Tungstic Acid: Catalytic Applications and Dissolution Behavior

Tungstic acid serves as a precursor for the production of catalysts. It is used in the synthesis of heterogeneous catalysts that play a crucial role in chemical reactions, such as the production of sulfuric acid and the hydrodesulfurisation of petroleum products.

Methods for the reaction of alkenes with activated tungstic acid

Tungsten was identified by the Spanish brothers Juan José and Fausto de Elhuyar in 1783. The yellow oxides of this metal had been well known by scientists of that time as it occurs in the form of hydrated species, WO3.nH2O (n = 1,2), which form when tungsten-containing solutions are acidified. The monohydrate, WO3.H2O, is the material known as tungstic acid. Product identity was confirmed by measuring the retention times of authentic samples of the compounds identified by mass spectroscopy. Analysis by gas chromatography/mass spectroscopy (GC-MS) serves both as a qualitative and quantitative analytical tool. The objectives of this experiment are to isolate 3-Cyclohexylcyclohexene from Cyclohexene, cyclohexanol 1-methyl from 1-methyl-1-cyclohexene, and Cyclohexane 1,1′-oxybis from Cyclohexanol by using tungstic acid as the catalysis and to determine the identity of the distillate product through gas chromatography/mass spectroscopy (GC-MS). The resultant solution analyzed with GC/MS is checked for purity and impurities intact with the compound produced.[1]

The smallest and simplest substrate to be tested was cyclopentene. Activated tungstic acid was added to cyclopentene, and the reaction mixture was stirred for 20 days at room temperature. During the course of the reaction, the tungstic acid changed from yellow to green. Activated tungstic acid is an environmentally friendly solid catalyst that is capable of catalyzing alkene reactions at room temperature. It can be easily recovered and reused. These reactions gave a wide range of products depending on the substrate and the reaction temperature used. In several cases, unique products were obtained. It was observed in this experiment that the mass spectrum of the product obtained is relatively close to the theoretical molecular weight of the original compounds. The synthesis of 3-Cyclohexylcyclohexene from Cyclohexene, cyclohexanol 1-methyl from 1-methyl-1-cyclohexene, and Cyclohexane 1,1′-oxybis from Cyclohexanol was able to perform all of the objectives for this experiment, which included synthesizing products from a precursor compound and obtaining a mass spectrum of the product via gas chromatography-mass spectrometry.

Study on the law and mechanism by which oxalic acid dissolves tungstic acid

Tungsten is a strategically important metal worldwide. Owing to its unique melting point, density, hardness and wear resistance, tungsten is extensively utilized in many sectors within the national economy and for national defense purposes.  In the process of “H2SO4 decomposition-H2O2 extraction-thermal decomposition” proposed by Xiao, the tungsten smelting intermediate product APT was replaced by tungstic acid. This process not only solves the problem of the “three wastes” generated by traditional tungsten smelting but also obviously shortens the smelting flow. The obtained high-purity H2WO4 can be roasted into WO3, from which other tungsten products can be prepared. However, hydrogen peroxide is unstable and decomposes easily at high temperatures, and the obtained decomposition solution cannot be recycled and used. This leads to a large amount of hydrogen peroxide consumption, thereby increasing production costs. The dissolution law and mechanism of tungstic acid in oxalic acid are systematically studied in this paper, with the aim of laying a theoretical foundation for the development of novel processes.[2]

This work examined the characteristics of the dissolution of tungstic acid in an oxalic acid solution and the thermal precipitation of H2WO4 from the solution. The mechanism and law of oxalic acid dissolution of H2WO4 were systematically investigated. The conclusions are as follows: During the dissolution process, an oxygen atom in WO2-4 is replaced, and C2O2-4 binds to W to form a bidentate ligand, transforming H2WO4 into [WO3(C2O4)∙H2O]2− with a 1:1 molar ratio of n(WO3)/n(C2O2-4). When the oxalic acid concentration was 0.05–0.4 mol/L, the reaction temperature was 25–65 ℃ and the liquid–solid ratio was 2:1–10:1 mL/g, the dissolution efficiency of tungstic acid in oxalic acid gradually increased as the oxalic acid concentration or liquid–solid ratio increased. An increase in the oxalic acid concentration and reaction time promoted the formation of H2[WO3(C2O4)∙H2O], whereas this compound was not stable at high temperatures and easily decomposed into H2WO4. Therefore, low temperatures (25 ℃–35 ℃) are more conducive to the dissolution of tungstic acid than high temperatures (45 ℃–65 ℃).

References

[1]Alrefaee SH, Apblett AW. Methods for the reaction of alkenes with activated tungstic acid. Heliyon. 2019 Nov 21;5(11):e02780. doi: 10.1016/j.heliyon.2019.e02780. PMID: 31844714; PMCID: PMC6895725.

[2]Chen Z, Liu Y, Liang Y, Pu T, Lai W. Study on the law and mechanism by which oxalic acid dissolves tungstic acid. BMC Chem. 2025 May 29;19(1):149. doi: 10.1186/s13065-025-01510-5. PMID: 40442769; PMCID: PMC12121132.