3.3.8-9 Ketones, aldehydes, carboxylic acids and derivatives

Question 1

What reaction and mechanism occurs when NaBH4 is added to an aldehyde/ketone?
What are the conditions?

Answer 1

Reaction: reduction
Mechanism: nucelophilic addition
Conditions: NaBH4 dissolved in methanol and water

Question 2

What is the mechanism for the reaction between KCN and an aldehyde/ketone?
What are the conditions and products?

Answer 2

Mechanism: nucleophilic addition
Conditions: KCN and acid catalyst (HCN added)
Products: hydroxynitrile

Question 3

Which carboxylic acids are water soluble and why?

Answer 3

• Carboxylic acids with fewer than 6 carbons
• Water molecule able to hydrogen bond with the -COOH

Question 4

Draw the ionisation of ethanoic acid, where does the equilibrium lie?

Answer 4

CH3COOH ⇌ CH3COO- + H+

Equilibrium lies to the left, ethanoic acid doesn’t fully ionise as it is a weak acid

Question 5

How do you form a ester from a carboxylic acid?

think: mechanism, conditions and reactents

Answer 5

Mechanism: nucleophilic addition elimination
Reactents: carboxylic acid + alcohol
Conditions: strong acid catalyst (H2SO4)

Question 6

How do you name an ester?

Answer 6

Alky group (alcohol)
-oate (carboxylic acid)

Question 7

What are some common uses of esters?

Answer 7

• Fragrances and flavouring
• Plasticisers (added to polymers to increase flexibility)
• Solvent

Question 8

What is a triglyceride made from?

Answer 8

• Glycerol (triol)
• 3 fatty acids (carboxylic acid)

Question 9

How do you hydrolyse an ester in acid conditions?

Answer 9

Ester + H2O ⇌ alcohol + carboxylic acid
Conditions: dilute H2SO4 catalyst, RTP

Question 10

How do you hydrolyse an ester in alkaline conditions?

Answer 10

Ester + NaOH → alcohol + sodium carboxylate
Conditions: warm NaOH

Question 11

What is the difference and similarities between the acid and alkaline hydrolysis of esters?

Answer 11

• Acid hydrolysis is reversible, alkaline not
• Acid hydrolysis uses a dilute H2SO4 catalyst, alkaline hydrolysis uses no catalyst
• Acid and alkaline hydrolysis both produce an alcohol
• Alkaline hydrolysis prodces a carboxylate salt, acid hydrolysis produces a carboxylic acid

Question 12

How can animal fats and vegetable oils be hydrolysed?
What does it produce?

Answer 12

Hydrolysis in akaline conditions (NaOH)
Soaps = carboxylate salts

Question 13

How do you produce biodiesel?

think: name of reaction, conditions, reactents, products

Answer 13

Transesterification:

Rapeseed oil + methanol ⇌ glycerol + FAME

KOH/NaOH catalyst (can be acid/alkali though)

FAME = fatty acid methyl esters (biodiesel)

Question 14

Why is an excess of methanol used in the production of biosiesel?

Answer 14

• Reaction is reversible
• Shifts equilibrium to the right so more biosiesel is produced

Question 15

What are the side products when the following are involved in an acylation reaction:
a) acyl chloride
b) acid anhydride

Answer 15

a) HCl
b) R-COOH (CH3COOH)

Question 16

What is the mechanism involved in acylation reactions?

Answer 16

Nucleophilic addition-elimination

Question 17

How can you form an ester from an acyl chloride?

Answer 17

Add alcohol

Question 18

How can you form an amide from an acyl chloride?

Answer 18

+ Primary amine (R-NH2)
+ Ammonia (NH3)

Question 19

How do you manufacture aspirin?

Answer 19

Salicylic acid + ethanoic anhydride → aspirin + ethanoic acid
(acylation reaction)

Question 20

Why are acid anhydrides generally prefered over acyl chlorides?

Answer 20

• Acyl chlorides produce corrosive HCl gas
• Acyl chloride is toxic itself
• Acid anhydride produces carboxylic acids which are less corrosive than HCl
• Acid anhydride is less reactive (easier to control) and cheaper

Question 21

What method is used to produce purified crystals of aspirin?

Answer 21

Recrystallisation