Carbon disulfide

Carbon disulfide is a colorless, volatile liquid with the formula CS₂. The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical solvent. It has an "ether-like" odor, but commercial samples are typically contaminated with foul-smelling impurities.^[1]

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Occurrence and manufacture

Small amounts of carbon disulfide are released by volcanic eruptions and marshes. CS₂ once was manufactured by combining carbon (or coke) and sulfur at high temperatures. A lower temperature reaction, requiring only 600 °C utilizes natural gas as the carbon source in the presence of kieselgel or alumina catalysts:^[1]

CH₄ + 1/2 S₈ → CS₂ + 2 H₂S

The reaction is analogous to the combustion of methane. Although it is structurally similar to carbon dioxide, CS₂ is highly flammable:

CS₂ + 3 O₂ → CO₂ + 2 SO₂

Reactions

Compared to CO₂, CS₂ is more reactive toward nucleophiles and more easily reduced. These differences in reactivity can be attributed to the weaker π donor-ability of the sulfido centers, which renders the carbon more electrophilic. It is widely used in the synthesis of organosulfur compounds such as Metham sodium, a soil fumigant.

Addition of nucleophiles

Nucleophiles such as amines afford dithiocarbamates:

2R₂NH + CS₂ → [R₂NH₂⁺][R₂NCS₂^-]

Xanthates form similarly from alkoxides:

RONa + CS₂ → [Na⁺][ROCS₂^-]

This reaction is the basis of the manufacture of regenerated cellulose, the main ingredient of viscose rayon and cellophane. Both xanthates and the related thioxanthates (derived from treatment of CS₂ with sodium thiolates) are used as flotation agents in mineral processing. Sodium sulfide affords trithiocarbonate:

Na₂S + CS₂ → [Na⁺]₂[CS₃^2-]

Reduction

Sodium reduces CS₂ to give the heterocycle "dmit^2-":^[2]

3 CS₂ + 4 Na → Na₂C₃S₅ + Na₂S

Direct electrochemical reduction affords the tetrathiooxalate anion:^[3]

2 CS₂ + 2e^- → C₂S₄^2-

Chlorination

Chlorination of CS₂ is the principal route to carbon tetrachloride:^[1]

CS₂ + 3 Cl₂ → CCl₄ + S₂Cl₂

This conversion proceeds via the intermediacy of thiophosgene, CSCl₂.

Coordination chemistry

CS₂ is a ligand for many metal complexes, forming pi complexes. One example is CpCo(η²-CS₂)(PMe₃).^[4]

Commercial Availability

CS₂, being highly flammable and having one of the lowest autoignition temperatures, cannot be transported easily using commercial means. Worldwide exports of this chemical are negligible.

Pressurized Liquid Nitrogen Based Sample

Johnson Mathey's sister company Alfa Aesar was the first company to introduce carbon disulfide in the form of pressurized bottle containing a solution of pressurized nitrogen, coupling agent, stablizer, and carbon disulfide, with an active carbon disulfide content of 85%. Dilution with nitrogen rendered contents inflammable. In 2007 Alfa Aesar stopped selling carbon disulfide samples.

Health effects

At very high levels, carbon disulfide may be life-threatening because it affects the nervous system. Significant safety data come from the viscose rayon Industry, where both carbon disulfide as well as small amounts of H₂S may be present.

References