I searched a lot to find the products of the haloform reaction of acetylacetone (pentane-2,4-dione), but I didn't find any results.

What are the products of the haloform reaction of acetylacetone?

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    $\begingroup$ Not sure about this but it looks like malonic acid should be formed. $\endgroup$ – Binary Geek Mar 29 '15 at 18:22

Because acetylacetone is a 1,3-dione, the carbonyls are very enolizable. This makes the hydrogens attached to carbon 3 on acetylacetone very acidic. When introducing the conditions for a haloform reaction, base is added. The base will take carbon 3's hydrogens, in the presence of some halogen, they will be replaced, this happens twice. Now, with the product 3,3-dihalopentane-2,4-dione, the reaction will end.

If you insist on a haloform reaction occurring, a much stronger base will be needed and the reaction vessel would probably need to be heated. It will proceed as usual and create first 2,2-dihalo-3-oxobutanoic acid (2,2-dihaloacetoacetic acid). The reaction will probably stop at this point. Upon heating though, this compound may decarboxylate to give 1,1-dihaloacetone and carbon dioxide. If you wanted to continue with this, you could do another haloform reaction to first generate perhaloacetone, and if you wanted to, this may be able to become trihaloethanoic acid and haloform.

But realistically, the reaction would end at the 2,2-disubstituted dihalo acetoacetic acid (2,2-dihalo-3-oxobutanoic acid)

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    $\begingroup$ This is kinda hard to follow without chemical structure diagrams, it would be nice to see what's happening visual. $\endgroup$ – James Dealon Jul 1 '17 at 17:33

In 1933 Hurd and Thomas1 investigated the action of bleaching powder (calcium hypochorite) on ethyl acetoacetate (1). They isolated dichloroacetic acid (2) in 60% yield without the production of chloroform. Their conclusion was that chorination did not occur on the methyl group (no chloroform) and that dichloro acetoacetic ester 2 was the intermediate. Reasonably, hydroxide attacks at the ketone, as is typical with disubstituted β-ketoesters.2 Acetic acid was not isolated but is implied by the mechanistic considerations.

In a similar fashion acetylacetone (4) would be expected to afford dichloride 5. Cleavage by base (red arrows addition to the carbonyl; blue arrows for cleavage) yields the anion of dichloroacetone (6), which is in equilibrium with its protonated form 11. Further chlorination of anion 6 yields trichloroacetone 10. A final haloform reaction provides chloroform 7 and calcium acetate 9.

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1) Hurd, C. D. and Thomas, C. L., J. Am. Chem. Soc., 1933, 55, 1646.
2) The hydroxide cleavage of ethyl 1-methyl-2-oxo-cyclopentanecarboxylate affords α-methyladipic acid.


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