Sodium dichromate


Sodium dichromate
Sodium dichromate.
Identifiers
CAS number 10588-01-9 YesY
7789-12-0 (dihydrate)
PubChem 25408
ChemSpider 23723 YesY
EC number 234-190-3
UN number 3288
ChEBI CHEBI:39483 YesY
RTECS number HX7750000
HX7750000 (dihydrate)
Jmol-3D images Image 1
Properties
Molecular formula Na2Cr2O7
Molar mass 261.97 g/mol (anhydrous)
298.00 g/mol (dihydrate)
Density 2.52 g/cm3
Melting point

356.7 °C
dehydrates at 100 °C

Boiling point

decomposes 400 °C

Solubility in water 730 g/L at 25 °C
Hazards
MSDS ICSC 1369
EU Index 024-004-00-7 (anhydrous)
024-004-01-4 (dihydrate)
EU classification Oxidant (O)
Carc. Cat. 2
Muta. Cat. 2
Repr. Cat. 2
Very toxic (T+)
Harmful (Xn)
Corrosive (C)
Dangerous for the environment (N)
R-phrases R45, R46, R60, R61, R8, R21, R25, R26, R34, R42/43, R48/23, R50/53,
S-phrases S53, S45, S60, S61
NFPA 704
NFPA 704.svg
0
3
0
OX
LD50 50 mg/kg
Related compounds
Other anions Sodium chromate
Sodium molybdate
Sodium tungstate
Other cations Potassium dichromate
Ammonium dichromate
 YesY dichromate (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Sodium dichromate is the chemical compound with the formula Na2Cr2O7. Usually, however, the salt is handled as its dihydrate Na2Cr2O7·2H2O. Virtually all chromium ore is processed via conversion to sodium dichromate. In this way, many millions of kilograms of sodium dichromate are produced annually.[1] In terms of reactivity and appearance, sodium dichromate and potassium dichromate are very similar. The sodium salt is, however, around twenty times more soluble in water than the potassium salt (49 g/L at 0 °C) and its equivalent weight is also lower, which is often desirable.[2]

Contents

Production

Sodium dichromate is generated on a large scale from ores containing chromium(III) oxides. The ore is fused with a base, typically sodium carbonate, at around 1000 °C in the presence of air (source of oxygen):

2 Cr2O3 + 4 Na2CO3 + 3 O2 → 4 Na2CrO4 + 4 CO2

This step solubilizes the chromium and allows it to be extracted into hot water. At this stage, other components of the ore such as aluminium and iron compounds, are poorly soluble. Acidification of the resulting aqueous extract with sulfuric acid or carbon dioxide affords the dichromate, which is isolated at the dihydrate by crystallization. Since chromium(VI) is toxic, especially as the dust, such factories are subject to stringent regulations. For example, effluent from such refineries is treated with reducing agents to return any chromium(VI) to chromium(III), which is less threatening to the environment.[1] A variety of hydrates of this salt are known, ranging from the decahydrate below 19.5 °C (CAS# 13517-17-4) as well as hexa-, tetra-, and dihydrates. Above 62 °C, these salts lose water spontaneously to give the anhydrous material.

Reactions

Dichromate and chromate salts are oxidizing agents. For the tanning of leather, sodium dichromate is first reduced with sulfur dioxide.

In the area of organic synthesis,[2] this compound oxidizes benzylic and allylic C-H bonds to carbonyl derivatives. For example, 2,4,6-trinitrotoluene is oxidized to the corresponding carboxylic acid.[3]. Similarly, 2,3-dimethylnaphthalene is oxidized by Na2Cr2O7 to 2,3-naphthalenedicarboxylic acid.[4]

Secondary alcohols are oxidized to the corresponding ketone, e.g. menthol to menthone;[5] dihydrocholesterol to cholestanone:[6]

3 R2CHOH + Cr2O72- + 2 H+ → 3 R2C=O + Cr2O3 + 4 H2O

Relative to the potassium salt, the main advantage of sodium dichromate is its greater solubility in water and polar solvents like acetic acid.

Safety

Like all hexavalent chromium compounds, sodium dichromate is considered hazardous. It is also a known carcinogen[7].

References

  1. ^ a b Gerd Anger, Jost Halstenberg, Klaus Hochgeschwender, Christoph Scherhag, Ulrich Korallus, Herbert Knopf, Peter Schmidt, Manfred Ohlinger, "Chromium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.
  2. ^ a b Freeman, F. "Sodium Dichromate" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.
  3. ^ Clarke, H. T.; Hartman, W. W. (1941), "2,4,6-Trinitrobenzoic Acid", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0543 ; Coll. Vol. 1: 543 
  4. ^ Friedman, L. (1973), "2,3-Naphthalenedicarboxylic Acid", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5p0810 ; Coll. Vol. 5: 810 
  5. ^ L. T. Sandborn (1929), "l-Menthone", Org. Synth. 9: 59, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0340 ; Coll. Vol. 1: 340 
  6. ^ W. F. Bruce (1941), "Cholestanone", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv2p0139 ; Coll. Vol. 2: 139 
  7. ^ ILO 1369 - Sodium Dichromate [1]

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • sodium dichromate — n. a red, crystalline salt, Na2Cr2O7, used as an oxidizing agent, corrosion inhibitor, antiseptic, etc …   English World dictionary

  • sodium dichromate — noun a red orange salt used as a mordant • Syn: ↑sodium bichromate • Hypernyms: ↑mordant, ↑salt * * * sodium dichromate, an orange crystalline salt, used as an oxidizing agent, as a reagent, and as an antiseptic. Formula: Na2Cr2O7•2H2O …   Useful english dictionary

  • sodium dichromate — natrio dichromatas statusas T sritis chemija formulė Na₂Cr₂O₇ atitikmenys: angl. sodium dichromate rus. натрий двухромовокислый; натрия бихромат; натрия дихромат ryšiai: sinonimas – dinatrio μ okso( )heksaoksodichromatas …   Chemijos terminų aiškinamasis žodynas

  • sodium dichromate — Chem. a red or orange crystalline, water soluble solid, Na2Cr2O7·2H2O, used as an oxidizing agent in the manufacture of dyes and inks, as a corrosion inhibitor, a mordant, a laboratory reagent, in the tanning of leather, and in electroplating.… …   Universalium

  • sodium dichromate — /soʊdiəm daɪˈkroʊmeɪt/ (say sohdeeuhm duy krohmayt) noun Chemistry a red, water soluble, crystalline salt, Na2Cr2O7.2H2O, used as an oxidising agent, in electroplating, and in the manufacture of inks and dyes. Also, sodium bichromate …   Australian English dictionary

  • sodium dichromate — so′dium dichro′mate n. chem. a red or orange, crystalline, water soluble solid, Na2Cr2O7∙2H2O, used as an oxidizing agent in the manufacture of dyes and inks and in electroplating • Etymology: 1900–05 …   From formal English to slang

  • Sodium sulfate — Other names …   Wikipedia

  • Sodium chromate — Sodium chromate …   Wikipedia

  • sodium bichromate — noun a red orange salt used as a mordant • Syn: ↑sodium dichromate • Hypernyms: ↑mordant, ↑salt * * * noun : sodium dichromate * * * Chem. See sodium dichromat …   Useful english dictionary

  • sodium bichromate — Chem. See sodium dichromate. * * * …   Universalium