Carbon disulfide (\(\text{CS}_2\)) is an industrial chemical compound widely used in global manufacturing processes. It has a long history as a solvent and remains commercially important today. Due to its unique chemical properties, it serves as an intermediate for creating many common materials. However, its volatile nature and toxicity require stringent controls and careful handling.
Chemical Structure and Physical Characteristics
Carbon disulfide has the chemical formula \(\text{CS}_2\), consisting of a single carbon atom double-bonded to two sulfur atoms in a linear structure. In its purest form, it is a clear, colorless liquid that is highly volatile and evaporates easily at room temperature. The pure compound has a pleasant, ether-like odor, but commercial-grade products contain sulfur impurities that give it a strong, disagreeable smell.
The compound is extremely flammable, boasting a very low flash point. Its vapors can form explosive mixtures with air across a wide concentration range. While most carbon disulfide is manufactured industrially by combining carbon sources like natural gas with sulfur at high temperatures, small quantities occur naturally. Natural sources include emissions from volcanic eruptions and biological processes within marshes.
Principal Industrial Uses
The most significant application of carbon disulfide is in the production of regenerated cellulose fibers, primarily viscose rayon, and transparent cellophane film. This manufacturing uses the viscose process, where cellulose reacts with \(\text{CS}_2\) to create a soluble derivative known as cellulose xanthate. The xanthate solution is then extruded into an acid bath, which regenerates the cellulose fiber or film while releasing the carbon disulfide.
Carbon disulfide is also a chemical building block for synthesizing other industrial compounds. Historically, it served as a feedstock for producing carbon tetrachloride, a now restricted solvent. It is still used in the rubber industry to create dithiocarbamates and xanthates, which act as accelerators in vulcanization and as flotation agents in mineral processing. In the past, it was used as an agricultural fumigant for stored grains, but this use has been largely discontinued due to safety concerns.
Effects on the Human Body
Exposure to carbon disulfide poses risks to human health, primarily through the inhalation of its vapors, though absorption can also occur through the skin. Acute exposure to high concentrations can cause immediate symptoms of central nervous system (CNS) depression, including nausea, headache, and dizziness. In severe cases, this leads to delirium, psychosis, and unconsciousness. These effects reflect the compound’s ability to rapidly cross the blood-brain barrier.
Chronic, long-term exposure to lower concentrations is associated with systemic damage, particularly to the nervous and cardiovascular systems. The neurotoxicity manifests as polyneuropathy, characterized by numbness and weakness, and can produce Parkinsonian symptoms like rigidity and tremors. This damage stems from \(\text{CS}_2\) reacting with amino groups in the body to form dithiocarbamates, which interfere with the metabolism of certain enzymes and vitamins.
In the cardiovascular system, chronic exposure increases the risk of coronary artery disease and cerebrovascular events, such as stroke. The compound accelerates arteriosclerosis by directly injuring vessel walls and disrupting lipid metabolism. \(\text{CS}_2\) exposure has also been linked to reproductive issues, including decreased sperm count in men and menstrual disturbances in women.
Environmental Behavior and Safety Regulations
When released into the environment, carbon disulfide is highly volatile and quickly evaporates into the atmosphere, which is the primary destination for industrial emissions. Once in the air, the compound has a relatively short atmospheric half-life, estimated to be around eight days, as it reacts with hydroxyl radicals. In water, it is considered non-persistent with an even shorter half-life, usually less than two days.
Due to its toxicity and extreme flammability, regulatory bodies have established strict limits to protect workers and the public. The Occupational Safety and Health Administration (OSHA) sets the Permissible Exposure Limit (PEL) for workers at 20 parts per million (ppm) averaged over an eight-hour workday. However, organizations like the National Institute for Occupational Safety and Health (NIOSH) and the American Conference of Governmental Industrial Hygienists (ACGIH) recommend a much lower limit of 1 ppm to prevent long-term neurological damage. Safe handling requires excellent ventilation and strict precautions to prevent ignition, since its vapors can be set alight by heat sources, including an ordinary light bulb.