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Question of 147

Q.Observe the given chemical reactions and answer the questions followed :
I. A + SOCl2 → CH3CH2Cl + SO2 + HCl
II. CH3CH2Cl ––(B, acetone)––> CH3CH2I
III. CH3CH2Cl ––(alc. KOH)––> C

(i) Identify A, B and C
(1)
(ii) Write the name of the reaction II.
(1)
(iii) In reaction III, if we use aqueous KOH, instead of alcoholic KOH, what will be the product ? (1)
Kerala DhseKerala DHSE Plus Two Board 2025Subjective· 3mImportance★★★★★
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Reaction I is the thionyl chloride conversion of an alcohol to a chloroalkane, reaction II is a Finkelstein halogen-exchange, and reaction III is a base-induced elimination whose outcome (substitution vs elimination) depends on whether the base is alcoholic or aqueous KOH.

  1. Reaction I: A + SOCl2 → CH3CH2Cl + SO2 + HCl. SOCl2 converts an alcohol into the corresponding chloroalkane (this is the standard, cleanest lab method to prepare an alkyl chloride). So A must be ethanol, CH3CH2OH. CH3CH2OH + SOCl2 → CH3CH2Cl + SO2 + HCl Reaction II: CH3CH2Cl --(B, acetone)--> CH3CH2I. Converting a chloroalkane to the corresponding iodoalkane using a halide salt in dry acetone is the Finkelstein reaction, and the reagent used is NaI. So B = NaI. CH3CH2Cl + NaI --(dry acetone)--> CH3CH2I + NaCl (NaCl precipitates out of acetone, driving the reaction forward) Reaction III: CH3CH2Cl --(alc. KOH)--> C. Alcoholic KOH promotes β-elimination (dehydrohalogenation) of a haloalkane, removing HCl to form an alkene. So C = ethene, CH2=CH2. CH3CH2Cl --(alc. KOH, heat)--> CH2=CH2 + KCl + H2O
  2. Reaction II (CH3CH2Cl → CH3CH2I using NaI/acetone) is called the Finkelstein reaction. …

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