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 pKa 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”
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
o Hydrolysis of acid derivatives
· 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.
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
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.
· 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.
o Polymerization
§ When you put molecules with dual functional groups in together, you get long chains
· 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.
· 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