What Is Chlorobenzene?
Chlorobenzene is an aromatic halide in which one hydrogen in the benzene ring is replaced by chlorine.
Formerly called chlorobenzol, the name is still used in some cases. Chlorobenzene usually refers to the monosubstituted form, monochlorobenzene.
Chlorobenzene is a colorless liquid that is used in a wide variety of applications as a raw material intermediate for many organic compounds. It is mainly available as a raw material for diphenyl ether and chloronitrobenzene. It is a hazardous material classified as Class 4 Petroleum No. 2 under the Fire Service Act.
Uses of Chlorobenzene
Chlorobenzene is used as a raw material for organic compounds, pharmaceutical intermediates, and dye intermediates. Its reactivity in electrophilic substitution reactions is higher than that of benzene, making it useful as a raw material for many compounds.
Chlorobenzene was once used in large quantities as a raw material for DTT (dichlorodiphenyl trichloroethane), an organochlorine insecticide. In Japan, chlorobenzene was also actively used as a quarantine agent against lice and other insects, but DTT is now banned as an environmental pollutant.
Properties of Chlorobenzene
Chlorobenzene has a melting point of -45.2°C, a boiling point of 131°C, and a flash point of -19°C.
The half-lethal dose (LD50) is 2.9 g/kg, indicating low to moderate toxicity. The permissible exposure limit is 75 ppm (350 mg/m3) as an 8-hour weighted average for workers handling chlorobenzene.
Structure of Chlorobenzene
Chlorobenzene is an aryl halide. It has a molecular weight of 112.56, a chemical formula of C6H5Cl, a density of 1.1066 at 20°C, and a refractive index (nD) of 1.525.
Other Information on Chlorobenzene
1. Synthesis of Chlorobenzene
Chlorobenzene was first synthesized in 1851 by the reaction of phosphorus pentachloride and phenol; in 2014, chlorobenzene was reported to be present in Martian rocks.
It is now synthesized industrially by the substitution reaction of benzene with chlorine, using iron or iron chloride as a catalyst. As the chlorine substitution proceeds, dichlorobenzene may be produced, but it can be easily separated by cooling and recrystallization.
In the laboratory, it can be synthesized from aniline via benzenediazonium chloride using the Sandmeyer reaction. The Zandmeier reaction is a chemical reaction that uses copper salts as catalysts to obtain aryl halides from aromatic diazonium ions.
2. Reaction of Chlorobenzene
Nitration of chlorobenzene yields a mixture of 2-nitrochlorobenzene and 4-nitrochlorobenzene. These mononitrochlorobenzenes can be separated and used in nucleophilic substitution reactions for chloride, respectively. For example, from 2-nitro chlorobenzene, sodium hydroxide, sodium methoxide, sodium disulfide, and ammonia convert to 2-nitrophenol, 2-nitroanisole, bis(2-nitrophenyl)disulfide, and 2-nitroaniline. 4-nitrochlorobenzene is also similarly available.
One method of synthesizing phenol is to heat chlorobenzene, obtained by chlorinating benzene, with an aqueous solution of sodium hydroxide at high temperatures. In this reaction, sodium chloride is produced as a byproduct. However, the cumene process is often used for the industrial production of phenol.