Base-Catalyzed Enolization of an Aldehyde or Ketone in Aqueous Solution

Base-Catalyzed Enolization of an Aldehyde or Ketone in Aqueous Solution THE OVERALL REACTION  

Step 1 A proton is abstracted by hydroxide ion from the a-carbon atom of the carbonyl compound. 

Step 2 A water molecule acts as a Br0nsted acid to transfer a proton to the oxygen of the enolate ion. 

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FIGURE 18.3 Mechanism of the base-catalyzed enolization of an aldehyde or ketone in aqueous solution. 

When an aldehyde or a ketone with one or more a-hydrogens is dissolved in an aqueous solution that is enriched with D2O and contains catalytic amounts of either D or OD, exchange of a-hydrogens occurs af a rate that is proportional to the concentration of the acid or base catalyst. We account for incorporation of deuterium by proposing a rate-determining acid- or base-catalyzed enolization followed by incorporation of deuterium as the enol form converts to the keto form. 

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