Organic Chemistry

1
Chapter 20 More About OxidationReduction Reacti
ons
Organic Chemistry 6th Edition Paula Yurkanis
Bruice
2

• 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 CO, CN, and CX bonds.

3

• Reduction at carbon increases the number of CH
  bonds or
• decreases the number of CO, CN, or CX bonds.

• Oxidation at carbon decreases the number of CH
  bonds or
• increases the number of CO, CN, or CX bonds.

4
Hydrogen, sodium borohydride, and hydrazine are
the reducing agents
5
Bromine and chromic acid are the oxidizing agents
6
H2 as a Reducing Agent
7
Reduction by Catalytic Hydrogenation
Addition of two hydrogen atoms
8
Only the alkene substituted to benzene is reduced
Reduction of carbonnitrogen double and triple
bonds
9
Reduction of Ketones and Aldehydes
10
Rosenmund Reduction
11
(No Transcript)
12
Dissolving-Metal Reduction
Addition of an electron, a proton, an electron,
and a proton
13
Reduction by Addition of a Hydride Ion and a
Proton
14
Aldehydes, ketones, and acyl halides can be
reduced to alcohols by sodium borohydrides
15
LiAlH4 is a stronger reducing agent than
NaBH4 LiAlH4 is used to reduce compounds that
are unreactive toward NaBH4
16
DIBALH allows the addition of one equivalent of
hydride to an ester
Replacing some of the hydrogens of LiAlH4 with
OR groups decreases the reactivity of the metal
hydride
17
Formation of Amines by Reduction
18
NaBH4 can be used to selectively reduce an
aldehyde or a keto group in a compound
Alkenes and alkynes do not possess a partial
positive charge
19
Sodium borohydride can be used as a
chemoselective reducing agent
20
Oxidation of Alcohols
21
Oxidation of a Primary Alcohol
22
Mechanism of Alcohol Oxidation by the Swern
Oxidation
23
Oxidation of Aldehydes and Ketones
24
The Tollens reagent oxidizes only aldehydes
25
Both aldehydes and ketones can be oxidized by
peroxyacid the BaeyerVilliger oxidation
26
(No Transcript)
27
Mechanism of the BaeyerVilliger Oxidation
28
Predicting BaeyerVilliger reaction products
29
Controlling Stereochemistry in Synthesis
An enantioselective reaction forms more of one
enantiomer than of another
30
(No Transcript)
31
Hydroxylation of Alkenes
32
Mechanism for cis-Glycol Formation
Higher yields of the diol are obtained with
osmium tetroxide than with permaganate
33
Oxidative Cleavage of 1,2-Diols
34
Summary of Alkene Hydroxylation Reactions
35
Permaganate Cleavage of Alkenes
36
Examples of permaganate-mediated alkene cleavage
reactions
37
Oxidative Cleavage of Alkenes by Ozonolysis
Examples
38
Structure of Ozone
39
The alkene and ozone undergo a concerted
six-electron cycloaddition
Mechanism of ozonide formation
The molozonide is unstable because it has two OO
bonds, but the ozonide is stable
40
Ozonides can be cleaved to carbonyl compounds
41
Ozonolysis Mechanism
41
42
Examples of the Oxidative Cleavage of Alkenes by
Ozonolysis
43
The benzene ring is not oxidized under mild
ozonolysis conditions
44
Oxidative Cleavage of Alkynes
The same reagents that oxidize alkenes also
oxidize alkynes
45
Designing a Synthesis by Functional Group
Interconversion
Conversion of an aldehyde to other functional
groups
46
Conversion of a Ketone into an Ester or an
Alcohol