Chapter 6 acid anhydride

1. Chapter 7
ACID ANHYDRIDE
NorfazrinMohdHanif
Faculty of Applied Science
UiTMNegeriSembilan

2. 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.RC
O
OH HOC
O
R
RC
O
OC
O
R H
2O
two molecules of acid acid anhydride
General structure:RC
O
OC
O
R
acid anhydride
or (RCO)
2O

3. 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 →propanoicanhydrideH
3CC
O
OC
O
CH
3
IUPAC : ethanoic anhydride
common: acetic anhydride
CH
3CH
2C
O
OC
O
CH
2CH
3
IUPAC : propanoic anhydride
common: propionic anhydride

4. Anhydrides composed of two different acids are called mixed
anhydrides and are named by using the names of the individual acids.H
3CC
O
OC
O
H
IUPAC : ethanoic methanoic anhydride
common: acetic formic anhydride
NOMENCLATURE OF ACID
ANHYDRIDE
•Symmetricalanhydrides:changethewordacidofthecarboxylicacid
tothewordanhydride.
•Mixedanhydrides:alphabetizingthenamesforbothacidsand
replacingthewordacidwiththewordanhydride.

5. Acid chloride and carboxylic acid
Acid chloride and carboxylatesalt
Heating carboxylic acids with ZnO
Heating dicarboxylicacids
PREPARATION OF ACID
ANHYDRIDES

6. FROM ACYL CHLORIDESether
EXAMPLE
RC
O
Cl R'C
O
O RC
O
OC
O
R'
ether
CH
3CH
2C
O
Cl CH
3C
O
O CH
3CH
2C
O
OC
O
CH
3
carboxylate salts
1)Acylchlorides react with carboxylatesalts to form acid anhydrides.
Can be used to prepare both symmetrical and unsymmetrical
anhydrides

7. 2) Acylchlorides also reacts with carboxylic acid to
give acid anhydride.EXAMPLE
RC
O
Cl R'C
O
OH RC
O
OC
O
R'
CH
3C
O
Cl CH
3C
O
OH CH
3C
O
OC
O
CH
3
carboxylic acid
heat
HCl
HCl
heat

8. HEATING CARBOXYLIC ACIDS
WITH ZnO
Acid anhydride can be prepared from heating simple
carboxylic acids with zinc oxide.EXAMPLE
RC
O
OH
RC
O
OC
O
R
CH
3C
O
OH CH
3C
O
OC
O
CH
3
heat
ZnO
2
heat
ZnO
2

9. HEATING DICARBOXYLIC ACIDS
Certain cyclic anhydride can be prepared by heating
dicarboxylicacidsuch as succinicand phthalic
anhydride.HOCCH
2
O
CH
2C
O
OH
H
2O
300
O
C
OH
O
OH
O
230
O
C
O
O
O
H
2O
O
O
O

10. REACTIVITY OF ACID
ANHYDRIDES
Comparing acid anhydride with acylchloride.
-ethanoicanhydride has a bulky ethanoate, CH
3COO
-
group attached to the carbonyl carbon.
-ethanoylchloride has a simple Clatom attached to the
carbonyl carbon.
-therefore ethanoicanhydride is less reactive than ethanoyl
chloride.

11. REACTIONS OF ACID
ANHYDRIDES
Hydrolysis
Alcoholysis
Ammonolysis
Friedel-Crafts acylationof benzene

12. HYDROLYSIS
Acid anhydrides undergoes hydrolysis to produce carboxylic acids.
Can be carried out in acid or base.
Carboxylatesalts are formed if hydrolysis is done in basic solution.RC
O
OC
O
R HOH RC
O
OH RC
O
OH
EXAMPLE
H
+
RC
O
OC
O
R HOH RC
O
O RC
O
O
OH
H
3CC
O
OC
O
CH
3 HOH H
3CC
O
OH H
3CC
O
OH
H
+

13. ALCOHOLYSISRC
O
OC
O
R R'OH RC
O
OR' RC
O
OH
EXAMPLE
H
3CC
O
OC
O
CH
3 CH
3CH
2OH H
3CC
O
OCH
2CH
3 H
3CC
O
OH
H
3CC
O
OC
O
CH
3
OH
H
3CC
O
O H
3CC
O
OH
ester carboxylic acid
ethanoic anhydride ethanol ethyl ethanoate ethanoic acid
phenol phenyl ethanoate ethanoic acid
ethanoic anhydride
Acid anhydrides react with alcohol to produce esters and carboxylic acids.
Does not required catalyst, but still requires heating.

14. AMMONOLYSIS
Amide can be prepared through ammonolysisof acid
anhydrides with ammonia, primary and secondary amines.RC
O
O 2NH
3
RC
O
NH
2
2RNH
2
RC
O
NHR
2R
2NH RC
O
NR
2
C
O
R RC
O
ONH
4
+
RC
O
OC
O
R
RC
O
OC
O
R
RC
O
ORNH
3
+
RC
O
OR
2NH
2
+

15. H
3CC
O
O 2NH
3
H
3CC
O
NH
2
2CH
3NH
2 H
3CC
O
NHCH
3
C
O
CH
3 H
3CC
O
ONH
4
+
H
3CC
O
OC
O
CH
3
H
3CC
O
OCH
3NH
3
+ EXAMPLES:

16. FRIEDEL-CRAFTS ACYLATION OF
BENZENE
Acid anhydride reacts with benzene to produce ketones.
Carboxylic acids is the by-product.RC
O
OC
O
R
HOC
O
R
H
R
O
ketone carboxylic acid
AlCl
3
EXAMPLE
H
3CC
O
OC
O
CH
3
HOC
O
CH
3
H
CH
3
O
AlCl
3

17. Thank you..