Preparation Of DDT, BHC And Iodoform

By Anup Pokhrel

Dichloro-Diphenyl trichloroethane (DDT).

Its structure is

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IUPAC name of DDT is 2,2-bis(p-Chlorophenyl)-1,1,1-trichloroethane)DDT.

 

Preparation.

It is prepared by heating a mixture of choral and chlorobenzene in the molar ratio (1:2) in the presence of concentration H2SO4.

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Properties and uses of DDT.

It is an odourless white crystalline solid with melting point 1090C. It is almost insoluble in water but readily dissolves in benzene, kerosene oil, alcohol, etc. DDT is a powerful contact insecticide and is widely used for killing mosquito and other insects.

DDT is not biodegradable. Its residue accumulates in the environment and its long-term effect could be highly dangerous. It has been provided to be toxic to living beings. In human beings, it disturbs the sex hormones. DDT is still being widely used in poor countries due to non-availability of other cheaper insecticides.

BHC.

It is prepared by chlorination of benzene in presence of sunlight.

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IUPAC name of BHC is 1,2,3,4,5,6 Hexachlorocyclohexane(Benzene hexachloride)

Benzene hexachloride is a cyclohexane derivative and nine stereoisomers are possible. However, only five of them have been actually isolated from the mixture. They are called α, β, γ, Δ, ε forms. The mixture of stereoisomeric hexachlorides is an active component in BHC is γ isomer, called gammaxene or lindane.

Uses.

BHC is an important agricultural pesticide mainly used for exterminating white ants, leaf hopper, termite etc.

preparation..

In the laboratory, iodoform is prepared by the action of iodine on ethyl alcohol or acetone in the presence of an alkali. The reaction is known as iodoform reaction.

1. From ethyl alcohol.

Reactions involved in the preperation of iodoform from ethyl alcohol are.

2NaOH+I2NaOI+NaI+H2O2NaOH+I2→NaOI+NaI+H2O
WhereNaOI=SodiumhypoioditeWhereNaOI=Sodiumhypoiodite
CH3CH2OH+NaOI−→−−−−−OxidationCH3CHO+NaI+H2OCH3CH2OH+NaOI→OxidationCH3CHO+NaI+H2O
WhereCH3CH2OH=ethanolWhereCH3CH2OH=ethanol
CH3CHO=EthanalCH3CHO=Ethanal
CH3CHO+3NaOI−→−−−−−IodinationCl3CHO+3NaOHCH3CHO+3NaOI→IodinationCl3CHO+3NaOH
WhereCl3CHO=TriiodoethanalWhereCl3CHO=Triiodoethanal
Cl3CHO+NaOHxrightarrowHydrolysisCHI3+HCOONaCl3CHO+NaOHxrightarrowHydrolysisCHI3+HCOONa
WhereCHI3=IodoformWhereCHI3=Iodoform
WhereHCOONa=SodiumformateWhereHCOONa=Sodiumformate

The overall reaction may be written as.

CH3CH2OH+4I2+6NaOH−→−heatCHI3+5NaI+5H2O+HCOONaCH3CH2OH+4I2+6NaOH→heatCHI3+5NaI+5H2O+HCOONa
WhereCH3CH2OH=ethylethanolWhereCH3CH2OH=ethylethanol
CHI3=IodoformCHI3=Iodoform
HCOONa=SodiumformateHCOONa=Sodiumformate

2. From acetone.

Reaction involved in the preparation of iodoform from acetone are

2NaOH+I2NaOI+NaI+H2O2NaOH+I2→NaOI+NaI+H2O
CH3COCH3+3NaOI−→−−−−−IodinationCl3COCH3+3NaOHCH3COCH3+3NaOI→IodinationCl3COCH3+3NaOH
WhereCl3COCH3=TriiodoacetoneWhereCl3COCH3=Triiodoacetone
Cl3COCH3+NaOH−→−−−−−HydrolysisCHI3+CH3CooNaCl3COCH3+NaOH→HydrolysisCHI3+CH3CooNa
WhereCHI3=IodoformCH3COONa=SodiumacetateWhereCHI3=IodoformCH3COONa=Sodiumacetate

The overall reaction may be represented as.

CH3COCH3+3I2+4NaOH−→−heatCHI3+3NaI+CH3COONaCH3COCH3+3I2+4NaOH→heatCHI3+3NaI+CH3COONa
WhereCH3COCH3=AcetoneCHI3=IodoformCH3COONa=SodiumacetateWhereCH3COCH3=AcetoneCHI3=IodoformCH3COONa=Sodiumacetate

In th above reaction sodium carbonate can also be used in place of NaOH or KOH). If sodium carbonate is used the overall reactions are.

CH3CH2OH+4I2+3Na2CO3−→−heatCHI3+HCOONA+5NaI+2H2O+3CO2CH3CH2OH+4I2+3Na2CO3→heatCHI3+HCOONA+5NaI+2H2O+3CO2
WhereCH3CH2OH=ethanol(Ethylalcohol)WhereCH3CH2OH=ethanol(Ethylalcohol)
CH3COCH3+3I2+2Na2CO3−→−heatCHI3+CH3COONa+3NaI+2Co2CH3COCH3+3I2+2Na2CO3→heatCHI3+CH3COONa+3NaI+2Co2
WhereCH3COCH3=Propanone(Acetone)WhereCH3COCH3=Propanone(Acetone)

Properties of Iodoform.

Physical property.

The importance of physical property of iodoform is listed below.

  1. Iodoform is a pale yellow coloured crystalline solid with characteristic unpleasant odour.
  2. It is insoluble in water but soluble in ethanol and ether.
  3. Its melting point is 1190C.
  4. It has an antiseptic action due to the liberation of free iodine.

Chemical property.

Some important chemical property of Iodoform is as follows.

1. Stability.

It is not a very stable compound. On heating decomposes to give iodine vapours. The decomposition accelerates in presence of moisture, light, and air.

4CHI3+5O2−→−−Heat6I2+4CO2+2H2O4CHI3+5O2→Heat6I2+4CO2+2H2O

2. Hydrolysis.

Iodoform on boiling with alcoholic or concentrated aqueous solution of KOH give potassium formate.

CHI3+3KOH−→−BoilHCOOH+3KI+H2OCHI3+3KOH→BoilHCOOH+3KI+H2O
HCOOH+KOHHCOOK+H2OHCOOH+KOH→HCOOK+H2O

3. Reduction.

Iodoform on reduction with red phosphorus and hydriodic acid gives diiodomethane.

CHI3+2[H]−→−−−−RedPHICH2I2+HICHI3+2[H]→RedPHICH2I2+HI

4. Action with silver power.

Iodoform oh cheating with silver power forms acetylene.

2CHI3+6Ag−→−heatCHCH+6AgI2CHI3+6Ag→heatCH≡CH+6AgI
WhereCHCH=Ethyne(Acetylene)WhereCH≡CH=Ethyne(Acetylene)

Uses of Iodoform.

Some of the important uses of Iodoform are as follows.

  1. It is used as in antiseptic for dressing wounds and this nature is due to iodine that it liberates. However, of its unpleasant smell, it has now been replaced by better antiseptic.
  2. It is used in the manufacture of pharmaceuticals.
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