Pesticides

Smt. A. P. Itkapalle

Head, Dept. of Chemistry

G. M. Vasantnagar

B. Sc. T. Y.

Introduction

• Insects, fungi and weeds destroy crops and stored food grains.
• In order to control these insects, fungi, weeds, various inorganic and

organic chemicals are used. Such chemicals are commonly called

as pesticides.

• The chemical compounds used to control pests and diseases of

plants, to eradiate weeds, to kill pests and microorganisms that spoil

agricultural products, materials and articles and to control parasites

are called as pesticides.

Ex :- DDT, BHC, Endosulfan.

• Pesticides are poisonous and toxic substances and must be

handled carefully.

• The extensive use of the pesticides may cause pollution of air and

water.

Classification :-

Pesticides are classified according to their chemical composition,

their targets, ways they penetrate into an organism and the nature of their

action. Mainly pesticides are classified in two types.

1. Classification according to chemical composition :-

There are three main groups of pesticides.

1. Inorganic compounds:-

Ex :- compounds of mercury, fluorine, barium, copper, sulphur etc.

2. Pesticides of a vegetable, bacterial and fungal origin ( pyrethrins ).

3. Organic compounds:-

Ex:- Hexachloro cyclohexane, DDT, Endosulfan etc.

2. Classification according to the use of control

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1. Insecticides

The compounds which are used to kill the harmful insects and protect

the plants are called as insecticides. Ex:- DDT, BHC , Malathion.

2. Fungicides :-

The compounds which kills harmful fungi and protect the plants

are called as fungicides. Ex:- Copper sulphate, Dithiocarbamates.

3. Herbicides :-

The compounds which are used for destroying weeds are called as herbicides.

2,4 – Dichlorophenoxy

acetic acid ( 2,4- D))

2,4,5 - Trichlorophenoxy

acetic acid ( 2,4,5- T )

4. Rodenticides :-

The compounds which are used to kill the rats are called as rodenticides.

Ex:- Zinc phosphide, sodium fluoroacetate.

These chemicals are mixed with food and kept for rats to eat, if rat eat,

they die.

Synthesis and uses of the following pesticides :

2,4 – Dichlorophenoxy acetic acid ( 2,4 – D) :

Synthesis

When 2, 4 – dichlorophenol is heated with chloro- acetic acid, then 2,4 – Dichlorophenoxy acetic acid is formed.

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Uses :-

1. 2,4 –D is used as herbicides.

2. 2,4 –D is widely used for killing dicotyledonous weeds on fields of

cereal crops ( wheat, barley, oats )

• DDT [2,2- bis-(4-chlorophenyl)-1,1,1- trichloroethane]

DDT is also known as p, p'- dichloro diphenyl trichloro ethane. DDT is prepared by the condensation of one mole of chloral with two moles of monochloro benzene in the presence of conc. H₂SO₄.

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1. It is white crystalline substance, insoluble in water but soluble readily in most organic solvents.
2. It is widely used as a household insecticide to control files, mosquitoes, flees, bedbugs etc. it is also used as hoppers on potatoes, moth etc.

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• BHC (Benzene hexachloride )

Chlorination of benzene in presence of UV light gives benzene hexachloride.

1. BHC is a white powder, insoluble in water but soluble in organic solvents.
2. It is used as an insecticide against the common disease carrying insects, household and horticulture pests.
3. It is also used as an agricultural pesticide.

• Methoxy chlor [2, 2, bis – (4 – methoxy phenol)- 1, 1, 1 tri chloro ethane]

It is prepared by the condensation of anosol (4- methoxy benzene) with chloral in the presence of conc. H₂SO₄.

1. It is a grey powder, insoluble in water and soluble in organic solvents.
2. It is an effective insecticide but less toxic to animals and plants. Therefore, it is used safely on cattle, household insects and vegetable crops.
3. It can also be used in milk dairies and takes no toxic effect on milk.

e) Carbaryl

The treatment of methyl isocyanate with 1 – naphthol gives carbaryl.

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Alternatively, 1-naphthol is first converted to its chloroformate, which is then treated with methylamine to give carbaryl.

d) Monochrotophos

Monocrotophos is principally used in agriculture, as a relatively cheap pesticide.