Efficient isomerization of safrole by amino-grafted MCM-41 materials as basic catalysts

Design of base catalyst featuring large mesoporous surfaces allows performing base-catalysed reactions in the fields of production of perfumes. Post-synthesis grafting of organotrialkoxysilanes has effectively been applied to incorporate active organic functional groups onto the mesoporous silica surfaces. The novelty of our study is the use of mesoporous materials with different chemical compositions: silicate (MCM-41), aluminosilicate (AlMCM-41; Si/Al = 64) and niobosilicate (NbMCM-41; Si/Nb = 64) and consequently, different acidity, as supports for three aminopropylalkoxysilanes (APMS), [3-(2-aminoethylamino) propyl]trimethoxysilane (2APMS) and 3-[2-(2-aminoethylamino) ethylamino]propyltrimethoxysilane (3APMS). Isomerization of safrole to the corresponding thermodynamically stable isosafrole has been carried out on these amino-grafted MCM-41 materials. Maximum conversion of around 85% with a cis/trans ratio of 1/9 at 433 K in DMF as solvent was obtained. Isomerization is strongly dependent on the nature of the support and changed in the following order: APMS/AlMCM-41 > APMS/NbMCM-41 ≫ APMS/MCM-41. The nature of the amine chain is also responsible of the activity. The order of activity is APMS/AlMCM-41 > 2APMS/AlMCM-41 > 3APMS/AlMCM-41.

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► We show isomerization of safrole to isosafrole over recyclable amino-grafted MCM-41 materials, being the maximum conversion of around 85% with a cis/trans ratio of 1/9 at 433 K in DMF.
► Isomerization is strongly dependent on the nature of the support and changed in the following order: APMS/AlMCM-41 > APMS/NbMCM-41 ≫ APMS/MCM-41.
► The nature of the amine chain is also responsible of the activity. The order of activity is APMS/AlMCM-41 > 2APMS/AlMCM-41 > 3APMS/AlMCM-41.