Answer :

To prepare butan-2-one from a nitrile and a Grignard reagent, you can follow one of these two methods:

  1. Conversion of Nitrile to Ketone via Grignard Reagent Reaction

    Step 1: Formation of Grignard Reagent

    • First, a Grignard reagent (RMgX) is prepared from an appropriate alkyl halide (like ethyl bromide, CH₃CH₂Br) and magnesium in dry ether.

    Step 2: Reaction with the Nitrile

    • The Grignard reagent is then reacted with a nitrile, such as propionitrile (CH₃CH₂CN). At this point, the Grignard reagent attacks the carbon atom of the nitrile triple bond, forming an imine intermediate.

    Step 3: Hydrolysis of the Iminium Ion Intermediate

    • The imine intermediate is then hydrolyzed to produce the desired ketone butan-2-one (CH₃COCH₂CH₃). The hydrolysis is done using dilute acid (H⁺/H₂O).

  2. Sequential Reaction of Two Grignard Reagents

    Step 1: Initial Grignard Formation

    • Begin with the formation of the first Grignard reagent from methyllithium (or methylmagnesium halide).

    Step 2: Reaction with Nitrile

    • The first Grignard reagent is reacted with acetonitrile (CH₃CN), resulting in an iminonitrile.

    Step 3: Hydrolysis

    • Hydrolyze the resulting compound to obtain acetone.

    Step 4: Second Grignard Formation and Reaction

    • Prepare the second Grignard reagent, for example, ethylmagnesium bromide (CH₃CH₂MgBr).
    • React this with the acetone formed in the previous step to ultimately yield butan-2-ol, which can be oxidized with a mild oxidizing agent to give butan-2-one.

Both methods involve the creation of Grignard reagents and subsequent reactions with nitriles, followed by crucial steps of hydrolysis or oxidation to deliver the final product, butan-2-one. Grignard reactions are versatile tools in organic chemistry, particularly in forming carbon-carbon bonds and synthesizing various organic compounds.

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Rewritten by : Barada