Numford
Organic conversion

Propan-2-ol to propan-1-ol

2 steps: elimination, then hydroboration-oxidation

Class 12, Chapter 7 Alcohols, Phenols and Ethers

  1. OH
    Propan-2-olCH₃CH(OH)CH₃Alcohol
  2. Step 1

    85% H₃PO₄

    440 K

    i

    Secondary alcohols dehydrate more easily than primary ones.

    PropeneCH₃CH=CH₂Alkene
  3. Step 2

    (i) B₂H₆ (ii) H₂O₂, OH⁻

    Hydroboration-oxidation
    i

    Hydroboration-oxidation gives the anti-Markovnikov (primary) alcohol.

    OH
    Propan-1-olCH₃CH₂CH₂OHAlcohol

Exam answer

  1. Step 1: Propan-2-ol to propene: 85% H₃PO₄, 440 K.
  2. Step 2: Propene to propan-1-ol: (i) B₂H₆ (ii) H₂O₂, OH⁻.
Alternative routes (4)
  • Propan-2-ol → Propene → 1-Bromopropane → Propan-1-ol
    1. Propan-2-ol to propene: 85% H₃PO₄, 440 K.
    2. Propene to 1-bromopropane: HBr, peroxide.
    3. 1-Bromopropane to propan-1-ol: aq. NaOH (or aq. KOH).
  • Propan-2-ol → 2-Bromopropane → Propene → Propan-1-ol
    1. Propan-2-ol to 2-bromopropane: red P + Br₂ (PBr₃).
    2. 2-Bromopropane to propene: alc. KOH, heat.
    3. Propene to propan-1-ol: (i) B₂H₆ (ii) H₂O₂, OH⁻.
  • Propan-2-ol → 2-Bromopropane → Propene → 1-Bromopropane → Propan-1-ol
    1. Propan-2-ol to 2-bromopropane: red P + Br₂ (PBr₃).
    2. 2-Bromopropane to propene: alc. KOH, heat.
    3. Propene to 1-bromopropane: HBr, peroxide.
    4. 1-Bromopropane to propan-1-ol: aq. NaOH (or aq. KOH).
  • Propan-2-ol → Propene → 1-Bromopropane → Propan-1-amine → Propan-1-ol
    1. Propan-2-ol to propene: 85% H₃PO₄, 440 K.
    2. Propene to 1-bromopropane: HBr, peroxide.
    3. 1-Bromopropane to propan-1-amine: NH₃ (excess), ethanolic, sealed tube, 373 K.
    4. Propan-1-amine to propan-1-ol: NaNO₂ + HCl, 273 to 278 K.
Why these reagents

Reagent and reason, step by step

  • Step 1: Propan-2-ol to propene: 85% H₃PO₄, 440 K Secondary alcohols dehydrate more easily than primary ones.
  • Step 2: Propene to propan-1-ol: (i) B₂H₆ (ii) H₂O₂, OH⁻ Hydroboration-oxidation gives the anti-Markovnikov (primary) alcohol.
Questions

Propan-2-ol to propan-1-ol: quick answers

How many steps does it take to convert propan-2-ol to propan-1-ol?

2 steps: Propan-2-ol, then propene, then propan-1-ol.

Which named reaction is used to convert propan-2-ol to propan-1-ol?

Hydroboration-oxidation. An alkene adds diborane to give a trialkylborane, which is oxidised by hydrogen peroxide in alkali to give an alcohol with anti-Markovnikov orientation.

What is the reagent for step 1 of propan-2-ol to propan-1-ol?

Propan-2-ol to propene: 85% H₃PO₄, 440 K. Secondary alcohols dehydrate more easily than primary ones.

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