ABSTRACT
The vapour phase synthesis of indoles from anilines and diols was investigated using copper chromites and novel Zr02/Si02 catalysts. With the copper chromite catalysts an excess of aromatic amine was necessary to avoid polyalkylation products and the best results were obtained using a catalyst containing only promoters improving the physical properties (BaO, CaO and Si02), with operation at low temperature and LHSV values. The hourly productivity was improved by reducing the contact time, with a corresponding increase in the volume of carrier gas to be recycled. Both the excess of aniline derivatives and large volume of carrier gas required to operate at low contact time were avoided using novel Zr02/Si02 catalysts, able to operate with almost stoichiometric mixtures and using water as the main carrier gas. These catalysts showed catalytic results better than those reported in the literature, as well as a very good regenerability. This synthesis can be applied to a wide number of substrates (anilines and/or diols). In particular, using ethylene glycol the best yields in the corresponding indole were obtained when an alkyl group was located in the ortho-position to the amino group and the length of the chain was increased. Moreover, the differences in reactivity between aniline and alkylanilines were significantly smoothed by increasing the length of the diol chain.
