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.

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.

$$2NaOH+I_2→NaOI+NaI+H_2O$$

$$Where\,NaOI=Sodium\,hypoiodite$$

$$CH_3CH_2OH+NaOI\xrightarrow{Oxidation}CH_3CHO+NaI+H_2O$$

$$Where\,CH_3CH_2OH=ethanol$$

$$CH_3CHO=Ethanal$$

$$CH_3CHO+3NaOI\xrightarrow{Iodination}Cl_3CHO+3NaOH$$

$$Where\,Cl_3CHO=Triiodoethanal$$

$$Cl_3CHO+NaOHxrightarrow{Hydrolysis}CHI_3+HCOONa$$

$$Where\,CHI_3=Iodoform$$

$$Where\,HCOONa=Sodium\,formate$$

The overall reaction may be written as.

$$CH_3CH_2OH+4I_2+6NaOH\xrightarrow{heat}CHI_3+5NaI+5H_2O+HCOONa$$

$$Where\,CH_3CH_2OH=ethyl\,ethanol$$

$$CHI_3=Iodoform$$

$$HCOONa=Sodium\,formate$$

2. From acetone.

Reaction involved in the preparation of iodoform from acetone are

$$2NaOH+I_2→NaOI+NaI+H_2O$$

$$CH_3COCH_3+3NaOI\xrightarrow{Iodination}Cl_3COCH_3+3NaOH$$

$$Where\,Cl_3COCH_3=Triiodoacetone$$

$$Cl_3COCH_3+NaOH\xrightarrow{Hydrolysis}CHI_3+CH_3CooNa$$

$$Where\,CHI_3=Iodoform\,CH_3COONa=Sodium\,acetate$$

The overall reaction may be represented as.

$$CH_3COCH_3+3I_2+4NaOH\xrightarrow{heat}CHI_3+3NaI+CH_3COONa$$

$$Where\,CH_3COCH_3=Acetone\,CHI_3=Iodoform\,CH_3COONa=Sodium\,acetate$$

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.

$$CH_3CH_2OH+4I_2+3Na_2CO_3\xrightarrow{heat}CHI_3+HCOONA+5NaI+2H_2O+3CO_2$$

$$Where\,CH_3CH_2OH=ethanol\,(Ethyl\,alcohol)$$

$$CH_3COCH_3+3I_2+2Na_2CO_3\xrightarrow{heat}CHI_3+CH_3COONa+3NaI+2Co_2$$

$$Where\,CH_3COCH_3=Propanone\,(Acetone)$$

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.

$$4CHI_3+5O_2\xrightarrow{Heat}6I_2+4CO_2+2H_2O$$

2. Hydrolysis.

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

$$CHI_3+3KOH\xrightarrow{Boil}HCOOH+3KI+H_2O$$

$$HCOOH+KOH→HCOOK+H_2O$$

3. Reduction.

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

$$CHI_3+2[H]\xrightarrow{RedP\,HI}CH_2I_2+HI$$

4. Action with silver power.

Iodoform oh cheating with silver power forms acetylene.

$$2CHI_3+6Ag\xrightarrow{heat}CH≡CH+6AgI$$

$$Where\,CH≡CH=Ethyne\,(Acetylene)$$

Uses of Iodoform.

Som,e 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.

Reference.

Bahl, B S, Bahl, and Arun. Advanced Organic chemistry. S. Chand and company Ltd., n.d.

Sthapit, M K, R R Pradhananga, and K B Bajracharya. Foundations of chemistry. Taleju Prakashan, n.d.

Tewari, K S, S N Mehrotra, and N K Vishnoi. A textbook of organic chemistry. Vikash publishing House Pvt. ltd., n.d.

Verma, N K and S K Khanna. Compressive chemistry. 8th edition. Laxmi publications P. Ltd., 1999.