oxidation and reduction - wordpress.comdec 05, 2010 · 3. the oxidation value in an organic...

Oxidation And Reduction

Lecture-05

1Rahmana Emran / SF ITB

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


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


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)


Oxidation Values


Oxidation Values of C-Atoms in

Different Compounds


Titration of Diazo Dyes With Ti(III)


Change in Oxidation Values


PONCEAU 4R

N NS

S

HO

NaO

O

O

NaO

O

O

S

O

O

ONa

CLogP: 0.3888


Reduction Products of

PONCEAU 4R

NH2H2N

S

S

HO

NaO

O

ONaO

O

O

S

O

O

ONa

CLogP: -2.152

CLogP: 0.117


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


Voltammogram of Fe

Fe(III) Fe(II) Fe(II) Fe


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


Oxidation of Aldehyd to Carboxylic

Acid


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:


Production of Sulfonium-Ylid E: CH acidity of Sulfonium-ion D

End step: Keton/Aldehid, under beta-elimination

via cyclic intermediate


Oppenauer-Oxidation

Application: oxidation of steroid


Mechanism1. Exchange of Ligand:

2. Reaction of Lewis Acid (Al-alcanolate) and Base

(Acetone), activated C-alpha:


3. Hyride Shifting: from alcohol to activated alpha-C:

4. Dissoziation: release of oxidation product:


3. Oxidation of Diol and

Olefin1. Epoxidation (Prileschaew-Reaction): electrophilic

Addition


2. Lemieux-Johnson- und Malaprade-

Oxidation: Production of aldehyd from alkene

Mechanism of Lemieux-Johnson-Oxidation: 1. „Anlagerung“ of

osmium tetraoxide, 2. Hydrolisis


2. Malaprada Oxidation:


4. Oxidation of Keton to

EsterBaeyer-Villiger-Oxidation: 1. Addition of percarboxylic acid

to double bond, 2. Oxidation via cyclic intermediate


oxidation and reduction - wordpress.comdec 05, 2010 · 3. the oxidation value in an organic...

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