carboxylic acids and their derivatives. required background: aldehydes, ketones acidity of alcohols...
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Carboxylic acids and their derivatives
Required background:Aldehydes, ketonesAcidity of alcoholsReaction mechanisms
Essential for:Aminoacids, peptides
Outline
1. Acidity and basicity of carboxylic acids2. Fischer esterification3. Decarboxylation4. Acyl substitution5. Reduction of carboxylic acid derivatives6. Condensation polymers7. Overview of lipids8. Claisen condensation
O
OH
R H+
+
O
O-
R
O-
O
R
Carboxylic acids are stronger acids, than phenol, because the conjugate base (carboxylate)
is stabilized by the delocalization of the negative charge between two electronegative oxygens.
O
OH
ROH
OHHO3S
< < <
pKa = 16 pKa = 10 pKa = 5 pKa = -1
Acidity trend:
O
OH
RH
+ O+
OH
R
H
C+
O
O
R
H
H
O
O+
R
H
HO
O+
R
H
H
H+
Outline
1. Acidity and basicity of carboxylic acids2. Fischer esterification3. Decarboxylation4. Acyl substitution5. Reduction of carboxylic acid derivatives6. Condensation polymers7. Overview of lipids8. Claisen condensation
O
OH
RH
+O
OCH3
R+ CH3OH
H+
O+
OH
R
H
CH3OH
O
OH
R
H
O+
CH3H
~H+
O+
OH
R
H
OCH3
H
C+
O
R
OCH3
H
Outline
1. Acidity and basicity of carboxylic acids2. Fischer esterification3. Decarboxylation4. Acyl substitution5. Reduction of carboxylic acid derivatives6. Condensation polymers7. Overview of lipids8. Claisen condensation
O
O
R
H
HR +
O
O
H
R
O
NaOH, meltingNa2CO3
NaOH
O
O-
R R- + CO2
NaOHH2O
slight heating
R
OH
+CO2~H+
R
O
O
O
H
OH
O
slight heating
OH
OH
+CO2~H+
OH
O
Outline
1. Acidity and basicity of carboxylic acids2. Fischer esterification3. Decarboxylation4. Acyl substitution5. Reduction of carboxylic acid derivatives6. Condensation polymers7. Overview of lipids8. Claisen condensation
Examples of carboxylic acid derivatives
OCl
O
Br
2-bromopropyl 3-chlorobutanoate
O O
A cyclic ester (lactone)
dihydrofuran-2(3H)-oneO
Cl
propanoyl chloride
O
O O
benzoic anhydride
O
O O
acetic benzoic anhydride
OH
O
H3C CN
acetic acid acetonitrile
NH2
Cl O5-chlorohexanamide
Cl Cl
O
phosgene
NH2 NH2
O
urea
X
O
H
..
X
O-
H
..
Reacts with nucleophiles
Reacts with acids
Reacts with bases
Reactivity with nucleophiles is decreased by the stabilizing conjugation, which depends on the electron donating ability of X
Acid chlorides > anhydrides > esters, acids > amides > nitriles > salts
Reactions of carboxylic acid derivatives with nucleophiles
R X
O
Nu
R X
O-
NuR Nu
O
+ X
Reactions of acid chlorides
Cl
O
NH2
P h C H 2 C H 2 N H 2
P yr id in e
Cl
O-
NH2+
O
NH2+
O
NH
Py
OH
H3C CH3
C H 3 C (O )C l
P yr id in e
O
H3C CH3
O
CH3
75%
H3C
H3CCH3
OH
+
O
Cl P y
O
O
CH3
CH3
CH3
OH+
H3C
S
O
O
Cl
P y
TsCl H3C
S
O
O
O
90%
O
Cl+
O
O-
Na+
O
O
O
60%
Reactions of anhydrides
NH2
OH
+ OO
O
H 2 O
NH
OH
CH3
O
Paracetamol
OHCOOH
+ OO
O
H 2 O
O CH3
O
COOH
Aspirin
O OO C H 3 O H , re flu xCOOH
O
CH3
O
O OO
+NH2 H e a t
O
O
NH
OH
A c e t ic a n h yd r id e
h e a t
O
O
N
Reactions of esters O
O
N H 3
O
NH2
+OH
O
O
O
NHOH +
OH
N H 2 O H
A hydroxamic acid (forms a red complex with Fe(III))
R O
O
R1
R OR1
O-
OHR OH
O
+ R
R O-
O
+ R
Acid-catalyzed hydrolysis of esters is the reaction of esterification, going backwards.
Hydrolysis of carboxylic acid derivatives
Outline
1. Acidity and basicity of carboxylic acids2. Fischer esterification3. Decarboxylation4. Acyl substitution5. Reduction of carboxylic acid derivatives6. Condensation polymers7. Overview of lipids8. Claisen condensation
R
O
OC2H5
1 . L iA lH 4
2 . H + , H 2 O
a source of H-
R CH2OH
H-
R
O-
OC2H5H
R
O
H
H-
R
O-
HH
H+
R
O
NH2
RNH2
1 . L iA lH 4
2 . H 2 O
CN 1 . L iA lH 4
2 . H 2 O
NH2
74%
H2 / Ni
R
O
Cl
P d / C , H 2 , q u in o lin eR
O
H
Al-
H
O
OO
Li+
-78 oC
Outline
1. Acidity and basicity of carboxylic acids2. Fischer esterification3. Decarboxylation4. Acyl substitution5. Reduction of carboxylic acid derivatives6. Condensation polymers7. Overview of lipids8. Claisen condensation
O
O
OHOH
+ NH2
NH2
heat
O
O
OH
NNH
H
H
n
Nylon-6,6
+ OH
OH
heat
Dacron
COOHHOOC
O
O
O
O
OH
H
Outline
1. Acidity and basicity of carboxylic acids2. Fischer esterification3. Decarboxylation4. Acyl substitution5. Reduction of carboxylic acid derivatives6. Condensation polymers7. Overview of lipids8. Claisen condensation
Lipids are compounds of biological origin that dissolve in nonpolar solvents, such as chloroform and diethyl ether. The name lipid comes from the Greek word lipos, for fat. Unlike carbohydrates and proteins, which are defined in terms of their structures, lipids are defined by the physical operation that we use to isolate them. Not surprisingly, then, lipids include a variety of structural types. Examples are the following
Outline
1. Acidity and basicity of carboxylic acids2. Fischer esterification3. Decarboxylation4. Acyl substitution5. Reduction of carboxylic acid derivatives6. Condensation polymers7. Overview of lipids8. Claisen condensation
O
O
1 . N a O C 2 H 5
2 . H +
O O
O75%
CH2-
O
O
O-
O
O
O O O
O
CH-
O O
O
O
O
Base
H+
Claisen condensation
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