Chapter 19: Carboxylic Acids
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Transcript 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. 118C
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): 72C
Oleic acid (one cis double bond): 16C
Linoleic acid (two cis double bonds): -5C
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