Molybdovanadophosphoric acid

The title, "The Determination of Phosphorus, for example, would interest the present author, but at once questions arise. In what kind of material is the phosphorus determined Is a separation of the element necessary If so, what kind of method is applicable Is a colorimetric method of measurement used If so, what is the color-forming reagent If it is ammonium molybdate, is the system measured molybdophosphoric acid, molybdovanadophosphoric acid, or a heteropoly blue If the latter, what are the reductant and the conditions of reduction To the extent that the title does not answer these and other similar questions, the summary should. 

The limit test for phosphate is based upon the formation of ayellow colour reaction with molybdovanadic reagent (combination of ammonium vanadate and ammonium molybdate) in an acidic medium. However, the exact composition of the molybdovanadophosphoric acid complex is yet to be established. 

Heteropolyoxametalates are often used in combination with palladium salts as catalysts in oxidation processes using dioxygen as the oxidant. Indeed, the oxidative coupling reaction of benzenes with alkenes was also successfully achieved by use of the Pd(OAc)2/molybdovanadophosphoric acid (HPMoV)/02 system [14a]. For example, reaction of benzene with ethyl acrylate using this catalytic system in acetic acid afforded ethyl cinnamate as a major product in satisfactory yield. Typically, the reaction is conducted in acetic acid at 90 °C under 1 bar of 02. After 6 h the TON is 15. This number was recently improved to 121 [14b]. 

Another class of 12-heteropoly anions involves the replacement of molybdenum by pentavalent vanadium. The molybdovanadophosphoric acids,... 

Another route to methacryhc acid is via oxidative dehydrogenation of isobutyric acid (equation 13). This reaction is catalyzed by molybdovanadophosphoric acid (H3+ PMoi2- V 04o n = 0-3), whose redox potential and acidity are well-balanced for effecting this reaction. The acidity is necessary, although excess acidity accelerates the decomposition of isobutyric acid into CO and propene. 

Tani, M., Sakamoto, T, Mita, S., Sakaguchi, S. and Ishii, Y. (2005) Hydroxylation of benzene to phenol under air and carbon monoxide catalyzed by molybdovanadophosphoric acid. Angew. Chem. Int. Ed., 44, 2586-2588. 

Microgram quantities of phosphorus are conventionally determined by the phosphomolybdenum blue method. The molybdovanadophosphoric acid method is suitable for determining relatively large quantities of P(V). Sensitive spectrophotometric methods based on ion-associates with basic dyes deserve attention. 

Interfering species in the determination of phosphorus by the phosphomolybdenum blue method are As(V), Si, and Ge, which also react with molybdate to form the corresponding acids which are reduced to the respective heteropoly blues. Arsenic(V) does not interfere when reduced to As(III) using sulphite or thiourea. In the presence of vanadium(V), molybdovanadophosphoric acid is produced. Large amounts of vanadium(V) are reduced with Mohr s salt to V(IV) before the molybdate is added. The difference in the rates of formation of the phosphomolybdenum- and silicomolybdenum- blues has been utilized for the determination of phosphorus in the presence of silicon [29]. The interference of silicon can be prevented by the use of a sufficiently acidic medium [30]. ... 

Addition of molybdate to an acidic solution containing orthophosphate and vanadate, results in the formation of the yellow-orange molybdovanadophosphoric acid having the Mo V P ratio of 11 1 1 [35,36],... 

Large amounts of Fe(III) interfere, but may be masked with fluoride, the excess of which is complexed with boric acid. Reductants and certain coloured metal ions [e.g., Cr(VI), Ni, Co, Cu, and U(VI)] also interfere. Molybdovanadophosphoric acid may be separated from many coloured ions by extraction with oxygen-containing organic solvents [35]. Reducing agents must be absent. 

A. D. Basson, J. F. van Staden, and P. M. Catttin, Determination of Phosphorous as Molybdovanadophosphoric Acid in Phosphate Rock with a Flow-Injection Procedure. Fresenius Z. Anal. Chem., 307 (1981) 373. 

Oxidative coupling of arenes with alkenes consumes a stoichiometric amount of Pd(II). Efficient catalytic reaction of cinnamate (165) with benzene to afford 166 was carried out using BQ and f-butyl hydroperoxide as oxidant in AcOH [70]. The coupling proceeds smoothly in the presence of catalytic amounts of Pd(OAc)2 and molybdovanadophosphoric acid (HPMoV) under oxygen (1 atm) in AcOH [71]. 

Recently, a major advance in the development of the reoxidation step was achieved through the use of heteropoly acids. Ishii and coworkers [12] found that the oxidative coupling of benzenes with electron-deficient alkenes can be performed at ambient pressure under oxygen and even under an air atmosphere when using molybdovanadophosphoric... 

Figure 4.5 Oxidative vinylation at ambient oxygen pressure using molybdovanadophosphoric acid.

Oxidants other than Cu(OAc)2 and AgOAc have also been examined extensively to reoxidize palladium(O) in the arylation reaction of alkenes. Tsuji and Nagashima [21] reported that fert-butyl perbenzoate could be used as the stoichiometric oxidant to facihtate the palladium(n)-catalysed vinylation of benzene. Ishii and coworkers [22] found that the oxidative coupling reaction of substituted benzenes with acrylates could be achieved by the use of a catalytic amount of Pd(OAc)2 combined with molybdovanadophosphoric acid (HPMoV) under atmospheric oxygen as a terminal oxidant. 

Ueshima, M., Tuneki, H., and Shimizu, N. Heteropoly acid as oxidation catalyst. Oxidation of molybdovanadophosphoric acid and methacrolein. Hyoumen 1986, 24, 582-594. 

An SBA-15 (SBA, strong base anion) catalyst modified by a heteropoly acid-based IL was prepared by treating molybdovanadophosphoric acid with the IL-modified SBA via ion exchange (V2ILSBA), Scheme 2.18 [81]. This catalyst exhibited nice activity in the selective oxidation of benzylic, allylic, and secondary alcohols by air. However, the primary aliphatic alcohols were less reactive. By using selective oxidation of l-(napthylen-2-yl) ethanol to methyl napthyl ketone as model reaction, the reusabihty of the catalyst V2ILSBA was tested, and no deactivation was observed after five runs. 

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