Carbonyl chemistry- carboxylic acids to acid chlorides

Question 1

What is the reactivity of a carboxylate compared to a carboxylic acid

Answer 1

1. Carboxylate is even less electrophilic than carboxylic acid
2. It has a negative charge which is delocalised into the system- less reactive to nucleophile

Question 2

Describe properties of carboxylic acid

Answer 2

1. Bronsted acids and lewis bases
2. Strong acids due to stability of conjugate base (resonance)- H attached to OH group is acidic proton
3. More electron withdrawing R-group the more acidic the proton

Question 3

What are the 3 ways a carboxylic acid can be synthesised

Answer 3

1. Jones oxidation- From primary alcohol
2. Pinnick oxidation- From aldehyde
3. Acid hydrolysis- From nitrile

Question 4

Why is it important to be able to convert carboxylic acids to acid chlorides

Answer 4

1. Replaces poor leaving group (OH) with (Cl)

2. Key intermediate for making other carboxylic acid derivatives

Question 5

How is carboxylic acid converted to an acid chloride

Answer 5

1. Thionyl chloride
2. 60 degrees
3. Alternatives are- PCl5 / COCl2 and DMF

Question 6

What is the difference between acid anhydride and acid chlorides

Answer 6

1. Equally reactive

2. But acid anhydride is more stable than acid chloride

Question 7

How can you convert an acid chloride to an acid anhydride

Answer 7

1. Need a carboxylate group C double bonded to O and single bonded to O-

Question 8

What can an acyl chloride form

Answer 8

1. Tertiary alcohol
2. Primary alcohol
3. Aldehyde
4. Ester
5. Amide
6. Carboxylic acid

Question 9

How does an acyl chloride form a tertiary alcohol

Answer 9

1. Add R’MgX (2eq)

2. Then H+ (aq)

Question 10

How does an acyl chloride form a primary alcohol

Answer 10

1. Add NaBH4 (2eq)

2. Then H+ (aq)

Question 11

How does an acyl chloride form an aldehyde

Answer 11

1. Add H2, Pd, quinolene, BaSO4

Question 12

How does an acyl chloride form a carboxylic acid

Answer 12

1. Add H2O

Question 13

How does an acyl chloride form an amide

Answer 13

1. Add NHR2

Question 14

How does an acyl chloride form an ester

Answer 14

1. Add HOR’

Question 15

Describe the formation of tertiary alcohols from acyl chlorides

Answer 15

1. React with organometallics to give tertiary alcohol

2. Stability of the tetrahedral intermediate is key

Question 16

Describe what happens when CH3C(CH2)COCl is added to EtMgBr and THF and then H+ (aq)

Answer 16

1. First forms an unstable intermediate as chloride is present which is a good leaving group
2. This breaks down and MgClBr is formed on the side
3. A new tetrahedral intermediate is formed which is much more stable as no good leaving group present
4. This then forms the alcohol by addition of H+

Question 17

What can acid anhydrides form

Answer 17

1. Primary alcohol
2. Ester
3. Amide
4. Carboxylic acid

Question 18

How can an acid anhydride form a primary alcohol

Answer 18

1. Add NaBh4(xs)

2. Then H+ (aq)

Question 19

How can an acid anhydride form an amide

Answer 19

1. Add NHR2

Question 20

How can an acid anhydride form an ester

Answer 20

1. Add HOR’

Question 21

How can an acid anhydride form a carboxylic acid

Answer 21

1. Add H2O

2. Forms 2 eq of carboxylic acid

Question 22

Describe how can an acid anhydride form a carboxylic acid

Answer 22

1. Add H2O at 50 degrees
2. 2 Equivalents of carboxylic acid
3. If unsymmetrical acid anhydride make choice based on electronics then sterics