1. 32 The Aldehydes & Ketones
Organic Chemistry
32 The Aldehydes & Ketones
Leaving Certificate Chemistry

2. The First 4 Aldehydes Structural Formulae
Methanal: HCHO O
group present ― ―
1 Carbon-Long
― C
― H O H C H

3. The First 4 Aldehydes Structural Formulae
Ethanal: CH3CHO O ― ―
2 Carbons
Long
― C
― H
group present H O
Acetaldehyde (systematically ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part of their normal metabolism. It is also produced by oxidation of ethylene and is popularly believed to be a cause of hangovers from alcohol consumption.[4] Pathways of exposure include air, water, land or groundwater as well as drink and smoke.[5] H C C H H

4. The First 4 Aldehydes Structural Formulae
Propanal: C2H5CHO O ― ―
3 Carbons
Long
― C
― H
group present H H O H C C C H H H

5. The First 4 Aldehydes Structural Formulae
Butanal: C3H7CHO O ― ―
4 Carbons
Long
― C
― H
group present H H H O H C C C H C H H H

6. O H
Benzaldehyde
At room temperature it is a colourless liquid with a characteristic and pleasant almond-like odour C

7. Physical Properties of the aldehydes
Use electronegativity differences to predict what kinds of bonds are present in an aldehyde such as ethanal. HINT - USE THE RULES
Can you predict whether an aldehyde or its corresponding alkane would have a higher boiling point? HINT - Think about the intermolecular forces present
Can you explain why the boiling points of the aldehydes increase with the length of the chain? HINT - Think about the intermolecular forces present
Would the lower or higher members of the aldehydes be more soluble in water? HINT – water is polar. LIKE DISSOLVES LIKE

8. The First 2 Ketones Structural Formulae
Propanone: CH3COCH3 O ― ―
3 Carbons
Long
C ― C
― C
group present H O H
Nail Varnish Remover H C C C H H H
An isomer of propanal

9. The First 2 Ketones Structural Formulae
Butanone: CH3COC2H5 O
An isomer of butanal ― ―
4 Carbons
Long
C ― C
― C
group present H O H H H C C C C H H H H

10. Physical Properties of the ketones
Use electronegativity differences to predict what kinds of bonds are present in an ketones such as propanone. HINT - USE THE RULES
Can you predict whether an ketone or its corresponding alkane would have a higher boiling point? HINT - Think about the intermolecular forces present
Can you explain why the boiling points of the ketones increase with the length of the chain? HINT - Think about the intermolecular forces present
Would the lower or higher members of the ketones be more soluble in water? HINT – water is polar. LIKE DISSOLVES LIKE

11. Formation of an aldehyde or ketone
Oxidation of a primary or secondary alcohol

12. Oxidation of a primary alcohol
Methanol CH3OH O H H
Acidified Sodium Dichromate H C H H C OH
Methanal HCHO H H O H C OH
Excess
Methanoic Acid HCOOH

13. Oxidation of a primary alcohol
Ethanol C2H5OH H
Acidified Sodium Dichromate H H H C C OH H H H H O H O H C C H
Excess H C C OH
Ethanoic Acid CH3COOH
Ethanal CH3CHO H H

14. Oxidation of a primary alcohol
Acidified Sodium Dichromate H H H
Propanoic Acid C2H5COOH
Propanol C3H7OH
Propanal C2H5CHO
Excess

15. Oxidation of a primary alcohol
Butanol
Butanal
Butanoic Acid
On reaction with acidified sodium dichromate
In Excess

16. The Alkanes - H2 The Chloroalkanes + H2 The Alkenes + HCl , + Cl2
Substitution
using UV Light
Ethane C2H6
- H2
The Chloroalkanes
+ H2
Chloroethane C2H5Cl
The Alkenes
+ HCl , + Cl2
Ethene C2H4
+ H2O
The Alcohols
Ethanol C2H5OH
- H2O
Aluminium Oxide Catalyst
The Polymers
Polythene & Polypropene

17. The Alcohols The Aldehydes The Carboxylic Acids Ethanol C2H5OH
Acidified sodium dichromate
Hydrogen,
Nickel catalyst
Oxidation
Reduction
The Aldehydes
Ethanal CH3CHO
Acidified sodium dichromate
Reduction
Hydrogen,
Nickel catalyst
Oxidation
The Carboxylic Acids
Ethanoic Acid CH3COOH

18. Oxidation of a secondary alcohol
Acidified Sodium Dichromate H H H
Propanone
Propan-2-ol
Nail Varnish Remover
Oxidation of a secondary alcohol produces a ketone

19. Oxidation of a secondary alcohol
Acidified Sodium Dichromate H H H H
Butanone
Butan-2-ol
Oxidation of a secondary alcohol produces a ketone

20. The Ketones The Alcohols The Aldehydes The Carboxylic Acids
Oxidation of a secondary alcohol
The Ketones
Acidified sodium dichromate
The Alcohols
H2, Ni
Reduction
Propanone from propan-2-ol
Ethanol C2H5OH
Acidified sodium dichromate
Hydrogen,
Nickel catalyst
Oxidation
Reduction
The Aldehydes
Ethanal CH3CHO
Acidified sodium dichromate
Reduction
Hydrogen,
Nickel catalyst
Oxidation
The Carboxylic Acids
Ethanoic Acid CH3COOH

21. Tests to distinguish between an aldehyde and a ketone
Acidified Potassium Permanganate H
Add 5 cm3 of Acidified potassium permanganate H O
No reaction occurs with a ketone H
Add 2 cm3 of ethanal (aldehyde), heat and shake H C C OH H
The pink colour turns colurless
Ethanoico acid formed
CH3COOH
Test tube
Heat

22. Tests to distinguish between an aldehyde and a ketone
Fehling’s Test H
Add 1 cm3 of Fehling’s No. 1 & 1 cm3 of Fehling’s No. 2 solutions H O
No reaction occurs with a ketone H H C C OH
Add 1 cm3 of ethanal (aldehyde), heat and shake H
A brick red precipitate is observed
Ethanoic acid formed
CH3COOH
Test tube
Heat

23. Tests to distinguish between an aldehyde and a ketone
Tollen’s Reagent H
Add 3 cm3 of Silver Nitrate solution and 1 cm3 of Sodium Hydroxide solution H O
No reaction occurs with a ketone H H C C OH
Add a few drops of ammonia solution and shake. Then add 4-5 drops of ethanal and heat water bath
Ha;f reactions must be known H
Ethanoic acid formed
CH3COOH
A “silver mirror” is observed
Test tube
Heat

24. Watch video on you tube - http://www.youtube.com/watch?v=TRFkU6442oo
See animations videos
fehlings test
silver mirror test
And