Functional Classes II, Reactions - Organic Chemistry Concepts: An EFL Approach - page 122

FIGURE 7.34
Tollen's silver mirror test for aldehydes.
7.7.4 Reaction at the Carbonyl α -Carbon
The chemistry of acidic hydrogens on the α-carbons of carbonyl compounds is
extensive. In this topic, we show the concept by taking the example of the halo-
form reaction in Figure 7.35 . This reaction is not only a preparation of carbox-
ylic acids, but is also a visual test for the -CO·CH 3 acetyl group.
FIGURE 7.35
The haloform reaction.
Although the reaction is general, it is usually done with iodine because it gives
iodoform as solid yellow precipitate. Figure 7.36 shows the mechanism of this
reaction and the principles of enolate chemistry.
In the main reaction, hydroxide deprotonates the α-carbon to give an enolate.
Then, the enolate reacts with iodine. This is repeated two more times to give the
triiodoacetyl derivative. The final step in the sequence introduces the chemistry of
FIGURE 7.36
Mechanism of the iodoform reaction.