Q.(a) Among the following which one is chlorine containing insecticide ?

DDT is the chlorine-based insecticide among the options; the Wurtz–Fittig reaction couples an alkyl halide with an aryl halide using sodium; and in the given scheme aniline is diazotised to benzenediazonium chloride (A), which the Sandmeyer reaction with Cu2Cl2 converts to chlorobenzene (B).

a) Chlorine-containing insecticide

DDT (dichlorodiphenyltrichloroethane) is an organochlorine compound long used as an insecticide. Freon is a chlorofluorocarbon refrigerant (not an insecticide), phosgene is a toxic gas/chemical-warfare agent, and iodoform is an antiseptic.

Answer: (i) DDT

b) (i) Wurtz–Fittig reaction

When a mixture of an alkyl halide and an aryl halide is treated with sodium metal in dry ether, the two combine to form an alkyl-substituted arene (alkylbenzene), with sodium halide as by-product:

C6H5Br + CH3Br + 2Na →(dry ether) C6H5–CH3 (toluene) + 2NaBr

(If only aryl halides are used with sodium, the analogous coupling to give a biaryl is called the Fittig reaction.)

b) (ii) Identifying A and B

As described by the reaction scheme (see figure below): aniline (C6H5NH2) is treated with NaNO2/HX (dilute HCl) at a low temperature of 273–278 K — this is diazotisation, which converts the –NH2 group into a diazonium group:

…