Acid halides and Acid anhydrides

1. Acid Halides and Acid
Anhydrides
Presented to :Dr.M.Aslam
Presented by: M.Aneeq Javed

2. Acid Halides
• Acid halides are the derivatives of acids in which the OH function of
carboxyl group has been replaced by a halogen atom.
The acid halides are also referred to as acyl halides; the acyl group is R-CO-
The acid chlorides are by far the most important of all the acid halides and
will be discussed in detail. Their type formula may be represented as,

3. The acid chlorides are by far the most important of all the acid halides and will be discussed in detail. Their type formula
may be represented as,
They are named by dropping the ending -ic acid from either the common name or the IUPAC name and adding the suffix -
yl chloride‘
R C C l o r R C O C l o r R C O C l
O
H3C C Cl
O
Ethanoyl chloride
(Acetyl chloride)
H 2 C H 3 C C C l
O
p r o p a n o y l c h lo r id e
( p r o p io n y l c h lo r id e )

4. Methods Of Preparation
• Acid chlorides are prepared from appropriate carboxylic acids:
1) By reaction with thionyl chloride (SOCI2)
Acid Acid chloride
This method is superior to others as the by-products being gases
escape leaving the acid chloride in the pure state.
C O H
O
R + S O C l 2 C
O
R C l + H C l + S O 2

5. • 2) By reaction with phosphorus trichloride (PCI3)
Acetic Acid Acetyl chloride
3) By reaction with phosphorus pentachloride (PCI5)
C
O
C H 3 +
O H P C l 3 C
O
C H 3 C l + H 3 P O 3
C
O
C H 3 C H 2 +
O H P C l 5 C C l
O
C H 3 C H 2 + H C l + P O C L 3

6. • It is possible to prepare acid bromides and iodides by reactions analogous to those used in
the preparation of chlorides, However, in comparison to the chlorides, they are seldom
used.
PHYSICAL PROPERTIES
(1)All simple acid chlorides are colorless liquids of lower boiling point than the
correspondingacid
(2) They have sharp pungent smell, and are lachrymators (tear-producing).
(3) They emit pale fumes of hydrogen chloride when exposed in air on account of their
reactionwith water vapor.
(4) They are insoluble in water but slowly dissolve in it because of hydrolysis.
(5) The C=O stretching band in IR Spectrum occurs at frequency range 1780-
1850 cm¹.

7. Chemical Properties
• In RCOCI we have a carbonyl group attached to a highly electronegative
chlorine atom. Due to the electron-withdrawing effect of the Cl atom, the
electron density on the carbonyl carbon is diminished further. As a result, acid
chlorides are readily attacked by nucleophiles, whereby the Cl atom is replaced
by a nucleophile.
Thus acid chlorides are very reactive compounds, their characteristic reactions
being nucleophilic substitution reactions.

8. They react with weak nucleophiles as water, alcohols, ammonia and amines to produce the corresponding acid, ester,
amide or substituted amides. Some of their important reactions are listed below:
(1) Hydrolysis. They react with water when the chlorine atom is displaced by OH group to reform the original
organic acid
(2) Reaction with Alcohols. They react with an alcohol when the chlorine atom is displaced by alkoxy group.-OR', to
produce an este
H
3
C C C
l
O
+H
O
C
2
H
5 H
3
C C O
C
2
H
5 + H
C
l
O

9. (3) Reaction with Ammonia. They react with ammonia when the Cl atom is displaced byan amino group, -NH2, to
produce an amide.
(4) Reaction with 1 and 2 Amines. Acid halides react with 1 and 2° amines to produce substituted amides.
(5) Reaction with Salts of Carboxylic Acids. They react with sodium salts of carboxylic acids to R-C-NR2 HCI
form anhydrides.
H3C C Cl
O
+ H H3C C NH2 + HCl
O
NH2

10. 7) Reaction with organocuperate compounds. Acyl halides react with organocuperate compounds (R,CuLi) to form
ketones.
The ketone product of this reaction does not react with organocopper reagent. Only one of the Two R groups of
R,CuLi is used. The by-product, RCu, is inactive.The reaction between (a) acyl halides and Grignard reagents or (b)
acyl halides and organolithiumcompounds does not form ketones.
Reason: These reagents are too reactive, so the ketone intermediates react further to form 3º alcohols.
Hence the ketones cannot be isolated.
RMgBr + Acyl chlorides → [Ketone intermediates] → 3° Alcohols
RLi + Acyl chlorides→ [Ketone intermediates] → 3° Alcohols

11. (8) Friedel-Crafts Reaction. They react with aromatic hydrocarbons in the presence of anhydrousAICI, to form
ketones.

12. Acid Anhydrides OR Anhydrides
• The compounds derived by loss of a water molecule between two molecules of a
carboxylic acid are called Acid Anhydrides or simply Anhydrides.
The functional group of this series of acid derivatives is-CO-o-co-
Anhydrides are named by replacing the word 'acid' in the name of the parent acid
by 'anhydride".

13. •
Anhydrides derived from two molecules of different acids are called Mixed
Anhydrides.

14. Methods of Preparation
• Acid anhydrides may be prepared:
(1) By reaction of acid halide with a carboxylic acid
(2) By reaction of acid halide with salt of a carboxylic acid

15. Physical Properties
• (1) The lower simple anhydrides are colorless liquids with a sharp pungent
smell.
(2) They are insoluble in water for lack of hydrogen bonding. But they
dissolve after a while due to conversion to the soluble acid by hydrolysis.
(3) They have higher boiling points than the acid from which they are
derived. This is so because of their large size and enhanced van der Waal's
interactions.
(4) They are characterized by the C=O stretching band in IR spectrum at
frequency range 1800-1850and 1740-1790 cm

16. CHEMICAL PROPERTIES
• Anhydrides react with nucleophiles in the same way as acid chlorides. But
since -OCOR group is not as electronegative as a Cl atom, anhydrides are
less reactive than acid chlorides. Thus anhydrides give all the nucleophilic
substitution reactions shown by acid chlorides but with less vigor. The
mechanism of the nucleophilic substitution here is the same as stated for
acid chlorides with the difference that the by-product is a molecule of the
carboxylic acid instead of HCI.

17. •
Hydrolysis. Carboxylic acids are formed
. Reaction with Alcohols. Esters are formed.

18. .
(2) Reaction with Alcohols. Esters are formed
(3) Reaction with Ammonia. Amides are formed.
4) Reaction with Amines. Substituted amides are formed.

19. (5) Reaction with benzene in the presence of AICI,, Ketones are formed. This is calledFriedel-Crafts
reaction.