Umbelliferone is the common name of the lactone 7-hydroxycoumarin, an alcohol-soluble, white crystalline organic powder. More technically, the International Union of Pure and Applied Chemistry assigns it the name 7-hydroxychromen-2-one. This substance occurs widely in nature, most notably in the Umbelliferae or Apiaceae family of plants. It is an active ingredient in sunscreen preparations, even though some studies indicate that it might be capable of inducing causing genetic mutation. Umbelliferone also is used in pulsed-dye laser therapy for treating vascular lesions.
The name "umbelliferone," indicative of its plant origin, derives from the same root word as “umbrella.” This is because Umbelliferae plants are characterized by their flowering canopy or "umbel," which is exemplified by the Queen Anne’s Lace or wild carrot, Daucus carota. Related plants include carroway, celery, fennel and hemlock. Laboratory extraction of the lactone from plants was reported upon in the German chemical literature as early as 1860. Today, umbelliferone is more often prepared synthetically.
The structure of umbelliferone includes two six-member rings, one of which incorporates an oxygen atom. It is prepared in the laboratory by condensation. In this technique, a one-ring structure with a small side feature, perhaps a hydroxyl group, adds a molecular fragment at a carbon adjacent to it. These two side fragments then close by joining their other ends to form a second ring, the one with the oxygen atom. During this cyclization, called Pechmann condensation, a molecule of water is released.
Applied sunscreen decreases the user's exposure to harmful ultraviolet radiation. Although the complete ultraviolet spectrum covers the 10- to 400-nanometer wavelength region, it is only a specific portion of this, the part that reaches the lower atmosphere, that poses a hazard. That portion is divided into two regions — ultraviolet A (UVA) and ultraviolet B (UVB), which are about 320-400 nanometers and 290-320 nanometers, respectively. UVB can be especially harmful and has been strongly linked to skin cancer. Umbelliferone absorbs ultraviolet energy at 300, 305 and 325 nanometers, effectively reducing the amount of UVB radiation that can be absorbed by the skin.
Another application of umbelliferone is as whitener or optical brightener. Energy that is absorbed in the ultraviolet region triggers re-release, or fluorescence, in the blue region of the optical spectrum. This fluorescence imparts an appearance of whiteness, much as a bluing agent imparts whiteness to washed clothing. In fact, in the cleaning of textiles, the availability of optical brighteners such as umbelliferone has significantly reduced the demand for such bluing agents.