PTT 102ORGANIC CHEMISTRY

SEM I 2012/2013

Dr. Hayder kh. Q. Ali

School of Bioprocess EngineerUniMAP

Outline Carbonyl Condensation Micheal Reaction

Aldol

Claisen

1. Carbonyl Condensation Carbonyl compounds are both the electrophile and

nucleophile in carbonyl condensation reactions

Aldol Condensation Acetaldehyde reacts in basic solution (NaOEt, NaOH)

with another molecule of acetaldehyde The b-hydroxy aldehyde product is aldol (aldehyde +

alcohol) This is a general reaction of aldehydes and ketones

General Condensations

5

Mechanism of Aldol Reactions

Aldol reactions, like all carbonyl condensations, occur by nucleophilic addition of the enolate ion of the donor molecule to the carbonyl group of the acceptor molecule

The addition intermediate is protonated to give an alcohol product

Predicting Aldol ProductsThe product will have an alcohol and a carbonyl in a 1,3 relationship (a beta-hydroxy carbonyl)

1. Claisen Condensation

Condensation of Two Ester Molecules. The product of a Claisen condensation is a β-

keto ester. In a Claisen condensation, one molecule of

carbonyl compound is the nucleophile and second molecule is electrophile.

The new C-C bond connect the α-carbon of one molecule and the carbon that was formerly the carbonyl carbon of the other molecule

Mechanism of the Claisen Condensation

Similar to aldol condensation: nucleophilic acyl substitution of an ester enolate ion on the carbonyl group of a second ester molecule

If the starting ester has more than one acidic a hydrogen, the product b-keto ester has a doubly activated proton that can be abstracted by base

Requires a full equivalent of base rather than a catalytic amount

The deprotonation drives the reaction to the product

Learning Check:

Predict the product of Claisen condensation of ethyl propanoate

Solution:Predict the product of Claisen condensation of ethyl propanoate

Mixed Claisen Condensations

Successful when one of the two esters acts as the electrophilic acceptor in reactions with other ester anions to give mixed b-keto esters

2.Conjugate Carbonyl Additions: The Michael Reaction

Enolates can add as nucleophiles to ,b-unsaturated aldehydes and ketones to give the conjugate addition product

Mechanism of the Michael

Nucleophilic addition of a enolate ion donor to the b carbon of an ,b-unsaturated carbonyl acceptor

Learning Check: Make the following using a Michael Reaction:

Solution: Make the following using a Michael Reaction:

Which of the following statements explains why the following aldehyde will not undergo an aldol reaction with itself?

1. The benzene ring makes the carbonyl group unreactive towards aldol reactions.

2. A carbonyl group must be connected to two alkyl groups in order to undergo an aldol reaction.

3. The molecule does not possess any hydrogens α to the carbonyl group.

4. Electrophilic aromatic substitution competes favorably with the aldol reaction.

5. Nucleophilic acyl substitution competes favorably with the aldol reaction.

Learning Check:

Which of the following statements explains why the following aldehyde will not undergo an aldol reaction with itself?

1. The benzene ring makes the carbonyl group unreactive towards aldol reactions.

2. A carbonyl group must be connected to two alkyl groups in order to undergo an aldol reaction.

3. The molecule does not possess any hydrogens α to the carbonyl group.

4. Electrophilic aromatic substitution competes favorably with the aldol reaction.

5. Nucleophilic acyl substitution competes favorably with the aldol reaction.

Solution:

Predict the aldol reaction product of the following ketone.

O OH

1.O OH

2.O

HO

3.

O OH

4.

OHO

5.

O NaOH

Ethanol

Learning Check:

Predict the aldol reaction product of the following ketone.

O OH

1.O OH

2.O

HO

3.

O OH

4.

OHO

5.

O NaOH

Ethanol

Solution:

What type of reaction occurs in a Claisen condensation?

1. electrophilic aromatic substitution

2. nucleophilic addition3. hydrolysis4. nucleophilic acyl

substitution5. decarboxylation

Learning Check:

What type of reaction occurs in a Claisen condensation?

1. electrophilic aromatic substitution

2. nucleophilic addition3. hydrolysis4. nucleophilic acyl

substitution5. decarboxylation

Solution:

Select the correct Claisen condensation product for the following reaction.

1. 2. 3.

4. 5.

Learning Check:

Predict the outcome of the following reaction.

1. 2. 3.

4. 5.

Solution: