Carboxylic acids undergo several important reactions: 1) They react with bases to form salts via deprotonation. 2) They can be converted to acid chlorides using reagents like thionyl chloride, which produces gases as byproducts. 3) They form esters when reacted with alcohols in the presence of an acid catalyst. Electron withdrawing substituents increase acidity by stabilizing the conjugate base, while donating groups decrease acidity.

1. Reaction of carboxylic acid

2. Salt Formation
• They react readily with inorganic bases such as
hydroxide ion or ammonia to form salts.

3. Most acids are acidic enough to react
with sodium bicarbonate accompanied
by evolution of CO2

4. Carboxylic acids with ammonia

5. Conversion into acid chloride
• Carboxylic acid is often converted to acid
chloride than into any other of its functional
derivatives.
• Acid chloride is prepared by substitution of
chloride for the OH of COOH.

6. Three reagents are commonly used for
this purpose
• Thionyl chloride- SOCl2
• Phosphorous trichloride-PCl3
• Phosphorous pentachloride-PCl5

7. Thionyl chloride
Thionyl chloride is convenient since
the products formed besides the acid
chloride are gases and thus easily
separated from acid chloride; any
excess of low boiling thionyl chloride
[79C] is easily removed by distillation.

9. Conversion into ester

10. • A carboxylic acid is converted directly into an
ester when heated with an alcohol in the
presence of little mineral acid [ usually
H2SO4 or Dry HCl]
• This reaction is reversible.
• The reversibility is the disadvantage.

11. • The preference of acid chloride from acid and
preparation of ester from acid chloride are
essentially irreversible and go to completion.
• Direct esterification has the advantage of
being a single step synthesis.
• If either the acid or alcohol is cheaper or
readily available. It can be used in large excess
to shift the equilibrium towards the product
and thus increase the yield of ester.

12. • Sometimes the equilibrium is shifted by
removing one of the product.
• The presence of bulky group near the site of
reaction, whether in the alcohol or in the acid
, slows down esterification [ steric hindrance ]
•

13. Conversion into amides
• Amides are the compounds in which OH of
COOH is replaced by NH2.This are generally
prepared by reaction of ammonia with acid
chloride.

14. Reduction of acids to alcohols
Lithium Aluminium hydride is one of the two
reagents that can reduce an acid to an alcohol;
the initial product is an alkoxide from where
alcohol is liberated by hydrolysis.

15. • LiAlH4 is widely used because of its excellent
yield. It is used for reduction of not only acid
but also many other class of compound.
• It is expensive used only in industry.
• An alternative to direct reduction acids are
often converted into alcohols by a two step
process esterification and reduction of ester.

16. Halogenation of aliphatic acid
• Hell-Vohard- zelinsky reaction
• Aliphatic carboxylic acid react smoothly with
chlorine or bromine to yield a compound in
the presence of a small amount of
phosphorous ,aliphatic carboxylic acid . In this
reaction alpha hydrogen has been replaced by
halogen.
• Regioselectivity-only alpha halogenation. It is
of considerable importance in synthesis.

18. • The function of phosphorous is to convert a
little of acid in acid halide.
• In this form each molecule of acid sooner or
later undergoes alpha halogenation.
• Halogenation is the first step in the conversion
of a COOH into many substituted COOH.

19. IMPORTANT REACTION OF BENZOIC
ACID

20. Salt formation- Benzoic acid reacts
with sodium hydroxide to form
sodium benzoate

21. Salt formation- Benzoic acid reacts
with sodium bi carbonate to form
sodium benzoate

22. Esterification : benzoic acid with
ethanol in the presence of
concentrated sulphuric acid to form
ester

23. Benzoic acid reacts with phosphorous
penta chloride or thionyl chloride to
form benzoyl chloride

24. Benzoic acid undergoes reduction with
lithium aluminium hydride to give
benzyl alcohol.

25. Electrophilic substitution reaction

26. ACIDITY OF CARBOXYLIC ACID

27. Acidity of carboxylic acid
• Carboxylic acid are polar.
• It form hydrogen bond with each other and
with other kinds of molecule.
• The aliphatic acid shows same solubility
behavior as the alcohol.
• The first four are miscible with water and five
carbon is partly soluble and the higher acids
are virtually insoluble.

28. Acidity of carboxylic acid
• Water solubility is due to hydrogen bonding
between the carboxylic acid and water.
• Lower aliphatic acids –sharp odour
• Formic and acetic acid – irritating odour
• Butyric , valeric acid and caproic acid-
unpleasant odour
• Higher acid – less odour because of low
volatility.

29. • Acidity is chiefly determined by the
difference in stability between the acid
and its anion.
• Carboxylic acid are acid at all but it
readily gives H+ from OH of carboxylic
acid.

30. • Although both acids and anion are stabilized
by resonance, stabilisation is greater for the
anion than for acids.
• Equilibrium is shifted in the direction of
ionisation.
• Resonance is less important for the acid
because the contributing are of different
stability, whereas the equivalent structure for
the ion must necessarily be of equal stability.

31. • In structure II two atoms of similar
electronegativity carry opposite charges since
energy must be supplied to separate opposite
charges.
• Structure II should contain more energy and
hence less stable than structure I.
• Consideration of separation of charge is one of
the rules of thumb.

32. Structure of carboxylate
Carbon is joined by each oxygen by a one and
half bond. The negative charge is eventually
distributed over both the oxygen atoms.

33. • Anion is supported by the evidence of bond
length.
• In formic acid C= O bond and C-O single bond
have different length.
• sodium formate on other hand if it is resoance
hybrid ought to contain two equivalent C-O bond.
• X-ray and electron diffraction studies show the
expectations are correct.

34. Effect of substituent on acidity
• Changes in the structure of the group bearing COOH
affect the acidity.
• Any factor which stabilizes the anion more than it
stabilizes the acid should increases the acidity; any
factor which makes anion less stable should decrease
acidity.
• Electron withdrawing substituent should disperse the
negative charge , stabilize the anion and thus increase
acidity.
• Electron releasing/donating substituent should
intensify the negative charge, destabilize the anion,
and thus decrease acidity.

35. Electron withdrawing group Electron donating group

36. Electron withdrawing group
strengthen acids
• Chloro acetic acid is 100 times more strong as
acetic acid.
• Dichloro acetic acid is still stronger.
• Trichloro acetic acid is more than 10000 times
as strong as the unsubstituted acid.
• Alpha chloro acetic acid is strong as
chloroacetic acid. As the chlorine is moved
away from the COOH.

37. • Beta chloro butyric acid is six times as strong
as butyric acid
• Gamma butyic acid is only twice as strong.
• Inductive effect decreases rapidly with
distance and seldom important when acting
through more than four atoms.

38. • The aromatic acid are similarly effected by
substituents like CH3, OH and NH2 make benzoic
acid weaker.
• Substituents Cl and NO2 make benzoic acid
stronger.
• All ortho substituents exert an effect on the same
kind. The ortho effect undoubtedly has to do with
the nearness of the group involved, but it is more
than just steric hindrance arising from their bulk.
• Like inductive effect and resonance effect, rate of
reaction also useful in dealing with equilibria.