Schiff base is the name given on scientist Hugo Schiffs (26 April 1834 – 8 September 1915)
Schiff base is formed when aldehyde or ketone reacts with a primary amine, secondary amine, or ammonia.
This is an exothermic reaction, which menaces heat release when aldehyde or ketone combine with a Nitrogen-containing group that has at least one active Hydrogen atom.
E.g. - NH3 (Ammonia), RNH2 (Primary amine), R2NH (Secondary amine)
Let's go deeper into the chemistry of Schiff base: -
Mechanism of reaction
Schiffs base is formed by 5 steps reaction mechanism, They are:-
Step 1 - Attack of Nucleophile
Step 2 - Proton Transfer
Step 3 - Protonation
Step 4 - Removal of water
Step 5 - Deprotonation
Step 1. Attack of nucleophile -
As Nitrogen is more electronegative in nature and also have one lone pair of electron so it behaves as a donor.
Structure of ammonia and their extra lone pair of electron
On the other hand, Aldehydic oxygen attracts more electron toward itself so it becomes partial negative and on the other side Carbon become partial positive in nature. (This is also the reason why aldehyde are more reactive than ketone; +I effect)
The polarity of carbonyl Group
Step 2. Proton Transfer:
In step 2 since Nitrogen donated its lone pair of electrons to carbon, it becomes electro deficient, so it takes electrons from its neighbor Hydrogen and the same hydrogen attracted by the Oxygen of aldehyde.
Step 3 Protonation of Hydroxyl group: -
In this step, Proton means Hydrogen will attach to oxygen. (Here Hydrogen will come from any weak acid)
Step 4. Removal of Water
In this step since two hydrogens are attached to oxygen, which causes steric hindrance, so molecule will move toward stability with the release of the water molecule
Step 5: Deprotonation:
In this residue, nucleophiles will attack back Hydrogen and with leaving behind a colorful Schiff base.
Let us again recall this full reaction by forming of Vardentiol (One of the common Schiffs base of perfumery)
Vardentiol (Lilyall-Methyl anthranilate Schiff’s Base)
Vardentiol is formed by the reaction of Lysmeral (Lilyall) and methyl anthranilate.
Without giving any heat or without adding any acid anyone can visualize this reaction.
Take an equal proportion of lysmeral and Methyl anthranilate: -
Mix slowly either methyl anthranilate to Lysmeral or Lysmeral to methyl anthranilate
After some time it becomes opaque as water is releasing.
After maturation (for approx. 30 days) you will get Vardentiol:-
The reaction between Lilial and Methyl anthranilate are as follow: -
Using this simple chemistry anyone can make a number of Schiffs bases:-
Please do share your experience of Schiffs base in the comment section.
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Archana Shandilya
References - Wikipedia, The Good scent, Chemistry libretexts.