Sodium sulfite

As a soluble sodium salt of sulfurous acid, Sodium sulfite (Na2SO3) shows blenching, de-sulfurizing and dechlorinating properties which is widely applied in various fields. It is primarily used in the pulp and papermaking industry due to its blenching activity. It can serve as a good additive to help preserve the fresh appearance of good products. Besides, sodium sulfite is a component in many pharmaceuticals, which is effective to maintain the potency and stability of drugs. It can also be applied for water treatment as an oxygen scavenger agent and applied in flue gas desulfurization and preservation of photo developer solutions, etc.

Sodium sulfite (Na2SO3) is an antioxidant, used as a preservative except with meats. It is also used for water treatment and in photography and textile bleaching.

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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).

Sodium sulfite occurs as an odorless white powder or hexagonal prisms. Note that the commercially available sodium sulfite is often presented as a white to tan- or pink-colored powder that would not conform to the pharmacopeial specification.

Sodium sulfite is a white crystalline solid

These white crystals were prepared by passing sulfurous gas over moist sodium carbonate. Sodium sulfite is soluble in water but less so in alcohol. It was used as a preservative for alkaline developers and as a hypo clearing agent in photographic printing.

sodium sulfite has anti-septic, preservative, and anti-oxidant properties. Sodium sulfite is also a topical anti-fungal.

Paper industry (semichemical pulp), reduc- ing agent (dyes), water treatment, photographic developer, food preservative and antioxidant, tex- tile bleaching (antichlor).

ChEBI: An inorganic sodium salt having sulfite as the counterion.

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).

sodium sulphite: A white solid,Na₂SO₃, existing in an anhydrousform (r.d. 2.63) and as a heptahydrate(r.d. 1.59). Sodium sulphite is solublein water and because it is readily oxidizedit is widely used as a convenientreducing agent. It is preparedby reacting sulphur dioxide with eithersodium carbonate or sodium hydroxide.Dilute mineral acids reversethis process and release sulphur dioxide.Sodium sulphite is used as ableaching agent in textiles and inpaper manufacture. Its use as an antioxidantin some canned foodstuffsgives rise to a slightly sulphuroussmell immediately on opening, butits use is prohibited in meats or foodsthat contain vitamin B1. Sodium sulphitesolutions are occasionally usedas biological preservatives.

White odorless powder. Density 2.633 g / cm3. Moderately toxic. Sinks in water and dissolves slowly. Also transported as a heptahydrate Na2SO3.7H2O.

Soluble in water. Reacts with hot water, steam or acids to produce corrosive material.

Sodium sulfite 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].

Use prohibited in meats and other sources of Vitamin B 1

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.

Literature sources indicate that Sodium sulfite is noncombustible.

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.

Sodium sulfite is mainly used in photographic developers, for fixing prints, bleaching textile fibers, as a reducer in manufacturing dyes, as a remover of Cl in bleached textiles and paper, and as a preservative in the food industry for meat, egg yolks, and so on.

Poison by intravenous and subcutaneous routes. Moderately toxic by ingestion and intraperitoneal routes. Human mutation data reported. When heated to decomposition it emits very toxic fumes of Na2O and SOx. A reducing agent. See also SULFITES.

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

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.

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.

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.

UN3260 Corrosive solid, acidic, inorganic, n.o.s., Hazard class: 8; Labels: 8-Corrosive material.

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.]

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.

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.

Sodium sulfite is incompatible with acids, oxidizing agents, many proteins, and vitamin B1.

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.