Module J Oxidation & Reduction in Organic Chemistry

Alkenes Structure and Reactivity:  Oxidation results in a loss of electron-density at carbon

 This occurs when carbon becomes bonded to more
Reductions and Oxidations electronegative elements
Bruice’s Organic Chemistry: Chapters 5,6 Oxidation: break C-H (or C-C) and form C-O, C-N, C-X

Learning Outcomes:

1. What are oxidations and reductions in organic chemistry?  Reduction results in a gain of electron-density at carbon
2. How to reduce alkenes?
 This occurs when carbon becomes bonded to less electronegative
3. How to oxidize alkenes?
atoms, such as hydrogen (proton)
4. How to induce the oxidative cleavage of alkenes?
Reduction: form C-H (or C-C) and break C-O, C-N, C-X

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Oxidation and Reduction of Alkenes Module J

Addition reactions: The overall electron density change of
both C=C carbon atoms are considered: Alkenes Structure and Reactivity:
Reductions and Oxidations
Bruice’s Organic Chemistry: Chapters 5,6

Learning Outcomes:

1. What are oxidations and reductions in organic chemistry?

2. How to reduce alkenes?
3. How to oxidize alkenes?
(OH) 4. How to induce the oxidative cleavage of alkenes?

HOH
COH
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 Addition of H2: Hydrogenation Catalytic Hydrogenation
 Thermodynamically
favoured, but high
No reaction activation energy
 Needs catalyst: eg.
Unsaturated Saturated Pt, Pd, Ni, Rh, Ru

 Overall, a reduction
 The reaction is thermodynamically favoured
palladium on C
 Two new -bonds more energetically favoured than one -bond
 However, there is no spontaneous reaction
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Catalytic Hydrogenation Catalytic Hydrogenation Stereoselectivity

H H
 The addition of H2 to the alkene is syn

H2 becomes reactive as Alkene also

H atoms adsorbed on metal adsorbs on metal
surface surface

Step-wise addition of H Syn addition

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Catalytic Hydrogenation Stereoselectivity Catalytic Hydrogenation Stereospecificity
 Carbon-carbon multiple bonds reduced selectively
 Typically C=O, C=N bonds do not react

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Catalytic Hydrogenation Stereospecificity Hydrogenation of Oils

 A non-chemistry description of making margarine:

Rotated
we can understand more if we know the chemistry
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 Hydrogenation of Oils Hydrogenation of Oils

 Incomplete hydrogenation leads to reversible addition and

isomerization of alkene to the more stable isomer
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Module J
Oxidations of Alkenes
Alkenes Structure and Reactivity:  Compare:
Reductions and Oxidations
Bruice’s Organic Chemistry: Chapters 5,6

Learning Outcomes:

1. What are oxidations and reductions in organic chemistry?

2. How to reduce alkenes?
3. How to oxidize alkenes? 1,2-diol
4. How to induce the oxidative cleavage of alkenes? vicinal diol
vic-diol

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 Oxidations of Alkenes Dihydroxylation of Alkenes
 Compare:

Mechanism: WHY syn?

H 2O

Osmate ester
epoxide Concerted
addition
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Dihydroxylation of Alkenes Dihydroxylation of Alkenes

 Example:
 OsO4 (Osmium tetroxide) is highly
toxic and expensive
 To make this reaction more
practical, we can use a catalytic
amount of OsO4 together with OsO3

another stoichiometric oxidant

(eg. N-methylmorpholine N-oxide,
NMO) which can reoxidize the
used Os(VI) back to Os(VIII)O4

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Exercise 6 Exercise 6
 Provide the starting materials, reagents and conditions to synthesize  Provide the starting materials, reagents and conditions to synthesize
the following alcohols. the following alcohols.
 Give the IUPAC names of the two alkene starting materials.  Give the IUPAC names of the two alkene starting materials.
cat. OsO4
NMO

H2O
(Z)-hex-2-ene

1. BH3

2. NaOH,H2O2
(Z)-3-methylpent-2-ene

Epoxidation of Alkenes Epoxidation of Alkenes

Peroxyacid  Example of a peracid:
or  Meta-chloroperoxybenzoic acid (MCPBA)
Peracid

Carboxylic acid

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 Epoxidation of alkenes Module J
 Mechanism: Alkenes Structure and Reactivity:
Reductions and Oxidations
Bruice’s Organic Chemistry: Chapters 5,6

Learning Outcomes:

1. What are oxidations and reductions in organic chemistry?

2. How to reduce alkenes?
3. How to oxidize alkenes?
4. How to induce the oxidative cleavage of alkenes?

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Oxidative Cleavage of Alkenes: Ozonolysis Oxidative Cleavage of Alkenes: Ozonolysis

 Further oxidation results in cleavage of C-C bond

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Oxidative Cleavage of Alkenes: Ozonolysis Oxidative Cleavage of Alkenes: Ozonolysis
 Mechanism:
 Mechanism involves two cyclic ozonides

Molozonide

Zn

Ozonide

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Summary of Reactions of Alkenes Module J

 Reagent?
Alkenes Structure and Reactivity:


Conditions?
Regioselectivity?
Reductions and Oxidations
 Stereoselectivity?
 Stereospecificity? Bruice’s Organic Chemistry: Chapters 5,6
Ether  Mechanisms?
 Oxidation? Reduction? Check that you have achieved these learning outcomes, and can give
Not redox? examples to explain and answer each of these questions:

1. What are oxidations and reductions in organic chemistry?

 Can I combine these
reactions to do a 2. How to reduce alkenes?
synthesis? 3. How to oxidize alkenes?
4. How to induce the oxidative cleavage of alkenes?
Haloether
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