Search for insecticides – Part III

A.B. Sen & P. M. Bhargava

Published in: Journal of the Indian Chemical Society, 1949, 26, 287-290

Abstract:

Substituted ωωω-trichloroacetophenones have been prepared by the action of trichloracetvl chloride on certain halogen derivatives of benzene. Resorcinol monomethyl ether and o- chloroanisole have been condensed with chloral.

A highly active insecticide usually contains a toxic component and also groups which impart lipoid solubility. In previous communications (Sen and Bhargava, this Journal, 1948, 25, 278; 1949, 26, 243), the preparation of a number of compounds containing the chlorobenzene nucleus and a -CC13 group has been described. In this paper, the authors have utilised the Friedel-Crafts reaction and the DDT-type condensation for the preparation of a number of compounds containing the same groupings; in some cases the chlorine atom in the phenyl group has been substituted by other halogens or groupings like -OCH3, whose toxic nature has already been established.

The synthesis of a number of halogen substituted acetophenones (i.e .. 4-chloro-, ω-chloro-, 4-ω-dichloro-, ωω-dichloro-, 2 :4 -ω-trichloro-,ωωω-trichloro-, 4-bromo-, ω-bromo-, ω-ch loro- 4-bromo-, ω-bromo-4-chloro- and 4- ω-dibromo- acetophenones) by Friedel-Crafts reaction between halogen-substituted acetyl chlorides and halogenated benzenes, has already been described in the literature (Friedel and Crafts, Ann. chim. phys ., 1884 , vi, 1, 507; Gautier, ibid., 1888, vi, 14, 345; Collet, Compt. rend., 1897, 125, 718; Kunckell, Ber., 1907, 40, 1703; Schweitzer, Ber ., 1891, 24, 550; Collet, Bull . soc . chim., 1897, iii, 17, 69; Klags, Ber., 1902, 35, 2642; Boesken, Rec . irav. chim., 1901, 20, 106) . The authors have extended this reaction to chloro-, bromo-, fluoro- and o-dichlorobenzenes, the acid chloride used in all cases being trichloroacetyl chloride, and the resulting products obtained being 4-ωωω-tetrachloro-, 4-bromo-ωωω-trichloro-, 4-fluoro-ωωω-tricchloroand 3:4-ωωω -pentachloro – acetophenones respectively. In all these reactions, a little excess over one and a half mole of anhydrous aluminium chloride and trichloroacetyl chloride was used. It has been found that in case of fluorobenzene, charring occurs even at 40° .In the case of chloro- and bromo benzenes, complete resinification occurs at 78°, white very little reaction takes place at 0° .The Friedel-Crafts reaction between a-dichlorobenzene and trichloroacetyl chloride proceeds smoothly at 78°, a nearly theoretical yield of the product being obtained. No reaction occurs between P-dichlorobenzene and trichloroacetyl chloride even after refluxing in petroleum ether solution for 12 hours, unchanged P-dichlorobenzene being recovered.

4-ωωω-Tetrachloroacetophenone has been previously prepared by Gautier (A nn . chim. phys ., 1888, vi, 14, 403) , who obtained it by the chlorination of 4-ωω-trichloroacetophenone at 200° . The boiling point of the compound is reported to be 181°/ 45 mm. and m p. 28°. We have obtained the compound as a pink liquid solidifying on cooling at room temperature and possessing b.p .108 °-110° /15 mm. This compound and the corresponding bromo and fluoro compounds begin to darken almost immediately after distillation and assume a permanent dark colour within a short time. No such effect of light was observed on 3:4-ωωω-pentachloroacetophenone.

A very large number of compounds of the type of DDT have been prepared by similar condensations in the recent years. The authors have in this paper, also carried out the condensation of chloral with o-chloroanisole and monomethyl ether of resorcinol. In both the cases, solid products have been obtained in low yields ; these have been provisionally assigned the structure 1: 1: 1-trichloro-2: 2-di-(3′-methoxy-4′ chlorophenyl) ethane and 1:1:1-trichloro-2:2-di-(21-methoxy-41-hydroxyphenyl) ethane respectively on the basis that in such condensations, the -CHCC13 group generally occupies the Para position to the Cl or OH group.

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Search for insecticides – Part III. A B SEN & P M BHARGAVA. Journal of the Indian Chemical Society, 1949, 26, 287-290.

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