Montmorillonite clays Friedel-Crafts reaction

Zinc chloride exchanged clay catalysts have been reported to be highly active for the Friedel-Crafts alkylation and acylation reactions these are commercially sold by Contract Catalysts under the name Envirocats. These are montmorillonite catalysts modified by ZnCU and FeCli. Some of the reported examples of Friedel-Crafts reactions are given below there are claims that some of the processes are commercially practised. 

Thenaldehyde (thiophene-2-carbaldehyde) is readily available via the Vilsmeier-Haack reaction of DMF with thiophene catalyzed by phosphorus oxychloride. The Sommelet reaction with 2-chloromethylthiophene also gives reasonable yields (63AHC(l)l). Likewise, thiophene is readily acylated with acyl anhydrides or acid chlorides (equation 14), using mild Friedel-Crafts catalysts, such as tin(IV) chloride, zinc chloride, boron trifluoride, titanium tetrachloride, mercury(II) chloride, iodine and even silica-alumina gels or low-calcium-content montmorillonite clays (52HC(3)l). 

Polverejan et al. (117) reported on another catalytic application of mesos-tructured clay catalysts. Saponite-derived PCH has been used for the condensed-phase Friedel-Crafts alkylation of bulky 2,4-di-ferf-butylphenol (DBP) with cin-namyl alcohol to produce a large flavan, namely, 6,8-di-tert-butyl-2,3-dihy-dro[4H]benzopyran. Because the molecular dimensions of DBP are very large (1.35 X 0.79 X 0.49 nm), conventional zeolites and pillared clays are not suitable to catalyze this reaction, while the mesopores of saponite PCH are large enough to allow access to the interlayer acid sites. The catalytic results obtained on saponite-PCH are compared to those on H -saponite, zeolite HY, and acid-treated montmorillonite K-10 (Table 9). The reaction is visualized in figure 24. 

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