Chemical Properties
Sulfur dioxide is a colorless gas. It is stable, and non-corrosive when dry to common
materials except zinc. Sulfur dioxide is corrosive when wet and incompatible with strong
reducing or oxidizing agents, moisture, zinc, and its alloys. Sulfur dioxide has a large
number of industrial applications. For instance, sulfur dioxide is used in the manufacture
of sodium sulfi te, sulfuric acid, sulfuryl chloride, thionyl chloride, organic sulfonate,extensively as a bleaching agent, particularly in the bleaching of beet sugar, fl our, straw,
textiles, and wood pulp. Sulfur dioxide has industrial utility in the tanning of leather, in
brewing and preserving. Sulfur dioxide is a colorless gas with a characteristic and strong
suffocating odor.
Sulfur dioxide gas is released primarily from the combustion of fossil fuels (75%–85% of
the industrial sources), the smelting of sulfi de ores, volcanic emissions, and several other
natural sources. It is a US EPA priority air pollutant, but has many industrial and agricultural
uses. It is sometimes added as a warning marker and fi re retardant to liquid grain
fumigants.
Hazard
Toxic by inhalation, strong irritant to eyes
and mucous membranes, especially under pressure.
Dangerous air contaminant and constituent of smog.
Not permitted in meats and other sources of vitamin
B1. U.S. atmospheric standard 0.140 ppm. Pulmonary
function inhibitor and lower respiratory
tract irritant. Questionable carcinogen.
Reactivity Profile
SULFUR DIOXIDE is acidic. Reacts exothermically with bases such as amines, amides, metal oxides, and hydroxides. Frequently used as a reducing agent although SULFUR DIOXIDE is not a powerful one. Acts as a reducing bleach to decolorize many materials. Can act as an oxidizing agent. Supports combustion of powdered aluminum [Mellor 5:209-212 1946-47]. Reacts explosively with fluorine [Mellor 2:1 1946-47]. Supports burning of manganese [Mellor 12:187 1946-47]. Readily liquefied by compression. Contact between the liquid and water may result in vigorous or violent boiling and extremely rapid vaporization. If the water is hot an explosion may occur. Pressures may build to dangerous levels if the liquid contacts water in a closed container [Handling Chemicals Safely 1980]. Supports incandescent combustion of monocesium acetylide, monopotassium acetylide, cesium oxide, iron(II) oxide, tin oxide, and lead oxide [Mellor]. Ethylene oxide and SO2 can react violently in pyridine solution with pressurization if ethylene oxide is in excess (Nolan, 1983, Case History 51).
Air & Water Reactions
Dissolves in water to form sulfurous acid, a corrosive liquid. Moist sulfur dioxide is very corrosive due to the slow formation of sulfuric acid [Handling Chemicals Safely 1980 p. 876].
Health Hazard
Exposures to sulfur dioxide cause adverse health effects to users and occupational workers.
The gaseous sulfur dioxide is particularly irritating to the mucous membranes of the
upper respiratory tract. Chronic exposure to sulfur dioxide produces dryness of the throat,
cough, rhinitis, conjunctivitis, corneal burns, and corneal opacity. Acute exposure to high
concentrations of sulfur dioxide may also result in death due to asphyxia. By contrast,
chronic exposures to sulfur dioxide lead to nasopharyngitis, fatigue, and disturbances of
the pulmonary function. Animals exposed to chronic doses of sulfur dioxide have shown
thickening of the mucous layer in the trachea and also hypertrophy of goblet cells and
mucous glands resembling the pathology of chronic bronchitis. It has been found that
penetration of sulfur dioxide into the lungs is greater during mouth breathing than during
nose breathing. In fact, an increase in the fl ow rate of the gas would markedly increase the
penetration. Human subjects exposed for very brief periods to sulfur dioxide also showed
alterations in pulmonary mechanics. More information on the adverse effects of sulfur
dioxide and the manner of its potentiation in association with other chemicals may be
found in literature.
Health Hazard
SULFUR DIOXIDE may cause death or permanent injury after very short exposure to small quantities. 1,000 ppm causes death in from 10 minutes to several hours by respiratory depression. It is an eye and respiratory tract irritant. Persons with asthma, subnormal pulmonary functions or cardiovascular disease are at a greater risk.
Potential Exposure
Sulfur dioxide is used in the manufacture of sodium sulfite, sulfuric acid; sulfuryl chloride; thionyl chloride; organic sulfonates; disinfectants, fumigants, glass, wine, ice, industrial and edible protein; and vapor pressure thermometers. It is also used in the bleaching of beet sugar, flour, fruit, gelatin, glue, grain, oil, straw, textiles, wicker ware; wood pulp; and wool; in the tanning of leather; in brewing and preserving; and in the refrigeration industry. Exposure may also occur in various other industrial processes as it is a by-product of ore smelting, coal and fuel oil combustion; paper manufacturing and petroleum refining.
Fire Hazard
Containers may explode in heat of fire or they may rupture and release irritating toxic sulfur dioxide. Sulfur dioxide has explosive properties when SULFUR DIOXIDE comes in contact with sodium hydride; potassium chlorate at elevated temperatures; ethanol; ether; zinc ethylsulfurinate at very cool temperatures (-15C); fluorine; chlorine trifluoride and chlorates. SULFUR DIOXIDE will react with water or steam to produce toxic and corrosive fumes. When the liquid is heated SULFUR DIOXIDE may release irritating, toxic sulfur dioxide gas. Avoid ammonia, monocesium or monopotassium acetylide; dicesium monoxide; iron (II) oxide; tin oxide; lead (IV) oxide; chromium; manganese; molten sodium, powder aluminum and rubidium. Sulfur dioxide has explosive properties when SULFUR DIOXIDE comes in contact with sodium hydride; potassium chlorate at elevated temperatures; ethanol; ether; zinc ethylsulfurinate at very cool temperatures (-15C); fluorine; chlorine trifluoride and chlorates. SULFUR DIOXIDE will react with water or steam to produce toxic and corrosive fumes. Hazardous polymerization may not occur.
First aid
If this chemical gets into the eyes, remove any contact lenses at once and irrigate immediately for at least 15 minutes, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts the skin, remove contaminated clothing and wash immediately with soap and water. Seek medical attention immediately. If this chemical has been inhaled, remove from exposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if heart action has stopped. Transfer promptly to a medical facility. When this chemical has been swallowed, get medical attention. 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. If frostbite has occurred, seek medical attention immediately; do NOT rub the affected areas or flush them with water. In order to prevent further tissue damage, do NOT attempt to remove frozen clothing from frostbitten areas. If frostbite has NOT occurred, immediately and thoroughly wash contaminated skin with soap and water.
Shipping
UN1079 Sulfur dioxide, Hazard Class: 2.3; Labels: 2.3-Poisonous gas, 8-Corrosive material, Inhalation Hazard Zone C. Cylinders must be transported in a secure upright position, in a well-ventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner
Incompatibilities
Reacts with water to form sulfurous acid, a medium-strong acid. Reacts violently with ammonia, acrolein, acetylene; alkali metals; such as sodium, potassium, magnesium, and zinc; chlorine, ethylene oxide; amines, butadiene. Attacks many metals including aluminum, iron, steel, brass, copper, nickel; especially in presence of water or steam. Incompatible with halogens. Attacks plastics, rubber and coatings.
Description
Sulfur dioxide is a compound formed by the
combination of the elements sulfur and oxygen.
On a weight basis, the proportion of the elements is about I part sulfur to I part oxygen, or
more exactly, 50.05 percent to 49.95 percent,
respectively. At standard conditions of temperature and pressure, sulfur dioxide is a colorless gas with a characteristic pungent odor. It
may be cooled and compressed to a colorless
liquid, which, at one atmosphere pressure, boils
at 14°F (10.0°C) and freezes at -104.6°F (-75.9°C). Sulfur dioxide liquid is heavier than
water, and has a specific gravity of 1.436 at
32°F (0°C). As a gas, it is more than twice as
heavy as air; its relative density is 2.2638 at
atmospheric pressure and 32°F (0°C).
Sulfur dioxide is not flammable or explosive
in either the gaseous or liquid state. It is a relatively stable chemical. Temperatures above
3632°F (2000°C) are required to bring about
detectable decomposition of sulfur dioxide. Dry
sulfur dioxide (less than 100 ppm water) is not
corrosive to ordinary metals. However, in the
presence of even small amounts of water, sulfur
dioxide becomes corrosive to most metals, with
exceptions including lead, Type 316 stainless
steel, and certain alloys. Glass and certain plastics are also resistant to moist sulfur dioxide.
Waste Disposal
Return refillable compressed gas cylinders to supplier. Pass into soda ash solution, then add calcium hypochlorite; neutralize and flush to sewer with water (A-38).
Occurrence
Reported found in orange juice, grapefruit juice, onion, boiled and cooked beef,starfruit and weinbrand brandy.
Definition
ChEBI: Sulfur dioxide is a sulfur oxide. It has a role as a food bleaching agent, a refrigerant and an Escherichia coli metabolite.
Preparation
Sulfur dioxide usually is prepared industrially by the burning in air or oxygen of sulfur or such compounds of sulfur as iron pyrite or copper pyrite. Large quantities of sulfur dioxide are formed in the combustion of sulfur-containing fuels. In the laboratory, the gas may be prepared by reducing sulfuric acid (H2SO4) to sulfurous acid (H2SO3), which decomposes into water and sulfur dioxide, or by treating sulfites (salts of sulfurous acid) with strong acids, such as hydrochloric acid, again forming sulfurous acid.
Production Methods
Sulfur dioxide can be made by burning sulfur, or by roasting sulfide
ores such as pyrites, sphalerite, and cinnabar.
Aroma threshold values
Recognition: 50 to 100 ppm
Purification Methods
Dry it by bubbling through conc H2SO4 and by passage over P2O5, then through a glass-wool plug. Freeze it with liquid air and pump it to a high vacuum to remove dissolved gases. It is easily liquefied by compression (2.5atmospheres at 15o), or by passing it through a glass spiral column in a freezing mixture of ice and salt. It is a colourless liquid with a density of 1.434 at 0o, which on rapid evaporation forms a snow white solid. It could be used as a solvent in certain reactions. HARMFUL SUFFOCATING VAPOURS.
Flammability and Explosibility
Sulfur dioxide is a noncombustible substance (NFPA rating = 0).
Pharmaceutical Applications
Sulfur dioxide is used as an antioxidant for pharmaceutical
injections. It is also used as a preservative and antioxidant in the
food and cosmetics industries.
Materials Uses
Service conditions must be defined to properly
specifY materials of construction for handling
sulfur dioxide. It is customary, however, to use
carbon steel for dry sulfur dioxide at ambient
temperatures. Reference should be made to the
latest edition of the ASME Code, Section VIlI,
Division I for vessels, and to the latest edition of ANSI/ASME 831.3, Chemical Plant and
Petroleum Refinery Piping for piping specifications.
Moist sulfur dioxide is corrosive to carbon
steel; therefore, other materials of construction
have to be considered in this case. A source of
data on the corrosivity of sulfur dioxide to various materials is the Corrosion Data Survey,
published by the National Association of Corrosion Engineers; suppliers of liquid sulfur dioxide are another source.
Safety
Sulfur dioxide is used in food and pharmaceutical products.
However, in large amounts, sulfur dioxide gas is highly irritant to
the eyes, skin, and mucous membranes. Inhalation can lead to
severe irritation of the respiratory tract. Direct contact with the
liquid form may cause frostbite. Sulfur dioxide and sulfites may also
cause allergic reactions and asthma.
Physiological effects
Exposure to sulfur dioxide gas in low concentrations produces an irritating effect on the mucous membranes of the eyes, nose, throat, and
lungs due to the fonnation of sulfurous acid as
the gas comes in contact with the moisture on
these surfaces. The effects of sulfur dioxide
according to exposure pathway are as follows:
Inhalation
Acute exposure through inhalation may result
in dryness and irritation of the nose and throat,choking, sneezing, coughing, and bronchospasm. Severe overexposure may cause
death through a systemic acidosis, from pulmonary edema, or from respiratory arrest. Prolonged or repeated exposure may cause impaired lung function, bronchitis, hacking cough,
nasal irritation and discharge, increased fatigue,
alteration in the senses of taste and smell, and
longer duration of common colds. In extreme
cases, dental caries, loss of fillings, gum disorders, and the rapid and painless destruction of
teeth may result from repeated overexposure.
Skin contact
Liquid sulfur dioxide can cause frostbite and
skin burns, and it converts to sulfurous acid in
moist environments, which may cause skin irritation.
Eye contact
Corneal bums, opacification of the cornea,
and blindness may result if liquid sulfur dioxide
is splashed in the eyes. Sulfur dioxide can
penetrate the intact cornea and cause iritis.
Ingestion
Severe bums to the mouth, throat, and gastrointestinal system may occur.
Exposure limits
ACGIH recommends a Threshold Limit
Value-Time-Weighted Average (TLV-TWA)
of 2 ppm (5.2 mg/m3) for sulfur dioxide. The
TLV-TWA is the time-weighted average concentration for a normal 8-hour workday and a
40-hour workweek, to which nearly all workers
may be repeatedly exposed, day after day, without adverse effect. The ACGIH also recommends a Threshold Limit Value-Short Term
Exposure Limit (TLV-STEL) of 5 ppm (13
mg/m3) for sulfur dioxide. The TLV-STEL is
the 15-minute TWA exposure that should not be
exceeded at any time during a workday even if
the 8-hour TWA is within the TLV-TWA. Exposures above the TLV-TWA up to the STEL
should not be longer than 15 minutes and should
not occur more than 4 times per day. There
should be at least 60 minutes between successive exposures in this range.
OSHA lists an 8-hour Time-Weighted Average-Permissible Exposure Limit (TWA-PEL)
of 5 ppm (13 mg/m3) for sulfur dioxide. TWAPEL is the exposure limit that shall not be exceeded by the 8-hour TWAin any 8-hour work
shift of a 40-hour workweek.
Carcinogenicity
Sulfur dioxide may act as a cancer promoter. The mortality of
arsenic smelter workers was higher when they had also been
exposed to sulfur dioxide. In addition, rats exposed to
3.5 or 10 ppm of sulfur dioxide developed squamous cell
carcinomas from inhalation of benzo[a]pyrene, but neither compound alone produced carcinomas under the conditions
of this experiment.
Environmental Fate
Concentrations of sulfur dioxide as low as 1–2 ppm have been
reported to cause severe stress to green plants, and dissolved
sulfur dioxide can be toxic to aquatic life. Sulfur, however, is
the sixth most abundant element in living creatures, and is
important in the structure and synthesis of proteins and
kinetics of cellular components. For the most part, sulfur
dioxide and other sulfites are rapidly metabolized by living
organisms, which avoids cytotoxic effects. Sulfite metabolism pathways abound in plants and animals due to the ubiquity of
sulfur and its compounds. For example, in certain plants, it has
been shown that more than 80% of injected sulfite was
metabolized to sulfate within 3 h.
Sulfur dioxide and other sulfites are generally highly soluble
compounds that interact with the environment through a variety
of processes. The primary functions of sulfites are those of
reducing agents, which can remove dissolved oxygen from
waterways; in the air, this ismanifested in the oxidation of sulfur
dioxide to produce someinsoluble particulate sulfate salts as well
as sulfuric acid. In waterways, the reduction of dissolved oxygen
in turn generates a favorable environment for anaerobic bacteria,
disrupting the local microbiota. Decreases in dissolved oxygen
caused by the presence of sulfites – typically below 5 ppm dissolved
oxygen – can negatively affect fish and other organisms
present in polluted waterways. Another effect of sulfite contamination
of waterways is the production of hydrogen sulfide gas,
which is a by-product of sulfite-induced redox processes.
storage
Sulfur dioxide is noncorrosive and stable when dry. It is usually
stored under pressure in cylinders, and should be kept in a cool, dry,
well-ventilated area, away from flammable materials.
Toxicity evaluation
Conversion of sulfur dioxide to bisulfite in the airway may
initiate bronchoconstriction, due to the ability of the more
reactive bisulfite ion to disrupt disulfide bonds in tissue
proteins, resulting in tissue damage and an inflammatory
response. Sulfites and bisulfites can further inhibit DNA
synthesis and cause human lymphocyte aberrations and can
lead to crosslinking in proteins and nucleic acids in general,
as well as generate free radicals during their oxidation to
sulfates.
Bronchoconstriction and other related effects may be
mediated by release of leukotrienes, prostaglandins, or other
inflammatory factors. Some evidence suggests that free radicals
and oxidative stress may play a role, and that metabolites of
SO2 (especially sulfites) may be responsible for clastogenicity.
Sulfur dioxide–induced bronchoconstriction, occurs when
the gas acts on tracheobronchial receptors to induce a cholinergic
reflex. Inhaled sulfur dioxide elicited a stronger reaction
in sulfite oxidase–deficient rats than endogenously accumulated
sulfites and S-sulfocysteine (a reaction product of sulfite
with cysteine residues in proteins). Noncholinergic mechanisms
for sulfur dioxide–induced bronchoconstriction have
been demonstrated in humans as well. In one study, asthmatic
subjects were administered indomethacin – a prostaglandin
synthetase inhibitor – followed by challenge with sulfur
dioxide gas; a reduction in airway responsiveness was
observed.
Regulatory Status
GRAS listed. Accepted for use as a food additive in Europe.
Included in the FDA Inactive Ingredients Database (IV infusions;
injection solutions). Included in the Canadian List of Acceptable
Non-medicinal Ingredients.
GRADES AVAILABLE
Sulfur dioxide is available in technical and
food grades for use in both commercial and
industrial applications.
