The occurrence of Cr(VI) is rare naturally. Hexavalent form – Cr(VI) – is more toxic than trivalent form – Cr(III) for its high oxidizing potential – and easily penetrates biological membranes. The +3 and +6 forms are the most important as the +2, +4, and +5 forms are unstable and are rapidly converted to +3, which in turn is oxidized to +6 ( Towill et al.
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^ The environmental impact of hexavalent chromium inspired the 2000 biographical Hollywood movie Erin Brockovich.Chromium can exist in oxidation states ranging from -2 to +6, but is most frequently found in the environment in the trivalent (+3) and hexavalent (+6) oxidation states.Journal of the American Chemical Society. N and (CrO 3) n ( n = 1–5): Photoelectron Spectroscopy and Density Functional Calculations". "Probing the Electronic and Structural Properties of Chromium Oxide Clusters (CrO Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 7-5 Albert Wilkinson, Geoffrey Murillo, Carlos A. Environmental Health and Preventive Medicine. "Mutagenic and carcinogenic actions of chromium and its compounds". ^ Mamyrbaev, Arstan Abdramanovich Dzharkenov, Timur Agataevich Imangazina, Zina Amangalievna Satybaldieva, Umit Abulkhairovna ().Ullmann's Encyclopedia of Industrial Chemistry. ^ a b c Sigma-Aldrich Co., Chromium(VI) oxide.Solubilities of Inorganic and Organic Compounds (2nd ed.). CRC Handbook of Chemistry and Physics (90th ed.). The related chromium(III) derivatives are not particularly dangerous thus, reductants are used to destroy chromium(VI) samples.Ĭhromium trioxide, being a powerful oxidizer, will ignite organic materials such as alcohols on contact. It is the main example of hexavalent chromium, an environmental hazard. A chromic acid/ phosphoric acid solution is also the preferred stripping agent of anodic coatings of all types.Ĭhromium trioxide is highly toxic, corrosive, and carcinogenic.
On the International Space Station, it is used to control bacteria growth in the wastewater storage tank. Chromic acid solution is also used in applying types of anodic coating to aluminium, which are primarily used in aerospace applications. It is also used in the production of synthetic rubies. The trioxide reacts with cadmium, zinc, and other metals to generate passivating chromate films that resist corrosion. It is typically employed with additives that affect the plating process but do not react with the trioxide. The reactions are shown below:Ĥ CrO 3 + 3 RCH 2OH + 12 H + → 3 RCOOH + 4 Cr 3+ + 9 H 2OĢ CrO 3 + 3 R 2CHOH + 6 H + → 3 R 2C=O + 2 Cr 3+ + 6 H 2OĬhromium trioxide is mainly used in chrome plating. In these oxidations, the Cr(VI) converts primary alcohols to the corresponding carboxylic acids and secondary alcohols to ketones. It is used in organic synthesis as an oxidant, often as a solution in acetic acid, or acetone in the case of the Jones oxidation. Ĭhromium trioxide decomposes above 197 ☌, liberating oxygen and eventually giving Cr 2O 3: The structure of monomeric CrO 3 has been calculated using density functional theory, and is predicted to be pyramidal ( point group C 3v) rather than planar (point group D 3h). Two oxygen atoms are not shared, giving an overall stoichiometry of 1:3. Each chromium center therefore shares two oxygen centers with neighbors. The solid consists of chains of tetrahedrally coordinated chromium atoms that share vertices. Production, structure, and basic reactions Ĭhromium trioxide is generated by treating sodium dichromate with sulfuric acid: H 2SO 4 + Na 2Cr 2O 7 → 2 CrO 3 + Na 2SO 4 + H 2OĪpproximately 100,000 tonnes are produced annually by this or similar routes. Chromium trioxide is a powerful oxidiser, a mutagen, and a carcinogen. Millions of kilograms are produced annually, mainly for electroplating. The substance dissolves in water concomitant with hydrolysis. This compound is a dark-purple solid under anhydrous conditions and bright orange when wet. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula CrO 3.
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