CHAPTER 13: Unit 6. Chemical reactions of Aldehyde & Ketone

Learning Objectives

1. Name the typical reactions take place with aldehydes and ketones.
2. Describe the reactions of aldehyde and ketones.

A.) Oxidation : Oxidation means either loss of hydrogen or gain of oxygen. Similarly, reduction means gain of hydrogen or loss of oxygen.Aldehydes are easily oxidized to carboxylic acids, ketones do not undergo oxidation. During oxidation, oxygen is added between C-H bond. Since ketone have C-C relatively stronger single bond, oxygen cannot be inserted.Reduction of aldehydes and ketones produces primary and secondary alcohols respectively. Hydrogen is added to carbonyl group carbon in both aldehyde and ketone.

B.) Reduction: Aldehydes and ketones are easily reduced by hydrogen gas (H2), in presence of a catalyst (Ni, Pt or Cu)  to form alcohols. the reduction, via hydrogenation, of aldehydes produces primary alcohols andreduction of ketone yields secondary alcohols.

The distinction between Aldehydes and Ketones: Tollen’s test and Benedicts testTollens’ reagent, for example, is an alkaline solution of silver (Ag+) ion complexed with ammonia (NH3), which keeps the Ag+ ion in solution.H3N—Ag+—NH3When Tollens’ reagent oxidizes an aldehyde, the Ag+ ion is reduced to free silver (Ag).Deposited on a clean glass surface, the silver produces a mirror (Figure 3.1 “Aldehyde Reactions”). Ordinary ketones do not react with Tollens’ reagent.Positive Tollen’s test: Solid Silver depositedBenedict’s Test: The blue copper solution turns to brick red Cu2O solid precipitate.Because Ketones cannot be oxidized, these treatments with a mild oxidizing agent is used as a test to distinguish between aldehydes and ketones.