Selective Oxidation by H₅[PV₂Mo₁₀O₄₀] in a Highly Acidic Medium

Abstract

Dissolution of the polyoxometalate (POM) cluster anion H 5 [PV 2 Mo 10 O 40 ] ( 1 ; a mixture of positional isomers) in 50% aq H 2 SO 4 dramatically enhances its ability to oxidize methylarenes, while fully retaining the high selectivities typical of this versatile oxidant. To better understand this impressive reactivity, we now provide new information regarding the nature of 1 (115 mM) in 50% (9.4 M) H 2 SO 4 . Data from 51 V NMR spectroscopy and cyclic voltammetry reveal that as the volume of H 2 SO 4 in water is incrementally increased to 50%, V(V) ions are stoichiometrically released from 1 , generating two reactive pervanadyl, VO 2 + , ions, each with a one-electron reduction potential of ca. 0.95 V (versus Ag/AgCl), compared to 0.46 V for 1 in 1.0 M aq H 2 SO 4 . Phosphorus-31 NMR spectra obtained in parallel reveal the presence of PO 4 3– , which at 50% H 2 SO 4 accounts for all the P(V) initially present in 1 . Addition of (NH 4 ) 2 SO 4 leads to the formation of crystalline [NH 4 ] 6 [Mo 2 O 5 (SO 4 ) 4 ] (34% yield based on Mo), whose structure (from single-crystal X-ray diffraction) features a corner-shared, permolybdenyl [Mo 2 O 5 ] 2+ core, conceptually derived by acid condensation of two MoO 3 moieties. While 1 in 50% aq H 2 SO 4 oxidizes p -xylene to p -methylbenzaldehyde with conversion and selectivity both greater than 90%, reaction with VO 2 + alone gives the same high conversion, but at a significantly lower selectivity. Importantly, selectivity is fully restored by adding [NH 4 ] 6 [Mo 2 O 5 (SO 4 ) 4 ], suggesting a central role for Mo(VI) in attenuating the (generally) poor selectivity achievable using VO 2 + alone. Finally, 31 P and 51 V NMR spectra show that intact 1 is fully restored upon dilution to 1 M H 2 SO 4 .

Adipic acid formation from cyclohexanediol using platinum and vanadium catalysts: elucidating the role of homogeneous vanadium species

“…32 Interestingly, work by Tiwari et al on polyoxometalate structures, specifically H 5 ijPV 2 Mo 10 O 40 ], have shown that the dissolution of two reactive pervanadyl ions by H 2 SO 4 is a reversible process, which can be controlled by the pH. 33 Vanadium bronzes, which when combined with other metals such as sodium, copper or silver, can show stability in aqueous media and have various applications in areas such as, photocatalysts and in electrochemical energy storage, however elemental analysis of aqueous media is not always reported. 34,35 In this report we show the synthesis of several vanadium bronzes with the aim of achieving stabilisation in aqueous media.…”

Wireless Lateral Flow Device for Biosensing

“…The changes of conductivity on the pPy film coated on the nitrocellulose membrane were first quantified by four-point probe method. It was determined that the intrinsic reactivity of H 2 O 2 with pPy was too slow, and hence we added phosphovanado­molybdate (H 5 [PV 2 Mo 10 O 40 ]) as a water-soluble oxidation (redox) catalyst that has been shown to be compatible with oxidases. , The phosphovanado­molybdate solution was premixed with glucose solutions before being applied to the test strips. Table and Table S2 detail the conductivity changes observed with different concentrations of glucose or sodium pyruvate.…”

Polyoxometalate‐Single Atom Catalysts (POM‐SACs) in Energy Research and Catalysis

“…This work highlights how POM-SACs or POM-SSCs could be utilized for dynamic coordination chemistry and on-demand delivery of reactive molecular species. [97] [93] b) Five structural isomers of the oxidation catalyst H 5 [V 2 PMo 10 O 40 ]. [78]…”