Chlorobenzene
From Wikipedia, the free encyclopedia
| Chlorobenzene | |
|---|---|
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| IUPAC name | chlorobenzene |
| Other names | benzene chloride monochlorobenzene Phenyl chloride |
| Identifiers | |
| CAS number | [108-90-7] |
| RTECS number | CZ0175000 |
| SMILES | ClC1=CC=CC=C1 |
| Properties | |
| Molecular formula | C6H5Cl |
| Molar mass | 112.56 g/mol |
| Appearance | colorless liquid |
| Density | 1.11 g/cm³, liquid |
| Melting point |
-45 °C (228 K) |
| Boiling point |
131 °C (404 K) |
| Solubility in water | low |
| Solubility in other solvents | most organic solvents |
| Hazards | |
| R-phrases | 10 20 51/53 |
| S-phrases | 24/25 61 |
| Flash point | 29 °C |
| Related compounds | |
| Related compounds | benzene 1,4-dichlorobenzene |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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Chlorobenzene is an aromatic organic compound with the chemical formula C6H5Cl. It is a colorless, flammable liquid first made in 1851 by reacting phenol and phosphorus pentachloride.[citation needed]
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[edit] Uses
Chlorobenzene has been used in the manufacture of certain pesticides, most notably DDT by reaction with chloral (trichloroacetaldehyde). It once found use in the production of phenol. Today the major use of chlorobenzene is as an intermediate in the production of nitrochlorobenzenes and diphenyl oxide, which are important in the production of commodities such as herbicides, dyestuffs, and rubber. Chlorobenzene is also used as a high-boiling solvent in organic synthesis as well as many industrial applications.
[edit] Synthesis
Chlorobenzene is prepared by chlorination of benzene, usually in the presence of a catalytic amount of Lewis acid such as ferric chloride:
The catalyst is necessary because Cl2 does not have enough electrophilicity to react with the stable aromatic benzene.
Because chlorine is electronegative, C6H5Cl exhibits decreased susceptibility to attack by other electrophiles. For this reason, when close attention is paid to stoichiometry, the chlorination process produces only small amounts of dichloro- and trichlorobenzenes.
[edit] Mechanism
There are two ideas of how this reaction occurs. One understanding is that a molecule of Cl2 can donate a lone pair of electrons (Lewis base) to the valence of iron in ferric chloride (Lewis acid), forming the electrophilic complex shown:[1]
Because chlorine is significantly electronegative, the chlorine with positive charge pulls electron density through the sigma bond to the other chlorine, thus making the outer "neutral" chlorine the electrophilic species. This chlorine is the chlorine attacked by a pair of electrons from the pi system of benzene. This in turn forms FeCl4-, which then abstracts a hydrogen from the resonance-stabilized sigma complex of benzene to restore aromaticity, regenerate the catalyst, and form HCl.
A second understanding is that Cl2 can dissociate to form a complex anion with FeCl3 in which a Cl+ species is attracted to the FeCl4- anion:[2]
A pair of pi electrons will bond to the very reactive Cl+ species and, as above, FeCl4- will abstract the proton, regenerate the catalyst, and form HCl.
