Download - Carboxylic Acids
Carboxylic acids:
R-COOH, R-CO2H,
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
R COH
O
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 1C—C—C—C—C=Oδ γ β α used in common names
CH3CH2CH2CHCOOH
BrCH3CHCH2COOH
CH3
bromovaleric acid -methylbutyric acid
isovaleric acid
COOH
COOH COOH COOH
CH3
CH3CH3
benzoic acid
o-toluic acid m-toluic acid p-toluic acid
special names
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
BrCH3CH2CHCO2H 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
CO2Hphthalic acid isophthalic acid
terephthalic acid
CCOOHH
CCOOHH
CCOOHH
CHHOOC
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
HOC
OH
O
NaOC
ONa
O
HOC
ONa
O
carbonic acid sodium bicarbonatesodium hydrogen carbonate
sodium carbonate
NaHCO3
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 ionicwater 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 acid2-methyl-1-propanol` 2-methylpropanoic acid
2. oxidation of arenes:
CH3
CH3
H3C
CH2CH3
KMnO4, heat
KMnO4, heat
KMnO4, heat
COOH
COOH
HOOC
COOH
toluene benzoic acid
p-xylene terephthalic acid
ethylbenzene benzoic acid
+ CO2
note: aromatic acids only!
3. carbonation of Grignard reagent:
R-X RMgX RCO2MgX RCOOH
Increases the carbon chain by one carbon.
Mg CO2 H+
CH3CH2CH2-Br CH3CH2CH2MgBr CH3CH2CH2COOHn-propyl bromide butyric acid
Mg CO2 H+
C
O
O
RMgX + R CO
O-+ +MgX
H+
R CO
OH
CH3
Br
Mg
CH3
MgBr
CO2 H+
CH3
COOH
p-toluic acid
CH3
Br2, hvCH2Br
MgCH2MgBr
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 RCOOH1o alkyl halide
Adds one more carbon to the chain.R-X must be 1o or CH3!
CH3
Br2, hvCH2Br
NaCN
CH2 CN
H2O, H+, heat
CH2 COOH
CH3CH2CH2CH2CH2CH2-BrKCN
CH3CH2CH2CH2CH2CH2-CN
H2O, H+, heat
CH3CH2CH2CH2CH2CH2-COOH
1-bromohexane
heptanoic acid
toluene
phenylacetic acid
CO2H
CH2OH
CH3
Br
C N
MgBr
KMnO4, heat
KMnO4
MgCO2; then H+
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.
HA + H2O
H3O+ + A-po
tent
ial e
nerg
y
ionization
ΔH
The smaller the ΔH, the more the equilibrium lies to the right, giving a larger Ka ( a stronger acid ).
R CO-
OR C
O-
O
R CO
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.
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
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
R COH
O SOCl2
or PCl3orPCl5
R CCl
O
CO2H + SOCl2 COCl
CH3CH2CH2 CO
OH
PCl3CH3CH2CH2 C
O
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
C CO
O
CH3
+ H2O
SOCl2
CCH3OH
O
OH+ CH3OH
O
Cl
H+
)c 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
OH
O
3-Methylbutanoic acid
PCl3
Cl
O NH3
NH2
O
CO
OH
PCl3C
O
ClC
O
NH2
NH3
NH3
amide
CO
O NH4
ammonium salt
3. Reduction:
RCO2H + LiAlH4; then H+ RCH2OH
1o alcohol
Carboxylic acids resist catalytic reduction under normal conditions.
RCOOH + H2, Ni NR
CH3CH2CH2CH2CH2CH2CH2COOH
Octanoic acid(Caprylic acid)
LiAlH4 H+
CH3CH2CH2CH2CH2CH2CH2CH2OH
1-Octanol
CH2 CO
OH
H2, PtNR
LiAlH4
H+
CH2CH2OH
4. Alpha-halogenation: (Hell-Volhard-Zelinsky reaction)
RCH2COOH + X2, P RCHCOOH + HX X α-haloacid X2 = Cl2, Br2
COOH
Br2,PNR (no alpha H)
CH3CH2CH2CH2COOH + Br2,P CH3CH2CH2CHCOOH
Brpentanoic acid2-bromopentanoic acid
RCH2COOH + Br2,P RCHCOOH + HBr
Br
NH2OH
RCHCOOH RCHCOOH
RCH=CHCOOHRCH2CHCOOH
Br
aminoacid
NaOH;then H+
NH3
KOH(alc)
then H+
5. EAS: (-COOH is deactivating and meta- directing)
CO2H
CO2H
NO2
CO2H
SO3H
CO2H
Br
NR
HNO3,H2SO4
H2SO4,SO3
Br2,Fe
CH3Cl,AlCl3
benzoic acid
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
CH3 a
b
c
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