Recrystallised Dibenzalacetone: Properties, Preparation, and Uses
Dibenzalacetone is a yellow, recrystallised compound synthesized by the Claisen-Schmidt condensation reaction between benzaldehyde and acetone. Its ability to absorb ultraviolet (UV) light made it suitable for sunscreen formulations in the past.
Description and Physical Properties
Dibenzalacetone appears as a yellow solid after recrystallisation. Its crystalline form can resemble waxy lumps, highlighting its solid-state character. The compound has a distinctive odor, somewhat like benzaldehyde but with additional subtle notes. These properties align with its conjugated structure, which influences color and volatility.
Preparation via Claisen-Schmidt Condensation
The synthesis involves a base-catalyzed condensation of benzaldehyde with acetone. This reaction forms two carbon–carbon double bonds consecutively, connecting two benzaldehyde units to one acetone molecule. The Claisen-Schmidt mechanism proceeds through an enolate intermediate from acetone attacking benzaldehyde’s carbonyl carbon, followed by dehydration steps to yield dibenzalacetone.
- Reactants: benzaldehyde and acetone
- Catalyst: typically a base like NaOH
- Mechanism: enolate formation, nucleophilic attack, and dehydration
- Product: α,β-unsaturated ketone with extended conjugation
This synthesis is common in organic teaching laboratories, connecting theory with practical organic synthesis and reaction mechanisms.
Use in Sunscreens Due to UV Absorption
Dibenzalacetone effectively absorbs UV light owing to its conjugated double bonds and aromatic rings. This property allows it to protect skin by filtering harmful UV radiation. Although once popular in sunscreens, it has been largely replaced by other UV filters with improved safety and stability profiles.
During educational experiments, students verify its UV absorbing ability using UV lamps, confirming its functional role in photoprotection.
Summary of Key Points
| Aspect | Details |
|---|---|
| Appearance | Yellow recrystallised solid |
| Synthesis | Claisen-Schmidt condensation between benzaldehyde and acetone |
| Mechanism | Base-catalyzed formation of enolate, nucleophilic addition, and dehydration |
| Odor | Similar to benzaldehyde, with distinct notes |
| UV Absorption | Strong; enables sunscreen application |
| Current Use | Mostly for educational purposes, replaced in sunscreens |
What is the role of Claisen-Schmidt condensation in preparing Dibenzalacetone?
Dibenzalacetone is synthesized by the Claisen-Schmidt condensation reaction. This reaction occurs between benzaldehyde and acetone, forming the compound through carbon-carbon bond formation. It is a key step in its preparation.
Why was Dibenzalacetone used in sunscreens?
It was used because Dibenzalacetone can absorb ultraviolet (UV) light. This property helped protect skin from UV radiation. However, it is no longer common in modern sunscreens.
What physical characteristics does recrystallised Dibenzalacetone have?
Recrystallised Dibenzalacetone appears as a yellow solid. Its solid form results from purification by recrystallization. It also has a distinct smell somewhat like benzaldehyde.
How do students commonly experience Dibenzalacetone in organic chemistry labs?
Students often synthesize Dibenzalacetone practically, performing the Claisen-Schmidt condensation. They test its UV absorption using UV light. It reinforces concepts of reaction mechanisms and functional properties.
Does Dibenzalacetone have any distinct smell related to its components?
Yes, it has a smell similar to benzaldehyde, reflecting its chemical origin. This scent can be noticed during preparation or handling of the compound in lab settings.
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