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11.4: Beckmann Rearrangement

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    190076

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    The Beckmann rearrangement results when an oxime (an N-hydroxyimine) is treated with concentrated acid and heated.

    ERbeckmann.png

    The oxime, in turn, is generated by treatment of a ketone with hydroxylamine. A catalytic amount of acid can activate the carbonyl, accelerating the otherwise sluggish reaction.

    ERbeckmannoxime.png

    The reaction, like the pinacol rearrangement, is triggered by the loss of water from the starting material. The incipient cation that results undergoes a 1,2-shift. Subsequently, the re-addition of water to the rearranged cation results in a new compound.

    ERbeckmanncenter.png

    By "incipient", we describe a cation that is only on the brink of forming, but has not actually occurred yet. The 1,2-shift happens as soon as the partial positive charge on the nitrogen becomes great enough to draw the electrons from the neighbouring bond.

    ERbeckmannCore.png

    The complete mechanism is described pictorially below.

    ERbeckmannmech.png

    Exercise \(\PageIndex{1}\)

    Predict the products of the following Beckmann rearrangements.

    ERBeckmannExample.png
    Answer

    ERWolffsolns.png

    This page titled 11.4: Beckmann Rearrangement is shared under a CC BY-NC 3.0 license and was authored, remixed, and/or curated by Chris Schaller via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.