chromium trioxide
{{Chembox
| Watchedfields = changed
| verifiedrevid = 477001582
| ImageFile = CrO3-from-xtal-1970-bulk-3D-balls.png
| ImageClass = bg-transparent
| ImageSize = 200px
| ImageName = Ball-and-stick model of chromium trioxide
| ImageCaption = {{legend|rgb(158, 176, 224)|Chromium, Cr}}{{legend|red|Oxygen, O}}
| ImageFile1 = Chromium(VI) oxide.jpg
| ImageSize1 = 220px
| ImageName1 = Powder of chromium trioxide
| IUPACName = Chromium trioxide
| OtherNames = Chromic anhydride, Chromium(VI) oxide, Chromic acid (misnomer)
| SystematicName =
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 14212
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 8LV49809UC
| InChI = 1/Cr.3O/rCrO3/c2-1(3)4
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 48240
| SMILES = O=[Cr](=O)=O
| InChIKey = WGLPBDUCMAPZCE-YFSAMUSXAF
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Cr.3O
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = WGLPBDUCMAPZCE-UHFFFAOYSA-N
| CASNo = 1333-82-0
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 14915
| RTECS = GB6650000
| UNNumber = 1463
}}
| Section2 = {{Chembox Properties
| Cr=1|O=3
| Appearance = Dark red granular solid, deliquescent
| Odor = Odorless
| MeltingPtC = 197
| BoilingPtC = 250
| BoilingPt_notes =
decomposes
| Solubility = {{ubl|164.8 g/(100 mL) (0 °C)|169 g/(100 mL) (25 °C){{CRC90}}|172.6 g/(100 mL) (40 °C)|198.1 g/(100 mL) (100 °C){{cite book|last1 = Seidell|first1 = Atherton|last2 = Linke|first2 = William F.|year = 1919|title = Solubilities of Inorganic and Organic Compounds|url = https://archive.org/details/solubilitiesino01seidgoog|publisher = D. Van Nostrand Company|edition = 2nd|page = [https://archive.org/details/solubilitiesino01seidgoog/page/n276 250]}}}}
| SolubleOther = Soluble in sulfuric acid, nitric acid, diethyl ether, acetic acid, acetone
}}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = −589.3 kJ/mol{{cite book|last = Pradyot|first = Patnaik|year = 2003|title = Handbook of Inorganic Chemicals|publisher = The McGraw-Hill Companies, Inc.|isbn = 0-07-049439-8}}
| Entropy = 73.2 J/(mol·K){{cite web|url=http://chemister.ru/Database/properties-en.php?dbid=1&id=3425|title=chromium(VI) oxide|website=chemister.ru}}
}}
| Section7 = {{Chembox Hazards
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics1194.htm ICSC 1194]
| GHSPictograms = {{GHS03}}{{GHS05}}{{GHS06}}{{GHS08}}{{GHS09}}{{Sigma-Aldrich|id=675644|name=Chromium(VI) oxide|accessdate=2021-11-22}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|271|301+311|314|317|330|334|335|340|350|361f|372|410}}
| PPhrases = {{P-phrases|210|260|280|303+361+353|304+340+310|305+351+338}}
| NFPA-H = 4
| NFPA-F = 0
| NFPA-R = 2
| NFPA-S = OX
| LD50 = 80 mg/kg (rats, oral)
}}
}}
Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula {{chem2|CrO3}}. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.{{cite web|url = http://www.chemicalland21.com/industrialchem/inorganic/CHROMIUM%20TRIOXIDE.htm|title = Chromium trioxide|publisher = AroKor Holdings Inc.|website = chemicalland21.com|access-date = 2014-06-15}}
This compound is a dark-purple solid under anhydrous conditions and bright orange when wet. The substance dissolves in water accompanied by hydrolysis.{{clarify|reason=the wording is arcane - what does it mean?|date=June 2023}} Millions of kilograms are produced annually, mainly for electroplating.{{Cite book | doi = 10.1002/14356007.a07_067| chapter = Chromium Compounds| title = Ullmann's Encyclopedia of Industrial Chemistry| year = 2000| last1 = Anger | first1 = G. | last2 = Halstenberg | first2 = J. | last3 = Hochgeschwender | first3 = K. | last4 = Scherhag | first4 = C. | last5 = Korallus | first5 = U. | last6 = Knopf | first6 = H. | last7 = Schmidt | first7 = P. | last8 = Ohlinger | first8 = M. | isbn = 3527306730}} Chromium trioxide is a powerful oxidiser, a mutagen, and a carcinogen.{{cite journal | last1=Mamyrbaev | first1=Arstan Abdramanovich | last2=Dzharkenov | first2=Timur Agataevich | last3=Imangazina | first3=Zina Amangalievna | last4=Satybaldieva | first4=Umit Abulkhairovna | title=Mutagenic and carcinogenic actions of chromium and its compounds | journal=Environmental Health and Preventive Medicine | publisher=Springer Science and Business Media LLC | volume=20 | issue=3 | date=2015-04-16 | issn=1342-078X | doi=10.1007/s12199-015-0458-2 | pages=159–167| pmid=25877777 | pmc=4434237}}
Production, structure, and basic reactions
Chromium trioxide is generated by treating sodium dichromate with sulfuric acid:
:{{chem2|H2SO4 + Na2Cr2O7 → 2 CrO3 + Na2SO4 + H2O}}
Approximately 100,000 tonnes are produced annually by this or similar routes.
The solid consists of chains of tetrahedrally coordinated chromium atoms that share vertices. Each chromium center therefore shares two oxygen centers with neighbors. Two oxygen atoms are not shared, giving an overall stoichiometry of 1:3.{{Cotton&Wilkinson6th}}{{Cite journal | doi = 10.1107/S0567740870002182| title = The crystal structure of (CrO3)∞| journal = Acta Crystallographica Section B| volume = 26| issue = 3| pages = 222| year = 1970| last1 = Stephens | first1 = J. S.| last2 = Cruickshank | first2 = D. W. J.}} File:CrO3-from-xtal-1970-chain-3D-balls.png, Cr}}{{legend|red|Oxygen, O}}]]
The structure of monomeric {{chem2|CrO3}} has been calculated using density functional theory, and is predicted to be pyramidal (point group C3v) rather than planar (point group D3h).{{Cite journal | doi = 10.1021/ja077984d| title = Probing the Electronic and Structural Properties of Chromium Oxide Clusters {{chem|(CrO|3|)|n|-}} and (CrO3)n (n = 1–5): Photoelectron Spectroscopy and Density Functional Calculations| journal = Journal of the American Chemical Society| volume = 130| issue = 15| pages = 5167–77| year = 2008| last1 = Zhai | first1 = H. J. | last2 = Li | first2 = S. | last3 = Dixon | first3 = D. A. | last4 = Wang | first4 = L. S. |pmid = 18327905}}
:File:CrO3-monomer-from-DFT-PW91-aD-2008-side-3D-balls.png
Chromium trioxide decomposes above 197 °C, liberating oxygen and eventually giving chromium(III) oxide:
:{{chem2|4 CrO3 → 2 Cr2O3 + 3 O2}}
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. In these oxidations, the Cr(VI) converts primary alcohols to the corresponding carboxylic acids and secondary alcohols to ketones. The reactions are shown below:
- Primary alcohols to carboxylic acids
- :{{chem2|4 CrO3 + 3 RCH2OH + 12 H+ → 3 RCOOH + 4 Cr(3+) + 9 H2O}}
- Secondary alcohols to ketones
- :{{chem2|2 CrO3 + 3 R2CHOH + 6 H+ → 3 R2C\dO + 2 Cr(3+) + 6 H2O}}
Applications
Chromium trioxide is mainly used in chrome plating. It is typically employed with additives that affect the plating process but do not react with the trioxide. The trioxide reacts with cadmium, zinc, and other metals to generate passivating chromate films that resist corrosion. It is also used in the production of synthetic rubies. Chromic acid solution is also used in applying types of anodic coating to aluminium, which are primarily used in aerospace applications. On the International Space Station, it is used to control bacteria growth in the wastewater storage tank. A chromic acid/phosphoric acid solution is also the preferred stripping agent of anodic coatings of all types.
Safety
Chromium trioxide is highly toxic, corrosive, and carcinogenic.{{cite web|url = http://hazard.com/msds/mf/baker/baker/files/c4400.htm|publisher = J. T. Baker|title = Chromium Trioxide (MSDS)|access-date = 2007-09-13|archive-url = https://web.archive.org/web/20150112092613/http://hazard.com/msds/mf/baker/baker/files/c4400.htm|archive-date = 2015-01-12|url-status = dead}} It is the main example of hexavalent chromium, an environmental hazard.The environmental impact of hexavalent chromium inspired the 2000 biographical Hollywood movie Erin Brockovich. The related chromium(III) derivatives are not particularly dangerous; thus, reductants are used to destroy chromium(VI) samples.
Chromium trioxide, being a powerful oxidizer, will ignite organic materials such as alcohols on contact.
Images
Reaction between potassium dichromate and sulfuric acid (1).jpg|A concentrated solution of potassium dichromate in water.
Reaction between potassium dichromate and sulfuric acid (2).jpg|Addition of sulfuric acid to the solution.
Reaction between potassium dichromate and sulfuric acid (3).jpg|Crystallization of chromium trioxide from the reaction.
Reaction between chromium(VI) oxide and ethanol (1).JPG|Reaction between chromium trioxide and ethanol
Reaction between chromium(VI) oxide and ethanol (2).JPG
Reaction between chromium(VI) oxide and ethanol (3).JPG
References
{{reflist}}
External links
{{Commons category|Chromium trioxide}}
- [https://www.atsdr.cdc.gov/csem/chromium/ ATSDR Case Studies in Environmental Medicine: Chromium Toxicity] U.S. Department of Health and Human Services
- [http://www.periodicvideos.com/videos/mv_chromium_trioxide.htm Chromium Trioxide] at The Periodic Table of Videos (University of Nottingham)
- [https://www.organic-chemistry.org/chemicals/oxidations/chromium-trioxide.shtm Reactions with Chromium Trioxide as Oxidizing Agent]
{{Chromium compounds}}
{{Oxides}}
{{oxygen compounds}}