acid derivatives Flashcards
how are acid anhydrides formed?
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.
what are carboxylic acid derivatives?
compounds that are related to carboxylic acids (the OH group has been replaced by something else)
what is the general formula of an acid anhyride?
R-C(=O)-O-C(=O)-R’
what is the suffix for naming acid anhydrides?
-anoic anhydride
how are acyl chlorides formed?
they are derived from carboxylic acids by replacing the OH group by a Cl atom
what is the general formula of an acyl chloride?
R-C(=O)-Cl
what is the suffix for naming acyl chlorides?
-anoyl chloride
how are amides formed?
they are derived from carboxylic acids by replacing the OH group by a
NH2 group
what is the general formula of an amide?
R-C(=O)-NH2
what is the suffix for naming amides?
-anamide
what is acylation?
the process of replacing a hydrogen atom in certain molecules with an acyl group
acylation can be carried out using…
acyl chlorides and acyl anhydrides
the reactions of acyl chlorides/anhydrides with water, alcohols, ammonia, and primary amines are examples of…
nucleophilic addition-elimination reactions
reaction of acyl chloride and water:
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
reaction of acyl chloride and alcohol:
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
reaction of acyl chloride and ammonia
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
what is the OVERALL equation for the reaction of acyl chloride and ammonia?
acyl chloride + 2NH3 –> amide + ammonium chloride
reaction with acyl chloride and primary amine:
THIS HAPPENS IN TWO STAGES:
stage one: acyl chloride + amine –> N-subbed amide + HCL
stage two: amine + hydrogen chloride –> ammonium salt
what is the OVERALL equation for the reaction of acyl chloride and primary amine?
acyl chloride + 2amine –> n-subbed amide + ammonium salt
what is the difference between acylation of acyl chlorides and acid anhydrides?
- 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
reaction of acid anhydrides and water:
acid anhydride + water –> 2 x carboxylic acids
reaction of acid anhydride and alcohol:
acid anhydride + alcohol –> ester + carboxylic acid
reaction of acid anhydride and ammonia:
THIS HAPPENS IN TWO STAGES:
stage one: acid anhydride + ammonia –> amide + carboxylic acid
stage two: ammonia + carboxylic acid –> ammonium salt
what is the OVERALL EQUATION for the reaction of acid anhydride and ammonia?
acid anhydride + 2NH3 –> amide + ammonium salt
reaction of acid anhydride and primary amines:
THIS HAPPENS IN TWO STAGES:
stage one: acid anhydride + amine –> n-subbed amide + carboxylic acid
stage two: amine + carboxylic acid –> ammonium salt
what is the OVERALL EQUATION for the reaction of acid anhydride and primary amine?
acid anhydride + 2amine –> n-subbed amide + ammonium salt
what is aspirin?
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
what is the reaction for the manufacture of aspirin?
salicylic acid + ethanoic anhydride –> aspirin + ethanoic acid
what are the industrial advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of aspirin?
- 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
what is recrystallisation?
a very important technique used to purify solids by removing
unwanted by-products
what are the practical steps for recrystallisation?
- Dissolve the impure crystals in the min. vol. of hot solvent.
- 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. - Allow the solution to cool and crystallise.
- The impurities will remain in solution. - Filter off the crystals using suction filtration.
- Suction filtration is faster than gravity filtration + gives a
drier solid. - Dry crystals between 2 sheets of filter paper
