An Introduction to Carbon Disulfide
The compounds of carbon are very interesting to us because of its shell structure, its ability to form long chains of C-C bonding, and its affinity to bond with other small atoms like sulfur and oxygen. CS2 is an important compound of carbon worth studying due to its widespread industrial uses and its chemical properties. This one-carbon compound is used widely in the commercial manufacturing of cellulose rayon, carbon tetrachloride, or CCl4. This is also used for manufacturing various organic compounds. It is the distinct chemical and physical properties of CS2 that make these possible.
Properties of Carbon Disulfide
Pure CS2 is a colorless volatile liquid with a sweet ether-like smell. However, most of the commercially used and available carbon disulfide is impure and has a slight yellow color with a distinctively unpleasant odor. However, it can appear as a vapor since it has a relatively low boiling point of 46.2o C and a melting point of -111.5o C. The vapor is heavier than air with a vapor density of 2.67. This vapor can even be ignited by the heat of a light bulb and hence forms explosive mixtures easily.
CS2 is a highly flammable material with its flash point at -30oC. Hence CS2 is always stored under a layer of water. This is aided by the fact that it’s heavier than water and is not miscible in it. This is because CS2 is a nonpolar molecule and hence it cannot form hydrogen bonds with the water molecules. However, it has low reactivity at low temperatures.
Although it’s soluble in many organic solvents like benzene, chloroform, etc.
Manufacturing Carbon Disulfide
The commercial manufacture of Carbon disulfide began as early as 1880 using the reaction of sulfur with charcoal. Ethane, propane, and propane are also used for the production of Carbon disulfide.
As sulfur reacts with carbon around 750 – 900° C, then the charcoal-sulfur process takes place at this temperature. The temperature will help in converting the low reactive S2 to a more reactive S atom and these sulfur atoms combine with the carbon.
C+2S → CS2
This is an endothermic reaction and we obtain a liquid carbon disulfide. However, this is not an energy-efficient process as this requires a very high temperature. A better way is to combine methane with S8 is around 600o C.
2CH4 + S8 → 2CS2 + 4H2S
This is known as the Hydrocarbon-Sulphur process. The only drawback is of H2S production is a very bad odor.
Some Important Carbon Disulfide Reactions
A way to understand more about any compound is to study its reaction with different substances. Learning about carbon disulfide reactions will help us in understanding more about the compound. As mentioned earlier CS2 is a volatile liquid and reacts with air if left uncovered and produces toxic gas, sulfur dioxide.
CS2 + 3O2 → CO2 + 2SO2
Although non-reactive with water at room temperature at about 150oC, it will react with water to form carbon dioxide and hydrogen sulfide.
CS2 + 2H2O → CO2 + 2H2S
As mentioned earlier CS2 is used for the industrial production of CCl4. It is attained by reacting chlorine molecules with CS2 in the presence of a catalyst MnCl2/AlCl3.This is called chlorination.
CS2 + 3Cl2 → CCl4 + S2Cl2
Because CS2 has lone electron pairs on the sulfur atoms, CS2 acts as an electrophile. Hence carbon disulfide will react with nucleophiles like amines, to form complex compounds.
The reaction of amines with CS2 gives complex compound dithiocarbamates:
2R2NH + CS2 → [NH2+] [R2NCS2-]
The reaction of alkoxides with CS2 is one of the most important steps in the manufacturing of rayon.
RONa + CS2 → [Na+][ROCS2-]
As seen above, xanthates are formed from this reaction and this is important for the manufacture of regenerated cellulose, which is one of the main ingredients of rayon, viscose, cellophane, etc. The xanthates formed are also used in mineral processing.
These reactions are due to the structure and properties of CS2. The properties of CS2 help us to understand why certain reactions happen and vice versa.
1. Explain CS2 Structure
CS2 has a single carbon atom bonded with 2 sulfur atoms. Carbon has 4 valence electrons and sulfur has 6 valence electrons. Hence the structure of CS2 is S＝C＝S. Here a double bond between carbon and sulfur is required to fill the octet of carbon and hence we have an sp hybridization.
That means carbon disulfide has a linear structure. The carbon-sulfur bond length is 155.26pm.
Here sulfur is the more electronegative atom and hence there is a dipole moment in the direction of carbon to sulfur. However since CS2 has a linear structure in the AX2 geometry, two dipole moments are acting in the opposite direction from carbon to sulfur and hence they cancel out.
CS2 is a linear, nonpolar molecule with sp hybridization and bond length = 155.26pm.
2. What are the Uses of Carbon Disulfide?
CS2 is a versatile compound that is primarily used in the production of rayon and cellophane. It is also used in the manufacturing of carbon tetrachloride. CS2 is used for the cold vulcanization of rubber which is an essential process to give rubber its strength, elasticity, and resistance. It is an important additive for the manufacture of various organosulfur compounds such as xanthates etc. which are used in metallurgy. It’s also used as a flame lubricant in cutting glass and for generating petroleum catalysts. It’s also used as a solvent for phosphorus, sulfur, iodine, and fats.