Oxidation And Reduction
Lecture-05
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1. Oxidation
• Oxidation is a reaction, during which the
average oxidation value of a compound
increases
• This can undergo due to:
Withdrawal of electrons
Withdrawal of hydrogen =
Dehydrogenation
Insertion of oxygen
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2. Reduction
• Reduction is a reaction, during which
the average oxidation value of a
compound decreases
• This can undergo due to:
Insertion of electrons
Insertion of hydrogen = hydrogenation
Withdrawal of oxygen
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3. The Oxidation Value in an Organic
Compound
• Determination of formal charge in three steps:
Step1: in a bond, all binding electrons are added to more electronegative partner
Step 2: in a bond of two identical bond partners, a half of the binding electrons are added to each bond partner
Step 3: Compare the sum of outside electrons of an atom in the compound with that of atom in question in elemental state
(Vergleich dieser Anzahl an Außenelektronen am Atom in der Verbindung mit der Anzahl der Außenelektronen des betreffenden Atoms im elementaren Zustand)
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Oxidation Values
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Oxidation Values of C-Atoms in
Different Compounds
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Titration of Diazo Dyes With Ti(III)
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Change in Oxidation Values
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PONCEAU 4R
N NS
S
HO
NaO
O
O
NaO
O
O
S
O
O
ONa
CLogP: 0.3888
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Reduction Products of
PONCEAU 4R
NH2H2N
S
S
HO
NaO
O
ONaO
O
O
S
O
O
ONa
CLogP: -2.152
CLogP: 0.117
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4. Oxidability (Oxidierbarkeit)
• Oxidability is the ability of a substance or a functional Group to be oxidized = Reducing ability
• A measure for the oxidability of functional group is the ionization potential, which can be polarographically determined (half wave potential). The measurement of ionization potential should be carried out to calculate the energy needed to abstract an electron from a substance
• The oxidability is a property of a substance. It depends not only from physical parameter, ionization potential, but also from chemical behavior, i.e. the reactivity against oxidizing agent
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Voltammogram of Fe
Fe(III) Fe(II) Fe(II) Fe
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5. Oxidation Reaction
• Alcohol, Aldehyd, Carboxylic Acid
• Chromate as oxidizing agent: Chrom(VI)-
Compounds (Chromates) in different solvents
are used
• Examples:
I. HCrO4 - in H2O: preparation: dissolve CrO3 in
H2O
II. CrO3 in acetone: Jones-Reagenz. Reaction:
Jones-Oxidation.
The basic reaction mechanism in the oxidation of
alcohols or aldehyds are as follows:13Rahmana Emran / SF ITB
Oxidation of an Alcohol to Aldehyd or
Keton
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Oxidation of Aldehyd to Carboxylic
Acid
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Swern-Oxidation:
• The use of dimethylsulfoxide as Oxidizing
agent:
• The activation of DMSO:
Sulfonium-Ion Sulfonium-IonOxalylchloride 16Rahmana Emran / SF ITB
Sulfonium-ion A and B are strong electrophiles and react in a
substitution reaction with alcohol to produce Sulfuran C.
Sulfuran
Dissoziation to sulfonium-ion D:
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Production of Sulfonium-Ylid E: CH acidity of Sulfonium-ion D
End step: Keton/Aldehid, under beta-elimination
via cyclic intermediate
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Oppenauer-Oxidation
Application: oxidation of steroid
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Mechanism1. Exchange of Ligand:
2. Reaction of Lewis Acid (Al-alcanolate) and Base
(Acetone), activated C-alpha:
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3. Hyride Shifting: from alcohol to activated alpha-C:
4. Dissoziation: release of oxidation product:
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3. Oxidation of Diol and
Olefin1. Epoxidation (Prileschaew-Reaction): electrophilic
Addition
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2. Lemieux-Johnson- und Malaprade-
Oxidation: Production of aldehyd from alkene
Mechanism of Lemieux-Johnson-Oxidation: 1. „Anlagerung“ of
osmium tetraoxide, 2. Hydrolisis
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2. Malaprada Oxidation:
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4. Oxidation of Keton to
EsterBaeyer-Villiger-Oxidation: 1. Addition of percarboxylic acid
to double bond, 2. Oxidation via cyclic intermediate
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