Topic 12: Carboxylic acids

Question 1

What makes carboxylic acid more acidic than alcohol?

Answer 1

When deprotonated, carboxylic acids can delocalize the (-) charge between the 2 O atoms, thus the carboxylate ion is more stable than the alkoxide ion.

Question 2

How do carboxylic acids react in aqueous solution?

Answer 2

Carboxylic acids are deprotonated to yield H+ ions, but as carboxylic acids are stronger base to H2O, it acts as base and equilibrium favor making carboxylic acids.

Question 3

How do carboxylic acids react with strong bases?

Answer 3

Deprotonate to produce water-soluable carboxylate salts and the reaction is reversible

Question 4

What are some derivatives of carboxylic acids?

Answer 4

Aldehydes, ketones, acid chlorides
Esters, thioesters, amides

Question 5

How is ester produced from carboxylic acid?

Answer 5

Carboxylic acid reacts with alcohol, H+ catalyst and heat to produce ester

Question 6

How are the intermolecular hydrogen bonds in carboxylic acids compared to other organic compounds?
What are the effects of such difference?

Answer 6

Carboxylic acids in liquid and solid state have stronger intermolecular H bonds compared to other organic compounds.
So they are more polar, thus more polar and have higher boiling points.

Question 7

Why are carboxylic acids more soluble in water than its derivatives?

Answer 7

The H bonds in carboxylic acids are stronger, thus form more extensive H bond with water molecules.

Question 8

Compare the reactivity of carboxylic acid derivatives (ester, thioester, amide, acid chloride) and explain

Answer 8

Acid chloride > thioester > ester > amide
Cl and S are in different row in periodic table than O and N
–> longer bonds with C, thus poorer orbital overlap
–> weaker bond, thus higher reactivity

Question 9

Explain the hydrolysis and certain conditions for carboxylic acid derivatives reactions

Answer 9

• Acid chloride + H2O –> carboxylic acid + HCl
• Ester + H20 –(with H+ as catalyst)> carboxylic acid + alcohol
• Thioester + H2O –(with H+ as catalyst)> carboxylic acid + R’SH
• Amide: after reacts with water
  + acid and heat added: carboxylic acid + protonated amine (ammonium salt)
  + base and heat added: deprotonated carboxylic acid (carboxylate salt) + R’NH2

Question 10

Explain the reduction and oxidation from and to carboxylic acids

Answer 10

• Oxidizing primary alcohol and aldehyde produces carboxylic acids.
• Reducing carboxylic acid with LiAlH4 and H3O+ produces alcohol.

Question 11

How are ester and amide produced from carboxylic acid via acyl chloride?

Answer 11

• Carboxylic acid can be turned into acyl chloride for higher reactivity by using SOCl2
  + acyl chloride + alcohol –> ester
  + acyl chloride + amine –> amide