4-Dimethylaminopyridine grafted on MCM-41 as an efficient and highly stable catalyst for the production of α-tocopherol acetate

N,N′-dimethyl-N-(4-pyridyl)-1,2-ethanediamine (DMPE) as a special N-alkylation precursor of 4-dimethylaminopyridine (DMAP) was grafted on the surface of γ-chloropropylated functionalized mesoporous silica MCM-41 to prepare immobilized DMAP. Characterization results of small angle X-ray diffraction, thermogravimetry and derivative thermogravimetry, Fourier transform infrared, scanning electron microscopy, energy-dispersive X-ray and transmission electron microscopy indicated that DMAP was successfully covalently bound to the surface of MCM-41. The highest loading of DMAP reached 0.9 mmol/g, which was 2.5 times higher than that of DMAP immobilized on the normal silica gel. The prepared immobilized DMAP as nucleophilic heterogeneous catalysts was successfully used for the acetylation reaction to produce α-tocopherol acetate. The highest yield reached 90.1% under the optimal condition which was summarized as follows: immobilized DMAP 100 mg, substrates mole ratio (acetic anhydride/α-tocopherol) 3:1, reaction temperature 50 ℃, stirring intensity 500 rpm, reaction in toluene for 12 h. The recyclability and stability of the DMAP grafted MCM-41 were excellent, as demonstrated by its use 20 times during batch operation without any loss of productivity.