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Sodium bisulfite

Sodium bisulfite
Sodium bisulfite.png
Ball-and-stick model of a bisulfite anion (left) and a sodium cation (right)
Names
IUPAC name
Sodium hydrogen sulfite
Other names
E222
Identifiers
7631-90-5 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:26709 YesY
ChEMBL ChEMBL1689285 N
ChemSpider 571016 YesY
ECHA InfoCard 100.028.680
E number E222 (preservatives)
PubChem 23665763
RTECS number VZ2000000
Properties
NaHSO3
Molar mass 104.061 g/mol
Appearance White solid
Odor slight sulfurous odor
Density 1.48 g/cm3
Melting point 150 °C (302 °F; 423 K)
Boiling point 315 °C (599 °F; 588 K)
42 g/100 mL
1.526
Hazards
Harmful (Xn)
R-phrases R22 R31
S-phrases (S2), S25, S46
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)
 2340 mg/kg (oral, rat)
US health exposure limits (NIOSH):
PEL (Permissible)
 none
REL (Recommended)
 TWA 5 mg/m3
IDLH (Immediate danger)
 N.D.
Related compounds
Other anions
Sodium sulfite
Sodium metabisulfite
Other cations
Potassium bisulfite
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Sodium bisulfite (sodium hydrogen sulfite) is a chemical compound with the chemical formula NaHSO3. Sodium bisulfite is a food additive with E number E222. This salt of bisulfite can be prepared by bubbling sulfur dioxide in a solution of sodium carbonate in water. Sodium bisulfite in contact with chlorine bleach (aqueous solution of sodium hypochlorite) will generate heat and form sodium bisulfate and sodium chloride.

Sodium bisulfite can be prepared by bubbling excess sulfur dioxide through a solution of suitable base, such as sodium hydroxide or sodium bicarbonate.

Sodium bisulfite is a weakly acidic species with a pKa of 6.97. Its conjugate base is the sulfite ion, SO32−:

The theoretical fully protonated species is sulfurous acid (H2SO3); however this does not exist in solution and treatment of sodium bisulfite with acids will result in decomposition with telltale effervescence of sulfur dioxide.

In organic chemistry sodium bisulfite has several uses. It forms a bisulfite adduct with aldehyde groups and with certain cyclic ketones to a sulfonic acid.

This reaction has limited synthetic value(s) but it is used in purification procedures. Contaminated aldehydes in a solution precipitate as the bisulfite adduct which can be isolated by filtration. The reverse reaction takes place in presence of a base such as sodium bicarbonate or sodium hydroxide and the bisulfite is liberated as sulfur dioxide.


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