Aqueous Solutions of Mo-V-Phosphoric Heteropoly Acids as Bifunctional Catalysts For Preparation of 9,10-Anthraquinone and its Hydrogenated Derivatives.

Acid-catalyzed condensation of 1,3-butadiene with para-quinones and oxidation of resulting adducts can be performed as a one-pot process in the presence of aqueous solutions of Mo-V-phosphoric heteropoly acids (HPA) with the general formula H aP zMo yV xO b. These solutions have bifunctional catalytic properties; they are both strong Brønsted acids and reversible oxidants. Condensation of hydroquinone, 1,4-benzoquinone, or 1,4-naphthoquinone with 1,3-butadiene in the HPA solutions results in 9,10-anthraquinone (AQ) in a mixture with tetrahydro-AQ (THA) and dihydro-AQ (DHA). In this one-pot process, which proceeds in the absence of organic solvents, the HPA solution is reduced. A slightly soluble mixture of THA, DHA, and AQ is precipitated and filtered off. The non-Keggin-type H12P3Mo18V7O85 solution is the most effective in this process. This solution can be rapidly regenerated by dioxygen or air at temperatures of up to 170 °C and then reused. The prepared THA+DHA+AQ mixture can be used as a catalyst for alkaline delignification of wood. Our homogeneous bifunctional HPA catalyst is very stable and promising for use in similar one-pot processes. [ABSTRACT FROM AUTHOR]