Oxidation of 2,6-dimethylphenol to 2,6-dimethyl-1,4-benzoquinone with hydrogen peroxide catalyzed by TiO2-CeO2 mixed xerogels.

M. PALACIO; VILLABRILLE P.; ROMANELLI, G; DRA. PATRICIA VÁZQUEZ; CARMEN CÁCERES

Congreso; NACS - North American Catalisis Society 2009; 2009

Titania (TiO 2 ) is widely used in the field of heterogeneous catalysis [1]. It has been demonstrated that it is a solid whose catalytic properties may be modified by a supported cation. It is usual to add other atoms to titania, such as cerium, in order to improve its properties, for example its structural stability. Pure and stoichiometric titania changes its stoichiometry when it is doped with a cation having a valence different than 4+, or when the titanium valence is reduced from 4+ to 3 +. The chemical and electronic properties of this nonstoichiometric titania depend on the defect density and the impurity concentration in the crystal [2]. The nonstoichiometric titania, in our case, was prepared by sol-gel technique. The most important property of CeO 2 is that it can be used as an oxygen reservoir, which stores and releases oxygen via the redox shift between Ce+4 and Ce+3 under oxidizing and reducing conditions, respectively [3]. According to the above-mentioned studies titania-ceria mixed xerogels were prepared in a previous paper [4]. They were characterized and tested as catalysts in the oxidation of 2,6- dimethylphenol (2,6-DMP) to 2,6-dimethyl-p-benzoquinone (2,6-DMBQ) (Scheme 1), using aqueous hydrogen peroxide as oxidant. This quinone is a key intermediate for the synthesis of a number of medicines and physiologically active substances; it can be used for the synthesis of trimethylbenzoquinone or for the preparation of indophenol [5]. On the other hand, previously we studied this reaction using aqueous hydrogen peroxide as oxidant at low temperature (20 °C) with catalysts based on heteropolyacids [6]. With the objective to enlarge the studies carried out about this oxidation reaction, in this work titania-ceria mixed xerogels are used as heterogeneous catalysts and mixed ethanol-water as solvent giving a possible mechanism of reaction.