Search for insecticides – Part I

A.B. Sen & P. M. Bhargava

Published in: Journal of the Indian Chemical Society, 1948, 25, 277-281.


Preparation of certain trichloro-2-hydroxy-2-halogenated-phenylethanes and halogenated phenyl esters of trichloroacetic acid has been described.

Two theories have been put forward concerning the remarkable insecticidal powers of dichlorodiphenyltrichloroethane (Busvine, Nature, 1945, 156, 169). One postulates that toxic component is the linked p-chlorobenzene rings, while the chloroform residue -CC13 imparts lipoid solubility (Läuger, Martin and Müller, Helv. Chim. Acta, 1944, 27, 892). According to the other theory, the lipoid solubility is attributed to the chlorobenzene rings, while the remainder of the molecule is supposed to be responsible for toxicity, by splitting off HCl at the vital centres (Martin and Wain, Nature, 1944, 154, 512)

In this paper, two types of reactions have been carried out in order to introduce a toxic and a lipoid soluble group in the molecule, with a view to studying the effect of these different groups on insecticidal action.

The first is the condensation of chloral with the Grignard reagents of polyhalogenated benzenes. Condensation of chloral with Grignard reagents of p-chlorobromobenzene, o-chlorobromobenzene and 1 : 2-dichloro-4-bromobenzene yields 1 : 1:1-trichloro-2-hydroxy- 2- (4-chlorophenyl)ethane, 1 : 1:1-trichloro-2-hydroxy -2-(2-chlorophenyl)ethane and 1:1 :1trichloro- 2-hydroxy- 2-(3 :4-dichlorophenyl)ethane respectively. Of these compounds, the first [i.e. 1:1:1-trichloro-2-hydroxy-2-(4-chlorophenyl) ethane] has been obtained previously, as a by-product in the manufacture of DDT (Forest, Stephenson and Waters, J. Chem. Soc., 1946, 333). According to them, the compound is contained in the lower boiling fraction (b. p.115° / 0.5 mm.) which is obtained as a by-product in the technical preparation of DDT, and that the compound yields an acetyl derivative which on hydrolysis regenerates the original hydroxy compound as a solid. The present authors have obtained 1:1:1-trichloro-2-hydroxy-2- (4-chlorophenyl) ethane as a viscous liquid, b. p. 196° -198°/ 11 mm. It yields an acetyl derivative which is not hydrolysed by N /2- sulphuric acid. 1:1:1-Trichloro-2-hydroxy- 2-(2-chlorophenyl) ethane also yields an acetyl derivative, but the acetyl derivative of 1:1: 1-trichloro-2-hydroxy-2-(3:4-dichlorophenyl) ethane could not be obtained.

It has been incidentally found that the bromination of chlorobenzene in CCl,, solution , in the presence of Al-Hg couple, results in the formation of p-chlorobromobenzene in a good yield, whereas if the same reaction is carried out without a solvent, the reaction is much more vigorous and the product formed is mainly the isomeric o-chlorobromobenzene.

Another series of compounds, which have been prepared, is of the type of esters. These have been obtained by the condensation of the sodium salts of p-chlorophenol, 2:4-dichlorophenol and 2:4:6-trichlorophenol with trichloroacetyl chloride. p-Chlorophenol gives a theoretical yield of the trichloroacetyl ester (I ). 2 :4-Dichlorophtnol, which has one ortho position occupied by chlorine, gives 55% yield of the ester (II), while in the case of 2:4:6-trichlorophenol, which has both the ortho positions substituted, the yield of the trichloroacetyl ester (III) is very low (54%).


Search for insecticides – Part I. A B SEN & P M BHARGAVA. Journal of the Indian Chemical Society, 1948, 25, 277-281.


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