Transcript Reduction of Aldehydes and Ketones

14.3 Oxidation and Reduction of
Aldehydes and Ketones
In Tollens’ test, a “silver
mirror” forms when the
oxidation of an aldehyde
reduces silver ions to
metallic silver.
The silvery surface of a
mirror is formed in a
similar way.
Learning Goal Draw the condensed or line-angle structural
formulas for the reactants and products in the oxidation or
reduction of aldehydes and ketones.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Oxidation of Aldehydes
• Aldehydes oxidize readily to form carboxylic acids.
• Ketones do not undergo oxidation.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Tollens’ Test: Silver Mirror
Tollens’ test
• may be used to distinguish between aldehydes and
ketones.
• utilizes Tollens’ reagent, which is a solution of Ag+ (AgNO3)
and ammonia.
• oxidizes aldehydes but not ketones.
• reduces Ag+, as the aldehyde is oxidized and forms a layer
called a “silver mirror” on the inside of the container.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Benedict’s Test
Benedict’s test
• gives a positive result with
compounds that have an
aldehyde functional group and an
adjacent hydroxyl group.
• utilizes Benedict’s solution, which
contains Cu2+ (CuSO4). When the
solution is added to this type of
aldehyde and heated, a brick-red
solid of Cu2O forms
• is negative with simple aldehydes
and ketones.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Benedict’s Test: 2-Hydroxy Aldehyde
Because sugars such as glucose contain this type of aldehyde
grouping, Benedict’s reagent can be used to determine the
presence of glucose in blood or urine.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Reduction of Aldehydes and Ketones
Aldehydes and ketones
• are reduced by hydrogen (H2) or sodium borohydride
(NaBH4) and a catalyst such as nickel, platinum, or
palladium.
• are reduced to alcohols by decreasing the number of
carbon–oxygen bonds.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Reduction of Aldehydes and Ketones
Aldehydes are reduced to primary alcohols, and ketones are
reduced to secondary alcohols.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Write the condensed structural formula and the name of the
oxidized product when each of the following is mixed with
Tollens’ reagent.
A. Butanal
B. Acetaldehyde
C. Ethyl methyl ketone
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Write the condensed structural formula and the name of the
oxidized product when each of the following is mixed with
Tollens’ reagent.
A. Butanal  butanoic acid

B. Acetaldehyde  ethanoic acid

General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Write the condensed structural formula and the name of the
oxidized product when each of the following is mixed with
Tollens’ reagent.
C. Ethyl methyl ketone  None; ketones are not oxidized
by Tollens’ reagent.
 No reaction
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Study Check
Predict the product for each of the following reactions:
Pt
+ H2 
A.
Ni
B.
+ H2 
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Solution
Predict the product for each of the following reactions:
Pt
+ H2 
A.
Aldehydes are reduced to primary alcohols.
Ni
B.
+ H2 
Keytones are reduced to secondary alcohols.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.