Preparation of haloalkanes and haloarenesहैलोऐल्केन और हैलोऐरीन का विरचनPreparation of haloalkanes and haloarenes
Class 12 Chemistry · Chapter 6 · interactive diagram
Parts and what they mean
- From alcohols (ऐल्कोहॉलों से) — OH is replaced by X using conc. halogen acids (1°/2° need ZnCl₂ with HCl), PX₃ (PBr₃/PI₃ made in situ from red P + Br₂/I₂) or PCl₅. Reactivity of alcohols: 3° > 2° > 1°.
- Thionyl chloride — preferred (थायोनिल क्लोराइड — वरीय) — SO₂ and HCl are gases and escape, so pure alkyl chloride is left (NCERT).
- Free radical halogenation of alkanes (ऐल्केनों का मुक्त मूलक हैलोजनीकरण) — Gives a complex mixture of isomeric mono- and polyhaloalkanes — low yield of any one compound.
- Addition of HX to alkenes (ऐल्कीनों पर HX का योग) — Propene gives two products; the Markovnikov product predominates (e.g. 2-iodopropane with HI).
- Addition of bromine (test for C=C) (ब्रोमीन का योग (C=C का परीक्षण)) — Reddish-brown colour of Br₂ in CCl₄ is discharged; colourless vic-dibromide forms.
- Finkelstein reaction (फ़िंकेल्स्टाइन अभिक्रिया) — NaCl/NaBr precipitates in dry acetone, pushing the equilibrium forward (Le Chatelier).
- Swarts reaction (स्वार्ट्स अभिक्रिया) — Alkyl chloride/bromide heated with a metallic fluoride: AgF, Hg₂F₂, CoF₂ or SbF₃.
- Electrophilic substitution of arenes (ऐरीनों का इलेक्ट्रॉनरागी प्रतिस्थापन) — Cl₂/Br₂ with Fe or FeCl₃ (Lewis acid). o- and p-isomers separate easily (very different m.p.). Iodination needs an oxidising agent (HNO₃, HIO₄); fluorine is too reactive.
- Sandmeyer reaction (सैंडमेयर अभिक्रिया) — Aromatic 1° amine + NaNO₂ in cold mineral acid → diazonium salt; with Cu₂Cl₂/Cu₂Br₂ the –N₂⁺ group is replaced by –Cl/–Br.
- Iodobenzene: just shake with KI (आयडोबेन्ज़ीन: केवल KI के साथ हिलाएँ) — No cuprous halide needed for –I.
Original diagram drawn by Simple Learning Hub, based on the NCERT textbook. Report a mistake