1,2,4-trimethylbenzene, heterogeneous

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Heterogeneous catalysts are also capable of achieving high regiospeci-ficity. Thus Raney Nickel, a catalyst that has not been widely used in triti-ation studies, labels only the side chains of toluene and butylbenzene under mild conditions.On the other hand the Lewis acids, EtAlCl2 and BBra, tritiate the equivalent 2,4,6-positions of 1,3,5-trimethylbenzene despite the obvious steric hindrance. 

To a screw-capped vial containing the NHC precursor (Scheme 8.56) (0.005 mmol), Pd(dba)2 (0.005 mmol), and LiHMDS (2.3 mmol) are added 2-bromo-l,3,5-trimethylbenzene (1.0 mmol) and tert-butyl acetate (1.1 mmol) followed by toluene (2.5 ml) [101]. The vial is sealed with a cap containing a PTFE septum and removed from the drybox. The heterogeneous reaction mixture is stirred at room temperature for 12 h. The crude reaction is diluted with EtjO and quenched with aqueous NH Cl. The organic phase is washed with a saturated aqueous... 

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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