Ammonium dichromate

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Ammonium dichromate
(NH4)2Cr2O7.JPG
Ammonium-dichromate-2D.png
Ammonium-dichromate-xtal-2007-CM-3D-balls.png
Names
IUPAC name
Ammonium dichromate
Other names
Ammonium bichromate
Ammonium pyrochromate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.029.221 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
RTECS number
  • HX7650000
UNII
UN number 1439
  • InChI=1S/2Cr.2H3N.7O/h;;2*1H3;;;;;;;/q;;;;;;;;;2*-1/p+2 Yes check.svgY
    Key: JOSWYUNQBRPBDN-UHFFFAOYSA-P Yes check.svgY
  • InChI=1/2Cr.2H3N.7O/h;;2*1H3;;;;;;;/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
  • [O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O.[NH4+].[NH4+]
Properties
(NH4)2Cr2O7
Molar mass 252.07 g/mol
AppearanceOrange-red crystals
Odor odorless
Density 2.115 g/cm3
Melting point 180 °C (356 °F; 453 K) decomposes
18.2 g/100 ml (0 °C)
35.6 g/100 ml (20 °C)
40 g/100 ml (25 °C)
156 g/100 ml (100 °C)
Solubility insoluble in acetone
soluble in ethanol
Structure
monoclinic
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Very toxic, explosive, oxidizing, carcinogenic, mutagenic, dangerous for the environment
GHS labelling:
GHS-pictogram-explos.svg GHS-pictogram-rondflam.svg GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg [1]
H272, H301, H312, H314, H317, H330, H334, H340, H350, H360, H372, H410 [1]
P201, P220, P260, P273, P280, P284 [1]
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelInstability 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazard OX: Oxidizer. E.g. potassium perchlorate
4
2
3
OX
190 °C (374 °F; 463 K)
Lethal dose or concentration (LD, LC):
20–250 mg/kg
Safety data sheet (SDS) ICSC 1368
Related compounds
Other cations
Potassium dichromate
Sodium dichromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Ammonium dichromate is an 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.

Contents

Ammonium dichromate is sometimes known as Vesuvian Fire, because of its use in demonstrations of tabletop "volcanoes". [2] However, this demonstration has become unpopular in schools due to the compound's carcinogenic nature. It has also 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. [3]

The (NH4)2Cr2O7 crystal (C2/c, z = 4) contains a single type of ammonium ion, at sites of symmetry C1(2,3). Each NH+
4 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. [4]

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. [5] It is also used as a mordant for dyeing pigments, in manufacturing of alizarin, chrome alum, leather tanning and oil purification. [3]

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. [6]

Reactions

Tabletop volcanoes and thermal decomposition

A few drops of ethanol are added to a small pile of ammonium dichromate ((NH4)2Cr2O7) and ignited. Sparks are emitted and an ash-like product is formed. The phenomenon resembles the eruption of a volcano. The reaction starts at 180 °С, becoming self-sustaining at approximately 225 °С. [7]
Ammonium dichromate decomposition Ammooniumdikromaadi polemine.JPG
Ammonium dichromate 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 ammonium nitrate, it is 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 proven carcinogen. It is also a strong irritant.[ citation needed ]

Incidents

In sealed containers, ammonium dichromate is likely to explode if heated. [9] In 1986, two workers were killed and 14 others injured at Diamond Shamrock Chemicals in Ashtabula, Ohio, when 2,000 lb (910 kg) of ammonium dichromate exploded as it was being dried in a heater. [15]

Related Research Articles

<span class="mw-page-title-main">Manganese dioxide</span> Chemical compound

Manganese dioxide is the inorganic compound with the formula MnO
2. This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for MnO
2 is for dry-cell batteries, such as the alkaline battery and the zinc–carbon battery. MnO
2 is also used as a pigment and as a precursor to other manganese compounds, such as KMnO
4. It is used as a reagent in organic synthesis, for example, for the oxidation of allylic alcohols. MnO
2 has an α-polymorph that can incorporate a variety of atoms in the "tunnels" or "channels" between the manganese oxide octahedra. There is considerable interest in α-MnO
2 as a possible cathode for lithium-ion batteries.

Chromic acid is jargon for a solution formed by the addition of sulfuric acid to aqueous solutions of dichromate. It consists at least in part of chromium trioxide.

<span class="mw-page-title-main">Ceric ammonium nitrate</span> Chemical compound

Ceric ammonium nitrate (CAN) is the inorganic compound with the formula (NH4)2[Ce(NO3)6]. This orange-red, water-soluble cerium salt is a specialised oxidizing agent in organic synthesis and a standard oxidant in quantitative analysis.

<span class="mw-page-title-main">Potassium dichromate</span> Chemical compound

Potassium dichromate, K2Cr2O7, is a common inorganic chemical reagent, most commonly used as an oxidizing agent in various laboratory and industrial applications. As with all hexavalent chromium compounds, it is acutely and chronically harmful to health. It is a crystalline ionic solid with a very bright, red-orange color. The salt is popular in laboratories because it is not deliquescent, in contrast to the more industrially relevant salt sodium dichromate.

<span class="mw-page-title-main">Chromium trioxide</span> Chemical compound

Chromium trioxide is an inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple solid under anhydrous conditions and bright orange when wet. The substance dissolves in water accompanied by hydrolysis. Millions of kilograms are produced annually, mainly for electroplating. Chromium trioxide is a powerful oxidiser, a mutagen, and a carcinogen.

<span class="mw-page-title-main">Chromium(III) oxide</span> Chemical compound

Chromium(III) oxide is an inorganic compound with the formula Cr
2O
3. It is one of the principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.

<span class="mw-page-title-main">Copper chromite</span> Chemical compound

Copper chromite often refers to inorganic compounds with the formula Cu2Cr2Ox. They are black solids. Cu2Cr2O4 is a well-defined material. The other copper chromite often is described as Cu2Cr2O5. It is used to catalyze reactions in organic chemistry.

<span class="mw-page-title-main">Chromium(III) fluoride</span> Chemical compound

Chromium(III) fluoride is an inorganic compound with the chemical formula CrF3. It forms several hydrates. The compound CrF3 is a green crystalline solid that is insoluble in common solvents, but the hydrates [Cr(H2O)6]F3 (violet) and [Cr(H2O)6]F3·3H2O (green) are soluble in water. The anhydrous form sublimes at 1100–1200 °C.

<span class="mw-page-title-main">Manganese heptoxide</span> Chemical compound

Manganese(VII) oxide is an inorganic compound with the formula Mn2O7 Manganese heptoxide is a volatile liquid with an oily consistency. It is a highly reactive and powerful oxidizer that reacts explosively with nearly any organic compound. It was first described in 1860. It is the acid anhydride of permanganic acid.

<span class="mw-page-title-main">Chromium compounds</span> Chemical compounds containing chromium

Chromium compounds are compounds containing the element chromium (Cr). Chromium is a member of group 6 of the transition metals. The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist.

<span class="mw-page-title-main">Hexafluorophosphate</span> Anion with the chemical formula PF6–

Hexafluorophosphate is an anion with chemical formula of [PF6]−. It is an octahedral species that imparts no color to its salts. [PF6]− is isoelectronic with sulfur hexafluoride, SF6, and the hexafluorosilicate dianion, [SiF6]2−, and hexafluoroantimonate [SbF6]−. In this anion, phosphorus has a valence of 5. Being poorly nucleophilic, hexafluorophosphate is classified as a non-coordinating anion.

<span class="mw-page-title-main">Collins reagent</span> Chemical compound

Collins reagent is the complex of chromium(VI) oxide with pyridine in dichloromethane. This metal-pyridine complex, a red solid, is used to oxidize primary alcohols to the corresponding aldehydes and secondary alcohols to the corresponding ketones. This complex is a hygroscopic orange solid.

Alcohol oxidation is a collection of oxidation reactions in organic chemistry that convert alcohols to aldehydes, ketones, carboxylic acids, and esters. The reaction mainly applies to primary and secondary alcohols. Secondary alcohols form ketones, while primary alcohols form aldehydes or carboxylic acids.

<span class="mw-page-title-main">Chromium(VI) oxide peroxide</span> Chemical compound

Chromium(VI) oxide peroxide is the name given to a collection of chromium coordination complexes. They have the formula CrO(O2)2L where L is a ligand. These species are dark blue and often labile. They all feature oxo ligand and two peroxo ligands, with the remaining coordination sites occupied by water, hydroxide, ether, or other Lewis bases.

Oxidation with chromium(VI) complexes involves the conversion of alcohols to carbonyl compounds or more highly oxidized products through the action of molecular chromium(VI) oxides and salts. The principal reagents are Collins reagent, PDC, and PCC. These reagents represent improvements over inorganic chromium(VI) reagents such as Jones reagent.

<span class="mw-page-title-main">Jones oxidation</span> Oxidation of alcohol

The Jones oxidation is an organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones. The reaction was an early method for the oxidation of alcohols. Its use has subsided because milder, more selective reagents have been developed, e.g. Collins reagent.

<span class="mw-page-title-main">Molybdate</span> Chemical compound of the form –O–MoO₂–O–

In chemistry, a molybdate is a compound containing an oxyanion with molybdenum in its highest oxidation state of +6: O−−Mo(=O)2−O−. Molybdenum can form a very large range of such oxyanions, which can be discrete structures or polymeric extended structures, although the latter are only found in the solid state. The larger oxyanions are members of group of compounds termed polyoxometalates, and because they contain only one type of metal atom are often called isopolymetalates. The discrete molybdenum oxyanions range in size from the simplest MoO2−
4, found in potassium molybdate up to extremely large structures found in isopoly-molybdenum blues that contain for example 154 Mo atoms. The behaviour of molybdenum is different from the other elements in group 6. Chromium only forms the chromates, CrO2−
4, Cr
2O2−
7, Cr
3O2−
10 and Cr
4O2−
13 ions which are all based on tetrahedral chromium. Tungsten is similar to molybdenum and forms many tungstates containing 6 coordinate tungsten.

A chromate ester is a chemical structure that contains a chromium atom (symbol Cr) in a +6 oxidation state that is connected via an oxygen (O) linkage to a carbon (C) atom. The Cr itself is in its chromate form, with several oxygens attached, and the Cr–O–C attachment makes this chemical group structurally similar to other ester functional groups. They can be synthesized from various chromium(VI) metal compounds, such as CrO3, chromium chloride complexes, and aqueous chromate ions, and tend to react via redox reactions to liberate chromium(IV).

<span class="mw-page-title-main">Chromyl fluoride</span> Chemical compound

Chromyl fluoride is an inorganic compound with the formula CrO2F2. It is a violet-red colored crystalline solid that melts to an orange-red liquid.

References

  1. 1 2 3 Sigma-Aldrich Co., Ammonium dichromate. Retrieved on 2013-07-20.
  2. ↑ "Ammonium Dichromate Volcano". Chemistry Comes Alive!. J. Chem. Educ. (dead link 29 March 2021)
  3. 1 2 Richard J. Lewis Hawley's Condensed Chemical Dictionary. Wiley & Sons, Inc: New York, 2007 ISBN   978-0-471-76865-4
  4. ↑ Keresztury, G.; Knop, O. (1982). "Infrared spectra of the ammonium ion in crystals. Part XII. Low-temperature transitions in ammonium dichromate, (NH4)2Cr2O7". Can. J. Chem. 60 (15): 1972–1976. doi:10.1139/v82-277.
  5. ↑ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN   0-07-049439-8
  6. ↑ Havard, J. M.; Shim, S. Y.; Fr; eacute; chet, 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 (3): 719–725. doi:10.1021/cm980603y.
  7. ↑
    Planned and performed by Marina Stojanovska, Miha Bukleski and Vladimir Petruševski, Department of Chemistry, FNSM, Ss. Cyril and Methodius University, Skopje, Macedonia.
  8. ↑ Neugebauer, C. A.; Margrave, J. L. (1957). "The Heat of Formation of Ammonium Dichromate". J. Phys. Chem. 61 (10): 1429–1430. doi:10.1021/j150556a040.
  9. 1 2 3 Young, A.J. (2005). "CLIP, Chemical Laboratory Information Profile: Ammonium Dichromate". J. Chem. Educ. 82 (11): 1617. doi:10.1021/ed082p1617. Archived from the original on 2008-09-05. Retrieved 2009-06-14.
  10. ↑ G. A. P. Dalgaard; A. C. Hazell; 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, Andrew K.; Pöppl, László; Rajam, Sundara (1983). "A Melt Mechanism for the Thermal Decomposition of Ammonium Dichromate". J. Chem. Soc., Faraday Trans. 1 . 79 (9): 2143–2151. doi:10.1039/f19837902143.
  12. ↑ Shirini, F.; et al. (2003). "Solvent free oxidation of thiols by (NH4)2Cr2O7 in the presence of Mg(HSO4)2 and wet SiO2". Journal of Chemical Research . 2003: 28–29. doi: 10.3184/030823403103172823 . S2CID   197126514.
  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 (11): 467–477. doi: 10.3184/030823401103168541 . S2CID   197118772.
  14. ↑ F. Shirini; M. A. Zolfigol; FOO† 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 .
  15. ↑ Diamond, S. (19 January 1986). "Chemical Explosion In Ohio". The New York Times. p. 22.
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