Organic - Halogenation at alpha carbon ketones

[UndergradGuy7]

Destroyer has cyclohexanone + Cl2 excess and H3O+

Their answer says that all of the alpha hydrogens are replaced (so you add 4 Cl's). Like so

Don't acidic conditions only make 1 alpha hydrogen be replaced? Textbook and online sources say yes. I searched the forum and no one could agree in old threads about which is right.

So should the answer add Cl to one of the alpha carbons only, or 1 Cl to each alpha carbon (2 Cl total, 1 Cl to carbon to the left and 1 Cl to the carbon on the right)?

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[jirotrom]

I had trouble with this as well... I originally answered it with only one Cl substituting an alpha hydrogen, but when I read the answer I figured because it was in excess it substitutes all. If someone can verify this I would be very thankful as well

 

[orgohacks]

Destroyer has cyclohexanone + Cl2 excess and H3O+

Their answer says that all of the alpha hydrogens are replaced (so you add 4 Cl's). Like so

Don't acidic conditions only make 1 alpha hydrogen be replaced? Textbook and online sources say yes. I searched the forum and no one could agree in old threads about which is right.

So should the answer add Cl to one of the alpha carbons only, or 1 Cl to each alpha carbon (2 Cl total, 1 Cl to carbon to the left and 1 Cl to the carbon on the right)?

Depends on # of equivalents of your reagent. If you have 1 equiv Cl2, you will add 1 Cl atom (the other Cl becomes HCl). If you have excess Cl2, you're going to replace all of the hydrogens. The reaction goes through the enol form. As long as you can form an enol, you can continue to add Cl2.

 

[UndergradGuy7]

Why do sources say that there is a different between acidic and basic conditions then? There is no difference? Is the only different that under basic conditions you can change the alpha carbon from CH3 -> CX3 and then add 1 more OH- to remove the -CX3 to make it a carboxylic acid?

 

[orgohacks]

Why do sources say that there is a different between acidic and basic conditions then? There is no difference? Is the only different that under basic conditions you can change the alpha carbon from CH3 -> CX3 and then add 1 more OH- to remove the -CX3 to make it a carboxylic acid?

One difference is that you're going through the enolate versus the enol. You're right that under certain types of conditions you can get haloform products under basic conditions whereas these are not seen under acidic conditions.

Hard to say more without having a better look at the sources you mention.