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
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
5 4 3 2 1
C—C—C—C—C=O
δ γ β α
Br
CH3CH2CH2CHCOOH
 bromovaleric acid
used in common names
CH3
CH3CHCH2COOH
 -methylbutyric acid
isovaleric acid
COOH
special names
benzoic acid
COOH
CH3
COOH
COOH
CH3
CH3
o-toluic acid
m-toluic acid
p-toluic acid
IUPAC nomenclature for carboxylic acids:
parent chain = longest, continuous carbon chain that contains
the carboxyl group  alkane, drop –e, add –oic acid
HCOOH
methanoic acid
CH3CO2H
ethanoic acid
CH3CH2CO2H
propanoic acid
CH3
CH3CHCOOH
2-methylpropanoic acid
Br
CH3CH2CHCO2H
2-bromobutanoic acid
dicarboxylic acids:
HOOC-COOH
oxalic acid
HO2C-CH2-CO2H
malonic acid
HO2C-CH2CH2-CO2H
succinic acid
HO2C-CH2CH2CH2-CO2H
glutaric acid
HOOC-(CH2)4-COOH
adipic acid
HOOC-(CH2)5-COOH
pimelic acid
Oh, my! Such good apple pie!
CO2H
CO2H
CO2H
CO2H
CO2H
CO2H
phthalic acid
H
H
C
C
isophthalic acid
terephthalic acid
COOH
H
COOH
HOOC
maleic acid
C
C
COOH
H
fumaric acid
salts of carboxylic acids:
name of cation + name of acid: drop –ic acid, add –ate
CH3CO2Na
sodium acetate or sodium ethanoate
CH3CH2CH2CO2NH4
ammonium butyrate
ammonium butanoate
(CH3CH2COO)2Mg
magnesium propionate
magnesium propanoate
HO
O
C
OH
carbonic acid
HO
O
C
ONa
sodium bicarbonate
sodium hydrogen carbonate
NaHCO3
NaO
O
C
ONa
sodium carbonate
Na2CO3
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
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.
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
1. oxidation of 1o alcohols:
CH3CH2CH2CH2-OH
+
CrO3  CH3CH2CH2CO2H
n-butyl alcohol
1-butanol
CH3
CH3CHCH2-OH
isobutyl alcohol
2-methyl-1-propanol`
butyric acid
butanoic acid
+ KMnO4 
CH3
CH3CHCOOH
isobutyric acid
2-methylpropanoic acid
2. oxidation of arenes:
CH3
KMnO4, heat
COOH
toluene
CH3
benzoic acid
COOH
KMnO4, heat
note: aromatic
acids only!
HOOC
H3C
terephthalic acid
p-xylene
KMnO4, heat
CH2CH3
ethylbenzene
COOH + CO2
benzoic acid
3. carbonation of Grignard reagent:
Mg
R-X
H+
CO2
RMgX
RCO2MgX
RCOOH
Increases the carbon chain by one carbon.
CO2 H+
Mg
CH3CH2CH2-Br
n-propyl bromide
RMgX +
O
C
O
CH3CH2CH2MgBr
O
R C
O-
CH3CH2CH2COOH
butyric acid
H+
+
+MgX
O
R C
OH
CH3
CH3
Mg
CH3
CO2
Br
H+
MgBr
COOH
p-toluic acid
Br2, hv
CH3
Mg
CH2Br
CH2MgBr
CO2
H+
CH2 COOH
phenylacetic acid
4. Hydrolysis of a nitrile:
H2O, H+
R-CN
R-CO2H
heat
H2O, OH-
R-CN
R-CO2- + H+  R-CO2H
heat
R-X + NaCN  R-CN + H+, H2O, heat  RCOOH
1o alkyl halide
Adds one more carbon to the chain.
R-X must be 1o or CH3!
CH3
Br2, hv
NaCN
CH2Br
toluene
CH2 CN
H2O, H+, heat
CH2 COOH
phenylacetic acid
KCN
CH3CH2CH2CH2CH2CH2-Br
CH3CH2CH2CH2CH2CH2-CN
1-bromohexane
H2O, H+, heat
CH3CH2CH2CH2CH2CH2-COOH
heptanoic acid
CH2OH
KMnO4
CH3
KMnO4, heat
CO2H
Br
Mg
MgBr
C N
H2O, H+, heat
CO2; then H+
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
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
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.
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 ).
OR C
O
O
R C
O-
O
R C
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.
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.
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
-NH2, -NHR, -NR2
-OH
-OR
-NHCOCH3
-C6H5
-R
-H
-X
-CHO, -COR
-SO3H
-COOH, -COOR
-CN
-NR3+
-NO2
electron donating
electron withdrawing
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
2. Conversion into functional derivatives:
a)  acid chlorides
O
R C
OH
SOCl2
O
R C
Cl
or PCl3
orPCl5
CO2H + SOCl2
O
CH3CH2CH2 C
OH
COCl
PCl3
O
CH3CH2CH2 C
Cl
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
O
C
OH
H+
+
CH3OH
SOCl2
O
C
Cl
CH3OH
O
+ H2O
C
O CH3
c)  amides
“indirect” only!
RCOOH + SOCl2  RCOCl + NH3  RCONH2
amide
O
PCl3
OH
3-Methylbutanoic acid
O
NH3
Cl
O
NH2
Directly reacting ammonia with a carboxylic acid results in an
ammonium salt:
RCOOH + NH3  RCOO-NH4+
acid
base
O
C
OH
PCl3
O
C
Cl
NH3
O
C
NH2
amide
NH3
O
C
O
NH4
ammonium salt
3. Reduction:
RCO2H + LiAlH4; then H+  RCH2OH
1o alcohol
LiAlH4
H+
CH3CH2CH2CH2CH2CH2CH2COOH
Octanoic acid
(Caprylic acid)
CH3CH2CH2CH2CH2CH2CH2CH2OH
1-Octanol
Carboxylic acids resist catalytic reduction under normal
conditions.
RCOOH + H2, Ni  NR
O
CH2 C
OH
H2, Pt
LiAlH4
H+
CH2CH2OH
NR
4. Alpha-halogenation: (Hell-Volhard-Zelinsky reaction)
RCH2COOH + X2, P  RCHCOOH + HX
X
α-haloacid
X2 = Cl2, Br2
CH3CH2CH2CH2COOH
+
Br2,P
pentanoic acid
COOH
Br2,P
NR (no alpha H)
CH3CH2CH2CHCOOH
Br
2-bromopentanoic acid
RCH2COOH + Br2,P
RCHCOOH + HBr
+
H;
O
Na
H
n
the
Br
NH3
RCHCOOH
RCHCOOH
NH2
OH
KOH(alc)
RCH2CHCOOH
Br
then H+
RCH=CHCOOH
aminoacid
5. EAS: (-COOH is deactivating and meta- directing)
CO2H
HNO3,H2SO4
NO2
CO2H
CO2H
H2SO4,SO3
SO3H
CO2H
benzoic acid
Br2,Fe
Br
CH3Cl,AlCl3
NR
spectroscopy:
IR: -COOH
O—H stretch 2500 – 3000 cm-1 (b)
C=O stretch
nmr: -COOH
10.5 – 12 ppm
1680 – 1725 (s)
p-toluic acid
-COO—H
stretch
C=O
COOH c
b
CH3
c
a
b
a
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
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