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Xanthene Dyes


Xanthene (9H-xanthene, 10H-9-oxaanthracene) is the organic compound with the formula CH2[C6H4]­O. It is a yellow solid that is soluble in common organic solvents. Xanthene itself is an obscure compound, but many of its derivatives are useful dyes.

Xanthene Dyes
Figure 1. Structure of Xanthene.

Xanthene Dyes

Dyes that contain a xanthene core include fluorescein, eosins, and rhodamines. Xanthene dyes tend to be fluorescent, yellow to pink to bluish red, brilliant dyes. Many xanthene dyes can be prepared by condensation of derivates of phthalic anhydride with derivates of resorcinol or 3-aminophenol.

Xanthene Dyes
Figure 2. Rhodamines are commercial dyes with xanthene cores.

Xanthone

Xanthone is an organic compound with the molecular formula C13H8O2. It can be prepared by the heating of phenyl salicylate. In 1939, xanthone was introduced as an insecticide and it currently finds uses as ovicide for codling moth eggs and as a larvicide. Xanthone is also used in the preparation of xanthydrol, which is used in the determination of urea levels in the blood. It can also be used as a photocatalyst. The chemical structure of xanthone forms the central core of a variety of naturally occurring organic compounds, such as mangostin, which are sometimes collectively referred to as xanthones or xanthonoids. Over 200 xanthones have been identified. Many xanthones are phytochemicals found in plants in the families Bonnetiaceae, Clusiaceae, Podostemaceae, and others. They are also found in some species of the genus Iris. Some xanthones are found in the pericarp of the mangosteen fruit.

Xanthene Dyes
Figure 3. Structure of Xanthone.

Chemical properties

Natural flavonoids mostly exist in the form of glycosides, and can be composed of various flavonoid glycosides due to different types, quantities, coupling positions and coupling methods of sugar. The sugars that make up the flavonoid glycosides include monosaccharides, disaccharides, trisaccharides, and acylated sugars. Flavonoid glycosides are amorphous powders, and the rest of flavonoids are mostly crystalline solids. The different colors of flavonoids add more color to the natural pigment family. This is because the cross-conjugated system is formed in the mother nucleus, and the conjugated chain is extended by electron transfer and rearrangement, thereby showing color. Flavonoid glycosides are generally easily soluble in polar solvents such as water, ethanol, and methanol; but they are hardly soluble or insoluble in organic solvents such as benzene and chloroform. The longer the sugar chain, the greater the water solubility. Flavonoids are acidic because they often have phenolic hydroxyl groups in the molecule. The acidity varies depending on the number and position of the phenolic hydroxyl groups.

References:

  1. Gessner, Thomas.; et al. Triarylmethane and Diarylmethane Dyes. Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH.
  2. Romero, Nathan A.; et al. Organic Photoredox Catalysis. Chemical Reviews. 2016, 116 (17): 10075–10166.

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