Alquilguanidinas imobilizadas em matrizes inorganicas

AUTOR(ES)

Ricardo da Silva Sercheli

DATA DE PUBLICAÇÃO

1999

RESUMO

The preparation of novel base catalysts by the immobilisation of alkylguanidines in hydrophobic zeolite Y, hexagonal mesoporous silica MCM-41 and SiO2 sol-gel matrixes was studied. The encapsulated alkylguanidines were prepared by the reaction of primary amines with dicyclohexylcarbodiimide previously diffused into the zeolite. The anchoring of alkylguanidines was carried out by organofuctionalisation ofthe MCM-41 surface with and 3-glycidoxypropyltrimetoxysilane and subsequent nucleophilic attack of the alkylguanidines at the oxirane ring on the organosilane. The entrapment of an alkylguanidine in SiO2 sol-gel matrixes was effected by the addition of the alkylguanidine to the sol mixtures. The catalysts prepared by encapsulation of alkylguanidines in hydrophobic zeolite Y show low activities in reactions of benzaldehyde with acetone and transesterification of soybean oil with methanol, compared to those obtained in the homogeneously catalysed reactions. However, no leaching of the alkylguanidines was observed. The catalysts prepared by anchoring of alkylguanidines at the surface of MCM-41 show similar catalytic activities to those observed in the reaction of benzaldehyde with acetone when methanol is used as a solvent, besides reasonable activities for the transesterification of soybean oil with methanol. These catalysts show leaching of the bases from the supports during the reactions. However, the activities are not only due to the leached guanidine. The activity of the entrapped alkylguanidine in SiO2 matrixes is also low and comparable to that of encapsulated alkylguanidines. Furthermore, the base leaches out from the support during the transesterification reaction, probably due to dissolution of the amorphous structure of the support. Despite the alkylguanidines immobilised on the different supports do not show the expected efficiency, all show a higher selectivity for the addition product in the reaction of benzaldehyde with acetone, as opposed to the homogeneously catalysed reaction, which forms the condensation product preferentially.

ASSUNTO(S)

sintese organica cromatografia de gas catalisadores

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