How to Make Fluorescein for Fun and Learning

TL;DR

To make fluorescein, mix phthalic anhydride and resorcinol with sulfuric acid, then heat to 190-200°C for about 30 minutes. After cooling, extract fluorescein using acetone and diethyl ether, followed by washing and drying to isolate the final product. Fluorescein, known for its low toxicity, has applications in medical diagnostics and fluorescent markers.

Transcript

Fluorescien's a pretty interesting molecule with quite a wide variety of uses because it's quite fluorescent but has a very low toxicity. In particular this low toxicity allows it to be used for everyday things as well as in the medical field for diagnostics. I actually find it pretty interesting that the toxicity is low enough that it can be injec... Read More

Key Insights

• 😘 Fluorescein has a wide range of uses due to its low toxicity and fluorescent properties.
• ❓ The synthesis of fluorescein involves a series of chemical reactions and catalysts.
• ❓ Purifying fluorescein can yield a dry powder, while dissolving the crude product provides a quick solution.

Questions & Answers

Q: What are some uses of fluorescein?

Fluorescein has various uses, including medical diagnostics for mapping the vascular system and diagnosing diseases, as well as being a common ingredient in highlighter markers.

Q: How is fluorescein synthesized?

Fluorescein is synthesized by reacting phthalic anhydride with resorcinol using sulfuric acid as a catalyst. This reaction undergoes a series of steps, including Friedel-Crafts reactions and Fischer esterification.

Q: Can you skip the purification steps when making fluorescein?

Yes, if you're looking for a quick solution, you can dissolve the crude product in sodium hydroxide solution without going through the purification steps. However, purifying the fluorescein will yield a dry powder.

Q: Why does fluorescein appear red in a concentrated solution but green in water?

In a concentrated solution, the high concentration of fluorescein molecules quenches their own fluorescence, resulting in red color. When dropped into water, the concentration decreases, allowing fluorescence to appear as green.

Summary & Key Takeaways

• Fluorescein is a low-toxicity molecule used in medical diagnostics and highlighter markers.

• The synthesis of fluorescein involves a chemical reaction between phthalic anhydride and resorcinol, catalyzed by sulfuric acid.

• To isolate fluorescein, the crude product is dissolved in acetone, followed by multiple extractions using diethyl ether and water.