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| ImageSize = 200px
| ImageSize = 200px
| ImageName = Ball-and-stick model of chromium trioxide
| ImageName = Ball-and-stick model of chromium trioxide
| ImageCaption = {{legend|rgb(158, 176, 224)|[[Chromium]], Cr}}{{legend|red|[[Oxygen]], O}}
| ImageFile1 = Chrom(VI)-oxid.jpg
| ImageFile1 = Chromium(VI) oxide.jpg
| ImageSize1 = 220px
| ImageSize1 = 220px
| ImageName1 = Powder of chromium trioxide
| ImageName1 = Powder of chromium trioxide
| IUPACName = Chromium trioxide
| IUPACName = Chromium trioxide
| OtherNames = Chromic anhydride, Chromium(VI) oxide, Chromic acid (misnomer)
| OtherNames = Chromic anhydride, Chromium(VI) oxide, Chromic acid ([[misnomer]])
| SystematicName =
|Section1={{Chembox Identifiers
| Section1 = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 14212
| ChemSpiderID = 14212
Line 29: Line 31:
| RTECS = GB6650000
| RTECS = GB6650000
| UNNumber = 1463
| UNNumber = 1463
}}
}}
|Section2={{Chembox Properties
| Section2 = {{Chembox Properties
| Cr=1 | O=3
| Cr=1|O=3
| Appearance = Dark red granular solid, [[deliquescent]]
| Appearance = Dark red granular solid, [[deliquescent]]
| Odor = Odorless
| Odor = Odorless
| Density = 2.7 g/cm<sup>3</sup> (20 °C)<ref name=crc />
| Density = 2.7 g/cm<sup>3</sup> (20 °C)<ref name=crc />
| MeltingPtC = 197
| MeltingPtC = 197
| MeltingPt_notes = <ref name=crc />
| MeltingPt_ref = <ref name=crc />
| BoilingPtC = 250
| BoilingPtC = 250
| BoilingPt_notes = <br> decomposes<ref name=crc />
| BoilingPt_notes = <br> decomposes<ref name=crc />
| Solubility = 164.8 g/{{abbr|100 mL|100 mL of solvent}} (0 °C)<br> 169 g/100 mL (25 °C)<ref name=crc>{{CRC90}}</ref><br> 172.6 g/100 mL (40 °C)<br> 198.1 g/100 mL (100 °C)<ref name=sioc>{{cite book|last = Seidell|first = Atherton|last2 = Linke|first2 = William F.|year = 1919|title = Solubilities of Inorganic and Organic Compounds|publisher = D. Van Nostrand Company|edition = 2nd|page = 250}}</ref>
| Solubility = {{ubl|164.8 g/(100 mL) (0&nbsp;°C)|169 g/(100 mL) (25&nbsp;°C)<ref name=crc>{{CRC90}}</ref>|172.6 g/(100 mL) (40 °C)|198.1 g/(100 mL) (100&nbsp;°C)<ref name=sioc>{{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]}}</ref>}}
| SolubleOther = Soluble in [[sulfuric acid|H<sub>2</sub>SO<sub>4</sub>]], [[nitric acid|HNO<sub>3</sub>]], [[diethyl ether|(C<sub>2</sub>H<sub>5</sub>)<sub>2</sub>O]], [[acetic acid|CH<sub>3</sub>COOH]], [[acetone]]
| SolubleOther = Soluble in [[sulfuric acid|{{chem2|H2SO4}}]], [[nitric acid|{{chem2|HNO3}}]], [[diethyl ether|{{chem2|(CH3CH2)2O}}]], [[acetic acid|{{chem2|CH3COOH}}]], [[acetone|{{chem2|(CH3)2CO}}]]
| MagSus = +40·10<sup>−6</sup> cm<sup>3</sup>/mol<ref name=crc />
| MagSus = +40·10<sup>−6</sup> cm<sup>3</sup>/mol<ref name=crc />
}}
}}
|Section4={{Chembox Thermochemistry
| Section4 = {{Chembox Thermochemistry
| DeltaHf = −589.3 kJ/mol<ref name=pphoic>{{cite book|last = Pradyot|first = Patnaik|year = 2003|title = Handbook of Inorganic Chemicals|publisher = The McGraw-Hill Companies, Inc.|isbn = 0-07-049439-8}}</ref>
| DeltaHf = −589.3 kJ/mol<ref name=pphoic>{{cite book|last = Pradyot|first = Patnaik|year = 2003|title = Handbook of Inorganic Chemicals|publisher = The McGraw-Hill Companies, Inc.|isbn = 0-07-049439-8}}</ref>
| Entropy = 73.2 J/mol·K<ref name=chemister>{{cite web|url=http://chemister.ru/Database/properties-en.php?dbid=1&id=3425|title=chromium(VI) oxide|website=chemister.ru}}</ref>
| Entropy = 73.2 J/(mol·K)<ref name=chemister>{{cite web|url=http://chemister.ru/Database/properties-en.php?dbid=1&id=3425|title=chromium(VI) oxide|website=chemister.ru}}</ref>
}}
}}
|Section5={{Chembox Hazards
| Section7 = {{Chembox Hazards
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics1194.htm ICSC 1194]
| ExternalSDS = [http://www.inchem.org/documents/icsc/icsc/eics1194.htm ICSC 1194]
| GHSPictograms = {{GHS03}}{{GHS05}}{{GHS06}}{{GHS08}}{{GHS09}}<ref name="sigma">{{Sigma-Aldrich|id=675644|name=Chromium(VI) oxide|accessdate=2014-06-15}}</ref>
| GHSPictograms = {{GHS03}}{{GHS05}}{{GHS06}}{{GHS08}}{{GHS09}}<ref name="sigma">{{Sigma-Aldrich|id=675644|name=Chromium(VI) oxide|accessdate=2021-11-22}}</ref>
| GHSSignalWord = Danger
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|271|300|301|302|303|304|305|310|311|312|313|314|315|316|317|318|319|320|330|334|335|336|340|350|361|372|410}}<ref name="sigma" />
| HPhrases = {{H-phrases|271|301+311|314|317|330|334|335|340|350|361f|372|410}}<ref name="sigma" />
| PPhrases = {{P-phrases|201|220|260|273|280|284}}<ref name="sigma" />
| PPhrases = {{P-phrases|210|260|280|303+361+353|304+340+310|305+351+338}}<ref name="sigma" />
| NFPA-H = 3
| NFPA-H = 4
| NFPA-F = 0
| NFPA-F = 0
| NFPA-R = 2
| NFPA-R = 2
Line 62: Line 64:
}}
}}


'''Chromium trioxide''' is an [[inorganic compound]] with the [[chemical formula|formula]] CrO<sub>3</sub>. It is the [[acidic oxide|acidic anhydride]] of [[chromic acid]], and is sometimes marketed under the same name.<ref name = chemicalland21>{{cite web|url = http://www.chemicalland21.com/industrialchem/inorganic/CHROMIUM%20TRIOXIDE.htm|title = Chromium trioxide|publisher = AroKor Holdings Inc.|website = chemicalland21.com|accessdate = 2014-06-15}}</ref>
'''Chromium trioxide''' (also known as '''chromium(VI) oxide''' or '''chromic anhydride''') is an [[inorganic compound]] with the [[chemical formula|formula]] {{chem2|CrO3}}. It is the [[acidic oxide|acidic anhydride]] of [[chromic acid]], and is sometimes marketed under the same name.<ref name = chemicalland21>{{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}}</ref>
This compound is a dark-purple [[solid]] under anhydrous conditions, bright orange when wet and which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for [[electroplating]].<ref name=ullmanns>{{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}}</ref> Chromium trioxide is a powerful oxidiser and a suspected [[carcinogen]].
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]].<ref name=ullmanns>{{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}}</ref> Chromium trioxide is a powerful oxidiser, a [[mutagen]], and a [[carcinogen]].<ref>{{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}}</ref>


==Production, structure, and basic reactions==
==Production, structure, and basic reactions==
Chromium trioxide is generated by treating [[sodium chromate]] or the corresponding [[sodium dichromate]] with [[sulfuric acid]]:<ref name = chemicalland21 />
Chromium trioxide is generated by treating [[sodium dichromate]] with [[sulfuric acid]]:<ref name = chemicalland21 />
:{{chem2|H2SO4 + Na2Cr2O7 → 2 CrO3 + Na2SO4 + H2O}}
:H<sub>2</sub>SO<sub>4</sub> + Na<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> → 2 CrO<sub>3</sub> + Na<sub>2</sub>SO<sub>4</sub> + H<sub>2</sub>O

⚫
Approximately 100M kg are produced annually by this or similar routes.<ref name=ullmanns/>


⚫
Approximately 100,000 tonnes are produced annually by this or similar routes.<ref name=ullmanns/>
⚫
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.<ref name = cotton>{{Cotton&Wilkinson6th}}</ref><ref name=adb>{{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.}}</ref>


⚫
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.<ref name = cotton>{{Cotton&Wilkinson6th}}</ref><ref name=adb>{{Cite journal | doi = 10.1107/S0567740870002182| title = The crystal structure of (CrO<sub>3</sub>)<sub>∞</sub>| journal = Acta Crystallographica Section B| volume = 26| issue = 3| pages = 222| year = 1970| last1 = Stephens | first1 = J. S.| last2 = Cruickshank | first2 = D. W. J.}}</ref> [[File:CrO3-from-xtal-1970-chain-3D-balls.png|450px|thumb|center|Ball-and-stick model of chains in the crystal structure of {{chem2|CrO3}}{{legend|rgb(158, 176, 224)|[[Chromium]], Cr}}{{legend|red|[[Oxygen]], O}}]]
:[[File:CrO3-from-xtal-1970-chain-3D-balls.png|450px|Ball-and-stick model of chains in the crystal structure of CrO3]]


The structure of monomeric CrO<sub>3</sub> has been calculated using [[density functional theory]], and is predicted to be [[Trigonal pyramidal molecular geometry|pyramidal]] ([[Molecular symmetry#Point Group|point group]] C<sub>3v</sub>) rather than [[Trigonal planar molecular geometry|planar]] (point group D<sub>3h</sub>).<ref name=cdoi>{{Cite journal | doi = 10.1021/ja077984d| title = Probing the Electronic and Structural Properties of Chromium Oxide Clusters (CrO3)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| year = 2008| last1 = Zhai | first1 = H. J. | last2 = Li | first2 = S. | last3 = Dixon | first3 = D. A. | last4 = Wang | first4 = L. S. }}</ref>
The structure of monomeric {{chem2|CrO3}} has been calculated using [[density functional theory]], and is predicted to be [[Trigonal pyramidal molecular geometry|pyramidal]] ([[Molecular symmetry#Point Group|point group]] C<sub>3v</sub>) rather than [[Trigonal planar molecular geometry|planar]] (point group D<sub>3h</sub>).<ref name=cdoi>{{Cite journal | doi = 10.1021/ja077984d| title = Probing the Electronic and Structural Properties of Chromium Oxide Clusters {{chem|(CrO|3|)|''n''|-}} and (CrO<sub>3</sub>)<sub>''n''</sub> (''n''&nbsp;= 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}}</ref>


:[[File:CrO3-monomer-from-DFT-PW91-aD-2008-side-3D-balls.png|150px|Ball-and-stick model of the DFT-calculated structure of the CrO3 monomer]]
:[[File:CrO3-monomer-from-DFT-PW91-aD-2008-side-3D-balls.png|150px|Ball-and-stick model of the DFT-calculated structure of the CrO3 monomer]]


Chromium trioxide decomposes above 197&nbsp;°C liberating oxygen eventually giving [[chromium(III) oxide|Cr<sub>2</sub>O<sub>3</sub>]]:
Chromium trioxide decomposes above 197&nbsp;°C, liberating oxygen and eventually giving [[chromium(III) oxide|{{chem2|Cr2O3}}]]:
:{{chem2|4 CrO3 → 2 Cr2O3 + 3 O2}}
:4 CrO<sub>3</sub> → 2 Cr<sub>2</sub>O<sub>3</sub> + 3 O<sub>2</sub>


It is used in [[organic synthesis]] as an oxidant, often as a solution in [[acetic acid]],<ref name = cotton /> or [[acetone]] in the case of the [[Jones oxidation]]. In these oxidations, the Cr(VI) converts [[primary alcohol]]s to the corresponding [[carboxylic acid]]s and [[secondary alcohol]]s to [[ketone]]s. The reactions are given below:
It is used in [[organic synthesis]] as an oxidant, often as a solution in [[acetic acid]],<ref name = cotton /> or [[acetone]] in the case of the [[Jones oxidation]]. In these oxidations, the Cr(VI) converts [[primary alcohol]]s to the corresponding [[carboxylic acid]]s and [[secondary alcohol]]s to [[ketone]]s. The reactions are shown below:


* Primary alcohols
* Primary alcohols to carboxylic acids
::4 CrO<sub>3</sub> + 3 RCH<sub>2</sub>OH + 12 H<sup>+</sup> → 3 RCOOH + 4 Cr<sup>3+</sup> + 9 H<sub>2</sub>O
*:{{chem2|4 CrO3 + 3 RCH2OH + 12 H+ → 3 RCOOH + 4 Cr(3+) + 9 H2O}}
* Secondary alcohols
* Secondary alcohols to ketones
::2 CrO<sub>3</sub> + 3 R<sub>2</sub>CHOH + 6 H<sup>+</sup> → 3 R<sub>2</sub>C=O + 2 Cr<sup>3+</sup> + 6 H<sub>2</sub>O
*:{{chem2|2 CrO3 + 3 R2CHOH + 6 H+ → 3 R2C\dO + 2 Cr(3+) + 6 H2O}}


==Applications==
==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 ruby|synthetic rubies]]. Chromic acid solution is also used in applying types of [[anodizing|anodic coating]] to [[aluminium]], which are primarily used in aerospace applications. A Chromic Acid/ Phosphoric Acid solution is also the preferred [[stripping (chemistry)|stripping agent]] of anodic coatings of all types.
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 ruby|synthetic rubies]]. Chromic acid solution is also used in applying types of [[anodizing|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 (chemistry)|stripping agent]] of anodic coatings of all types.


==Safety==
==Safety==
Chromium trioxide is highly toxic, corrosive, and carcinogenic.<ref>{{cite web|url = http://hazard.com/msds/mf/baker/baker/files/c4400.htm|publisher = J. T. Baker|title = Chromium Trioxide (MSDS)|accessdate = 2007-09-13}}</ref> It is the main example of [[hexavalent chromium]], an [[environmental hazard]]. <ref>The environmental impact of hexavalent chromium inspired the 2000 biographical Hollywood movie [[Erin Brockovich (film)|Erin Brockovich]].</ref>The related chromium(III) derivatives are not particularly dangerous; thus, [[reductant]]s are used to destroy chromium(VI) samples.
Chromium trioxide is highly toxic, corrosive, and carcinogenic.<ref>{{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}}</ref> It is the main example of [[hexavalent chromium]], an [[environmental hazard]].<ref>The environmental impact of hexavalent chromium inspired the 2000 biographical Hollywood movie ''[[Erin Brockovich (film)|Erin Brockovich]]''.</ref> The related chromium(III) derivatives are not particularly dangerous; thus, [[reductant]]s are used to destroy chromium(VI) samples.


Chromium trioxide, being a powerful oxidizer, will ignite organic materials such as [[alcohols]] [[Hypergolic propellant|on contact]].
Chromium trioxide, being a powerful oxidizer, will ignite organic materials such as [[alcohols]] [[Hypergolic propellant|on contact]].
Line 114: Line 114:
==External links==
==External links==
{{Commons category|Chromium trioxide}}
{{Commons category|Chromium trioxide}}
* [http://www.atsdr.cdc.gov/csem/chromium ATSDR Case Studies in Environmental Medicine: Chromium Toxicity] U.S. [[Department of Health and Human Services]]
* [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)
* [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]
* [https://www.organic-chemistry.org/chemicals/oxidations/chromium-trioxide.shtm Reactions with Chromium Trioxide as Oxidizing Agent]
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{{oxygen compounds}}
{{oxygen compounds}}


[[Category:Oxides]]
[[Category:Acidic oxides]]
[[Category:Chromium(Ⅵ) compounds]]
[[Category:Chromium(VI) compounds]]

Latest revision as of 21:54, 16 March 2024

Chromium trioxide
Ball-and-stick model of chromium trioxide
  Chromium, Cr
  Oxygen, O
Powder of chromium trioxide
Names
IUPAC name
Chromium trioxide
Other names
Chromic anhydride, Chromium(VI) oxide, Chromic acid (misnomer)
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.014.189 Edit this at Wikidata
RTECS number
  • GB6650000
UNII
UN number 1463
  • InChI=1S/Cr.3O checkY
    Key: WGLPBDUCMAPZCE-UHFFFAOYSA-N checkY
  • InChI=1/Cr.3O/rCrO3/c2-1(3)4
    Key: WGLPBDUCMAPZCE-YFSAMUSXAF
  • O=[Cr](=O)=O
Properties
CrO3
Molar mass 99.993 g·mol−1
Appearance Dark red granular solid, deliquescent
Odor Odorless
Density 2.7 g/cm3 (20 °C)[1]
Melting point 197 °C (387 °F; 470 K)[1]
Boiling point 250 °C (482 °F; 523 K)
decomposes[1]
  • 164.8 g/(100 mL) (0 °C)
  • 169 g/(100 mL) (25 °C)[1]
  • 172.6 g/(100 mL) (40 °C)
  • 198.1 g/(100 mL) (100 °C)[2]
Solubility Soluble in H2SO4, HNO3, (CH3CH2)2O, CH3COOH, (CH3)2CO
+40·10−6 cm3/mol[1]
Thermochemistry
73.2 J/(mol·K)[3]
−589.3 kJ/mol[4]
Hazards
GHS labelling:
GHS03: OxidizingGHS05: CorrosiveGHS06: ToxicGHS08: Health hazardGHS09: Environmental hazard[5]
Danger
H271, H301+H311, H314, H317, H330, H334, H335, H340, H350, H361f, H372, H410[5]
P210, P260, P280, P303+P361+P353, P304+P340+P310, P305+P351+P338[5]
NFPA 704 (fire diamond)
[6]
NFPA 704 four-colored diamondHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
4
0
2
OX
Lethal dose or concentration (LD, LC):
80 mg/kg (rats, oral)[6]
Safety data sheet (SDS) ICSC 1194
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Chromium trioxide (also known as chromium(VI) oxide oder chromic anhydride) is an inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.[6] This compound is a dark-purple solid under anhydrous conditions and bright orange when wet. The substance dissolves in water accompanied by hydrolysis.[clarification needed] Millions of kilograms are produced annually, mainly for electroplating.[7] Chromium trioxide is a powerful oxidiser, a mutagen, and a carcinogen.[8]

Production, structure, and basic reactions

[edit]

Chromium trioxide is generated by treating sodium dichromate with sulfuric acid:[6]

H2SO4 + Na2Cr2O7 → 2 CrO3 + Na2SO4 + H2O

Approximately 100,000 tonnes are produced annually by this or similar routes.[7]

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.[9][10]

Ball-and-stick model of chains in the crystal structure of CrO3
  Chromium, Cr
  Oxygen, O

The structure of monomeric CrO3 has been calculated using density functional theory, and is predicted to be pyramidal (point group C3v) rather than planar (point group D3h).[11]

Ball-and-stick model of the DFT-calculated structure of the CrO3 monomer

Chromium trioxide decomposes above 197 °C, liberating oxygen and eventually giving Cr2O3:

4 CrO3 → 2 Cr2O3 + 3 O2

It is used in organic synthesis as an oxidant, often as a solution in acetic acid,[9] 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
    4 CrO3 + 3 RCH2OH + 12 H+ → 3 RCOOH + 4 Cr3+ + 9 H2O
  • Secondary alcohols to ketones
    2 CrO3 + 3 R2CHOH + 6 H+ → 3 R2C=O + 2 Cr3+ + 6 H2O

Applications

[edit]

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

[edit]

Chromium trioxide is highly toxic, corrosive, and carcinogenic.[12] It is the main example of hexavalent chromium, an environmental hazard.[13] 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

[edit]
  • A concentrated solution of potassium dichromate in water.
    A concentrated solution of potassium dichromate in water.
  • Addition of sulfuric acid to the solution.
    Addition of sulfuric acid to the solution.
  • Crystallization of chromium trioxide from the reaction.
    Crystallization of chromium trioxide from the reaction.
  • Reaction between chromium trioxide and ethanol
    Reaction between chromium trioxide and ethanol

References

[edit]
  1. ^ a b c d e Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0.
  2. ^ Seidell, Atherton; Linke, William F. (1919). Solubilities of Inorganic and Organic Compounds (2nd ed.). D. Van Nostrand Company. p. 250.
  3. ^ "chromium(VI) oxide". chemister.ru.
  4. ^ Pradyot, Patnaik (2003). Handbook of Inorganic Chemicals. The McGraw-Hill Companies, Inc. ISBN 0-07-049439-8.
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  8. ^ Mamyrbaev, Arstan Abdramanovich; Dzharkenov, Timur Agataevich; Imangazina, Zina Amangalievna; Satybaldieva, Umit Abulkhairovna (2015-04-16). "Mutagenic and carcinogenic actions of chromium and its compounds". Environmental Health and Preventive Medicine. 20 (3). Springer Science and Business Media LLC: 159–167. doi:10.1007/s12199-015-0458-2. ISSN 1342-078X. PMC 4434237. PMID 25877777.
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  11. ^ Zhai, H. J.; Li, S.; Dixon, D. A.; Wang, L. S. (2008). "Probing the Electronic and Structural Properties of Chromium Oxide Clusters (CrO
    3    )−
    n     and (CrO3)n (n = 1–5): Photoelectron Spectroscopy and Density Functional Calculations". Journal of the American Chemical Society. 130 (15): 5167–77. doi:10.1021/ja077984d. PMID 18327905.
  12. ^ "Chromium Trioxide (MSDS)". J. T. Baker. Archived from the original on 2015-01-12. Retrieved 2007-09-13.
  13. ^ The environmental impact of hexavalent chromium inspired the 2000 biographical Hollywood movie Erin Brockovich.
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