Hydrogenation of 2-ethyl-9,10-anthraquinone on Pd/SiO2 catalysts The role of humidity in the transformation of hydroquinone form

Abstract The role of humidity in the hydrogenation of 2-ethyl-9,10-anthraquinone (eAQ) and especially in the further transformation of 2-ethylanthracen-9,10-diol (eAQH 2 ) primary and desirable product formed on eAQ hydrogenation was studied. Three 0.5% Pd/SiO 2 catalysts differing in the content of Na 2 CO 3 and thus in alkaline properties were used. They were obtained by successive removing of Na 2 CO 3 from the catalyst prepared by precipitation of palladium hydroxide onto Na 2 CO 3 pre-impregnated SiO 2 . Hydrogenation experiments were carried out in “standard” and subsequently in “wet” systems at 62 °C, atmospheric pressure of H 2 in mixture of 2-octanol–xylene (1:1) as the solvent. Humidity influences the whole hydrogenation process, fundamental reaction, the hydrogenation of eAQ to eAQH 2 (quinone–hydroquinone stage) and further transformation of eAQH 2 . A complicated effect of humidity is observed. Humidity has an effect on consecutive reactions transforming eAQH 2 via OXO-tautomer to intermediate product 2-ethyl-9,10-dihydro-9,10-dihydroxyanthracene (INT), precursor of 2-ethylanthrone (eAN). The influence of humidity varies depending on the content of Na 2 CO 3 in catalysts and thus their alkaline properties. The observed effects are correlated with adsorption configuration of reagents and especially eAQH 2 and INT. Highly alkaline medium as well as humidity facilitated adsorption in the carbonyl group—bonded configuration thus enhancing the transformation of eAQH 2 by hydrogenolytic reactions and especially the formation of eAN.