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Sodium dichromate

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Title: Sodium dichromate  
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Sodium dichromate

Sodium dichromate
Names
IUPAC name
Sodium dichromate
Other names
Chromic acid disodium salt
Identifiers
 Y
(dihydrate)
ChEBI  Y
ChemSpider  Y
EC number 234-190-3
Jmol-3D images Image
PubChem
RTECS number HX7750000
HX7750000 (dihydrate)
UN number 3288
Properties
Na2Cr2O7
Molar mass 261.97 g/mol (anhydrous)
298.00 g/mol (dihydrate)
Appearance bright red
Odor odorless
Density 2.52 g/cm3
Melting point 356.7 °C (674.1 °F; 629.8 K)
Boiling point 400 °C (752 °F; 673 K) decomposes
73 g/100 mL at 25 °C
Solubility in other solvents soluble in methanol, ethanol
1.661 (dihydrate)
Hazards
Safety data sheet ICSC 1369
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 R50/53,
S-phrases S53, S45, S60, S61
NFPA 704
0
3
0
OX
Lethal dose or concentration (LD, LC):
LD50 (Median dose)
50 mg/kg
Related compounds
Other anions
Sodium chromate
Sodium molybdate
Sodium tungstate
Other cations
Potassium dichromate
Ammonium dichromate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 Y  (: Y/N?)

Sodium dichromate is the 2NaCr2O7. Usually, however, the salt is handled as its dihydrate Na2Cr2O7·2H2O. Virtually all chromium ore is processed via conversion to sodium dichromate and virtually all compounds and materials based on chromium are prepared from this salt.[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 1
  • Reactions 2
  • Safety 3
  • References 4

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:

2 Na2CrO4 + 2 CO2 + H2O → Na2Cr2O7 + 2 NaHCO3

The dichromate is isolated as the dihydrate by crystallization. In this way, many millions of kilograms of sodium dichromate are produced annually.

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

  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. doi:10.1002/14356007.a07_067
  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. ^ a b Clarke, H. T.; Hartman, W. W. (1941). "2,4,6-Trinitrobenzoic Acid".  
  4. ^ Friedman, L. (1973). "2,3-Naphthalenedicarboxylic Acid".  
  5. ^ L. T. Sandborn (1929). -Menthone"l".  
  6. ^ W. F. Bruce (1941). "Cholestanone".  
  7. ^ Daintith, edited by John (2004). The Facts on File dictionary of organic chemistry. New York: Facts on file. p. 253.  
  8. ^ ILO 1369 - Sodium Dichromate

References

Like all hexavalent chromium compounds, sodium dichromate is considered hazardous. It is also a known carcinogen.[8]

Safety

When heated strongly, sodium dichromate decomposes to form sodium chromate, chromium(III) oxide and oxygen: 4 Na2Cr2O7 → 4 Na2CrO4 + 2 Cr2O3 + 3 O2 [3][7] Sodium Dichromate can be used in fluorene to fluorenone conversion.

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

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

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

[4] to 2,3-naphthalenedicarboxylic acid.7O2Cr2 Similarly, 2,3-dimethylnaphthalene is oxidized by Na[3] is oxidized to the corresponding carboxylic acid.2,4,6-trinitrotoluene derivatives. For example, carbonyl to C-H bonds allylic and benzylic this compound oxidizes [2]

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