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Organic Chemistry: Haloform Reaction

  1. Apr 4, 2005 #1

    What are the necessary and sufficient conditions for a compound to give a positive Haloform Test (Iodoform test for instance)?

    Is it necessary to have a [itex]CH_{3}CO-[/itex] group or is it necessary to have a [itex]XCH_{2}-[/itex] group where X is some group? Is the occurence of a [itex]CH_{3}CO-[/itex] group a sufficient condition?

    I would be very grateful if someone could help me with this...

    Thanks and cheers
  2. jcsd
  3. Apr 4, 2005 #2


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    Haloform test is ideally positive for methyl ketones; the C=O group attached to a methyl group increases the overall acidity of methyl protons due to tautomerization to enol form. So the X you wrote should be a strong electron withdrawing substituent, or at least a group with a highly electronegative atom.

    However, you should take into account that the reactant is alkali iodine, or hypoiodite; so any reactant capable of reducing hypoiodite would consume it, causing a positive error. It would be wise to include a bit excess of hypoiodite.

    Try to find the mechanism responsible for iodoform formation, the mechanism probably goes from an enol intermediate.

    Good luck.
  4. Apr 5, 2005 #3
    Thanks chem_tr...

    I am referring to the reaction of a given compound with KOH/I2 which we call the Iodoform Test. The mechanism as I know it involves first the iodination of the Me group attached to the carbonyl carbon to a CI3 group followed by "base removal of H+ ions" with a I- nucleophile successively attacking the intermediate to finally form iodoform (precipitate).

    So it now does appear that having a MeCO- group is a necessary condition....

    Thanks and cheers
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