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Chapter 20 – Carboxylic Acids

Nomenclature
o IUPAC
 This is our highest priority group
 Find the longest chain, drop the “e” and add “oic acid”
Decane → decanoic acid



Structure and physical properties
o Extended hydrogen bonding leads to high boiling points.
Acidity
o pKa’s are around 4-5
o If electron withdrawing groups are near the carboxyl group, then the pK a is
lowered.
 This is because the electron withdrawing group can stabilize the
negatively charged conjugate base.
Salts of carboxylic acids
o Nomenclature – remove the “ic acid” and add “ate”
-
OH
3-methylbutanoic acid

3-methylbutanoate
o The carboxylate ions are now much more water-soluble
Synthesis of carboxylic acids
o Oxidation of primary alcohols with chromic acid or KMnO4
 See Chapter 11 for review
o Cleavage of alkenes with vigorous KMnO4
 This gives ketones or carboxylic acids, depending on the specific alkene.
 See Chapter 8 for review
o Cleavage of alkynes with O3 or vigorous KMnO4
 See Chapter 9 for review
o Carboxylation of Grignards
1)
2) H+
CH3--MgBr
o Hydrolysis of acid derivatives
Any acid
derivative

H20
acid or base
carboxylic acid
or carboxylate
+ other piece
Fischer Esterification
o This is a big one to know!
 Even if you don’t know this mechanism for this class, your prehealth
standardized tests will expect you to know it.
o Overall: Carboxylic acid + alcohol → ester + water
o Step 1: protonation of carbonyl to “activate” it for attack.
H+
o Step 2: Alcohol attacks carbonyl carbon of the acid
o Step 3: Deprotonation of the oxygen from the alcohol
o Step 4: Protonation of one of the oxygens from the acid
H+
o Step 5: Loss of water, forming a resonance-stabilized carbocation
o Step 6: Deprotonation of carbonyl

Hydrolysis of esters
o Can be acid catalyzed.
o When it’s base-catalyzed, it’s called saponification.
 When you hydrolyze triglycerides with base, you get carboxylates with
long fatty chains.
 These chains form micelles.
 Water-soluble with lipophilic interiors.
nonpolar
dirt

Direct formation of amides
o What would happen if you put the following reagents into a vessel?

Just acid-base chemistry.
o In order to make the amide, you have to heat it up.
heat
H2O
o Polymerization
 When you put molecules with dual functional groups in together, you get
long chains
heat
(
)
n

Reaction with alkyl lithiums
o This is the only time we see alkyl lithiums behaving differently from Grignards
o The alkyl lithium first deprotonates the carboxyl group, giving the carboxylate
o A second alkyl lithium then adds to the carbonyl
o After protonation, you have the hydrate, which forms the ketone.
CH3-Li
CH3-Li
-
-

Reduction of carboxylic acids
o COOH to 1° alcohol
 You’ve already seen this – add LiAlH4
o Conversion to the ketone
o Reduction to the aldehyde.
 Convert to acid chloride, then use LiAl(OtBu)3H
H+