Download Chapter 19: Carboxylic Acids

CHAPTER 14: CARBOXYLIC
ACIDS
INTRODUCTION
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.


Fatty acids are long-chain aliphatic acids
Aromatic acids have an aryl group bonded to COOH.
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
COMMON NAMES
Many aliphatic acids have historical names.
 Positions of substituents on the chain are labeled with
Greek letters.

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Ph
Cl O
CH3CH2CHC OH
-chlorobutyric acid
CH3CH2CH2CHCH2COOH
-phenylcaproic acid
NOMENCLATURE

Common names you need to know:

Formic acid (methanoic acid)
O
H
OH

Acetic Acid (ethanoic acid)
O

Benzoic Acid
HO
O
OH
Propionic Acid (propanoic acid)
 Butyric acid (butanoic acid)
 Valeric acid (pentanoic acid)

IUPAC NAMES
Remove -e from alkane (or alkene) name, add -oic
acid.
 The carbon of the carboxyl group is #1.

CH3CH2CHC OH
Ph
H
H
C C
COOH
2-chlorobutanoic acid
trans-3-phenyl-2-propenoic acid
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Cl O
Nomenclature
• For acyclic acid chlorides: change the suffix –ic acid of the parent
carboxylic acid to the suffix –yl chloride; or
• When the –COCl group is bonded to a ring: change the suffix
carboxylic acid to –carbonyl chloride.
–
NAMING CYCLIC ACIDS
Cycloalkanes bonded to -COOH are named as
cycloalkanecarboxylic acids.
 Aromatic acids are named as benzoic acids.

CH(CH3)2
2-isopropylcyclopentanecarboxylic acid
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COOH
COOH
OH
o-hydroxybenzoic acid
DICARBOXYLIC ACIDS
Aliphatic diacids are usually called by their common
names.
 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
3-bromohexanedioic acid
-bromoadipic acid (common)
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Br
STRUCTURE OF CARBOXYL
Carbon is sp2 hybridized.
 Bond angles are close to 120.
 O-H eclipsed with C=O, to get overlap of  orbital
with orbital of lone pair on oxygen.

BOILING POINTS
Higher boiling points than similar alcohols, due to
dimer formation.
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Acetic acid, b.p. 118C
PHYSICAL PROPERTIES
MELTING POINTS
Aliphatic acids with more than 8 carbons are solids
at room temperature.
 Double bonds (especially cis) lower the melting
point. Note these 18-C acids:

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Stearic acid (saturated): 72C
 Oleic acid (one cis double bond): 16C
 Linoleic acid (two cis double bonds): -5C

SOLUBILITY
Water solubility decreases with the length of the
carbon chain.
 Up to 4 carbons, acid is miscible in water.
 More soluble in alcohol.
 Also soluble in relatively nonpolar solvents like
chloroform because it dissolves as a dimer.

ACIDITY
They are weak acids. The Ka value for most unsubsituted aliphatic
and aromatic carboxylic acids fall within the range from 10-4 to 10-5.
Recall small pKa stronger acid
large pKa waker acid
Ka are related as such pKa= -log(Ka)
pka+pKb=14
ACIDITY
Substitution of the alpha-carbon of an atom or a
group of atoms of higher electronegativity than
carbon increases the acidity of carboxylic acid.
 The inductive effect of an electronegative atom

SUBSTITUENT EFFECTS
ON ACIDITY
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=>
SALTS OF CARBOXYLIC ACIDS
Sodium hydroxide removes a proton to form the
salt.
 Adding a strong acid, like HCl, regenerates the
carboxylic acid.

CH3
C OH
NaOH
HCl
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O
O
CH3
_ +
C O Na
Cha
=>
pter
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SALTS
NAMING ACID SALTS
Name the cation.
 Then name the anion by replacing the
-ic acid with -ate.

-
CH3CH2CHCH2COO K
+
potassium -chlorovalerate (common)
potassium 3-chloropentanoate (IUPAC)
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Cl
COMPLETE REACTIONS AND NAME THE
SALTS
A) Butanoic Acid + Sodium Hydroxide
B) 2-hydroxypropanoic (lactic acid) acid + sodium
bicarbonate

A)
COOH + NaOH
Butanoic
Acid

B)
Sodium
Hydroxide
COONa +H2O
Sodium
Water
Butanoate
OH
OH
COOH + NaHCO3
2-Hydroxypropanoic
Sodium
Acid
Bicarbonate
(Lactic Acid COMMON)
COONa
+ H2O +CO2
Sodium 2-hydroxypropanoate
(sodium lactate, common)
REDUCTION OF CARBOXYL GROUP TO
1 ALCOHOLS
Use strong reducing agent, LiAlH4 (Lithium Aluminum
Hydride)
 And either diethyl ether or Tetrahydrofuran (THF) as
solvents; it reduces carboxylic acid to alcohol, but does
not reduce it to a ketone.

FISCHER ESTERIFICATION
After the German Chemist Emil Fischer
 Carboxylic Acid (strong acid as a catalyst) + alcohol
yields ester + water.
 All steps are reversible.
 Reaction reaches equilibrium.

O
COOH
+ CH3CH2OH
+
H
COCH2CH3
+ HOH
ACID CHLORIDES
The functional group of an acid halide is a carbonyl
bonded to a halogen atom
 Acid chlorides are the most frequently used in lab
and in industrial organic chemistry.
 The most common way to synthesize acid chlorides
is to treat a carboxylic acid with thionyl chloride
(SOCl2) or oxalyl chloride with the acid.

O
O
C OH
+
O O
C Cl
C C
Cl
Cl
(Oxalyl Chloride)
+ HCl + CO + CO2