Addition of H2O—Hydration

Because imines and enamines are formed by a set of reversible reactions, both can be converted back to carbonyl compounds by hydrolysis with mild acid. The mechanism of these reactions is exactly the reverse of the mechanism written for the formation of imines and enamines. In the hydrolysis of enamines, the carbonyl carbon in the product comes from the hybridized carbon bonded to the N atom in the starting material. 

Problem 21.26 What two enamines are formed when 2-methylcyclohexanone is treated with (CHgjgNH Problem 21.27 Explain why benzaldehyde cannot form an enamine with a 2° amine. 

Problem 21.28 What carbonyl compound and amine are formed by the hydrolysis of each compound  

Treatment of a carbonyl compound with H2O in the presence of an acid or base catalyst adds the elements of H and OH across the carbon-oxygen Jt bond, forming a gcm-diol or hydrate. 

Hydration of a carbonyl group gives a good yield of gem-Aio only with an unhindered aldehyde like formaldehyde, and with aldehydes containing nearby electron-withdrawing groups. 

This can be illustrated by comparing the amount of hydrate formed from formaldehyde, acetaldehyde, and acetone. 

Formaldehyde, the least stable carbonyl compound, forms the largest percentage of hydrate. On the other hand, acetone and other ketones, which have two electron-donor R groups, form 1% of the hydrate at equihbrium. Other electronic factors come into play as well. 

Electron-donating groups near the carbonyl carbon stabilize the carbonyl group, decreasing the amount of the hydrate at equilibrium. 

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The Wittig reaction Addition of 1 ° amines Addition of 2° amines Addition of H2O— Hydration... 

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