What is Carbonyl Sulfide?

Carbonyl sulfide is a chemical compound of carbon, sulfur and oxygen, with each molecule containing one atom of each element. It has the chemical formula OCS but is commonly written COS. It is a colorless, flammable gas with an unpleasant sulfur odor. It has several industrial uses but is most commonly used as an intermediate compound in the making of organic herbicides.

The main uses of carbonyl sulfide are in the making of organic herbicides; in the manufacturing of other chemicals, such as organic sulfur compounds; and as a fumigant. It is a byproduct of the production of carbon disulfide. Carbonyl sulfide hydrolysis is a process that produces hydrogen sulfide, which is used to make sulfuric acid. It also is used in the production of a class of chemicals called alkyl carbonates.

Carbonyl sulfide is also found as an impurity in certain petroleum products, as well as refinery byproducts. It also is found in the exhaust gases of some fuels that contain sulfur. It occurs naturally as well, and it is released into the air by volcanoes, by marshes and in small amounts by many types of trees.

According to the World Wide Science Organization, carbonyl sulfide is a major source of atmospheric sulfur corrosion of metals such as copper and bronze, among others. It is considered by the United States Environmental Protection Agency (EPA) to be a pollutant under the Clean Air Act. According to the EPA, more than 16 million pounds (about 7.2 million kg) were released into the air in the U.S. in 1992, and information suggests that recent amounts might be higher.

Little research has been done on the direct toxicity of carbonyl sulfide to humans, but the EPA reports that in sufficient amounts, inhalation can cause narcotic effects in humans, and it is a skin and eye irritant. Other data suggests that high doses can cause convulsions and death because of respiratory failure. One study done on rats showed that exposure to carbonyl sulfide for a certain amount of time can be fatal to some of the animals.

Carbonyl sulfide is classified as a fire hazard and is very flammable and potentially explosive when exposed to flame. Acceptable fire suppression methods are carbon dioxide, water spray and dry chemical extinguishers. When burned, it emits high levels of carbon monoxide, a poisonous, colorless, odorless gas, as well as hydrogen sulfide, which also is a toxic material.

Once considered relatively harmless, carbonyl sulfide is now considered to be undesirable as a component of many fuels and refinery products and by products. Carbonyl sulfide removal is the subject of several patents. Many companies use the process to remove this noxious substance from products like propane and natural gas.