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 L. caper goat
CH3(CH2)5CO2H ---
CH3(CH2)6CO2H caprylic acid
CH3(CH2)7CO2H ---
CH3(CH2)8CO2H capric acid
CH3(CH2)9CO2H ---
CH3(CH2)10CO2H lauric acid oil of lauryl
5 4 3 2 1
C—C—C—C—C=O
δ γ β α used in common names
Br CH3
CH3CH2CH2CHCOOH CH3CHCH2COOH
bromovaleric acid -methylbutyric acid
isovaleric acid
COOH
special names
benzoic acid
COOH COOH COOH
CH3
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 isophthalic acid
terephthalic acid
H COOH H COOH
C C
C C
H COOH HOOC H
maleic acid 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
O O
C C
HO OH HO ONa
carbonic acid sodium bicarbonate
sodium hydrogen carbonate
NaHCO3
O
C
NaO 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 stronger weaker weaker
acid base base acid
RCO2H RCO2-
covalent ionic
water insoluble 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 butyric acid
1-butanol butanoic acid
CH3 CH3
CH3CHCH2-OH + KMnO4 CH3CHCOOH
isobutyl alcohol isobutyric acid
2-methyl-1-propanol` 2-methylpropanoic acid
2. oxidation of arenes:
KMnO4, heat
CH3 COOH
toluene benzoic acid
CH3 COOH note: aromatic
KMnO4, heat
acids only!
H3C HOOC
p-xylene terephthalic acid
KMnO4, heat
CH2CH3 COOH + CO2
ethylbenzene benzoic acid
3. carbonation of Grignard reagent:
Mg CO2 H+
R-X RMgX RCO2MgX RCOOH
Increases the carbon chain by one carbon.
Mg CO2 H+
CH3CH2CH2-Br CH3CH2CH2MgBr CH3CH2CH2COOH
n-propyl bromide butyric acid
H+
O O O
+ +MgX
RMgX + C R C R C
O- OH
O
CH3 CH3 CH3
Mg CO2 H+
Br MgBr COOH
p-toluic acid
Br2, hv Mg
CH3 CH2Br CH2MgBr
CO2
H+
CH2 COOH
phenylacetic acid
4. Hydrolysis of a nitrile:
H2O, H+
R-CN R-CO2H
heat
H2O, OH-
R-CN 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!
Br2, hv NaCN
CH3 CH2Br CH2 CN
toluene
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 MgBr
Mg
CO2; then H+
C N
H2O, H+, heat
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 < HCCH < ROH < HOH < H2CO3 < RCO2H < HF
d) quantitative
HA + H2O H3O+ + A- ionization in water
Ka = [H3O+] [A-] / [HA]
Ka for carboxylic acids 10-5
Why are carboxylic acids more acidic than alcohols?
ROH + H2O H3O+ + RO-
RCOOH + H2O H3O+ + RCOO-
ΔGo = -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 ).
O O-
R C R C
O- 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.
COO-
G
Electron donating groups will destabilize the anion, increase the ΔH, shift the
ionization in water to the left, decreasing the Ka, decreasing acid strength.
COO-
G
-NH2, -NHR, -NR2
-OH
-OR electron donating
-NHCOCH3
-C6H5
-R
-H
-X
-CHO, -COR
-SO3H
-COOH, -COOR electron withdrawing
-CN
-NR3+
-NO2
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 SOCl2 O
R C R C
OH or PCl3 Cl
orPCl5
CO2H + SOCl2 COCl
O PCl3 O
CH3CH2CH2 C CH3CH2CH2 C
OH 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 H+ O
C + CH3OH C + H2O
OH O CH3
SOCl2
O CH3OH
C
Cl
c) amides
―indirect‖ only!
RCOOH + SOCl2 RCOCl + NH3 RCONH2
amide
O O
PCl3 NH3 O
OH Cl NH2
3-Methylbutanoic acid
Directly reacting ammonia with a carboxylic acid results in an
ammonium salt:
RCOOH + NH3 RCOO-NH4+
acid base
O PCl3 O NH3 O
C C C
OH Cl NH2
amide
NH3
O
C ammonium salt
O NH4
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 H2, Pt
CH2 C NR
OH
LiAlH4
H+
CH2CH2OH
4. Alpha-halogenation: (Hell-Volhard-Zelinsky reaction)
RCH2COOH + X2, P RCHCOOH + HX
X
α-haloacid
X2 = Cl2, Br2
CH3CH2CH2CH2COOH + Br2,P CH3CH2CH2CHCOOH
pentanoic acid Br
2-bromopentanoic acid
COOH
Br2,P
NR (no alpha H)
RCH2COOH + Br2,P RCHCOOH + HBr
+ Br
nH
; the
OH NH3
Na
RCHCOOH RCHCOOH
aminoacid
NH2
OH
KOH(alc)
RCH2CHCOOH RCH=CHCOOH
Br then H+
5. EAS: (-COOH is deactivating and meta- directing)
CO2H
HNO3,H2SO4
NO2
CO2H
H2SO4,SO3
CO2H
SO3H
CO2H
benzoic acid Br2,Fe
Br
CH3Cl,AlCl3
NR
spectroscopy:
IR: -COOH O—H stretch 2500 – 3000 cm-1 (b)
C=O stretch 1680 – 1725 (s)
nmr: -COOH 10.5 – 12 ppm
p-toluic acid
-COO—H
stretch
C=O
COOH c
b
CH3 a
c 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