Catalytic flash vacuum pyrolysis (CFVP): An environment-friendly approach to synthesize bioactive dibenzoazepinone

LENER GERMAN; MOYANO ELIZABETH LAURA; CARBONIO RAÚL ERNESTO

Rosario

Workshop; 1st Argentienien Workshop in enviorenmental Science; 2009

Dibenzoazepinones like 2 show interesting pharmacological properties (scheme 1). The conventional synthesis of this class of compounds has been performed in several steps giving very low yields. A gas phase thermolysis technique, the flash vacuum pyrolysis (fvp) has been used as an appropriate and alternative method to obtain dibenzoazepinone 2 from benzotriazole 1. Fvp methodology has found wide applications on the preparation of thermolabile compound and reactive species, and also in the mechanistic study of thermal reactions. This technique presents many advantages: a-) the process is carried out without solvents; b-) the substance to be pyrolized remains in the hot zone for a considerably short time or contact time (~10-3 s); c-) the pyrolizate is immediately cooled to cryogenic temperatures (-200 ºC) after passage through the hot zone avoiding secondary process; and d-) the system allows the incorporation of solid catalysts to decrease the energetic requirements and to improve the selectivity of the reactions. Thus, the application of the fvp to the study of thermal behavior of heterocyclic compound has been widely investigated. Heterogeneous fvp systems using catalytic materials called catalytic flash vaccum pyrolysis (cfvp) have potential applications and this new methodology can provide an alternative synthetic tool to bioactive heterocyclic compounds. Thus, azatropone 2 (87% yield) was obtained from 1 at 450 ºC using MCM-41 solid catalyst in a friendly process. To continue the development of new cfvp systems using reusable solid catalysts to improve the selectivity towards the synthesis of dibenzoazepinones, we studied the catalytic effect of mixed oxides type ABO4 (sheelite, A= Ca2+, Sr2+, Ba2+, Bi3+; B= Mo6+, W6+, V5+) on the reactivity of benzotriazol 1. These solids have shown a good alternative to mesoporous catalysts due to their thermal stability, surface area, re-utility and its easy synthesis. The different cations that occupy sites A and B play an important role in the process which could indicate an important influence of the Lewis acid sites in the course of the reactions. On the other hand, the cations that occupy the site B shows a vital role in the temperature of conversion of the benzotriazole 1 which may indicate that the redox properties are also important in the catalysis process.