chapter 3
DESCRIPTION
Chapter 3. Carboxylic Acids. Carboxylic Acids. The functional group of carboxylic acids consists of a C=O with -OH bonded to the same carbon. Carboxyl group is usually written -COOH. Aliphatic acids have an alkyl group bonded to -COOH. Aromatic acids have an aryl group. - PowerPoint PPT PresentationTRANSCRIPT
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Carboxylic Acids
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Chapter 20 2
Carboxylic AcidsThe functional group of carboxylic acids
consists of a C=O with -OH bonded to the same carbon.
Carboxyl group is usually written -COOH.Aliphatic acids have an alkyl group bonded
to -COOH.Aromatic acids have an aryl group.Fatty acids are long-chain aliphatic acids.
=>
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Carboxylic Acids Carboxylic acid, compounds of the type
RCOOH such as Acetic acid ( present in vinegar), Malonic acid and Benzoic Acid.
CH3COOHH2C
COOH
COOH
COOH
Acetic acid Malonic acid Benzoic acid
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4
Common NamesMany aliphatic acids have historical names.Positions of substituents on the chain are
labeled with Greek letters.
1-Carboxylic Acid Nomenclature
CH3CH2CH2CHCOOH
BrCH3CHCH2COOH
CH3
bromovaleric acid -methylbutyric acid
isovaleric acid
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COOH
COOH COOH COOH
CH3
CH3CH3
benzoic acid
o-toluic acid m-toluic acid p-toluic acid
special names
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Chapter 20 6
IUPAC NamesRemove -e from alkane (or alkene) name,
add -oic acid.The carbon of the carboxyl group is #1.
CH3CH2CHC
Cl
OH
O
2-chlorobutanoic acid
PhC
HC
H
COOH
trans-3-phenyl-2-propenoic acid (cinnamic acid)
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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
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Dicarboxylic AcidsAliphatic diacids are usually called by their
common names (to be memorized).For IUPAC name, number the chain from the
end closest to a substituent.Two carboxyl groups on a benzene ring
indicate a phthalic acid.
HOOCCH2CHCH2CH2COOH
Br
3-bromohexanedioic acid -bromoadipic acid =>
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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
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CO2H
CO2H
CO2H
CO2H
CO2H
CO2Hphthalic acid isophthalic acid
terephthalic acid
CCOOHH
CCOOHH
CCOOHH
CHHOOC
maleic acid fumaric acid
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Chapter 20 11
Naming Cyclic AcidsCycloalkanes bonded to -COOH are named as
cycloalkanecarboxylic acids.Aromatic acids are named as benzoic acids.
COOH
CH(CH3)2
2-isopropylcyclopentanecarboxylic acid
COOH
OH
o-hydroxybenzoic acid(salicylic acid)
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2-Physical properties1- Boiling pointIntermolecular forces, especially hydrogen
bonding, are stronger in carboxylic acids than in other compounds of similar shape and molecular weight.
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Acetic acid exists as a hydrogen-bonded dimer in the gas phase. The hydroxyl group of each molecule is hydrogen-bonded to the carbonyl oxygen of the other.
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2-2-Solubility in WaterSolubility in WaterCarboxylic acids are similar to alcohols in respect to their solubility in water
Form hydrogen bonds to water
HH33CCCC
OO HH OO
OOHHOO
HH
HH
HH
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3-Acidity of carboxylic acidsMost carboxylic acids have a pKa close to 5.Carboxylic acids are weak acids but carboxylic
acids are far more acidic than alcohols.
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The greater difference in ionization energy (∆ G) of ethanol and acetic acid reflects a greater stabilization of acetate ion relative to ethoxide ion.
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Greater acidity of carboxylic acids is attributedstabilization of carboxylate ion by inductive effect of carbonyl group
And by resonance stabilization of carboxylate ion.
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Salts of Carboxylic Acids
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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
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4-Substituent and acid strength Alkyl substituents have negligible
effect
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Electronegative substituents increase acidity
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Electronegative substituents withdraw electrons from carboxyl group; increase K for loss of H+
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Effect of substituent decreases the acidity as number of bonds between X and carboxyl group increases.
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COOH
OCH3
COOH COOH
NO2
COOH
NO2
COOH
NO2
p-methoxy benzoic acid m-nitro p-nitro o-nitro
pKa = 4.46 pKa = 4.19 pKa = 3.47 pKa = 3.41 pKa = 2.16
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Ionization of Substituted Benzoic AcidsHybridization Effectsp2-hybridized carbon is more electron-withdrawing
than sp3, and sp is more electron-withdrawing than sp2
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Effect is small unless X is electronegative; effect is largest for ortho substituent
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5-Synthesis of carboxylic acids1- Oxidation of alkylbenzene
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2- Oxidation of primary alcohols
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3- Oxidation of aldehydes
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4-Carboxylation of Grignard reagents
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5- Hydroylsis of nitriles
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6- Reactions of Carboxylic acids1- Formation of Acyl chlorides
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2-Lithium aluminium hydride reduction
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3-Esterification
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Mechanism of Esterification
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Intramolecular ester formation (Lactones)
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4-α-Halogenation
This reaction of α- bormination of carboxylic acid is called Hell- Volhard- Zelinasky reaction
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5- Decarboxylation of carboxylic acids
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