1. Dr AKM Shafiqul Islam School of Bioprocess Engineering 06.10.08
Carboxylic acids
Dr AKM Shafiqul Islam
School of Bioprocess Engineering

2. Carboxylic Acids
The functional group of a carboxylic acid is a carboxyl group,
Carbonyl with hydroxy
represented in one of three ways

3. Fill in the table below.
formic acid
methanoic acid
acetic acid
ethanoic acid
propionic acid
propanoic acid
butyric acid
butanoic acid
valeric acid
pentanoic acid
caproic acid
hexanoic acid
benzoic acid
benzoic acid

4. 4-amino-3-methylhexanoic acid
2. Carboxylic acids that have branches are often given IUPAC names, where the numbering of the longest carbon chain begins at the Carbonyl carbon. Name the following compounds.
2-bromopropanoic acid
3-chlorobutanoic acid
4-amino-3-methylhexanoic acid

5. Carboxylic Aromatic Acids
salicylic acid
(2-hydroxybenzenecarboxylic)
benzoic acid
o-phthalic acid
(benzene-1,2-dicarboxylic)
gallic acid
(3,4,5-trihydroxy
-benzenecarboxylic)
vanillic acid
(4-hydroxy-3-methoxy
-benzenecarboxylic)
cinnamic acid
(3-phenylprop
-2-enoic)

6. Where are they to be found?
Carboxylic acids and their derivatives:
Tart taste of citrus fruits, vinegar, and rhubarb
Sharp sting of red ants
Unsavory smell and taste of rancid butter
Vitamin C is a carboxylic acid
Pleasant taste and odor of fruits are due to carboxylic acid derivatives: esters

7. Physical Properties
The carboxyl group contains three polar covalent bonds; C=O, C-O, and O-H
the polarity of these bonds determines the major physical properties of carboxylic acids
δ-O – Hδ+
δ+C=Oδ- R

8. Electron DelocalizationH ••
• • + – R C O H ••
• • 6

9. Electron DelocalizationH ••
• • + – R C O H ••
• • R C O H ••
• • + –
stabilizes carbonyl group 6

10. Physical Properties The carbonyl group has a large dipole
The hydroxy group is capable of hydrogen bonding.
The molecules can H-bond to each other
How does this affect boiling point?
Higher than aldehydes and ketone – no H-bonds
Higher than alcohols – H-bonds, not strong dipole

11. Solubility in Water
Carboxylic acids are similar to alcohols in respect to their solubility in water
Form hydrogen bonds to water
H3CC O H 10

12. Physical Properties
carboxylic acids are more soluble in water than are alcohols, ethers, aldehydes, and ketones of comparable molecular weight

13. + + acid base alkoxide anion
Alkoxide anions don’t have resonance-stabilization.
Alcohols are weaker acids than carboxylic acids.

14. Physical Properties Sharp and or sour odor/taste
Vinegar, rancid butter, sweat, sauerkraut

15. Carboxylic acids derivatives
When the carbonyl group is substituted by atoms other than carbon or hydrogen, as in
where Z is oxygen, nitrogen, or halogen, the compound becomes a carboxylic acid or a carboxylic acid derivative.

16. Carboxylic acid and derivatives
Ester Acid anhydride Amide Acid halide

17. Carboxylic Acid Derivatives
Hydroxy Acids

18. Beta-hydroxy acid Salicylic Acid exfoliant
oil soluble – penetrates oil containing pores to remove dead skin cells
less irritating than alpha acids

19. Reactions carboxylic acids
as acids
conversion into functional derivatives
 acid chlorides
 esters
 amides
reduction
alpha-halogenation
EAS

20. Reactions : Acid/Base Carboxylic acids are weak acids
Give up the H bonded to O to water or base
Tendency for acid to give up proton (H+) is indicated by pKa; lower pKa indicates stronger acid
Carboxylic acids: pKa
In comparison:
Hydrochloric acid pKa = -7
Sulfuric acid pKa = -3
Alcohol pKa = 15-16

21. Comparison Of pKa Values
Hydrochloric acid pKa = -7
Sulfuric acid pKa = -3
Alcohol pKa = 15-16
Carboxylic acid pKa = 4

22. Acidity of Carboxylic Acids
1. Both acetic acid and ethanol have an acidic hydrogen on the OH group. Why is the pKa value for acetic acid (pKa = 4.74) lower than the pKa for ethanol (pKa = 15.9)? In other words, why are carboxylic acids more acidic than alcohols. Consider resonance-stabilized anions. +
acid
base
carboxylate anion

23. resonance-stabilized carboxylate anion½- = ½-
resonance-stabilized carboxylate anion +
acid
base
carboxylate anion
The greater the stability of the carboxylate anion, the farther the shift to the right.
The farther the shift to the right, the greater the acidity.

24. As acids: a) with active metals RCO2H + Na  RCO2-Na+ + H2(g)
b) with bases
RCO2H NaOH  RCO2-Na H2O
c) relative acid strength?
CH4 < NH3 < HCCH < ROH < HOH < H2CO3 < RCO2H < HF
d) quantitative
HA + H2O  H3O+ + A- onization in water
Ka = [H3O+] [A-] / [HA]

25. Dehydration of Carboxylic Acid
* water must be removed (to avoid hydrolysis)
* limited use

26. Reaction With Bases
All carboxylic acids react with strong bases to form water-soluble salts

27. Reactions with bases Salts of carboxylic acids
Drop the –ic acid
Change to –ate
Sodium benzoate & monosodium glutamate
Sodium benzoate – inhibit mold
MSG – flavor enhancer

28. Conversion into functional derivatives
a) acid chlorides

29.  esters
“direct” esterification: H+
RCOOH R´OH  RCO2R´ H2O
-reversible and often does not favor the ester
-use an excess of the alcohol or acid to shift equilibrium
-or remove the products to shift equilibrium to completion
“indirect” esterification:
RCOOH PCl3  RCOCl R´OH  RCO2R´
-convert the acid into the acid chloride first; not reversible

31.  amides
“indirect” only!
RCOOH SOCl2  RCOCl NH3  RCONH2
amide
Directly reacting ammonia with a carboxylic acid results in an ammonium salt:
RCOOH NH3  RCOO-NH4+
acid base

33. Reduction:
RCO2H LiAlH4; then H+  RCH2OH
1o alcohol
Carboxylic acids resist catalytic reduction under normal conditions.
RCOOH H2, Ni  NR

35. Alpha-halogenation: (Hell-Volhard-Zelinsky reaction)
RCH2COOH X2, P  RCHCOOH HX X
α-haloacid
X2 = Cl2, Br2

37. 5. EAS: (-COOH is deactivating and meta- directing)