Some Acid-Base-catalyzed Reactions of the Carbonyl Group

Some Acid-Base-catalyzed Reactions of the Carbonyl Group 

The very large dipole moment associated with the carbonyl group, C=0, of about 2.50 Debyes makes the group a very attractive reagent 

The rate of establishment of the equilibria with water is quite variable being fast with CH2O and slow with acetone. However, the rates are ver sensitive to catalysis by acids, bases, and even metal ions. In the case 0 acetaldehyde, the dehydration of the diol in acetone solution is follower 

The rate-determining step is 3, the transfer of the OH proton to the conjugate base A . For the reverse process, the hydration of acetaldehyde, reaction 4 is rate-determining. For the base-catalyzed reaction the proposed mechanism is very similar  

The acid-catalyzed exchange of acetone with H20 which was discussed in the preceding section must go through an analogous mechanism. The addition of alcohols to aldehydes and ketones to form acetals (and their hydrolysis) is, however, found to be specifically H+-catalyzed, indicating that in the hydrolysis the slow step is the dissociation of the cation 

---