Base-catalyzed halogenation of Aldehydes and Ketones.

[FROGGBUSTER]

All hydrogens of all alpha carbons will be halogenated correct?

But for acid-catalyzed halogenation, there will only be single halogenation correct?

Would appreciate it if you guys could just check this, thanks!!

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[vayntraubinator]

All hydrogens of all alpha carbons will be halogenated correct?

But for acid-catalyzed halogenation, there will only be single halogenation correct?

Would appreciate it if you guys could just check this, thanks!!

Yes, it's harder to protonate the carbonyl with each additional halogen because an added halogen has an inductive electron effect(its electronegative), so acid-catalyzed halogenation adds only one halogen to the alpha carbon.

 

[vayntraubinator]

Yes, it's harder to protonate the carbonyl with each additional halogen because an added halogen has an inductive electron effect(its electronegative), so acid-catalyzed halogenation adds only one halogen to the alpha carbon.

Also, I believe it's only 2 hydrogens that are halogenated unless the alpha carbon is a methyl group, in which case that halofrom reaction occurs and 3 halogens are added via base0catalyzed reaction.

 

[FROGGBUSTER]

Also, I believe it's only 2 hydrogens that are halogenated unless the alpha carbon is a methyl group, in which case that halofrom reaction occurs and 3 halogens are added via base0catalyzed reaction.

Would 2 halogens be added on both alpha carbons? (in the case of base-catalzyed reaction)

Also, are you saying if there is a methyl group, the Haloform rxn would preferentially occur?

 

[vayntraubinator]

Would 2 halogens be added on both alpha carbons? (in the case of base-catalzyed reaction)

Also, are you saying if there is a methyl group, the Haloform rxn would preferentially occur?

1) yes, assuming the alpha carbon is part of a longer chain of carbons and has 2 hydrogens to replace on each alpha carbon. If there are 2 alpha carbons and we put it in excess reactants all alpha hydrogens should be replaced.

2) Haloform will occur only with a methyl group (Haloform has 3 halogens put onto the alpha carbon) attached to the ketone.

http://en.wikipedia.org/wiki/Haloform_reaction