W10 Carbonyl reactions

Question 1

Reduction of carboxylic acid or ester

Answer 1

Attack of C by hydride

forms aldehyde, also forms alcohol (under acidic conditions or water)

nucleophilic substitution

requires LiAlH₄ (strong enough to reduce carboxylic acids)

Question 2

Reduction of aldehyde/ketone

Answer 2

Nucleophilic addition

Attack of C in carbonyl by hydride

Produces an alkoxide

In acidic conditions: then produces 1(aldehyde) or 2(ketone) alcohol

Question 3

Aldehyde/ketone + water

Answer 3

Nucleophilic addition

O in water attacks carbon atom

Forms an intermediate in acid base equilibrium with a hydrate

Question 4

Aldehyde/ketone reacting with alcohol

Answer 4

Nucleophilic addition

Acidic conditions

Aldehyde -> hemiacetal of an aldehyde -> acetal of an aldehyde

Ketone -> hemiacetal of a ketone -> acetal of a ketone

Question 5

Describe mechanism for nucleophilic substitution of carbonyl groups

Answer 5

Called addition-elimination reactions

• Step 1: addition of nucleophile
• Step 2: elimination of leaving group -> new compound with C=O

Question 6

Oxidising agents

Answer 6

• Different oxidising agents have different strengths
• CrO₃ = gentler = isolate aldehyde under gentle conditions
• MnO₄- = powerful = immediately oxidises primary alcohol to the carboxylic acid
• Jones reagent: CrO3/H2SO4 is a particularly reliable oxidant

Question 7

Reducing agents

Answer 7

Lithium aluminium hydride LiAlH₄

STRONG -> can reduce carboxylic acids to alcohols

Sodium borohydride NaBH₄

WEAK -> can’t reduce carboxylic acids

Question 8

Carboxylic acid reaction with thionyl chloride

Answer 8

Nucleophilic substitution

Forms an acid chloride

Hydroxyl is leaving group

Question 9

Acid chloride reacting with alcohol

Answer 9

Nucleophilic substitution

chloride leaves

Forms an ester

Note: lazy notation is shown for reaction -> 1) nucleophile attack 2) leaving group

Question 10

acid chlorides reacting with primary or secondary amines

Answer 10

Nucleophilic substitution

Forms a primary or secondary amide

H+ and Cl- are lost (forms HCl molecule)

Question 11

reactions of anhydrides

Answer 11

• Similar reactivity to acid chloride
  
  • Can react with alcohols to produce esters
  • Can react with amines to produce amides
• Note: one equivalent of carboxylic acid is released