1. CARBOXYLIC ACIDS

2. CARBOXYLIC ACIDS and their derivatives
Carboxylic acid anhydride
Carboxylic acid ester
Carboxylic acid
R = alkyl
cycloalkyl
alkenyl
alkynyl
aromatic ring
Carboxylic acid chloride
Carboxylic acid amide
Nitrile

3. CARBOXYLIC GROUP ELECTRONIC STRUCTURE
Lone-pair electrons
Acidic hydrogen
π-bond
Lone-pair electrons
Hydrocarbon
framework

4. CARBOXYLIC GROUP THREE-DIMENSIONAL SHAPE
sp2
sp3
Acetic acid - model
sp3
sp2
C-C 1.52 Å C=O 1.25 Å C-OH Å

5. CARBOXYLIC ACIDS – various sites of reactivity
Lewis basicity (greater)
(nucleophilic centre)
Lewis basicity (lesser)
(nucleophilic centre)
α-hydrogen chemistry
Brőnsted acidity
Lewis acidity
(electrophilic centre)

6. COMMON CARBOXYLIC ACIDS
Aliphatic acids
formic acid
butyric acid
acetic acid
valeric acid
pivalic acid
propionic acid

7. COMMON CARBOXYLIC ACIDS
Unsaturated acids
acrylic acid
propiolic acid
crotonic acid
fumaric acid
trans
maleic acid
methacrylic acid
cis

8. COMMON CARBOXYLIC ACIDS
Dicarboxylic acids
oxalic acid
glutaric acid
malonic acid
adipic acid
succinic acid

9. COMMON CARBOXYLIC ACIDS
Aromatic acids
benzoic acid
phthalic acid
benzoic acid

10. Physical constants of some CARBOXYLIC ACIDS

11. Carboxylic acids form dimers by strong Hydrogen Bonding
Hence they have high boiling points

12. Dissociation of carboxylic acid vs alcohol
Equivalent resonance structures:
negative charge always on O
Unstabilized alkoxide anion

13. Dissociation of carboxylic acid vs alcohol Resonance stabilization
ENERGY
Alkoxide anion
Resonance stabilization
Carboxylate anion
alcohol
acid
REACTION PROGRESS

14. Which will be more acidic?
Acidity of carboxylic proton vs -proton in ketone
Carboxylic group
Which will be more acidic?
Ketone

15. Both anions are resonance stabilized

16. Acidity of carboxylic proton vs -proton in ketone
Carboxylic acids: equivalent resonance structures:
negative charge always on O
Ketones: not equivalent resonance structures:
negative charge on O or on C!

17. Compare acetic acid, pKa = 4.75, with acetone, pKa = 19.3!!!

18. EVIDENCE FOR RESONANCE OF CARBOXYLATE ANION formic acid sodium formate
1.27 Å
1.20 Å
1.34 Å
1.27 Å
formic acid sodium formate

19. ACIDITY OF SOME CARBOXYLIC ACIDS
Structure Name pKa
HCl hydrochloric acid -7
F3CCOOH trifluoroacetic acid (TFA) 0.23
Cl3CCOOH trichloroacetic acid 0.64
Cl2CHCOOH dichloroacetic acid 1.26
FCH2COOH fluoroacetic acid
ClCH2COOH chloroacetic acid 2.85
BrCH2COOH bromoacetic acid 2.89
ICH2COOH iodoacetic acid 3.12
HCOOH formic acid 3.75
HOCH2COOH glycolic acid
ClCH2CH2COOH 3-chloropropanoic acid 3.98
C6H5COOH benzoic acid 4.19
H2C=CHCOOH acrylic acid
C6H5CH2COOH phenylacetic acid 4.31
CH3COOH acetic acid
CH3CH2COOH propanoic acid
CH3CH2OH ethanol 16
Stronger acid
Weaker acid

20. SUBSTITUENT EFFECT ON ACIDITY
acetic acid chloroacetic acid dichloroacetic acid trichloroacetic acid
pKa = pKa = pKa = pKa = 0.64
Weaker acid
Stronger acid

21. SUBSTITUENT EFFECT ON ACIDITY
Electron Withdrawing Group
stabilizes carboxylate anion
and strenghtens acidity
Electron Donating Group
destabilizes carboxylate anion
and weakens acidity

22. SUBSTITUENT EFFECTS ON ACIDITY Explain the difference in pKa values.
The greater the distance (number of bonds) between an electron-withdrawing group (here chlorine) and the point of ionization, the less effect an electron-withdrawing group has.

23. SUBSTITUENT EFFECT ON ACIDITY
Dicarboxylic acids
pKa pKa2
Oxalic acid
Succinic acid
Adipic acid

24. SUBSTITUENT EFFECT ON ACIDITY Para-substituted benzoic acids
pKa = pKa = pKa = 3.41
EDG – destabilizes
carboxylate anion,
decreases acidity
EWG – stabilizes
carboxylate anion,
increases acidity
Weaker acid
Stronger acid

25. SUBSTITUENT EFFECT ON ACIDITY Para-substituted benzoic acids
Y pKa
-OH
-OCH
-CH -H
-Br
-Cl
-CHO
-CN
-NO
EDG
(activating ring
in electrophilic
substitution)
EWG
(deactivating ring
in electrophilic
substitution)
Acidity

26. Preparation of carboxylic acids
(Industrial methods)

27. Preparation of carboxylic acids
Laboratory methods
1. Oxidation of alkylbenzenes, primary alcohols, aldehydes
88% yield
93% yield

28. 85% yield

29. 2. Hydrolysis of nitriles
3. Carboxylation of Grignard reagents
73% yield

30. General reactions of carboxylic acids
Deprotonation
Decarboxylation
Reduction
16 October 2017
α-Substitution
Nucleophilic acyl
substitution

31. Decarboxylation
Hunsdiecker reaction
93% yield
100% yield

32. Deprotonation Salt formation in alkaline solutions:
Na2CO3 can also be used

33. Deprotonation
Salt formation with ammonia (NH3) or amines (RNH2, R2NH, R3N):
Proton transfer from carboxyl oxygen to amine nitrogen

34. Reduction
87% yield
94% yield

35. -Substitution
-Halogenation of carboxylic acids – Hell, Volhard, Zelinskii reaction
90% yield

36. Mechanism of -Halogenation

37. Nucleophilic acyl substitution
Net effect – replacing of hydroxyl group with nuclephile
-OH is called leaving group

38. Fischer esterification as nucleophilic acyl substitution
Alcohol reactivity order:
primary > secondary > tertiary
R E A C T I V I T Y

39. Fischer esterification as nucleophilic acyl substitution
(mechanism)
The full mechanism for Fischer esterification as well as for the reverse reaction, acid-catalyzed hydrolysis of an ester to a carboxylic acid.