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PTT 102 Organic Chemistry Sem I 2012/2013

Rozaini Abdullah School of Bioprocess Eng UniMAP Week 10. PTT 102 Organic Chemistry Sem I 2012/2013. Outline. Aldol. Carbonyl Condensation Micheal Reaction. Claisen. 1. Carbonyl Condensation.

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PTT 102 Organic Chemistry Sem I 2012/2013

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  1. Rozaini Abdullah School of Bioprocess Eng UniMAP Week 10 PTT 102Organic Chemistry Sem I 2012/2013

  2. Outline Aldol • Carbonyl Condensation • Micheal Reaction Claisen

  3. 1. Carbonyl Condensation • Carbonyl compounds are both the electrophile and nucleophile in carbonyl condensation reactions

  4. Aldol Condensation • Acetaldehyde reacts in basic solution (NaOEt, NaOH) with another molecule of acetaldehyde • The b-hydroxyaldehydeproduct is aldol (aldehyde + alcohol) • This is a general reaction of aldehydes andketones

  5. General Condensations

  6. 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

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

  8. 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

  9. Mechanism of the ClaisenCondensation • Similar to aldol condensation: nucleophilicacyl 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 -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

  10. Learning Check: Predict the product of Claisen condensation of ethyl propanoate

  11. Solution: Predict the product of Claisen condensation of ethyl propanoate

  12. Mixed Claisen Condensations • Successful when one of the two esters acts as the electrophilic acceptor in reactions with other ester anions to give mixed -keto esters

  13. 2.Conjugate Carbonyl Additions: The MichaelReaction • Enolates can add as nucleophiles to ,-unsaturated aldehydes and ketones to give the conjugate addition product

  14. Mechanism of the Michael • Nucleophilic addition of a enolate ion donor to the  carbon of an ,-unsaturated carbonyl acceptor

  15. Learning Check: • Make the following using a Michael Reaction:

  16. Solution: • Make the following using a Michael Reaction:

  17. Learning Check: Which of the following statements explains why the following aldehyde will not undergo an aldol reaction with itself? • The benzene ring makes the carbonyl group unreactive towards aldol reactions. • A carbonyl group must be connected to two alkyl groups in order to undergo an aldol reaction. • The molecule does not possess any hydrogens α to the carbonyl group. • Electrophilic aromatic substitution competes favorably with the aldol reaction. • Nucleophilic acyl substitution competes favorably with the aldol reaction.

  18. Which of the following statements explains why the following aldehyde will not undergo an aldol reaction with itself? Solution: • The benzene ring makes the carbonyl group unreactive towards aldol reactions. • A carbonyl group must be connected to two alkyl groups in order to undergo an aldol reaction. • The molecule does not possess any hydrogens α to the carbonyl group. • Electrophilic aromatic substitution competes favorably with the aldol reaction. • Nucleophilic acyl substitution competes favorably with the aldol reaction.

  19. 2. 1. 3. 4. 5. Predict the aldol reaction product of the following ketone. Learning Check: • 1 • 2 • 3 • 4 • 5

  20. 2. 1. 3. 4. 5. Solution: Predict the aldol reaction product of the following ketone. • 1 • 2 • 3 • 4 • 5

  21. What type of reaction occurs in a Claisen condensation? Learning Check: • electrophilic aromatic substitution • nucleophilic addition • hydrolysis • nucleophilicacyl substitution • decarboxylation

  22. What type of reaction occurs in a Claisen condensation? Solution: • electrophilic aromatic substitution • nucleophilic addition • hydrolysis • nucleophilicacyl substitution • decarboxylation

  23. 1. 2. 3. 5. 4. Select the correct Claisen condensation product for the following reaction. Learning Check: • 1 • 2 • 3 • 4 • 5

  24. 2. 1. 3. 5. 4. Predict the outcome of the following reaction. Solution: • 1 • 2 • 3 • 4 • 5

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