. In an earlier paper we speculated on the possibility of networks of interacting sulfonic acid groups existing in hydrated resins and being responsible for the acid strength enhancement [8]. This was based on an earlier model proposed by Gates [25] and it remains our favoured explanation for the elevated acid strengths.…”

“…In previous work we have shown how sulfonated polystyrene resin catalysts exhibit significantly higher acid strengths and specific catalytic activities (per acid group) than sulfonic acids supported on silica in the presence of water [7,8]. The implication of this result is that the way in which the solvent interacts with both the catalyst and the support might play an important role in controlling the catalytic properties of the acid groups.…”

“…A level of 4.7-4.9 mmol g À1 is equivalent to about one acid group per styrene unit. Resins sulfonated at higher levels than this (''persulfonated'') have previously been shown to exhibit disproportionately high acid strengths and catalytic activities compared to stoichiometrically sulfonated resins [7][8][9][10][11][12][13][14].…”