Q.How can the following conversions be effected ?
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Start your 14-day free trial to unlock the full solution →(i) Convert the alcohol to a chloride, then swap Cl for F by the Swarts reaction. (ii) Add HBr to the terminal alkene, then eliminate with alcoholic KOH to give the more substituted (Zaitsev) alkene.
(i) Ethanol -> Fluoroethane (Score: 2)
Step 1: Convert ethanol to chloroethane using thionyl chloride (this avoids rearrangement and gives only gaseous, easily removed by-products):
CH3CH2OH + SOCl2 -> CH3CH2Cl + SO2 + HCl
Step 2: Alkyl fluorides cannot usually be made by direct reaction of an alcohol/halide with HF; instead, the Swarts reaction is used - heating the chloro/bromo alkane with an inorganic fluoride such as AgF (or Hg2F2, CoF2, SbF3):
CH3CH2Cl + AgF --Δ--> CH3CH2F + AgCl
(ii) But-1-ene -> But-2-ene (Score: 2)
Step 1: Markovnikov addition of HBr to but-1-ene places Br on C2 (the more substituted carbon), giving 2-bromobutane:
CH3-CH2-CH=CH2 + HBr -> CH3-CH2-CHBr-CH3
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