Chemical Properties
Sodium sulfite,Na2S03, is a white,water-soluble, crystalline solid with a sulfurous, salty taste. It decomposes when heated. Sodium sulfite is used as a source of sulfite,as a chemical intermediate and food preservative, in medicine and paper manufacturing, in photographic developing, and as a bleaching agent in the textile industry. Most boiler operators use sodium sulfite for chemicals cavenging of oxygen in the feedwater. Because it decomposes into acidic gases at the high temperatures that accompany high pressures, sodium sulfite should not be used for this purpose at pressures above 122atm (12.4MPa,or 1.8 ksi).
Definition
ChEBI: An inorganic sodium salt having sulfite as the counterion.
General Description
White odorless powder. Density 2.633 g/cm3. Moderately toxic. Sinks in water and dissolves slowly. Also transported as a heptahydrate Na2SO3.7H2O.
Reactivity Profile
SODIUM SULFITE(7757-83-7) is a reducing agent, particularly under basic conditions. Reacts with oxidizing agents such as peroxides, epoxides, oxoacids. Emits toxic fumes of sodium oxide and oxides of sulfur if heated to decomposition [Lewis, 3rd ed., 1993, p. 1174].
Air & Water Reactions
Soluble in water. Reacts with hot water, steam or acids to produce corrosive material.
Hazard
Use prohibited in meats and other sources
of Vitamin B
1
Health Hazard
When ingested, solutions cause gastric irritation by the liberation of sulfurous acid. Because of rapid oxidation to sulfate, sulfites are well tolerated until large doses are reached; then violent colic and diarrhea, circulatory disturbances, central nervous depression, and death can occur.
Potential Exposure
Sodium sulfite is used as a reducing agent; in boiler water treatment; food applications; in photographic developers and fixers; in bleaching of wool, paper, textiles, straw and silk; manufacture of dyes; dechlorination; preservation of meat, fruit and egg products; silvering of glass.
Fire Hazard
Literature sources indicate that this compound is noncombustible.
First aid
Move victim to fresh air. Call 911 or emergency medical service. Give artificial respiration if victim is not breathing. Do not use mouth-to-mouth method if victim ingested or inhaled the substance; give artificial respiration with the aid of a pocket mask equipped with a one-way valve or other proper respiratory medical device. Administer oxygen if breathing is difficult. Remove and isolate contaminated clothing and shoes. In case of contact with substance, immediately flush skin or eyes with running water for at least 20 minutes. For minor skin contact, avoid spreading material on unaffected skin. Keep victim warm and quiet. Effects of exposure (inhalation, ingestion, or skin contact) to substance may be delayed. Ensure that medical personnel are aware of the material(s) involved and take precautions to protect themselves. Medical observation is recommended for 24 to 48 hours after breathing overexposure, as pulmonary edema may be delayed. As first aid for pulmonary edema, a doctor or authorized paramedic may consider administering a drug or other inhalation therapy.
Shipping
UN3260 Corrosive solid, acidic, inorganic, n.o.s., Hazard class: 8; Labels: 8-Corrosive material.
Incompatibilities
A strong reducing agent. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases. Reacts with strong acids producing toxic sulfur dioxide.
Production Methods
Sodium bisulfite is prepared by reacting sulfur dioxide gas with
sodium hydroxide solution. The solid material is obtained by
evaporation of water. Further neutralization with sodium hydroxide
while keeping the temperature above 33.6°C leads to crystallization
of the anhydrous sodium sulfite (below this temperature the
heptahydrate form is obtained).
Pharmaceutical Applications
Sodium sulfite is used as an antioxidant in applications similar to
those for sodium metabisulfite. It is also an effective antimicrobial
preservative, particularly against fungi at low pH (0.1% w/v of
sodium sulfite is used). Sodium sulfite is used in cosmetics, food
products, and pharmaceutical applications such as parenteral
formulations, inhalations, oral formulations, and topical preparations.
Safety
Sodium sulfite is widely used in food and pharmaceutical
applications as an antioxidant. It is generally regarded as relatively
nontoxic and nonirritant when used as an excipient. However,
contact dermatitis and hypersensitivity reactions have been
reported. The acceptable daily intake for sodium sulfite has
been set at up to 350 mg/kg body-weight daily.
LD50 (mouse, IP): 0.950 g/kg
LD50 (mouse, IV): 0.130 g/kg
LD50 (mouse, oral): 0.820 g/kg
LD50 (rabbit, IV): 0.065 g/kg
LD50 (rabbit, oral): 1.181 g/kg
LD50 (rat, IV): 0.115 g/kg
Environmental Fate
Because sodium sulfite is a solid powder that is generally sold
as a ‘food grade’ substance, there is very little information
available on the environmental fate of sodium sulfite. It has
a molecular weight of 126.04 g mol-1. At 20°C, the solubility
in water is 250 000 mg l-1, and as it is an inorganic salt the
vapor is negligible (USEPA, 2011). The log octanol/water
partition coefficient is estimated to be 7.78.
If released into water or soil, sodium sulfite would most
likely be oxidized to sulfate, which would then be available for
use by bacteria or plants as a nutrient.
The US Environmental Protection Agency (EPA) EPI Suite
computer program (USEPA, 2011) estimates both a bioconcentration
factor and a bioaccumulation factor of 0.89. These
factors are less than one, meaning that bioconcentration and/or
bioaccumulation of sodium sulfite would be virtually negligible
and therefore would not cause any adverse effects to fish and
wildlife.
storage
Sodium sulfite should be stored in a well-closed container in a cool,
dry, place. In solution, sodium sulfite is slowly oxidized to sulfate by dissolved oxygen; strong acids lead to formation of sulfurous acid/
sulfur dioxide. On heating, sodium sulfite decomposes liberating
sulfur oxides.
Purification Methods
Crystallise the sulfite from warm water (0.5mL/g) by cooling to 0o. Also purify it by repeated crystallisation from deoxygenated water inside a glove-box, and finally drying it under vacuum. [Rhee & Dasgupta J Phys Chem 89 1799 1985.]
Toxicity evaluation
The exact mechanism of toxicity has not been elucidated,
although there is a lot of information on how sulfur-based
compounds are detoxified by the liver. Sodium sulfite is
a mild reducing agent that would most likely cause burning or
irritation at the site of exposure or application by altering
oxidation–reduction potential and pH.
Sulfites are used widely as antioxidants to keep foods from
prematurely spoiling and to keep them looking ‘fresh’ by preventing
oxidation and subsequent ‘browning.’ Many people,
however, are ‘sulfite sensitive.’ After ingestion of food or
beverages containing sulfite, these people may have allergictype
reactions such as asthmatic wheezing, hypotension,
tingling sensations, and flushing of the skin. The mechanism is
unclear but probably has to do with an individual-specific
chemical stimulation of the immune system, which in turn
releases small amounts of vasoactive substances.
Regulatory Status
GRAS listed. Accepted for use as a food additive in Europe.
Included in FDA Inactive Ingredients Database (epidural, IM, IV,
and SC injections; inhalation solution; ophthalmic solutions; oral
syrups and suspensions; otic solutions; topical creams and emulsions).
Included in nonparenteral medicines licensed in the UK.
