acid derivatives

Question 1

how are acid anhydrides formed?

Answer 1

when two molecules of a carboxylic acid join together and water is eliminated (condensation)

Acid anhydrides are derived from carboxylic acids by replacing the OH
group by the carboxylate (RCOO) group.

Question 1

what are carboxylic acid derivatives?

Answer 1

compounds that are related to carboxylic acids (the OH group has been replaced by something else)

Question 2

what is the general formula of an acid anhyride?

Answer 2

R-C(=O)-O-C(=O)-R’

Question 3

what is the suffix for naming acid anhydrides?

Answer 3

-anoic anhydride

Question 4

how are acyl chlorides formed?

Answer 4

they are derived from carboxylic acids by replacing the OH group by a Cl atom

Question 5

what is the general formula of an acyl chloride?

Answer 5

R-C(=O)-Cl

Question 6

what is the suffix for naming acyl chlorides?

Answer 6

-anoyl chloride

Question 7

how are amides formed?

Answer 7

they are derived from carboxylic acids by replacing the OH group by a
NH2 group

Question 8

what is the general formula of an amide?

Answer 8

R-C(=O)-NH2

Question 9

what is the suffix for naming amides?

Answer 9

-anamide

Question 10

what is acylation?

Answer 10

the process of replacing a hydrogen atom in certain molecules with an acyl group

Question 11

acylation can be carried out using…

Answer 11

acyl chlorides and acyl anhydrides

Question 12

the reactions of acyl chlorides/anhydrides with water, alcohols, ammonia, and primary amines are examples of…

Answer 12

nucleophilic addition-elimination reactions

Question 13

reaction of acyl chloride and water:

Answer 13

acyl chloride + water –> carb. acid + hydrogen chloride

• this is an example of hydrolysis (acyl chlorides are susceptible to hydrolysis if ANY water is present)
• this means acid anhydrides are preferred for synthetic routes in industry

Question 14

reaction of acyl chloride and alcohol:

Answer 14

acyl chloride + alcohol –> ester + hydrogen chloride

• this is a more effective method for preparation of esters as acylation is COMPLETE whereas esterification is in a constant equilibrium

Question 15

reaction of acyl chloride and ammonia

Answer 15

THIS HAPPENS IN TWO STAGES:

stage one: acyl chloride + ammonia –> amide + hydrogen chloride
NH3 = nucleophile in the first stage

stage two: ammonia + hydrogen chloride –> ammonium chloride
NH3 = base in second stage to neutralise the acidic by-product

Question 16

what is the OVERALL equation for the reaction of acyl chloride and ammonia?

Answer 16

acyl chloride + 2NH3 –> amide + ammonium chloride

Question 17

reaction with acyl chloride and primary amine:

Answer 17

THIS HAPPENS IN TWO STAGES:

stage one: acyl chloride + amine –> N-subbed amide + HCL

stage two: amine + hydrogen chloride –> ammonium salt

Question 18

what is the OVERALL equation for the reaction of acyl chloride and primary amine?

Answer 18

acyl chloride + 2amine –> n-subbed amide + ammonium salt

Question 19

what is the difference between acylation of acyl chlorides and acid anhydrides?

Answer 19

• anhydrides = slower and less vigorous reactions as they are less reactive
• a carboxylic acid is formed as a by-product, not HCl which is
  easier to deal with

Question 20

reaction of acid anhydrides and water:

Answer 20

acid anhydride + water –> 2 x carboxylic acids

Question 21

reaction of acid anhydride and alcohol:

Answer 21

acid anhydride + alcohol –> ester + carboxylic acid

Question 22

reaction of acid anhydride and ammonia:

Answer 22

THIS HAPPENS IN TWO STAGES:

stage one: acid anhydride + ammonia –> amide + carboxylic acid

stage two: ammonia + carboxylic acid –> ammonium salt

Question 23

what is the OVERALL EQUATION for the reaction of acid anhydride and ammonia?

Answer 23

acid anhydride + 2NH3 –> amide + ammonium salt

Question 24

reaction of acid anhydride and primary amines:

Answer 24

THIS HAPPENS IN TWO STAGES:

stage one: acid anhydride + amine –> n-subbed amide + carboxylic acid

stage two: amine + carboxylic acid –> ammonium salt

Question 25

what is the OVERALL EQUATION for the reaction of acid anhydride and primary amine?

Answer 25

acid anhydride + 2amine –> n-subbed amide + ammonium salt

Question 26

what is aspirin?

Answer 26

an ester made by the acylation of 2-hydroxybenzenecarboxylic acid (aka salicylic acid)

• the OH group is attached directly to the benzene ring and is esterified to form aspirin

Question 27

what is the reaction for the manufacture of aspirin?

Answer 27

salicylic acid + ethanoic anhydride –> aspirin + ethanoic acid

Question 28

what are the industrial advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of aspirin?

Answer 28

• less corrosive
• less vulnerable to hydrolysis
• less hazardous to use as it gives a less violent reaction
• it is cheaper than ethanoyl chloride
• it does not produce corrosive fumes of HCl

Question 29

what is recrystallisation?

Answer 29

a very important technique used to purify solids by removing
unwanted by-products

Question 30

what are the practical steps for recrystallisation?

Answer 30

1. Dissolve the impure crystals in the min. vol. of hot solvent.
2. Filter the hot solution by gravity filtration, using a hot funnel and
   fluted filter paper, to remove any insoluble impurities.
   - Filtering through a hot filter funnel + using fluted paper prevents
   ppt. of the solid.
3. Allow the solution to cool and crystallise.
   - The impurities will remain in solution.
4. Filter off the crystals using suction filtration.
   - Suction filtration is faster than gravity filtration + gives a
   drier solid.
5. Dry crystals between 2 sheets of filter paper