8. Aldehydes and Ketones Flashcards
What is the carbonyl group?
C double bonded to O
How are aldehydes named?
Using the suffix -al
How are ketones named?
Using the suffix -one, or the prefix oxo-
What is a primary alcohol oxidised to?
Aldehyde → Carboxylic acid
What is a secondary alcohol oxidised to?
Ketone
What would a suitable oxidising agent for primary and secondary alcohols be?
Acidified potassium dichromate
Why can ketones not be oxidised?
There is no hydrogen bonded to the carbonyl group
What is Fehling’s solution?
An alkaline solution that contains copper ions, which act as a mild oxidising agent
What happens when Fehling’s solution is mixed with an aldehyde and heated?
The aldehyde is oxidised to a carboxylic acid and the blue copper (II) ions are reduced to copper (I) oxide as a brick red precipitate
What is Tollen’s reagent made of?
Aqueous solutions of ammonia and silver nitrate
What happens when Tollen’s reagent is mixed with an aldehyde?
The aldehyde is oxidised to a carboxylic acid and the silver (I) ions are reduced to metallic silver
How can the oxidation process that produces aldehydes and ketones be reversed?
With a strong reducing agent (e.g. sodium tetrahydridoborate or lithium aluminium hydride)
What reducing agents can be used to reduce aldehydes and ketones?
- sodium tetrahydridoborate - NaBH4 (dissolved in water)
* lithium aluminium hydride (LiAlH4) - (dissolved in a non-aqueous solvent such as ethanol)
What do the reducing agents NaBH4 and LiAlH4 provide?
The hydride ion (H+) which acts as a nucleophile
In the reduction of aldehydes and ketones, what does the hydride ion from the reducing agent act as?
A nucleophile
What is formed when carboxylic acids are reduced?
Aldehyde → Primary Alcohol
What is formed when ketones are reduced?
Secondary alcohols
What type of mechanism is the reduction of an aldehyde?
Nucleophilic addition
What type of mechanism is the reduction of a ketone?
Nucleophilic addition
What does the addition of cyanide to an aldehyde or ketone form?
A hydroxynitrile
What kind of mechanism is it when cyanide and an aldehyde/ketone forms a hydroxynitrile?
Nucleophilic addition
What is the reagent when a hydroxynitrile is formed from an aldehyde/ketone?
KCN or NaCN (followed by H2SO4)
What is the nucleophile when a hydroxynitrile is formed from an aldehyde/ketone?
:CN-
Can hydroxynitrile be formed from aldehydes/ketones in a lab?
No
Why can’t hydroxynitrile be formed from aldehydes/ketones in a lab?
HCN is a very toxic gas and high flammable
How is HCN stored?
It is not stored, by made in situ by mixing KCN and dilute acid
What are the equations to show how HCN is produced in situ?
- sulphuric acid: 2KCN(s) + H2SO4 → 2HCN(g) + K2SO4
* hydrochloric acid: KCN(s) + HCl → HCN(g) + KCl
If HCN is stored, what is the best way to store it?
As a solid
Is HCN toxic?
Yes
In the formation of hydroxynitrile from aldehydes/ketones, when will chiral molecules be formed?
When the reactants are aldehydes or unsymmetrical ketones
Can the products of the reactions of cyanide with aldehyde/ketones display optical isomerism?
Yes - if the reactant is an aldehyde or an unsymmetrical ketone
Why do the products aldehydes and unsymmetrical ketones with HCN display optical isomerism?
The carbonyl group is planar meaning there is an equal chance that the nucleophile will attack either side of the molecule resulting in a racemate
Conditions of oxidation of an aldehyde to carboxylic acid?
Warm under reflux
Observation for oxidation of an aldehyde to carboxylic acid?
Orange to green
Conditions for reduction of carbonyl to alcohol?
Room temperature
Conditions for addition of HCN carbonyl to hydroxynitrile?
Room temperature
