# Why does trihaloacetaldehyde formed during the haloform reaction not undergo a Cannizzaro reaction?

We know trihaloacetaldehyde is formed during the haloform reaction of acetaldehyde with a halogen in strong base. Since it has no alpha hydrogens, I expected that it might undergo a Cannizzaro reaction, as we are using a strong base. Why not?

• en.wikipedia.org/wiki/Haloform_reaction is for ketones not aldehydes. Feb 12, 2016 at 18:09
• @Mithoron Please go through the same link, you will find: The only primary alcohol and aldehyde to undergo this reaction are ethanol and ethanal, Feb 12, 2016 at 18:20
• Och, didn't thought about them in this context... Well then it happens for the same reason all haloform reactions happen: CX3 anion is leaving group good enough to be substituted by OH-. Much better then H- for that matter. Feb 12, 2016 at 18:41

Here we have another factor limiting usage of Cannizzaro reactions, as although intermediate tetrahedral anion (6) could in principle undergo this reaction if $\ce{R = H-}$, it doesn't if there's a better leaving group then $\ce{H-}$. The point of haloform reactions is to make them if they aren't present already.