How is pure chloroform prepared? How is it oxidised in air or sunlight?
In industry, chloroform is produced by heating a mixture of chlorine or methane. At 400–500 °C, a free radical halogenation occurs, converting these precursors to progressively more chlorinated compounds:
CH4 + Cl2 → CH3Cl + HCl
CH3Cl + Cl2 → CH2Cl2 + HCl
CH2Cl2 + Cl2 → CHCl3 + HCl
Chloroform is slowly oxidised by air in the presence of light to an extremely poisonous gas, carbonyl chloride known as phosgene.