Selective heterogeneous catalysts Friedel-Crafts alkylation

Thus, the combination of increased acidity and increased solvent power can be exploited for cleaner acid-catalysed reactions of organic compounds, for example Friedel-Crafts alkylation, [31] or hydrolysis of esters [9,28]. The acidity of high-temperature D20 can be used to deuterate organic compounds but the process is more efficient with an additional heterogeneous acid catalyst [32]. A related application, but not a catalytic one, exploits the acidity of SC-H2O for the in situ generation of H2 from metallic Zn the H2 can then be used for the selective reduction of organic nitro-compounds [29,30], see Figure 9.1-2. 

Continuous Friedel-Crafts alkylation, with high selectivity, of mesitylene and ani-sole with propene or propan-2-ol in scCsHe or SCCO2 using a heterogeneous poly-siloxane solid acid catalyst (Deloxan, ASP 1/7) is described by Poliakoff et al. [52] (see Chapter 12). No comparison was made with the continuous alkylation in a conventional solvent and it is, therefore, diffiadt to judge the technical potential of this approach. 

Poliakoff et al. introduced the supercritical phase to the Friedel-Crafts alkylation reaction by using SCCO2 or by making propene, one of the reactants, the supercritical fluid [56]. This heterogeneous supercritical phase reaction was conducted continuously and the selectivity was very high if a solid acid Deloxan catalyst was utilized. 

Hitzler et al. (316) report the Friedel-Crafts alkylation of mesitylene (C6H3Me3) and anisole with propene or 2-propanol using a heterogeneous polysiloxane-supported solid acid catalyst (Degussa s Deloxan) in a small fixed-bed continuous reactor (10-ml volume) using SCF propene or CO2 as the reaction solvent. For the alkylation of mesitylene with propene at 160-180°C and 200 bar, yield of the monoalkylated product (l-isopropyl-2,4,6-trimethylbenzene) was only approximately 25% due to the formation of the dialkylated product as well as dimers and trimers of propene. Selectivity to the monoalkylated product was significantly higher (40% yield) for alkylation with 2-propanol in scCOa. 

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