Question

Formaldehyde (2 moles) + 3-pentanone (1 mole) --[NaOH]--> ???

Can this reaction actually happen?  I know formaldehyde doesn't have an alpha-carbon, so...

Or does 3-pentanone somehow react with itself?  No, right?  Since there's only one mole?

Thanks for the help!!!

Answer 1

For a carbonyl compound to undergo aldol condensation, the necessary condition is that it MUST possess atleast 1 "alpha-hydrogen" (an alpha-hydrogen is a hydrogen attached to an alpha-carbon, while an alpha carbon is the carbon attached DIRECTLY to the functional group)
since formaldehyde(i-e HCHO) has only 1 carbon which is the carbonyl carbon (i-e the functional group) and there is no alpha-carbon present and hence no alpha-hydrogen, so formaldehyde doesn't undergo aldol condensation.

Formaldehyde will undergo cannizzaro reaction. It is a chemical reaction that involves the base-induced disproportionation of an aldehyde lacking a hydrogen atom in the alpha position.

Answer 2

MECHANISM: The Cannizzaro reaction is a redox reaction in which two molecules of an aldehyde are reacted to produce a primary alcohol and a carboxylic acid using a hydroxide base. The reaction begins with hydroxide attack on the carbonyl carbon followed by deprotonation to give a dianion. This unstable intermediate releases a hydride anion which attacks another molecule of aldehyde. In this process the dianion converts to a carboxylate anion and the aldehyde to an alkoxide. The alkoxide then picks up a proton from water to provide the alcohol final product, while the caboxylate is converted to the carboxylic acid product after acid work-up.