Aldehyde & Ketone
Reactions
Formation of an Aldehyde
Oxidation of Primary Alcohols
• General equation:
– Primary alcohol
aldehyde
RCH2CH=O
EXAMPLE:
1-propanol
Formation of a Ketone
Oxidation of Secondary Alcohols
• General equation:
– Secondary alcohol
R
O
C
[O]
H
R
H
EXAMPLE:
2-propanol
ketone
O
R-C-R
Review from Chapter 13!!
Oxidation of Tertiary Alcohols
• General equation:
– Tertiary alcohol
NO REACTION!!!
YOU TRY THESE!
• Write an equation showing the oxidation of
the following alcohols. Be sure to name the
product formed.
(a) 1-pentanol
(b) 2-butanol
Oxidation of Aldehydes
• Aldehydes are easily oxidized further to form
carboxylic acids.
• Oxidation process:
Primary alcohol  Aldehyde  Carboxylic acid
[O]
[O]
1-butanol
2-methyl-1-propanol
[O]
[O]
Reduction Reactions
• Both aldehydes and ketones are easily
reduced back to the corresponding alcohol.
This process is called hydrogenation.
OH
O
H
+
R1
R2
Catalyst
R1
R2
H
H
Lab Tests for
Aldehydes and Ketones
Tollen’s Test
•Tests for ALDEHYDES (not ketones)
•Silver ion is reduced to silver metal
•The aldehyde is oxidized to a carboxylic acid
anion
•AKA the Silver Mirror Test
Tollen’s Test
O
R-CH
+
Aldehyde
silver
Ag(NH ) +
3 2
silver ammonia
O
R-C-O-
+ Ag0
carboxylic
complex
acid anion metal
“Tollen’s Reagent”
mirror
Write equations for the following reactions
1. ethanal + Tollen’s reagent
2. 2- pentanone + Tollen’s reagent
3. propanal + Tollen’s reagent
Benedict’s Test
Indicates the presence of an aldehyde
A buffered aqueous solution of copper (II)
hydroxide and sodium citrate
Reacts to oxidize aldehydes
Forms a red solid – Cu2O
Benedict’s Test
All sugars are aldehydes or ketones
Benedict’s solution can be used to test urine
for glucose (an aldehyde), which is common in
uncontrolled diabetes
The amount of red precipitate formed is
directly proportional to the amount of glucose
in the urine.
Benedict’s Test
 O OH OH H H
HC – C - C - C - C - CH2OH + 2Cu+2
H H OH OH
(from Benedict’s Solution)
O OH OH H H
-O - C - C - C - C - C -CH OH
2
H H OH OH
+ Cu2O
red precipitate
Addition Reactions
I. Addition of an Alcohol to an Aldehyde – Acetal
formation
O
H
H+
OH
H
R1-C-H + O-R2
R1-C-OR2 + O-R2
H
Aldehyde
alcohol
Hemiacetal (quite reactive)
H+
OR2
R1-C-OR2
H
Acetal
Addition Reactions
• -OR group is an alkoxyl group
• Hemiacetals are very reactive, so in the
presence of acid and excess alcohol, will
continue to react to form an acetal
Addition Reactions
2. Addition of an alcohol to a ketone – KETAL formation
O
H
OH
H
R1-C-R2 +
O-R3
H+
R1-C-OR3 +
OR3
R2
Ketone
alcohol
Hemiketal
H+
OR3
R1-C-OR3
R2
Ketal
Practice Problems
• Propanal + Methanol
• 3-hexanone + ethanol
Keto-Enol Tautomers
• Many aldehydes & ketones exist in a mixture
of two constitutional isomers, informally
referred to as tautomers.
R
R
1
O
2
R
Keto form
3
R
R
1
OH
2
R
Enol form
3
Practice
• Draw the enol form of the aldehydes and
ketones listed below.
– Ethanal
– 2-pentanone
– Butanal
Aldol Condensation
• Reaction in which aldehydes & ketones react
to form larger molecules. A new carboncarbon bond is formed in the process.
O
R
1
O
+
R
OH
-
OH or
R
2
O
1
enzyme
R
Aldehyde
Aldehyde
Aldol
• Actually occurs between an aldehyde in the
keto form and one in the enol form.
2
Example
• Write an equation for the aldol condensation
of two molecules of butanal.
O
Butanal
+
HO
OH
Butanal (enol form)
-
- -
O
3 hydroxy 2 ethylhexanal