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Carboxylic acids
1. Carboxylic acids:
O
R-COOH, R-CO2H, R C
OH
Common names:
HCO2H
formic acid
L. formica ant
CH3CO2H
acetic acid
L. acetum vinegar
CH3CH2CO2H
propionic acid G. “first salt”
CH3CH2CH2CO2H
butyric acid
L. butyrum butter
CH3CH2CH2CH2CO2H
valeric acid
L. valerans
2. Carboxylic acids, common names:
…
CH3(CH2)4CO2H
caproic acid
CH3(CH2)5CO2H
---
CH3(CH2)6CO2H
caprylic acid
CH3(CH2)7CO2H
---
CH3(CH2)8CO2H
capric acid
CH3(CH2)9CO2H
---
CH3(CH2)10CO2H
lauric acid
L. caper goat
oil of lauryl
3. 5 4 3 2 1
C—C—C—C—C=O
δ γ β α
Br
CH3CH2CH2CHCOOH
α− bromovaleric acid
used in common names
CH3
CH3CHCH2COOH
β -methylbutyric acid
isovaleric acid
8. salts of carboxylic acids:
name of cation + name of acid: drop –ic acid, add –ate
CH3CO2Na
sodium acetate
CH3CH2CH2CO2NH4
or sodium ethanoate
ammonium butyrate
ammonium butanoate
(CH3CH2COO)2Mg
magnesium propionate
magnesium propanoate
10. physical properties:
polar + hydrogen bond relatively high mp/bp
water insoluble
exceptions: four carbons or less
acidic
turn blue litmus red
soluble in 5% NaOH
RCO2H + NaOH RCO2-Na+ + H2O
stronger
acid
stronger
base
weaker
base
weaker
acid
11. RCO2H
RCO2-
covalent
water insoluble
ionic
water soluble
Carboxylic acids are insoluble in water, but soluble in 5%
NaOH.
1. Identification.
2. Separation of carboxylic acids from basic/neutral organic
compounds.
The carboxylic acid can be extracted with aq. NaOH and
then regenerated by the addition of strong acid.
12. Carboxylic acids, syntheses:
1. oxidation of primary alcohols
RCH2OH + K2Cr2O7 RCOOH
2. oxidation of arenes
ArR + KMnO4, heat ArCOOH
3. carbonation of Grignard reagents
RMgX + CO2 RCO2MgX + H+
RCOOH
4. hydrolysis of nitriles
RCN + H2O, H+, heat RCOOH
15. 3. carbonation of Grignard reagent:
Mg
R-X
CO2
RMgX
H+
RCO2MgX
RCOOH
Increases the carbon chain by one carbon.
Mg
CH3CH2CH2-Br
n-propyl bromide
RMgX +
O
C
O
CO2 H+
CH3CH2CH2MgBr
O
R C
O-
CH3CH2CH2COOH
butyric acid
H+
+
+
MgX
O
R C
OH
20. carboxylic acids, reactions:
1. as acids
2. conversion into functional derivatives
a) acid chlorides
b) esters
c) amides
3. reduction
4. alpha-halogenation
5. EAS
21. 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+ + AKa = [H3O+] [A-] / [HA]
ionization in water
22. Ka for carboxylic acids ≈ 10-5
Why are carboxylic acids more acidic than alcohols?
ROH + H2O H3O+ + RORCOOH + H2O H3O+ + RCOOΔGo = -2.303 R T log Keq
The position of the equilibrium is determined by the free
energy change, ΔGo.
ΔGo = ΔH - TΔS
ΔGo ≈ ΔH
∴Ka is inversely related to ΔH, the potential
energy difference between the acid and its conjugate base. The
smaller the ΔH, the larger the Ka and the stronger the acid.
23. potential energy
H3O+ + A-
ΔH
HA + H2O
ionization
The smaller the ΔH, the more the equilibrium lies to the
right, giving a larger Ka ( a stronger acid ).
24. OR C
O
O
R C
O-
R C
O
O
Resonance stabilization of the carboxylate ion decreases
the ΔH, shifts the ionization in water to the right, increases
the Ka, and results in carboxylic acids being stronger acids.
25. Effect of substituent groups on acid strength?
CH3COOH
1.75 x 10-5
ClCH2COOH
136 x 10-5
Cl2CHCOOH
5,530 x 10-5
Cl3CCOOH
23,200 x 10-5
-Cl is electron withdrawing and delocalizes the negative
charge on the carboxylate ion, lowering the PE, decreasing
the ΔH, shifting the ionization to the right and increasing
acid strength.
26. Effect of substituent groups on acid strength of benzoic acids?
Electron withdrawing groups will stabilize the anion, decrease the ΔH, shift
the ionization to the right, increasing the Ka, increasing acid strength.
COOG
Electron donating groups will destabilize the anion, increase the ΔH, shift the
ionization in water to the left, decreasing the Ka, decreasing acid strength.
COOG
28. Relative acid strength?
Ka
p-aminobenzoic acid
1.4 x 10-5
p-hydroxybenzoic acid
2.6 x 10-5
p-methoxybenzoic acid
3.3 x 10-5
p-toluic acid
4.2 x 10-5
benzoic acid
6.3 x 10-5
p-chlorobenzoic acid
10.3 x 10-5
p-nitrobenzoic acid
36
x 10-5
29. 2. Conversion into functional derivatives:
a ) acid chlorides
O
R C
OH
SOCl2
O
R C
Cl
or PCl3
orPCl5
CO2H + SOCl2
CH3CH2CH2 C
O
OH
COCl
PCl3
CH3CH2CH2 C
O
Cl
30. b ) 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
32. c ) amides
“indirect” only!
RCOOH + SOCl2 RCOCl + NH3 RCONH2
amide
O
OH
3-Methylbutanoic acid
PCl3
O
NH3
Cl
O
NH2
Directly reacting ammonia with a carboxylic acid results in
an ammonium salt:
RCOOH + NH3 RCOO-NH4+
acid
base
42. Carboxylic acids, syntheses:
1. oxidation of primary alcohols
RCH2OH + K2Cr2O7 RCOOH
2. oxidation of arenes
ArR + KMnO4, heat ArCOOH
3. carbonation of Grignard reagents
RMgX + CO2 RCO2MgX + H+
RCOOH
4. hydrolysis of nitriles
RCN + H2O, H+, heat RCOOH
43. carboxylic acids, reactions:
1. as acids
2. conversion into functional derivatives
a) acid chlorides
b) esters
c) amides
3. reduction
4. alpha-halogenation
5. EAS
