3.3.8 - Aldehydes And Ketones Flashcards
Aldehydes end in …
And give example
- Anal
Eg pentanal
Ketones end in …
Give example ..
-one
Eg propanone
What is carbonyl group
C=O
Can ketones be oxidesued
No
Aldehydes can be readily oxidised to ..
Carboxylic acids
Propanal oxidised to…
Propanoic acid
How to distinguish between aldehyde and ketone
(2 ways)
Tollens reagent
Fehlings solution
+ve result for aldehyde using tollens
Silver mirror
-ve test result for ketone using tollens
No visible change
What colour is fehlings solution and whag is it
Blue solution of copper (ll) ions
Dissolves in NaOH
+ve test result for aldehydes using fehlings solution
Brick red ppt
Of copper (l) oxide
A primary alchol can be oxidised into a …. And then to a …
1• alcohol —-> aldehyde —> carboxylic acid
Secondary alcohol can be oxidised into a …
Ketone
Aldehydes can be reduced into ..
Primary alchol
Ketones can be reduced into …
Secondary Alcohol
What is the reducing agent
NaBH4
CN can react with carbonyls to undergo nucleophillic addition via
Reacting w KCN
or HCN
How to draw cyanide ion
- :CN
Lone pair … minus sign must be on top of carbon
Aldehydes and unsymmetric ketones form mixtures of _____ When reacted with KCN followed by a dilute acid
Enantiomers
Hazards of using KCN
- is an irritant, dangerous if digested or inhaled
- toxic and poisonous
why is KCN used instead of HCN
HCN is weak
General equation for reacting aldehyde with KCN
H+(aq)
RCHO(aq) + KCN(aq) —> RCH(OH)CN(aq) + K^+ (aq)
Equation for overall reaction between ketone and KCN
H+(aq)
RCOR’ (aq) + KCN (aq) —> RCR’(OH)CN (aq) + K+(aq)
why does NaBH4 reduced butanal but not butene
3 H–
ion / nucleophile is attracted to δ+ C
1
M4 electron rich C=C
1
M5 H–
ion / nucleophile is repelled by C=C
OR
C=C only attacked by/reacts with electrophiles
Why is a mixture of enantiomers formed when reacting an unsymmetrical ketone or any aldehyde (except methanal) with KCN
Double bonds in carbonyl groups ( C=O)
These C=O are planar so equal change that nucleophile will attach from either directions (top or bottom)
Thus an equal amount of each enantiomer will be formed
—> racemic mixture of products
Overall equations for reduction reactions for aldehydes and ketones using [H]
Aldehyde or ketone + [H] —> alcohol
Equation for reduction of ethanal using [H]
CH3CHO + 2[H] —> CH3CH2OH
This question is about ketones.
(a) Solution X reacts with liquid ketones to form a crystalline solid.
This reaction can be used to identify a ketone if the crystalline solid is
separated, purified by recrystallisation, and the melting point determined.
Describe how the crystalline solid is separated and purified.
filter
dissolve in minimum volume of hot solvent
cool / leave (to crystallise) AND filter (under reduced pressure)
Wash with cold solvent/water, and dry w filter paper
describe what happens when a reaction mixture is refluxed and why it is necessary, in this case, for complete oxidation to ethanoic acid
A mixture of liquids is heated to boiling point for a prolonged time
Vapour is formed which escapes from the liquid mixture, is changed
back into liquid and returned to the liquid mixture
Any ethanal and ethanol that initially evaporates can then be oxidised
