Technetium(IV) oxide

Technetium dioxide was first produced in 1949 by electrolyzing a solution of ammonium pertechnetate under ammonium hydroxide and this method is used for separating technetium from molybdenum and rhenium.{{cite journal |author1=L. B. Rogers |title=Electroseparation of Technetium from Rhenium and Molybdenum |journal=Journal of the American Chemical Society |date=1949 |volume=71 |issue=4 |pages=1507–1508 |doi=10.1021/ja01172a520 |language=en}} There are now more efficient ways of producing the compound, such as the reduction of ammonium pertechnetate by zinc metal and hydrochloric acid, stannous chloride, hydrazine, hydroxylamine, ascorbic acid,{{cite journal |author1=Edward Anders |title=THE RADIOCHEMISTRY OF TECHNETIUM |url=https://www.osti.gov/biblio/4073069 |website=OSTI.GOV |publisher=U.S. Department of Energy Office of Scientific and Technical Information |access-date=4 November 2022 |page=8 |doi=10.2172/4073069 |date=1960|osti=4073069 }} by the hydrolysis of potassium hexachlorotechnate{{cite journal |author1=C. M. Nelson |author2=G. E. Boyd |author3=Wm. T. Smith Jr. |title=Magnetochemistry of Technetium and Rhenium |journal=Journal of the American Chemical Society |date=1954 |volume=76 |issue=2 |pages=348–352 |doi=10.1021/ja01631a009 |publisher=ACS Publications |language=en}} or by the decomposition of ammonium pertechnetate at 700 °C under an inert atmosphere:{{cite thesis |author1=Bradley Covington Childs |title=Volatile Technetium Oxides: Implications for Nuclear Waste Vitrification |journal=UNLV Theses, Dissertations, Professional Papers, and Capstones |date=2017 |doi=10.34917/10985836}}

:2 NH₄TcO₄ → 2 TcO₂ + 4 H₂O + N₂

All of these methods except the last lead to the formation of the dihydrate.

The most modern method of producing this compound is by the reaction of ammonium pertechnetate with sodium dithionite.{{cite journal |author1=Nancy J. Hess |author2=Yuanxian Xia |author3=Dhanpat Rai |author4=Steven D. Conradson |title=Thermodynamic Model for the Solubility of TcO₂·xH₂O(am) in the Aqueous Tc(IV) – Na⁺ – Cl⁻ – H⁺ – OH⁻ – H₂O System |journal=Journal of Solution Chemistry |date=2004 |volume=33 |issue=2 |pages=199–226 |doi=10.1023/B:JOSL.0000030285.11512.1f |s2cid=96789279 |language=en}}

The dihydrate dehydrates to anhydrous technetium dioxide at 300 °C, and if further heated sublime at 1,100 °C under an inert atmosphere, however, if oxygen is present, it will react with the oxygen to produce technetium(VII) oxide at 450 °C. If water is present, pertechnetic acid is produced by the reaction of technetium(VII) oxide with water.

If technetium dioxide is treated with a base, such as sodium hydroxide, it forms the hydroxotechnetate(IV) ion, which is easily oxidized to pertechnetic acid in numerous ways, such as the reaction with alkaline hydrogen peroxide, concentrated nitric acid, bromine, or tetravalent cerium.{{cite journal |author1=Edward Andrews |title=Technetium and Astatine Chemistry |journal=Annual Review of Nuclear Science |date=1959 |volume=9 |pages=203–220 |doi=10.1146/annurev.ns.09.120159.001223 |publisher=Annual Reviews |bibcode=1959ARNPS...9..203A |language=en|doi-access=free }}

The solubility of technetium(IV) oxide is very low and is reported to be 3.9 μg/L. The main species when technetium dioxide is dissolved in water is TcO²⁺ at pH below 1.5, TcO(OH)⁺ pH between 1.5 and 2.5, TcO(OH)₂ pH between 2.5 and 10.9, and TcO(OH){{su|b=3|p=–}} above pH 10.9. The solubility can be affected by adding various organic ligands such as humic acid and EDTA, or by the addition of hydrochloric acid. This can be a problem if technetium(IV) oxide is released into the soil, as it will increase the solubility.{{cite journal |author1=Baohua Gu |author2=Wenming Dong |author3=Liyuan Liang |author4=Nathalie A. Wall |title=Dissolution of Technetium(IV) Oxide by Natural and Synthetic Organic Ligands under both Reducing and Oxidizing Conditions |journal=Environmental Science & Technology |date=2011 |volume=45 |issue=11 |pages=4771–4777 |doi=10.1021/es200110y |pmid=21539349 |bibcode=2011EnST...45.4771G |language=en}}

If technetium dioxide is electrolyzed in acidic conditions, the following reaction occurs:

:TcO₂·2H₂O → TcO{{su|b=4|p=–}} + 4 H⁺ + 3 e^–

The electrode potential measured for this reaction is {{val|-837.2|10.0}} kJ/mol.{{cite journal |author1=J. A. Rard |title=Critical review of the chemistry and thermodynamics of technetium and some of its inorganic compounds and aqueous species |url=https://www.osti.gov/biblio/5580852 |website=OSTI.GOV |publisher=U.S. Department of Energy Office of Scientific and Technical Information |access-date=4 November 2022 |language=en |doi=10.2172/5580852 |date=1983|osti=5580852 |s2cid=98137163 }}

The molar magnetic susceptibility of TcO₂·2H₂O was found to be χ_m = {{val|244e6}}{{Clarify|post-text=units|date=December 2023}}.

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{{Technetium compounds}}

{{Oxides}}

Category:Technetium compounds

Category:Oxides