General Description
Sodium dithionite is a whitish to light yellow crystalline solid having a sulfur dioxide-like odor. SODIUM HYDROSULFITE(7775-14-6) spontaneously heats on contact with air and moisture. This heat may be sufficient to ignite surrounding combustible materials. SODIUM HYDROSULFITE(7775-14-6) is soluble in water. Under prolonged exposure to fire or intense heat containers of this material may violently rupture. SODIUM HYDROSULFITE(7775-14-6) is used in dyeing and to bleach paper pulp.
Reactivity Profile
Inorganic reducing agents, such as SODIUM HYDROSULFITE, react with oxidizing agents to generate heat and products that may be flammable, combustible, or otherwise reactive. Their reactions with oxidizing agents may be violent. Sulfites and hydrosulfites (dithionites) can react explosively with strong oxidizing agents (sodium chlorite). Sulfites generate gaseous sulfur dioxide in contact with oxidizing acids and nonoxidizing acids.
Hazard
Fire risk in contact with moisture. To extin-
guish fires, flood the reacting mass with water.
Health Hazard
Fire will produce irritating, corrosive and/or toxic gases. Inhalation of decomposition products may cause severe injury or death. Contact with substance may cause severe burns to skin and eyes. Runoff from fire control may cause pollution.
Fire Hazard
Flammable/combustible material. May ignite on contact with moist air or moisture. May burn rapidly with flare-burning effect. Some react vigorously or explosively on contact with water. Some may decompose explosively when heated or involved in a fire. May re-ignite after fire is extinguished. Runoff may create fire or explosion hazard. Containers may explode when heated.
Chemical Properties
White solid
Definition
ChEBI: An inorganic sodium salt that is the disodium salt of dithionous acid.
Production Methods
An alternative route for dithionite production is the reduction of sodium bisulfite with sodium borohydride. Sodium borohydride is obtained by reacting boron trimethyl ester, B(OCH3)3, with sodium hydride, NaH. The resulting product is hydrolyzed with water, and methanol is evaporated. An alkaline, aqueous solution is obtained, containing about 12% NaBH4 and 40% NaOH. This solution is commercially available. Reaction to dithionite is made on-site by adding sulfur dioxide and some additional caustic soda. Storages, handling and mixing of sulfur dioxide and of the Borol® liquid are not everywhere cost competitive.
NaBH4+8NaOH+8SO2 → 4Na2S2O4+NaBO2+6H2O.
Flammability and Explosibility
Notclassified
storage
Sodium dithionite crystals are available in steel containers (1 or 2 tons) or in steel drums (200 kg). Because of the danger of spontaneous ignition in humid air, sodium dithionite must be stored under dry and cool conditions. The sites for the preparation of dithionite solutions must permit handling without risks, high humidity should be avoided and remote fire control should be available.
Commercial dithionite products are classified as self-igniting hazardous goods (Class 4.2, UN 1384). Local rules for transportation and storage must be obeyed.
Properties and Applications
|
INDEX/GRADE
|
SH-90
|
SH-88
|
SH-85
|
|
CONTENT
|
90%
|
88%
|
85%
|
|
Na
2
S
2
O
4
|
≥90%
|
≥88%
|
≥85%
|
|
Fe
|
≤20ppm
|
≤20ppm
|
≤20ppm
|
|
Zinc (Zn)
|
≤1ppm
|
≤1ppm
|
≤1ppm
|
|
Other heavy metal
（calculated as Pb）
|
≤1ppm
|
≤1ppm
|
≤1ppm
|
|
Water Insolubles
|
≤0.05%
|
≤0.05%
|
≤0.05%
|
|
Shelf Life(month)
|
12
|
12
|
12
|
