Carboxylic Acids Flashcards
Carboxylic Acid
- always terminal groups
- oic acid
- with three bonds to oxygen, one of the most oxidized functional groups
Salts of Carboxylic Acids
-named beginning with the cation followed by the name with the ending -oate instead of -oic acid
Dicarboxylic Acids
-smallest- oxalic acid
-named by adding -dioic acid
carboxylic acid on either end of the molecule
Hydrogen Bonding in Carboxylic Acids
- strong intermolecular attractions because both hydroxyl oxygen and carbonyl oxygen can participate in H bonding so they tend to form dimers
- multiple H bonds elevate the boiling points and melting points past those of corresponding alcohols
- can H bond because they contain a hydrogen bonded to a very electronegative atom
Acidity in Carboxylic Acids
- resonance stabilization occurs between both of the electronegative oxygen atoms
- delocalization of negative charge results in a very stable carboxylate anion
- the more stable the conjugate base, the easier it is for the proton to leave and thus the stronger the acid
- hydroxyl hydrogen is very acidic resulting in a negative charge that remains after the H is removed
Substituents Affecting Acidity of Carboxylic Acid
- electron donating groups destabilize the negative charge, and decrease stability (-NH2, -OCH3)
- closer the substituent to the carboxyl, the greater the effect will be
- electron withdrawing groups increase acidity (-NO2 or halides)
Dicarboxylic vs Monocarboxylic Acid Acidities
- BUT when one proton is removed from dicarboxylic acid, the carboxylate anion forms resulting in a decrease in acidity of the remaining carboxylic acid
- due to instability, the second proton is less acidic and harder to remove than the analogous proton of a monocarboxylic acid
- carboxylic acids are electron withdrawing so dicarboxylic acids are more acidic than the mono
β-dicarboxylic Acids
- there are 2 carboxylic acids separated by a single carbon
- high acidity of the α-hydrogens
- loss of the acidic hydrogen produces a carbanion which is stabilized by the electron withdrawing effect of both carboxyl groups
- dicarboxylic acids in which each carboxylic acid is positioned on the β-carbon of the other
Synthesis of Carboxylic Acids
- oxidant is usually a dichromate salt –(Na2Cr2O7 or K2Cr2O7), chromium trioxide (CrO3), or potassium permanganate (KMnO4)
- secondary and tertiary alcohols cannot be oxidized to carboxylic acids
- oxidation of primary alcohols and aldehydes
Nucleophilic Acyl Substitutions
- after opening the carbonyl through nucleophilic attack and forming tetrahedral intermediate, the carbonyl can reform, kicking off the leaving group
- nucleophilic molecule replaces the leaving group of an acyl derivative
- nucleophilic molecule replaces the leaving group of an acyl derivative
- acyl derivative - all molecules with a carboxylic acid derived carbonyl including carboxylic acids, amides, esters, anhydrides, and others
- favored by a good leaving group
- favored in acidic or basic conditions
- focuses on the existence of a leaving group in carboxylic acids and their derivcatives
Amide
- can be in acidic or basic conditions
- named by replacing -oic acid with -amide
- cyclic called lactams (add -lactam instead of -oic acid)
-carboxylic acids can be converted into amides if incoming nucleophile is ammonia (NH3) or an amine
Ester
-esterification - condensation reaction with water as a side product
-in acidic solutions, carbonyl oxygen can be protonated enhancing the polarity of the bond thereby placing additional positive charge on the carbonyl carbon and increasing its susceptibility to nucleophilic attack
-occurs most rapidly with primary alcohols
cyclic lactones
-hybrid between a carboxylic acid and an ether which can be made by reacting carboxylic acids with alcohols under acidic conditions
Anhydrides
- named by replacing acid with anhydride whether cyclic or linear
- ex- condensation of two molecules of ethanoic acid to form ethanoic anhydride
- formed by the condensation of 2 carboxylic acids
Reduction of Carboxylic Acids
-aldehyde intermediates may be formed but they too will be reduced to -OH
-reaction is through nucleophilic addition of hydride to the carbonyl group
-a gentler reducing agent- NaBH4, is not strong enough to reduce carboxylic acids
with LiALH4, carboxylic acids can be reduced to primary alcohols
Decarboxylation
-common way of getting rid of a carbon from the parent chain
-1,3-dicarboxylic acids and other β-keto acids may spontaneously decarboxylate when heated where the carboxyl group is lost and replaced with hydrogen
-electrophile and nucleophile are in the same molecule, so reaction proceeds through a 6 membered ring in its transition state
enol that is initially formed tautomerizes to the more stable keto form
-complete loss of the carboxyl group as a carbon dioxide
