Preparation
Laboratory Method
Aniline: Benzenediazonium chloride is obtained by replicating aniline with a mixture of NaNO2 and HCl at 0-5°C. Chlorobenzene is obtained by heating benzenediazonium chloride in the presence of cupreous chloride and hydrochloric acid.
C6H5NH2 + NH2 + HCl → C6H5 – N = N – Cl + 2H2O
The first reaction is called diazotization reaction and the second reaction is called sandmeyer reaction.
Read more about diazotization reaction and sandmeyer reaction
C6H5 – N = N – Cl → C6H5Cl + N2
Method of use
In a flask, dissolve 20 gram aniline in dilute HCl and cool it to 5°C. In this flask, NaNO2 solution is added, resulting in benzenediazonium chloride. Fill this solution in a separating funnel and drop it into a 500 ml flask.
In this flask, 10 gram cupreous chloride and 100 ml HCl solution water is kept on the heat. This flask is equipped with an ejector air capacitor. It mixes all the benzenediazonium chloride in the flask, then heats the flask at 60°C for half an hour on a water heater.
Benzene to Chlorobenzene
Chlorobenzene can be obtained from chlorination of benzene.
The chlorobenzene floats on the upper surface of the solution in the form of oily fluid. It is separated from the mixture by steam distillation method. The chlorobenzene thus obtained is dried by anhydrous CaCl2 and distilled at 132°C to obtain pure Chlorobenzene.
Phenol: Chlorobenzene is obtained by the reaction of phenol with phosphorus pentachloride.
C6H5OH + PCl5 → C6H5Cl + POCl3 + HCl
Benzene: Chlorobenzene can be obtained from chlorination of benzene.
C6H6 + Cl2 → C6H5Cl + HCl
Industrial Method
Chlorobenzene is obtained by mixing a mixture of benzene vapors, hydrogen chloride gas and oxygen (oxygen) at 250°C on a copper oxide catalyst. This reaction is used for the industrial manufacture of chlorobenzene. This method of industrial manufacture of chlorobenzene is called Rasching method.
2C6H6 + 2HCl + O2 → 2C6H5Cl + 2H2O
Physical properties
chlorobenzene is a colorless, volatile and aromatic liquid. Its boiling point is 132°C. It is insoluble in water and soluble in alcohol and ether. It is heavier than water and its relative density is 1.12.
Chemical properties
A chlorine atom in a molecule of chlorobenzene is attached to a benzene ring ie benzene nucleus. The chemical reactions of chlorobenzene can be divided into two parts.
- Reaction of Chlorine Atom
- Reaction of benzene nucleus
The reaction of Chlorine Atom
In these reactions, the chlorine atom is displaced by other atoms and groups. Due to the resonance in chlorobenzene, the chlorine atom is strongly attached to the benzene ring and its activation works.
In alkyl halide, the bond between the halogen atom and the alkyl group is relatively weak. Therefore, in alkyl halides, the halogen atom has high reactivity and can be easily displaced by many other atoms or groups.
Additionally, the chlorine atom in chlorobenzene contains partial positive charge. Whereas the chlorine atom in ethyl chloride is partially negative. Therefore, chlorine atom is not easily released as chloride atom chloride ion (Cl–) upon invasion of a nucleic lubricating reagent. Therefore, chlorobenzene has low reactivity to chlorine.
The major reactions of chlorobenzene in which the chlorine atom participates.
Is the following.
Reaction with NaOH: phenol is obtained by heating chlorobenzene with aqueous NaOH at about 300°C.
C6H5Cl + NaOH → C6H5OH + NaCl
Reaction with Ammonia: Aniline is obtained by heating chlorobenzene with ammonia at high pressure and around 250°C in the presence of Cu2O.
C6H5Cl + NH3 → C6H5NH2 + HCl
Aniline is also obtained when chlorobenzene is reacted with NaNH2 or KNH2 in a fluid ammonia solution.
C6H5Cl + NaNH2 → C6H5NH2 + NaCl
Reaction with cuprous cyanide: Phenyl cyanide (benzonitrile) is obtained by heating chlorobenzene with cuprous cyanide (CuCN) at about 250°C in the presence of pyridone.
C6H5Cl + CuCN → C6H5CN + CuCl
Reduction: On the reaction of chlorobenzene with Na – Hg and water, it is reduced and benzene is obtained. This reaction can also be carried out by Ni Al alloy and NaOH.
C6H5Cl + 2H → C6H6 + HCl
wurtz fittig reaction: The ether solution reacts with a homologous mixture of chlorobenzene and an alkyl halide to obtain an alkyl substituted benzene derivative, which is commonly called Arene.
Example:
C6H5Cl + 2Na + ClCH3 → C6H5CH3 + 2NaCl
This reaction is called wurtz fittig reaction.
Reaction Magnesium: ether solution reacts with magnesium to form phenylmagnesium chloride which is a grignard reagent.
C6H5Cl + Mg → C6H5 – Mg – Cl
Benzene nucleus reactions
Chlorobenzene has chlorine atoms ortho and para director group. Hence ortho and para substitution products are obtained on halogenation, nitration, sulfuration, etc. of Chlorobenzene. The chlorine atom is a weakly deactivating group.
This implies that the reactivity for substitution reactions of chlorobenzene is somewhat lower than that of benzene. The increasing order of reactivity for substitution reactions of benzene, toluene, and chlorobenzene is as follows.
Chlorobenzene < Benzene < Toluene
The major reactions of chlorobenzene in which the benzene nucleus participates.
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Halogenation: A mixture of ortho and para diChlorobenzene is obtained when chlorine is reacted with chlorine in the absence of sunlight and in the presence of halogen carrier.
Nitration: A mixture of ortho and para chloro nitrobenzene is obtained by the reaction of chlorobenzene with concentrated HNO3 and concentrated H2SO4.
Sulfuration: A mixture of ortho and para Chlorobenzene sulfonic acid is obtained by the reaction of Chlorobenzene with the corresponding H2SO4.
Friedel Crafts Reaction: A mixture of ortho and para chlorotoluene is obtained when the chlorobenzene is reacted with methyl chloride in the presence of anhydrous AlCl3.
Reaction with chloral: pp-Dichloro-diphenyl-trichloroethane formed upon heating Chlorobenzene with chloral in the presence of concentrated sulfuric acid. It is also called D.D.T..
It is a strong and major disinfectant. for more detail click here
What is chlorobenzene used for?
It is used in the manufacture of aniline, phenole, chloronitrobenzene, and disinfectant DDT.
