Heteropoly tungstic acid

Another catalytic process developed by Tokuyama Soda applies heteropoly-tungstic acid in the liquid phase at high temperature and pressure (240-290° C, 150-300 atm).53 54 Long catalyst lifetime, high conversion levels (60-70% per pass), and high selectivity (over 99%) are the very attractive features of the process. 

Melting a mixture of germanium dioxide and metal oxides produces ortho-and metagermanates of the corresponding metals. Aqueous solutions of ger-manate react with molyhdic and tungstic acids forming heteropoly acids of varying compositions. 

Salts of Molybdic and Tungstic Acids. What types of salts of molybdic and tungstic acids exist Give examples of isopoly- and heteropoly molybdenum and tungsten compounds. What is the composition of para- and metamolybdates and of para- and metatungstates Which molybdates and tungstates dissolve poorly in water ... 

It is generally believed that tungsten is bom in mineralizing fluids chiefly as tungstate ion, tungstic acid, sodium tungstate, or as heteropoly acid. The relative amount of these compoimds depends on temperature, pH, and silica concentration of the solution. Tungsten... 

Tungsten (W, at. mass 183.85) is an element similar to Mo and Cr. The basic properties of W(VI) are not so accentuated as those of Mo(VI). Tungstic acid is less soluble than molybdic acid in mineral acids. W(VI) gives tartrate, oxalate, fluoride, and chloride complexes, as well as heteropoly acids. Tungsten may occur also in the rather unstable V, IV, and III oxidation states. 

In general the heteropoly compounds of tungstic acid are more complexed and more resistant to hydrolysis than those of molybdic... 

Several recently described compounds of molybdic and tungstic acids with phosphoric acid, where the ratio of Mo (or W)/P is below 3 1 (e.g., 2 M0O3.P3OB or NagO 2 WOa PgOs), are not heteropoly compounds rather, the Mo or W is bound as a cation [4]. We shall omit their discussion. 

Salts of Heteropoly-, Tungstic, Molybdie and Tetraboiie Acids... 

The nitric acid oxidation of cycloalkenes yields, among other products, a,(0-dicarboxylic acids.663,664 The reaction is catalyzed by vanadium(V) ion.665,666 Oxidations with H202,284,667 PhIO,650 or KHSO5650 catalyzed by heteropoly acids284,650 or tungstic acid667 have been recently described. 

Heteropoly compounds are composed not only of the weak, oxygen-containing metallic acids (tungstic, molybdic and vanadic), but also of moderately strong to weak acids of nonmetals, e.g., boric, silicic, phosphoric, arsenic, telluric, etc., acids. Stable heteropoly compounds very frequently show nonmetallic to metallic acid ratios of 1 12, 1 6 or 1 9. Since the heteropoly compounds form under conditions similar to those in which isopoly compounds are obtained, that is, only in solutions containing H+ ions, it is assumed that the building blocks of the heteropolyanions are isopoly anions [1]. 

Figure 11.14 TPSR of isopropanol adsorbed over phospho-tungstic heteropoly acid H6P2W13O62 at 40 C (From Gambaro, L.A. and Briand, h.E.Appl. Catal. 2004, 264, 151-159. With permission.)...

---