Chlorobenzene (c6h5cl): Structure, Properties, Synthesis

The chlorobenzene is an aromatic compound of chemical formula C 6 H 5 Cl, specifically an aromatic halide. At room temperature it is a colorless, flammable liquid, which is frequently used as a solvent and degreaser. In addition, it serves as a raw material for the manufacture of numerous highly useful chemical compounds.

In the last century it served as the basis for the synthesis of the insecticide DDT, very useful in the eradication of diseases such as malaria. However, in 1970 its use was banned due to its high toxicity to humans. The chlorobenzene molecule is polar due to the greater electronegativity of chlorine relative to the carbon atom to which it is attached.

Chlorobenzene

This results in chlorine having a moderate density of negative charge δ- with respect to carbon and the rest of the aromatic ring. Likewise, chlorobenzene is practically insoluble in water, but it is soluble in liquids of an aromatic chemical nature, such as: chloroform, benzene, acetone, etc.

Additionally, Rhodococus phenolicus is a bacterial species capable of degrading chlorobenzene as the only carbon source.

Chemical structure

The upper image illustrates the structure of chlorobenzene. The black spheres of carbon make up the aromatic ring, while the white spheres and the green spheres make up the hydrogen and chlorine atoms, correspondingly.

Unlike the benzene molecule, chlorobenzene has a dipole moment. This is because the Cl atom is more electronegative than the rest of the sp 2 hybridized carbons .

For this reason there is not a uniform distribution of electron density in the ring, but most of it is directed towards the Cl atom.

According to this explanation, with an electron density map it could be corroborated that, although weak, there is a region δ- rich in electrons.

Consequently, chlorobenzene molecules interact with each other through dipole-dipole forces. However, they are not strong enough for this compound to exist in the solid phase at room temperature; for this reason it is a liquid (but with a higher boiling point than benzene).

Chemical properties

Odor

Its smell is mild, not unpleasant and similar to that of almonds.

Molecular weight

112.556 g / mol.

Boiling point

131.6 ° C (270 ° F) at 760 mmHg pressure.

Melting point

-45.2 ºC (-49 ºF)

Flash point

27 ºC (82 ºF)

Water solubility

499 mg / l at 25 ° C.

Solubility in organic compounds

It is miscible with ethanol and ethyl ether. It is very soluble in benzene, carbon tetrachloride, chloroform, and carbon disulfide.

Density

1.1058 g / cm3 at 20 ° C (1.11 g / cm3 at 68 ° F). It is a slightly denser liquid than water.

Vapor density

3.88 relative to air. 3.88 (air = 1).

Vapor pressure

8.8 mmHg at 68 ° F; 11.8 mmHg at 77 ° F; 120 mmHg at 25 ° C.

Autoignition

593 ºC (1,099 ºC)

Viscosity

0.806 mPoise at 20 ° C.

Corrosiveness

Attacks some types of plastics, rubbers, and some types of coatings.

Heat of combustion

-3,100 kJ / mol at 25 ° C.

Heat of vaporization

40.97 kJ / mol at 25 ° C.

Surface tension

33.5 dynes / cm at 20 ° C.

Ionization potential

9.07 eV.

Odor threshold

Recognition in air 2.1.10-1 ppm. Low odor: 0.98 mg / cm3; high odor: 280 mg / cm3.

Experimental freezing point

-45.55 ° C (-50 ° F).

Stability

It is incompatible with oxidizing agents.

Synthesis

In industry, the method introduced in 1851 is used, in which chlorine gas (Cl 2 ) is passed through the liquid benzene at a temperature of 240 ºC in the presence of ferric chloride (FeCl 3 ), which acts as a catalyst.

C 6 H 6 => C 6 H 5 Cl

Chlorobenzene is also prepared from aniline in the Sandmayer reaction. Aniline forms benzenediazonium chloride in the presence of sodium nitrite; and benzenediazonium chloride forms benzene chloride in the presence of copper chloride.

Applications

Uses in organic synthesis

-It is used as a solvent, degreasing agent and serves as a raw material for the elaboration of numerous highly useful compounds. Chlorobenzene was used in the synthesis of the insecticide DDT, currently in disuse due to its toxicity to man.

-Although to a lesser degree, chlorobenzene is used in the synthesis of phenol, a compound that has a fungicidal, bactericidal, insecticidal, antiseptic action and is also used in the production of agrochemicals, as well as in the manufacturing process of acetisalicylic acid.

-It is involved in the manufacture of diisocyanate, a degreasing agent for automobile parts.

-It is used to obtain p-nitrochlorobenzene and 2,4-dinitrochlorobenzene.

-It is used in the synthesis of triphenylphosphine, thiophenol and phenylsilane compounds.

-Triphenylphosphine is used in the synthesis of organic compounds; thiophenol is a pesticidal agent and pharmaceutical intermediate. Instead, phenylsilane is used in the silicone industry.

-It is part of the raw material for the manufacture of diphenyl oxide, which is used as a heat transfer agent, in the control of plant diseases and in the manufacture of other chemical products.

-P-nitrochlorobenzene obtained from chlorobenzene is a compound that is used as an intermediate in the manufacture of colorants, pigments, pharmaceuticals (paracetamol) and in rubber chemistry.

Uses for synthesis of organic solvents

Chlorobenzene is also used as a raw material for the manufacture of solvents used in the synthesis reactions of organic compounds, such as methylenediphenyldiisocyanate (MDI) and urethane.

MDI is involved in the synthesis of polyurethane, which fulfills numerous functions in the production of construction products, refrigerators and freezers, bed furniture, footwear, automobiles, coatings and adhesives, and other applications.

Likewise, urethane is a raw material for the production of adjuvant compounds for agriculture, paints, inks and cleaning solvents for use in electronics.

Medical uses

– 2,4-dinitrochlorobenzene has been used in dermatology in the treatment of alopecia areata. It has also been used in allergy studies and in the immunology of dermatitis, vitiligo and in the prognosis of the evolution in patients with malignant melanoma, genital warts and common warts.

-It has had therapeutic use in patients with HIV. On the other hand, immunomodulator functions have been attributed to it, an aspect that is subject to discussion.

References

  1. Dra. Alessandra B. Alió S. (1998). Dinitrochlorobenzene and its applications . [PDF]. Venezuelan Dermatology, VOL. 36, No. 1.
  2. Panoli Intermediates India Private Limited. Para-nitro chloro benzene (PNCB) . Retrieved on June 4, 2018, from: panoliindia.com
  3. Korry Barnes. (2018). Chlorobenzene: Properties, Reactivity & Uses . Retrieved on June 4, 2018, from: study.com
  4. Wikipedia. (2018). Chlorobenzene . Retrieved on June 4, 2018, from: en.wikipedia.org
  5. PubChem. (2018). Chlorobenzene . Retrieved on June 4, 2018, from: pubchem.ncbi.nlm.nih.gov

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