DERIVATIVES OF CARBOXYLIC ACIDS. Chemical. Properties. • colourless
liquids which fume in moist air. • acyl chlorides are more reactive than anhydrides
.
Acylation
1
A4
DERIVATIVES OF CARBOXYLIC ACIDS ACYL (ACID) CHLORIDES - RCOCl
ACID ANHYDRIDES - (RCO)2O
named from corresponding acid remove -ic add -yl chloride
named from corresponding acid remove acid add anhydride
CH3COCl C6H5COCl
ethanoyl chloride benzene carbonyl chloride
(CH3CO)2O ethanoic anhydride δ−
δ+
δ−
δ+
CH3 C
CH3 C
O
Cl
δ+
CH3 C
δ−
bonding in acyl chlorides
Chemical Properties
• • • • •
O
O δ− δ−
O
bonding in acid anhydrides
colourless liquids which fume in moist air acyl chlorides are more reactive than anhydrides attacked at the positive carbon centre by nucleophiles nucleophiles include water, alcohols, ammonia and amines undergo addition-elimination reactions
Uses of Acylation Industrially
Manufacture of
Cellulose acetate
- making fibres
Aspirin (acetyl salicylic acid)
- analgaesic
Ethanoic anhydride is more useful
Laboratory
Used to make
cheaper less corrosive less vulnerable to hydrolysis less dangerous reaction
Investigate how aspirin is made industrially and in the laboratory. Why are the reagents and chemicals different? What properties of Aspirin make it such a useful drug?
species attacked by nucleophiles at the positive carbon end of the C=O bond the nucleophile adds to the molecule either Cl or RCOO¯ is eliminated a proton is removed
General example - with water ACID CHLORIDES
H + H O
Cl
Cl C
O
R C O
R
H O H
H O H
O C
HCl
R C
O
OH
R
+
Cl
RCOCl
+
H2O
——>
RCOOH
+
HCl
ACID ANHYDRIDES O O
R C
R C O R C O H O H
H + H O
O R C H O H
O C
O
O
OH
R
+
RCOOH
R C
RCOO
(RCO)2O
+
H2O
——>
2RCOOH
Use these mechanisms to help construct others in the spaces which follow
SYNTHETIC POSSIBILITIES PRODUCT WITH
By-product
WATER
ALCOHOLS
AMMONIA
AMINES
ACYL CHLORIDE
CARBOXYLIC ACID
ESTER
AMIDE
N-SUBSTITUTED AMIDE
HCl
ACID ANHYDRIDE
CARBOXYLIC ACID
ESTER
AMIDE
N-SUBSTITUTED AMIDE
CARBOXYLIC ACID
Acylation
3
A4
ADDITION ELIMINATION - the reactions ACYL (ACID) CHLORIDES - RCOCl Water
Product(s)
carboxylic acid + HCl (fume in moist air / strong acidic solution formed)
Conditions
cold water
Equation
CH3COCl(l)
Mechanism
addition-elimination
+ H2O(l) ——>
H + H O
Cl
Cl C
CH3 C O
O
CH3
H O H
H O H
Alcohols
O C
O
ester + hydrogen chloride
Conditions
reflux in dry (anhydrous) conditions
Equation
CH3COCl(l)
Mechanism
addition-elimination
O
CH3
+ CH3OH(l) ——>
H O CH3
+
H O +
O C
CH3 C
Cl
What organic product is formed when the following pairs react? • C3H7COCl and H2O
Q.3
O
CH3
CH3
Q.2
CH3COOCH3(l) + HCl(g)
CH3
CH3 C O H O
HCl OH
Cl
Product(s)
Cl
CH3 C
CH3
+
Cl C
CH3COOH(aq) + HCl(aq)
• C2H5COCl and C2H5OH
How would you synthesis the following? • methyl butanoate
• butyl methanoate
• C6H5COOCH3
• CH3COOC(CH3)2
HCl O CH3
4
Acylation
A4
Ammonia
Product(s)
Amide + hydrogen chloride
Conditions
Low temperature and excess ammonia. Vigorous reaction.
Equation
CH3COCl(l)
+ NH3(aq)
——>
CH3CONH2(s) + HCl(g)
CH3COCl(l)
+ 2NH3(aq)
——>
CH3CONH2(s) + NH4Cl(s)
or Mechanism
Cl
Cl C
CH3 C O
O
CH3
+
H N H H
H H N H
Amines
addition-elimination H + H N H C CH3
O O
CH3 C
HCl NH2
Cl
Product(s)
N-substituted amide + hydrogen chloride
Conditions
anhydrous
Equation
CH3COCl(l) + C2H5NH2(aq)
——>
CH3CONHC2H5(s) + HCl(g)
CH3COCl(l) + 2C2H5NH2(aq)
——>
CH3CONHC2H5(s) + C2H5NH3Cl(s)
or Mechanism
addition-elimination - similar to that with ammonia
Cl
Cl C
O
CH3
CH3 C O +
H N H R
H R N H
H + R N H C CH3
O O
CH3 C
Cl
HCl NH R
Q.4
Why are two moles of ammonia (or amine) required in each equation?
Q.5
What pairs of chemicals would you use to synthesis the following? • butanamide