Functional Classes II, Reactions - Organic Chemistry Concepts: An EFL Approach - page 121

FIGURE 7.32
Primary amino-carbonyl condensation reaction.

Table 7.4 Amino-Carbonyl Condensation Products
Amino

Reagent Product Class

RNH 2

Amine

NR

Imine

H 2 NOH

Hydroxylamine

NOH

Oxime

RNHNH 2

Hydrazine

NNHR

Hydrazone

The best known example is the 2,4-dinitrophenylhydrazone derivative, or
2,4-DNP. Figure 7.33 shows how these are made by reaction of carbonyl com-
pounds with Brady's hydrazine reagent to give the orange-red colored deriva-
tives. The appearance of the 2,4-DNP precipitate is a visual test for aldehydes
and ketones.

FIGURE 7.33
Brady's test for aldehydes and ketones.

7.7.3 Oxidation of Aldehydes
In Section 7.6.4 we saw the oxidation of aldehydes to carboxylic acids as part
of the oxidation of 1° alcohols. In addition to preparing carboxylic acids, this
reaction is a simple method to tell whether an aldehyde or a ketone is present.

In a reaction known as the Tollen's silver mirror test, oxidation is done with an
aqueous ammonia/silver solution. During the reaction shown in Figure 7.34 ,
silver cations are reduced to metallic silver. The silver metal coats the reaction
vessel with a shiny mirror. This is a positive visual test for an aldehyde.