Green access to 2,3,5-p-benzoquinone using titania xerogels

MAGDALENA PALACIO; PAULA I. VILLABRILLE; PATRICIA VAZQUEZ; GUSTAVO P. ROMANELLI; CARMEN CACERES

Foz do Iguazu

Conferencia; International IUPAC Conference on Green Chemistry; 2012

IUPAC

The benzoquinone structure shows biologically important properties such as cardiovascular, antigerminative, antibacterial, antitumor, and antiprotozoan activities. The oxidation of 2,3,6-trimethylphenol (2,3,6-TMP) is the key step for the production of 2,3,5-trimethylbenzoquinone (2,3,5-TMBQ), which is an especially valuable starting material for the synthesis of vitamin E1, which is used extensively as antioxidant in food, medical treatments, and cosmetics2. The objective of this work is to look for a clean synthesis of these compounds using H2O2-titania xerogels system. RESULTS AND DISCUSSION According to this, ceria-titania, vanadia-titania and heteropolyoxomolybdates-titania catalysts were prepared with a load of 5% (w / w) of CeO2 (Ce-T)and V2O5 (V-T) and 10% (w / w) of H3PMo12O40 (PMo-T), H4SiMo12O40 (SiMo-T) and H4PMo11VO40 (VPMo-T) by a sol-gel process. These gels were dried in air at 50 ° C for 24 h and calcined in air at 200 ° C for 4 h. Moreover a sample of 100% (w / w) TiO2(T), was prepared so as to keep as reference material. The prepared solids were characterized by means of XRD, FT-IR, SEM. Their textural properties were determined by adsorption-desorption isotherms of N2 at 77 K. The oxidation of 2,3,6-TMP to 2,3,5-TMBQ was performed under vigorous stirring in a glass reactor at low temperature (Figure 1). The reactions were performed by adding 1 ml of H2O2, to a solution of 1 mmol of 2,3,6-TMP, 5 ml of ethanol 96% and 70 mg of catalyst. Samples of the reaction solution were extracted at different times and they were pre-treated and analyzed by gas chromatography. The selectivity to 2,3,5-TMBQ was kept between 95-98 % in all the cases. The conversion of 2,3,6-TMP reached 96 % and 91 % for VPMo-T and Ce-T catalyst, respectively, after 4 h of reaction (Figure 2). The catalysts were recovered and reused. The hydrogen peroxide descomposition in the reaction medium without the 2,3,6-TMP was studied. It can be observed that the Ce-T catalyst maintain its activity and present the lowest H2O2 conversion. CONCLUSION This procedure makes the current method feasible for the synthesis of 1,4-benzoquinones derivatives in a sustainable way with the environment (low temperature, cleaner oxidizing agent and safer solvents). It also leads to an easy separation and recovery of the catalysts for further use.