4.5 - Carboxylic acids and their derivatives

Question 1

What is the test for carboxylic acids

Answer 1

Structural formula (CnH2n+1COOH)

Conditions: Na2CO3 or NaHCO3
Observations: effervescence (CO2 gas)

Question 2

How are carboxylic acids formed from the oxidation of primary alcohols

Answer 2

Primary alcohol > carboxylic acid
- oxidation Cr2O7 2-/H+, heat and reflux
eg. C2H5OH + 2[O] > CH3CO2H + H2O

Question 3

What is the hydrolysis of esters to form a carboxylic acid

Answer 3

Acid hydrolysis
- H+/H2O and heat

CH3C=OOCH3 > CH3C=OOH + CH3OH

Alkaline hydrolysis
- OH-/H2O
CH3C=OOCH3 > CH3C=OO- + CH3OH
- must acidify the product to get the acid

Question 4

What is the hydrolysis of amides to form carboxylic acids

Answer 4

• Alkaline hydrolysis
  OH-/H2O and heat
  eg. CH3C=ONH2 🔛 CH3C=OO- + NH3 ( NH3 will turn red litmus blue)
  Acidify the product to form the acid
• Acid hydrolysis
  H+/H2O
  CH3C=ONH2 🔛 CH3C=OOH + NH4+

Question 5

What is the hydrolysis of a nitrile to form a carboxylic acid

Answer 5

Nitrile
- H+/H2O and heat

CH3CN > CH3C=O + NH4+

Production of aromatic carboxylic acids
- OH-/KMnO4 and heat

COOH side group always formed regardless of group attached to ring

Question 6

What is the reaction of carboxylic acids to form esters

Answer 6

Esterification
- concentrated H2SO4, heat and reflux
eg. CH3COOH + CH3OH 🔛 CH3C=OOCH3 + H2O

Question 7

What is the reduction of carboxylic acids to ethanol

Answer 7

Condtions: LiAlH4 and dry ether
eg. Ethanoic acid + LiAlH4 > ethanal + LiAlH4 > ethanol
CH3COOH + [H] > CH3C=OH + [H] > CH3CH2OH

Question 8

What is the decarboxylation reaction of carboxylic acids

Answer 8

Removal of CO2 from carboxylic acids
Conditions: heat and soda lime (Ca(OH)2/CaO and NaOH)

CH3COOH > CH4 + CO2

Question 9

What is the acidity of carboxylic acids

Answer 9

Carboxylic acids are weak acids so they partially dissociate, the electron density around the H+ is due to the electronegative O’s therefore it is easier to lose the O-H bond

CH3COOH and CH2ClCOOH
- chlorine makes the acid more negative, the electronegative Cl withdraws electron density so it is easier to lose the H+

Question 10

How are acid chlorides made

Answer 10

• an anhydrous exothermic reaction with H2O that is very reactive and very expensive

Use either
1. PCl3
eg. 3CH3COOH + PCl3 > 3CH3COCl + H3PO3

2. PCl5
   eg. CH3COPH + PCl5 > CH3COCl + POCl3 + HCl
3. SOCl2
   eg. CH3COOH + SOCl2 > CH3COCl + SO2 + Cl

Question 11

What is ethanoylation

Answer 11

• ethanoyl chloride used to add RCO group
• very reactive and expensive
• the reaction creates acid mist so another reagent used on large scale

Question 12

How are nitriles formed from halogenoalkanes

Answer 12

Halogenoalkane > nitrile
(Nucleophilic substitution)
Conditions: KCN, aqueous/alcohol, heat and reflux
eg. CH3CH2CH2NR + CN > CH3CH2CH2CN + Br-

Question 13

How are nitriles formed from carbonyls

Answer 13

Carbonyls > nitriles
- nucleophilic addition
Conditions: KCN, aqueous and refluxed
eg. CH3C=OH + HCN > CH3CHOHCN

Question 14

What is the reaction for the reduction of nitriles

Answer 14

• reduction of nitriles to amines
• LiAlH4 in dry ether
  eg. CH3CH2CN + 4[H] > CH3CH2CH2NH2

Question 15

How are amides formed from carboxylic acids

Answer 15

Carboxylic acid > amide
Conditions: NH3, heat, alcohol solvent and sealed tube
eg. CH3COOH + NH3 🔛 CH3CONH2 + H2O

Question 16

How are amides formed from carboxylic acids and amine in N substituted amide

Answer 16

• condensation reaction
  eg. CH3COOH + CH3NH2 > CH3C=ONHCH3 + H2O

amides can be hydrolysed into carboxylic acids or dehydrated using P2O5 and heat to form nitriles
eg. CH3CONH2 > CH3CN + H2O

Question 17

What reaction occurs in the hydrolysis of amides

Answer 17

• Alkaline hydrolysis
  NaOH/H2O and heat
  eg. CH3C=ONH2 + H2O > CH3C=OO- + NH3 (acidify the product)
• Acid hydrolysis
  H+/H2O and heat
  CH3C=ONH2 + H2O > CH3COOH + NH4+