Reactions of Aldehydes and Ketones with Sodium Hydroxide
E. Reactions of Aldehydes and Ketones with Sodium Hydroxide
Objectives:
To know the reactions of aldehydes and ketones with sodium hydroxide
a) State the function of Sodium Hydroxide in the test.
Sodium hydroxide (NaOH) is the oxidizing agent.
b) What are the principles involved in the test? What is its purpose?
Cannizzaro reaction is a reaction that uses a strong base, such as sodium hydroxide, which results to the formation of a carboxylic acid (or its corresponding salt) and an alcohol. It is only observed in aldehydes that do not contain alpha hydrogen atoms.
Aldol condensation is a reaction in which an enolate ion reacts with a carbonyl compound to form an α-hydroxyaldehyde or β-hydroxyketone, followed by a dehydration to give a conjugated enone.
c) Provide the type equations used in the test.
Cannizzaro reaction
Aldol condensation
d) Show the sample equations involved in the reactions between:
40% sodium hydroxide and your sample/s which gave a positive result
10% sodium hydroxide and your sample/s which gave a positive result
e) Provide a possible explanation for:
Positive results obtained with your sample/s
Fehling’s Test is a test used to determine whether a carbonyl-containing compound is an aldehyde or a ketone.
The aldehyde is oxidized, having a carboxylate anion, and in the process the copper (II) ions (blue solution) are reduced to copper (I) which forms red precipitate.
Negative results obtained with your sample/s
Ketones cannot be further oxidized therefore there is no formation of red precipitate. The blue solution is retained.
f) What is the purpose of acidification with HCl?
HCl is used to neutralize the excess base. It is also used to re-protonate one of the products.
*Note: what will give a positive result = no alpha hydrogens
Objectives:
To know the reactions of aldehydes and ketones with sodium hydroxide
a) State the function of Sodium Hydroxide in the test.
Sodium hydroxide (NaOH) is the oxidizing agent.
b) What are the principles involved in the test? What is its purpose?
Cannizzaro reaction is a reaction that uses a strong base, such as sodium hydroxide, which results to the formation of a carboxylic acid (or its corresponding salt) and an alcohol. It is only observed in aldehydes that do not contain alpha hydrogen atoms.
Aldol condensation is a reaction in which an enolate ion reacts with a carbonyl compound to form an α-hydroxyaldehyde or β-hydroxyketone, followed by a dehydration to give a conjugated enone.
c) Provide the type equations used in the test.
Cannizzaro reaction
Aldol condensation
d) Show the sample equations involved in the reactions between:
40% sodium hydroxide and your sample/s which gave a positive result
10% sodium hydroxide and your sample/s which gave a positive result
e) Provide a possible explanation for:
Positive results obtained with your sample/s
Fehling’s Test is a test used to determine whether a carbonyl-containing compound is an aldehyde or a ketone.
The aldehyde is oxidized, having a carboxylate anion, and in the process the copper (II) ions (blue solution) are reduced to copper (I) which forms red precipitate.
Negative results obtained with your sample/s
Ketones cannot be further oxidized therefore there is no formation of red precipitate. The blue solution is retained.
f) What is the purpose of acidification with HCl?
HCl is used to neutralize the excess base. It is also used to re-protonate one of the products.
*Note: what will give a positive result = no alpha hydrogens