Ammonium dichromate

Ammonium dichromate
Names
	IUPAC name Ammonium dichromate
	Other names Ammonium pyrochromate
Identifiers
CAS Number	7789-09-5 ;
3D model (JSmol)	Interactive image;
ChemSpider	23002 ;
ECHA InfoCard	100.029.221
RTECS number	HX7650000;
UN number	1439
CompTox Dashboard (EPA)	DTXSID70872953 ;
	InChI InChI=1S/2Cr.2H3N.7O/h;;21H3;;;;;;;/q;;;;;;;;;2-1/p+2 Key: JOSWYUNQBRPBDN-UHFFFAOYSA-P ; InChI=1/2Cr.2H3N.7O/h;;21H3;;;;;;;/q;;;;;;;;;2-1/p+2/rCr2O7.2H3N/c3-1(4,5)9-2(6,7)8;;/h;2*1H3/q-2;;/p+2 Key: JOSWYUNQBRPBDN-RFRSXZKWAS;
	SMILES [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O.[NH4+].[NH4+];
Properties
Chemical formula	(NH4)2Cr2O7
Molar mass	252.07 g/mol
Appearance	Orange-red crystals
Density	2.115 g/cm3
Melting point	180 °C (decomp.)
Solubility in water	18.2 g/100 mL (0 °C) ; 26.67 g/100 mL (20 °C) ; 156 g/100 mL (100 °C)
Solubility	insoluble in acetone ; soluble in alcohol
Hazards
	GHS labelling:
Pictograms	class="wikitable collapsible" style="min-width: 50em;"

See also

GHS hazard pictograms^[1]
Code	Symbol description	Image link
GHS01	{{GHS exploding bomb}}	Image:GHS-pictogram-explos.svg	Explosive
GHS02	{{GHS flame}}	Image:GHS-pictogram-flamme.svg
GHS03	{{GHS flame over circle}}	Image:GHS-pictogram-rondflam.svg
GHS04	{{GHS gas cylinder}}	Image:GHS-pictogram-bottle.svg
GHS05	{{GHS corrosion}}	Image:GHS-pictogram-acid.svg	Corrosive
GHS06	{{GHS skull and crossbones}}	Image:GHS-pictogram-skull.svg	Accute Toxic
GHS07	{{GHS exclamation mark}}	Image:GHS-pictogram-exclam.svg	Irritant
GHS08	{{GHS health hazard}}	Image:GHS-pictogram-silhouette.svg	Health Hazard
GHS09	{{GHS environment}}	Image:GHS-pictogram-pollu.svg	Environment

See also

GHS hazard pictograms^[1]
Code	Symbol description	Image link
GHS01	{{GHS exploding bomb}}	Image:GHS-pictogram-explos.svg	Explosive
GHS02	{{GHS flame}}	Image:GHS-pictogram-flamme.svg
GHS03	{{GHS flame over circle}}	Image:GHS-pictogram-rondflam.svg
GHS04	{{GHS gas cylinder}}	Image:GHS-pictogram-bottle.svg
GHS05	{{GHS corrosion}}	Image:GHS-pictogram-acid.svg	Corrosive
GHS06	{{GHS skull and crossbones}}	Image:GHS-pictogram-skull.svg	Accute Toxic
GHS07	{{GHS exclamation mark}}	Image:GHS-pictogram-exclam.svg	Irritant
GHS08	{{GHS health hazard}}	Image:GHS-pictogram-silhouette.svg	Health Hazard
GHS09	{{GHS environment}}	Image:GHS-pictogram-pollu.svg	Environment

See also

GHS hazard pictograms^[1]
Code	Symbol description	Image link
GHS01	{{GHS exploding bomb}}	Image:GHS-pictogram-explos.svg	Explosive
GHS02	{{GHS flame}}	Image:GHS-pictogram-flamme.svg
GHS03	{{GHS flame over circle}}	Image:GHS-pictogram-rondflam.svg
GHS04	{{GHS gas cylinder}}	Image:GHS-pictogram-bottle.svg
GHS05	{{GHS corrosion}}	Image:GHS-pictogram-acid.svg	Corrosive
GHS06	{{GHS skull and crossbones}}	Image:GHS-pictogram-skull.svg	Accute Toxic
GHS07	{{GHS exclamation mark}}	Image:GHS-pictogram-exclam.svg	Irritant
GHS08	{{GHS health hazard}}	Image:GHS-pictogram-silhouette.svg	Health Hazard
GHS09	{{GHS environment}}	Image:GHS-pictogram-pollu.svg	Environment

See also

GHS hazard pictograms^[1]
Code	Symbol description	Image link
GHS01	{{GHS exploding bomb}}	Image:GHS-pictogram-explos.svg	Explosive
GHS02	{{GHS flame}}	Image:GHS-pictogram-flamme.svg
GHS03	{{GHS flame over circle}}	Image:GHS-pictogram-rondflam.svg
GHS04	{{GHS gas cylinder}}	Image:GHS-pictogram-bottle.svg
GHS05	{{GHS corrosion}}	Image:GHS-pictogram-acid.svg	Corrosive
GHS06	{{GHS skull and crossbones}}	Image:GHS-pictogram-skull.svg	Accute Toxic
GHS07	{{GHS exclamation mark}}	Image:GHS-pictogram-exclam.svg	Irritant
GHS08	{{GHS health hazard}}	Image:GHS-pictogram-silhouette.svg	Health Hazard
GHS09	{{GHS environment}}	Image:GHS-pictogram-pollu.svg	Environment

See also

|-

| style="padding-left:1em;" |

Hazard statements

| H272, H301, H312, H314, H317, H330, H334, H340, H350, H360, H372, H410^[2]

|-

| style="padding-left:1em;" |

Precautionary statements

| P201, P220, P260, P273, P280, P284^[2]

|- | NFPA 704 (fire diamond)

|

2

1

OX

|- ! colspan=2 style="background: #f8eaba; text-align: center;" |Related compounds

|-

|

Other cations

| Potassium dichromate
Sodium dichromate |-

| colspan=2 style="text-align:left; background:#f8eaba; border:1px solid #a2a9b1;" |

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

verify (what is ^YN ?)

Infobox references

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|}

Ammonium dichromate is the inorganic compound with the formula (NH₄)₂Cr₂O₇. In this compound, as in all chromates and dichromates, chromium is in a +6 oxidation state, commonly known as hexavalent chromium. It is a salt consisting of ammonium ions and dichromate ions.

Ammonium dichromate is sometimes known as Vesuvian Fire, because of its use in demonstrations of tabletop "volcanoes".^[3] It has been used in pyrotechnics and in the early days of photography.

Properties

At room temperature and pressure, the compound exists as orange, acidic crystals soluble in water and alcohol. It is formed by the action of chromic acid on ammonium hydroxide with subsequent crystallisation.^[4]

The (NH₄)₂Cr₂O₇ crystal (C2/c, z=4) contains a single type of ammonium ion, at sites of symmetry C₁(2,3). Each NH₄⁺ centre is surrounded irregularly by eight oxygen atoms at N---O distances ranging from ca. 2.83 to ca. 3.17 Å, typical of hydrogen bonds.^[5]

Uses

It has been used in pyrotechnics and in the early days of photography as well as in lithography, as a source of pure nitrogen in the laboratory, and as a catalyst.^[6] It is also used as a mordant for dyeing pigments, in the manufacturing of alizarin, chrome alum, leather tanning and oil purification.^[4]

Photosensitive films containing PVA, ammonium dichromate, and a phosphor are spin-coated as aqueous slurries in the production of the phosphor raster of television screens and other devices. The ammonium dichromate acts as the photoactive site.^[7]

Reactions

Tabletop volcanoes and thermal decomposition

The volcano demonstration involves igniting a pile of the salt, which initiates the following exothermic conversion:^[8]

(NH
₄)
₂Cr
₂O
₇ (s) → Cr
₂O
₃ (s) + N
₂ (g) + 4 H
₂O (g) (ΔH=−429.1 ± 3 kcal/mol)

Like the well-known explosive ammonium nitrate, ammonium dichromate contains both an oxidizer (dichromate) and a reducer (ammonium), making it thermodynamically unstable.^[9]^[10] Its decomposition reaction proceeds to completion once initiated, producing voluminous dark green powdered chromium(III) oxide. Not all of the ammonium dichromate decomposes in this reaction. When the green powder is brought into water a yellow/orange solution is obtained from left over ammonium dichromate.

Observations obtained using relatively high magnification microscopy during a kinetic study of the thermal decomposition of ammonium dichromate provided evidence that salt breakdown proceeds with the intervention of an intermediate liquid phase rather than a solid phase. The characteristic darkening of (NH
₄)
₂Cr
₂O
₇ crystals as a consequence of the onset of decomposition can be ascribed to the dissociative loss of ammonia accompanied by progressive anion condensation to Cr
₃O²⁻
₁₀, Cr
₄O²⁻
₁₃, etc., ultimately yielding CrO
₃. The CrO
₃ has been identified as a possible molten intermediate participating in (NH
₄)
₂Cr
₂O
₇ decomposition.^[11]

Oxidation reactions

Ammonium dichromate is a strong oxidising agent and reacts, often violently, with any reducing agent. The stronger the reducing agent, the more violent the reaction.^[9] It has also been used to promote the oxidation of alcohols and thiols. Ammonium dichromate, in the presence of Mg(HSO₄)₂ and wet SiO₂ can act as a very efficient reagent for the oxidative coupling of thiols under solvent free conditions. The reactions produces reasonably good yields under relatively mild conditions.^[12] The compound is also used in the oxidation of aliphatic alcohols to their corresponding aldehydes and ketones in ZrCl₄/wet SiO₂ in solvent free conditions, again with relatively high yields.^[13]^[14]

Safety

Ammonium dichromate, like all chromium(VI) compounds, is highly toxic and a suspected carcinogen.^[15] It is also a strong irritant.

Incidents

In sealed containers, ammonium dichromate is likely to explode if heated.^[9] On January 19, 1986, The New York Times reported that two workers had been killed and 14 others injured at Diamond Shamrock Chemicals, Ashtabula, Ohio when 2000 lbs of ammonium dichromate exploded as they were being dried in a heater.^[16]

References

^ ^a ^b ^c ^d ^e "Globally Harmonized System of Classification and Labelling of Chemicals" (pdf). 2021. Annex 3: Codification of Statements and Pictograms (pp 268–385).
^ ^a ^b ^c Template:SigmaLink
^ "Ammonium Dichromate Volcano". Chemistry Comes Alive!. J. Chem. Ed.
^ ^a ^b Richard J. Lewis Hawley's Condensed Chemical Dictionary. Wiley & Sons, Inc: New York, 2007 ISBN 978-0-471-76865-4
^ Keresztury, G and Knop, O. (1982). "Infrared spectra of the ammonium ion in crystals. Part XII. Low-temperature transitions in ammonium dichromate, (NH₄)₂Cr₂O₇". Can. J. Chem.: 1972–1976.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
^ Havard, J.M., Shim, S.Y., and Fréchet, J.M. (1999). "Design of Photoresists with Reduced Environmental Impact. 1. Water-Soluble Resists Based on Photo-Cross-Linking of Poly(vinyl alcohol)". Chem. Mater. 11: 719–725. doi:10.1021/cm980603y.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Neugebauer, C. A and Margrave, J.L. (1957). "The Heat Formation of Ammonium Dichromate". J. Phys. Chem. 61 (10): 1429–1430. doi:10.1021/j150556a040.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ ^a ^b ^c Young, A.J. (2005). "CLIP, Chemical Laboratory Information Profile: Ammonium Dichromate". J. Chem. Educ. 82: 1617. doi:10.1021/ed082p1617.
^ G.A.P. Dalgaard, A.C. Hazell and R.G. Hazell (1974). ""The Crystal Structure of Ammonium Dichromate, (NH₄)₂Cr₂O₇". Acta Chemica Scandinavica. A28: 541–545. doi:10.3891/acta.chem.scand.28a-0541.
^ Galwey, A.K., P&Oumlppl, L, and Rajam, S. (1983). "A Melt Mechanism for the Thermal Decomposition of Ammonium Dichromate". J. Chem. Soc., Faraday Trans. 1. 79: 2143–2151. doi:10.1039/f19837902143.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Shirini, F.; et al. (2003). "Solvent free oxidation of thiols by (NH₄)₂Cr₂O₇ in the presence of Mg(HSO₄)₂ and wet SiO₂". J. Chem. Research (S). 2003: 28–29. doi:10.3184/030823403103172823. {{cite journal}}: Explicit use of et al. in: |author= (help)
^ Shirini, F.; et al. (2001). "ZrCl₄/wet SiO₂ promoted oxidation of alcohols by (NH₄)₂Cr₂O₇ in solution and solvent free condition". J. Chem. Research (S). 2001: 467–477. doi:10.3184/030823401103168541. {{cite journal}}: Explicit use of et al. in: |author= (help)
^ F. Shirini, M. A. Zolfigol,† and M. Khaleghi (2003). "Oxidation of Alcohols Using (NH₄)₂Cr₂O₇ in the Presence of Silica Chloride/Wet SiO₂ in Solution and under Solvent Free Conditions". Bull. Korean Chem. Soc. 24 (7): 1021–1022. doi:10.5012/bkcs.2003.24.7.1021.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Volkovich, V.A. and Griffiths, T.R. (2000). "Catalytic Oxidation of Ammonia: A Sparkling Experiment". J. Chem. Ed. 77 (2): 177. doi:10.1021/ed077p177.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Diamond, S. The New York Times, 1986, p 22.

[GHS2021_annex-3-1] "Globally Harmonized System of Classification and Labelling of Chemicals" (pdf). 2021. Annex 3: Codification of Statements and Pictograms (pp 268–385).

[sigma-2] Template:SigmaLink

[3] "Ammonium Dichromate Volcano". Chemistry Comes Alive!. J. Chem. Ed.

[lewis-4] Richard J. Lewis Hawley's Condensed Chemical Dictionary. Wiley & Sons, Inc: New York, 2007 ISBN 978-0-471-76865-4

[5] Keresztury, G and Knop, O. (1982). "Infrared spectra of the ammonium ion in crystals. Part XII. Low-temperature transitions in ammonium dichromate, (NH₄)₂Cr₂O₇". Can. J. Chem.: 1972–1976.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[6] Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8

[7] Havard, J.M., Shim, S.Y., and Fréchet, J.M. (1999). "Design of Photoresists with Reduced Environmental Impact. 1. Water-Soluble Resists Based on Photo-Cross-Linking of Poly(vinyl alcohol)". Chem. Mater. 11: 719–725. doi:10.1021/cm980603y.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[8] Neugebauer, C. A and Margrave, J.L. (1957). "The Heat Formation of Ammonium Dichromate". J. Phys. Chem. 61 (10): 1429–1430. doi:10.1021/j150556a040.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[young-9] Young, A.J. (2005). "CLIP, Chemical Laboratory Information Profile: Ammonium Dichromate". J. Chem. Educ. 82: 1617. doi:10.1021/ed082p1617.

[10] G.A.P. Dalgaard, A.C. Hazell and R.G. Hazell (1974). ""The Crystal Structure of Ammonium Dichromate, (NH₄)₂Cr₂O₇". Acta Chemica Scandinavica. A28: 541–545. doi:10.3891/acta.chem.scand.28a-0541.

[11] Galwey, A.K., P&Oumlppl, L, and Rajam, S. (1983). "A Melt Mechanism for the Thermal Decomposition of Ammonium Dichromate". J. Chem. Soc., Faraday Trans. 1. 79: 2143–2151. doi:10.1039/f19837902143.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[12] Shirini, F.; et al. (2003). "Solvent free oxidation of thiols by (NH₄)₂Cr₂O₇ in the presence of Mg(HSO₄)₂ and wet SiO₂". J. Chem. Research (S). 2003: 28–29. doi:10.3184/030823403103172823. {{cite journal}}: Explicit use of et al. in: |author= (help)

[13] Shirini, F.; et al. (2001). "ZrCl₄/wet SiO₂ promoted oxidation of alcohols by (NH₄)₂Cr₂O₇ in solution and solvent free condition". J. Chem. Research (S). 2001: 467–477. doi:10.3184/030823401103168541. {{cite journal}}: Explicit use of et al. in: |author= (help)

[14] F. Shirini, M. A. Zolfigol,† and M. Khaleghi (2003). "Oxidation of Alcohols Using (NH₄)₂Cr₂O₇ in the Presence of Silica Chloride/Wet SiO₂ in Solution and under Solvent Free Conditions". Bull. Korean Chem. Soc. 24 (7): 1021–1022. doi:10.5012/bkcs.2003.24.7.1021.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[15] Volkovich, V.A. and Griffiths, T.R. (2000). "Catalytic Oxidation of Ammonia: A Sparkling Experiment". J. Chem. Ed. 77 (2): 177. doi:10.1021/ed077p177.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[16] Diamond, S. The New York Times, 1986, p 22.

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