Organic Chemistry
4th Edition
Paula Yurkanis Bruice
Chapter 20
More About
Oxidation–Reduction
Reactions
Irene Lee
Case Western Reserve University
Cleveland, OH
©2004, Prentice Hall
• Oxidation is always coupled with reduction
• Loss of electrons is oxidation
• Gain of electrons is reduction
• The oxidation state of a carbon atom equals the total
number of its C–O, C–N, and C–X bonds
Hydrogen, sodium borohydride, and hydrazine are the
reducing agents
Bromine and chromic acid are the oxidizing agents
H2 as a Reducing Agent
Reduction by Catalytic Hydrogenation
Dissolving-Metal Reduction
Reduction by Addition of
a Hydride Ion and a Proton
LiAlH4 is a stronger reducing agent than NaBH4
LiAlH4 is used to reduce compounds that are
nonreactive toward NaBH4
DIBAL allows the addition of one equivalent of hydride to
an ester
Replacing some of hydrogens of LiAlH4 with OR groups
decreases the reactivity of the metal hydride
Formation of Amines by Reduction
NaBH4 can be used to selectively reduce an aldehyde or
a keto group in a compound
Oxidation of Alcohols
Oxidation of a Primary Alcohol
Mechanism of Alcohol Oxidation by
Chromic Acid
The oxidation of a primary alcohol can be stopped at the
aldehyde if pyridinium chlorochromate (PCC) is used
as the oxidizing agent
The Swern Oxidation
Mechanism of the Swern Oxidation
Oxidation of Aldehydes and Ketones
The Tollens Reagent Oxidizes Only
Aldehydes
Both aldehydes and ketones can be oxidized by
peroxyacid: The Baeyer–Villiger oxidation
Mechanism of the
Baeyer–Villiger Oxidation
Therefore, the product of the Baeyer–Villiger oxidation of
cyclohexyl methyl ketone will be cyclohexyl acetate,
because a secondary alkyl group is more likely to migrate
than a methyl group
Oxidation of Alkenes with Peroxyacids
Mechanism of Epoxidation of an Alkene
The addition of oxygen to an alkene is a stereospecific
reaction
Hydroxylation of Alkenes
Mechanism for cis-Glycol Formation
Higher yields of the diol are obtained with osmium
tetroxide
Oxidative Cleavage of 1,2-Diols
Oxidative Cleavage of Alkenes by
Ozonolysis
The alkene and ozone undergo a concerted cycloaddition
Mechanism of ozonide formation
The molozonide is unstable because it has two O–O
bonds
Ozonide is stable
Ozonides can be cleaved to carbonyl compounds
Examples of the Oxidative Cleavage of
Alkenes by Ozonolysis
A peroxyacid, OsO4, and (cold basic) KMnO4 break only
the p bond of the alkene
Ozone and acidic KMnO4 break both the p bond and the
s bond
Table 20.1 Summary of the Methods Used to Oxidize an Alkene
Oxidative Cleavage of Alkynes
O
O
KMnO 4
CH3C
CCH2CH3
CH3C
CCH2CH3
HO O
CH3C
CCH2CH3
O3
CH3COH
O
+
CH3CH2COH
H2O
O
CH3CH2CH2C
CH
O3
H2O
CH3CH2CH2COH
+
CO2
Conversion of an Aldehyde into Other
Functional Groups
Conversion of a Ketone into
an Ester or an Alcohol
Biological Oxidation–Reduction
Reactions
NAD+ oxidizes ethanol by accepting a hydride ion
NADH reduces a carbonyl compound by donating a
hydride ion