February 26, 2022
Acid Anhydrides
- In this chapter of IBDP Chemistry, it formed from the removal of water (H2O) from 2 carboxylic acid molecules
- To name, remove ‘acid’ from the parent carboxylic acid name and replace with ‘anhydride’ for the (CO)2O bond system
- e.g. 2 molecules of ethanoic acid --> ethanoic anhydride + water
- React in a similar way to acyl chlorides with alcohols, phenols, water, ammonia and amines
- Less reactive than acyl chlorides
- Useful for some lab preparations where acyl chlorides may be too reactive
Reactions of Acid Anhydrides with Water
- Hydrolysis
- Acid anhydride + water --> 2 carboxylic acids
- e.g. ethanoic anhydride + water --> 2 ethanoic acid
Reactions of Acid Anhydrides with Alcohols
Reactions of Acid Anhydrides with Ammonia
- Acid anhydride + ammonia --> primary amide + carboxylic acid
- e.g. ethanoic anhydride + NH3 --> ethanamide + ethanoic acid
Reactions of Acid Anhydrides with Amines
Nucleophilic Addition-Elimination Reactions
Addition: Step 1
- Lone pair of electrons from the nucleophile is attracted to and donated to the delta positive Carbon atom in the C=O group of the acyl chloride
- A dative covalent bond is formed between the nucleophile and the carbonyl Carbon atom
- The pi bond of the C=O group breaks, forming a negatively charged intermediate
Elimination: Step 2
- A lone pair of electrons on Oxygen reforms the C=O bond, causing a chloride ion to be removed
- A proton is also then lost to complete the elimination
Nucleophilic Addition-Elimination Mechanism
- Add lone pairs
- Add any charges from electronegativity etc.
- Curly arrows- show the transfer of electrons
- Add lone pairs
- Add any charges from electronegativity etc.
- Curly arrows- show the transfer of electrons
- Acid anhydrides are symmetrical- doesn’t matter which Carbon is used
This is the end of this topic.