Difference between revisions of "Fluorescein"
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Revision as of 05:26, 7 February 2016
| Names | |
|---|---|
| Systematic IUPAC name
3',6'-Dihydroxy-3H-spiro[2-benzofuran-1,9'-xanthen]-3-one | |
| Other names
Fluorescein, Resorcinolphthalein, diresorcinolphthalein, D&C yellow no. 7, Japan yellow 201, soap yellow
| |
| Properties | |
| C20H12O5 | |
| Molar mass | 332.31 |
| Appearance | Dark red powder |
| Density | 1.602 |
| Melting point | 314 to 316 °C (597 to 601 °F; 587 to 589 K) |
| Soluble in basic aqueous solutions, acetone and diethyl ether, slightly soluble in water | |
| Acidity (pKa) | 6.4 |
| Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
| Infobox references | |
Fluorescein (also known as resorcinophthalein or D&C yellow no. 7) is an organic compound that is a brick-red solid at room temperature. It dissolves slightly in water to give bright yellow, strongly fluorescent solutions. Sodium fluorescein, also known as uranine, has a much higher solubility in water.
Fluorescence
Fluorescein has an absorption peak at 494 nm and an emission peak at 512 nm. Its isosbestic point (wavelength that is equally absorbed at all pH values) is 464 nm.
Obtaining
Extraction
Certain brands of highlighters use a solution of fluorescein in water with a water-soluble binder. The ink cartridges of these highlighters may be extracted with isopropanol to give a solution of pure fluorescein. Some highlighters use pyranine instead, which has a strong blue fluorescence at high pH.
Bubble levels are often very dilute fluorescein solutions.
Synthesis
Fluorescein is easily prepared from resorcinol and phthalic anhydride through a Friedel-Crafts reaction with an acid catalyst, most often concentrated sulfuric acid. The product may be diluted into a basic solution to obtain a dark sodium fluorescein stock solution, which works for most demonstrations.
