chapter 6 acid anhydride
DESCRIPTION
TRANSCRIPT
Chapter 7
ACID ANHYDRIDE
Norfazrin Mohd Hanif
Faculty of Applied Science
UiTM Negeri Sembilan
STRUCTURE OF ACID ANHYDRIDE
• The word ‘anhydride’ means without water.
• Contains two molecules of an acid, with loss of a molecule of water.
• Addition of water to an anhydride regenerates two molecules of the
carboxylic acid.
R C
O
OH HO C
O
R R C
O
O C
O
R H2O
two molecules of acid acid anhydride
General structure:
R C
O
O C
O
R
acid anhydride
or (RCO)2O
NOMENCLATURE OF ACID
ANHYDRIDE
• The word ‘acid’ is changed to ‘anhydride’ in both common
name and the IUPAC name.
• Examples:
- ethanoic acid → ethanoic anhydride
- propanoic acid → propanoic anhydride
H3C C
O
O C
O
CH3
IUPAC : ethanoic anhydridecommon: acetic anhydride
CH3CH2 C
O
O C
O
CH2CH3
IUPAC : propanoic anhydridecommon: propionic anhydride
Anhydrides composed of two different acids are called mixed anhydrides and are named by using the names of the individual acids.
H3C C
O
O C
O
H
IUPAC : ethanoic methanoic anhydridecommon: acetic formic anhydride
NOMENCLATURE OF ACID
ANHYDRIDE
• Symmetrical anhydrides : change the word acid of the carboxylic acid
to the word anhydride.
• Mixed anhydrides : alphabetizing the names for both acids and
replacing the word acid with the word anhydride.
Acid chloride and carboxylic acid
Acid chloride and carboxylate salt
Heating carboxylic acids with ZnO
Heating dicarboxylic acids
PREPARATION OF ACID
ANHYDRIDES
FROM ACYL CHLORIDES
ether
EXAMPLE
R C
O
Cl R' C
O
O R C
O
O C
O
R'
ether
CH3CH2 C
O
Cl CH3 C
O
O CH3CH2 C
O
O C
O
CH3
carboxylate salts
1) Acyl chlorides react with carboxylate salts to form acid anhydrides.
Can be used to prepare both symmetrical and unsymmetrical
anhydrides
2) Acyl chlorides also reacts with carboxylic acid to
give acid anhydride.
EXAMPLE
R C
O
Cl R' C
O
OH R C
O
O C
O
R'
CH3 C
O
Cl CH3 C
O
OH CH3 C
O
O C
O
CH3
carboxylic acid
heatHCl
HClheat
HEATING CARBOXYLIC ACIDS
WITH ZnO
Acid anhydride can be prepared from heating simple
carboxylic acids with zinc oxide.
EXAMPLE
R C
O
OH R C
O
O C
O
R
CH3 C
O
OH CH3 C
O
O C
O
CH3
heat
ZnO
2
heat
ZnO
2
HEATING DICARBOXYLIC ACIDS
Certain cyclic anhydride can be prepared by heating
dicarboxylic acid such as succinic and phthalic
anhydride.
HO C CH2
O
CH2 C
O
OH H2O300OC
OH
O
OH
O
230OC
O
O
O
H2O
O
O
O
REACTIVITY OF ACID
ANHYDRIDES
Comparing acid anhydride with acyl chloride.
- ethanoic anhydride has a bulky ethanoate, CH3COO-
group attached to the carbonyl carbon.
- ethanoyl chloride has a simple Cl atom attached to the
carbonyl carbon.
- therefore ethanoic anhydride is less reactive than ethanoyl
chloride.
REACTIONS OF ACID
ANHYDRIDES
Hydrolysis
Alcoholysis
Ammonolysis
Friedel-Crafts acylation of benzene
HYDROLYSIS
Acid anhydrides undergoes hydrolysis to produce carboxylic acids.
Can be carried out in acid or base.
Carboxylate salts are formed if hydrolysis is done in basic solution.
R C
O
O C
O
R H OH R C
O
OH R C
O
OH
EXAMPLE
H+
R C
O
O C
O
R H OH R C
O
O R C
O
OOH
H3C C
O
O C
O
CH3 H OH H3C C
O
OH H3C C
O
OHH+
ALCOHOLYSIS
R C
O
O C
O
R R' OH R C
O
OR' R C
O
OH
EXAMPLE
H3C C
O
O C
O
CH3 CH3CH2 OH H3C C
O
OCH2CH3 H3C C
O
OH
H3C C
O
O C
O
CH3
OH
H3C C
O
O H3C C
O
OH
ester carboxylic acid
ethanoic anhydride ethanol ethyl ethanoate ethanoic acid
phenol phenyl ethanoate ethanoic acidethanoic anhydride
Acid anhydrides react with alcohol to produce esters and carboxylic acids.
Does not required catalyst, but still requires heating.
AMMONOLYSIS
Amide can be prepared through ammonolysis of acid
anhydrides with ammonia, primary and secondary amines.
R C
O
O 2NH3 R C
O
NH2
2RNH2 R C
O
NHR
2R2NH R C
O
NR2
C
O
R R C
O
O NH4+
R C
O
O C
O
R
R C
O
O C
O
R
R C
O
O RNH3+
R C
O
O R2NH2+
H3C C
O
O 2NH3 H3C C
O
NH2
2CH3NH2 H3C C
O
NHCH3
C
O
CH3 H3C C
O
O NH4+
H3C C
O
O C
O
CH3 H3C C
O
O CH3NH3+
EXAMPLES:
FRIEDEL-CRAFTS ACYLATION OF
BENZENE
Acid anhydride reacts with benzene to produce ketones.
Carboxylic acids is the by-product.
R C
O
O C
O
R HO C
O
R
HR
O
ketone carboxylic acid
AlCl3
EXAMPLE
H3C C
O
O C
O
CH3HO C
O
CH3
HCH3
O
AlCl3
Thank you..