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Chapter 13 Carboxylic acids13.1 Nomenclature13.2 Acidity of carboxylic acids Factors affecting the acidity of carboxylic acids Dicarboxylic acids13.3 Preparation of carboxylic acids13.3.1 Preparation of carboxylic acids by carbonation of Grignard reagents13.3.2 Preparation of carboxylic acids by the preparation and hydrolysis of nitriles
13.4 Reactions of Carboxylic acids13.4.1 Esterification13.4.2 α-Halogenation of carboxylic acids: Hell-Volhard-Zelinsky reaction 13.4.3 Decarboxylation of malonic acid and related compounds13.5 Spectroscopic analysis of carboxylic acids
C
OR OH
Carboxylic acid:Carboxyl group
(羧基)Acyl group
(酰基)
All of carboxylic acid derivativescontain the acyl group.
13.1 Nomenclature1. e oic acid
CH3CH2CHCH2CH2CCH3
OOH
CH3CH CHCH2CH2C
O
OH4-Hexenoic acid
( 4- 己烯酸)CHC
O
OH
OH
2-Hydroxy-2-phenylethanoic
acidMandelic acid
(扁桃酸)
4-Methylhexanoic acid( 4- 甲基己酸)2. For the compounds
with polyfunctional group carboxylic acids outrank all the common group.
Ch. P281Ch. P281
P308P308
3-Bromocyclohexane-carboxylic acid(3- 溴环己烷甲酸 )
3-Bromocyclohexane-carboxylic acid(3- 溴环己烷甲酸 )
HY > RCOOH > H2CO3 >C6H5OH > H2O > RCH2OH >pka: 4 ~ 5 6.38 10 15.74 16 ~ 19
~ 25 ~ 34 ~50C CH > RNH2 > RH
13.2 Acidity of carboxylic acids
C
O
OHR C
O
OR + H+
R CO
O
¦Ä
¦Äsp2 hybridization, p - πconjugation
HOCCH2CHCH2CH2CHCH2COH
O OCH2CH3
CH33-Ethyl-6-methyloctanedioic acid(3- 甲基 -6- 乙基辛二酸 )
3-Ethyl-6-methyloctanedioic acid(3- 甲基 -6- 乙基辛二酸 )
COOH
Br
1-Cyclopentene-carboxylic acid(1- 环戊烯甲酸 )
1-Cyclopentene-carboxylic acid(1- 环戊烯甲酸 )
COOH1
2
345
RCOOH + NaOH RCOO Na + H2OStronger
baseWeaker
baseWeaker
acidStronger
acidRCOOH + NaHCO3 RCOO Na + CO2 + H2O
Sodium bicarbonateRCOOH: Water insoluble; RCOO-M+(Carboxylic salt): Water solubleCarboxylic acids can be separated from alcohols and phenol.
RCOONa + HCl RCOOH + NaCl
OH
CH3
CH3
CH3
NaOHH2O
Water phase
Organic phase
COOH
CH3
CH3
COONa
ONa
CH3
CO2
Water phase
Organic phase
OH
CH3
COONa
H+
COOH
Factors affecting the acidity of carboxylic acids:Inductive effects of the substituents
C COOHCl
Cl
Cl
> C COOHCl
Cl
H
> C COOHCl
H
H
> C COOHH
H
H
pKa 0.7 1.48 2.85 4.75
With more electron-withdrawing groups, acidity of the carboxylic acid is stronger. Inductive effects fall off rapidly as number ofσbond increases.
P313,10.3P313,10.3
CH3 CH2 CH C
O
OH
Cl
> CH3 CH2CH C
O
OH
Cl
> CH2 CH2CH2 C
O
OH
Cl
pKa: 2.85 4.05 4.50
2-Chlorobutanoic 3-Chlorobutanoic 4-Chlorobutanoic acid acid acid
Carbon becomes more electron-withdrawing as its s character increases:
sp3 < sp2 < sp
CH3COOH CH2 CHCOOH COOH
pKa: 4.8 4.3 4.2
Dicarboxylic acids:HOOCCH2COOH
pKa1 = 2.9HOOCCH2COO + H+
HOOCCH2COO pKa2 = 5.2 OOCCH2COO + H+
Oxalic acid(草酸或乙二酸)
Malonic acid(丙二酸)
Heptanedionic acid(庚二酸)
pKa1: 1.2 2.8 4.3
HOOC CH2 COOH
HO2CCO2H > HO2CCH2CO2H > HO2C(CH2)5CO2H
OOC CH2 COOH Carboxylate group with Electron-donating (+I)
Carboxylic group with electron-withdrawing (-I)
CH2
C
O
O
CO
O
HCH2
C
O
O
CO
O
HField effect(场效应) : electronic effects is transferred by space
Ch.P375Ch.P375
13.3 Preparation of carboxylic acids13.3.1 Preparation of carboxylic acids by carboxylation (羧化作用) of Grignard reagentGrignard reagents react with carbon dioxide to yield Mg salt of carboxylic acids , acidification (酸化) produces RCOOH
BrMg
Et2O MgBr1) CO2
2) H3O+CO2H
2,2-Dimethylpropanoic acid
(80%)
Benzoic acid(85%)Carbonation = carboxylation
(CH3)3C MgCl + O C O O C O MgCl
C(CH3)3H3
+O(CH3)3CCOOH
P316, 10.4P316, 10.4
RX RCOOH1)2) Extension of C skeleton by 1 carbon atom.3) Limitation: OH, NH, SH or C=O
13.3.2 Preparation of carboxylic acids by the preparation and hydrolysis of nitriles (腈) SN2 reaction of alkyl halide with sodium cyanide produce nitrile (alkyl cyanide)( 烷基氰 ),Hydrolysis of nitrile yields RCOOH.
R-CH2X + CN R-CH2CNH+ or OH
H2O R-CH2COOH
+ NH4+ ( or NH3)
HOCH2CH2ClNaCN
80%HOCH2CH2CN
(1) NaOH
(2) H3+O
HOCH2CH2COOH(75% ~ 80%)
3-Hydroxy-propanenitrile
3-Hydroxy-propanoic acid
Ch.P368, (2)Ch.P368, (2)
BrCH2CH2CH2Br NaCN
H2ONCCH2CH2CH2CN
1,5-Pentanedioic acid(83-85%)
H2O, HCl
¡÷CCH2CH2CH2HO
OC OH
O1,3-Dibromopropane 1,5-Pentanedinitrile
(77-86%)
Preparation of α- hydroxy carboxylic acids
CH3CCH2CH2CH3
OH
COOHCH3CCH2CH2CH3
O
CH3CCH2CH2CH3
OCH3CCH2CH2CH3
OH
COOH
1. NaCN
2. H+ CH3CCH2CH2CH3
OH
CN
H2O, HCl
¡÷
2-Pentanone 2-Pentanonecyanohydrin
2-Hydroxy-pentanoic acid
(60%)
Preparation of dicarboxylic acids
13.4 Reactions of Carboxylic acids
AcidityAcidityNucleophilicacyl substitution
Nucleophilicacyl substitution
Reaction sites of carboxylic acids
Reduction to CH2Reduction to CH2
Decarboxylation脱羧反应
Decarboxylation脱羧反应
α-H reactionα-H reaction
C
O
RC OH
H
13.4.1 Esterification (酯化反应)
C
O
OHC6H5 + CH318O H C
O
C6H518OCH3 + H2O
Carboxylic acid Alcohol Ester Water
Which C—O bond was broken?Mechanism of acid-catalyzed esterification: Step 1 Protonation on the carbonyl group of the carboxylic acid
C
O
OHRH+
C
OH
OHR C
OH
OHR
P322P322
Step 2 Nucleophilic attack of a molecule of alcohol to the protonated carbonyl group
R'OH OHR
O HR'
C
OH
C
OH
OHR
Tetrahedral intermediate
OH2R
OR'
-H2OC
OH
R O R'C
OHOHR
O HR'
C
OHStep 3 The proton transfers and dehydration
Step 4 Deprotonation to form the ester
-H+
C
O
O R'RC
OH
R O R'
The fundamental mechanistic patterns(基本机理模式) of nucleophilic reaction of a carboxylic acid and its derivatives
1. Activation of the carbonyl group - protonation of carbonyl group2. Nucleophilic addition to the protonated carbonyl to form a tetrahedral intermediate3. Elimination from the tetrahedral intermediate to restore the carbonyl group
P318, 10.5P318, 10.5R C
O
Y R C
OH
YH+ :Nu
R C
OH
Y
Nu
R C
OH
NuR C
O
Nu-H+
RCH2COOH + Br2(1) P
(2) H2ORCHCOOH + HBr
Br
13.4.2α-Halogenation of carboxylic acids: Hell-Volhard-Zelinsky reactionAliphatic carboxylic acids react with Br2 or Cl2 in the presence of P or PX3 to give α- halo acids
α- Halo acid
CH3CH2CH2CO
OH+ Br2
P CH3CH2CHCO
BrBr
H2O CH3CH2CHCO
BrOH Ch.P379,(5)Ch.P379,(5)
α- Halo acids are important synthetic intermediates:
CH3CH2CHCOOH
Br
(1) K2CO3,H2O
100¡æ
(2) H+
CH3CH2CHCOOH
OH2-Hydroxybutanoic acid
(69%)A standard method for the preparation of α- amino acid:
(CH3)2CHCH2COOHBr2
PCl3(CH3)2CHCHCOOH
BrNH3
H2O(CH3)2CHCHCOOH
NH2
2-Amino-3-methylbutanoic acid (48%)
C
O
HO CH2C
O
O
Hslowly
HOC
CH2
OH
O C O
13. 4. 3 Decarboxylation (脱羧反应) of Malonic acid and related compounds
R C
O
OHdecarboxylation R H + CO2
HO C
O
C
O
CH3OH 150 ¡æC
O
CH2HO + CO2
Malonic acid Acetic acidCarbondioxide
Mechanism
HOC
O
CH3
Thermaldecarboxylation
Thermaldecarboxylation
C
O
HO CH2C
OH
O
Transitionstate
Malonic acid decarboxylates readily:
100 ~ 150 ¡æ-CO2
When α- H was replaced, decarboxylation also occurs readily.
2-(2-Cyclopentenyl)malonic acid
(2-Cyclopentenyl)acetic acid(96~99%)
Decarboxylation of β- keto acids leads to ketones
R C
O
C
O
CH3OH 100 ~ 150 ¡æC
O
CH2R-CO2
13.5 Spectroscopic analysis of carboxylic acids
IR: O - H Stretching 3500~2500 cm-1
C = O Stretching 1700 cm-1
NMR: COOH: 10-12 ppm
Ar - H
CH2
COOH