Download Reactions to know from Chapters 17, 18, 19

Reactions to know from Chapters 17, 18, and 19
1. Oxidation of aldehydes
O
O
K2Cr2SO4
H2SO4
H
Butanal
OH
Butanoic acid
 Aldehydes will oxidize in the presence of oxygen only [O], the above
oxidizing agent and catalyst will work, but not necessary.
 Ketones do not oxidize
2. Reduction of aldehydes and ketones
 Aldehydes are reduced to primary alcohols, ketones are reduced to
secondary alcohols
a) Using H2 and a metal catalyst (Pd)
O
OH
Pd
+ H2
2-pentanol
2-pentanone
 This is a non-selective process, it will reduce double bonds as well as
ketones and alcohols
b) Using NaBH4 as a reducing agent
NaBH4
O
OH
H2O
3-cyclopentenone
3-cyclopentenol
 NaBH4 is a moderate strength reducing agent that will selectively reduce
aldehydes and ketones to alcohols, but leave alkene double bonds intact.
Because the H- produced by NaBH4 attacks the partial positive carbonyl
carbon of the aldehyde or ketone.
3. The addition of alcohols to aldehydes and ketones
OH
O
+
HO
O
H
Hemi-acetal
Alcohol
Aldehyde
OH
O
+
HO
O
Alcohol
Ketone
Hemi-acetal
 Starting with either an aldehyde or a ketone, you can see that the hemiacetals formed are characterized by having a carbon bonded to an OH- group
and an OR- group.
 Here, the oxygen of the alcohol attacks and bonds with the carbonyl carbon
of the aldehyde or ketone
 If the alcohol group and the carbonyl carbon of an aldehyde or ketone are on
the same molecule, a cyclic hemi-acetal can be formed. (shown below)
O
5
3
4
1
2
H
OH
OH group and carbonyl group on the same molecule
Redraw
3
5
H
1
4
1
4
C
O
2
3
2
5
O
H
A cyclic ring forms
O
OH
 Alcohols can react with hemi-acetals to form acetals
H+
O
O
OH
O
OH
hemi-acetal
Alcohol
acetal
 Here, the OH- group of the hemi-acetal is protonated to H2O+ . The H2O+
leaves, and is then replaced by the OR- group of the alcohol.
 Notice that for the acetal, it is characterized by having a carbon bonded to
two OR- groups.
4. An acid-base reaction of a carboxylic acid
O
O
+ H2O
+ NaOH
O- Na+
OH
Sodium propanoate
Propanoic acid
 Here, the hydroxide ion takes the acidic proton from the carboxylic acid
leaving it with a negative charge.
 Salts of carboxylic acids are more soluble in water than the neutral acid
form.
5. Reduction of a carboxylic acid
Strong reducing agent
O
LiAl H4
OH
OH
H2O
 LiAlH4 is a much stronger reducing agent than LiBH4. It is necessary to
reduce carboxylic acids, which are somewhat resistant to reduction.
 Carboxylic acids are reduced to primary alcohols, there is no aldehyde
intermediate.
 LiAlH4 is a selective reducing agent that leaves alkene double bonds intact.
6. Fisher esterification of a carboxylic acid
O
O
H2SO4
+
OH
Carboxylic acid
+ H2O
O
HO
Alcohol
Ester
 In the final product (ester) the OH- group of the carboxylic acid has been
replaced by the OR- group of the alcohol
7. Decarboxylation of a carboxylic acid
O
Extreme heat
C
+ CO2
OH
O
O

O

Mild heat
+
CO2
OH
If a beta carbonyl carbon is present, the reaction takes place much easier
(mild heat as opposed to extreme heat)
8. Preparation of an amide
O
O
O
+
Heat
+
H2N
+ H2O
+H3N
N
H
O-
OH
 The first step is an acid base reaction between the carboxylic acid and the
amine. In the second step, heat is applied expelling a water molecule (O
from the carboxylic acid, 2H from the amine), and the amide bond is
formed.
9. a) Hydrolysis of an ester with an acid catalyst
H3O+
O
O
+
+ H2O
HO
OH
O
Propanoic acid
(carboxylic acid)
Ethyl propanoate
(ester)
Ethanol
(alcohol)
9. Hydrolysis of an ester with sodium hydroxide.
O
H2O
O
+
+ NaOH
HO
O-Na+
O
Sodium propanoate
(carboxylic salt)
Ethyl propanoate
(ester)
Ethanol
(alcohol)
10.Hydrolysis of a carboxylic anhydride
O
O
O
O
+
+ H2O
O
Acetic anhydride
(carboxylic anhydride)
OH
Acetic acid
(carboxylic acid)
HO
Acetic acid
(carboxylic acid)
11. Hydrolysis of an amide
O
O
+
HCl
+ H2O
OH
H2N
N
H
N-ethylpropanamide
(amide)
Propanoic acid
(carboxylic acid)
This is one way you break down proteins into amino acids!
ethanamine
(amine)