Phthalein dyes are a class of
dye
Juan de Guillebon, better known by his stage name DyE, is a French musician. He is known for the music video of the single "Fantasy
Fantasy is a genre of speculative fiction that involves supernatural or Magic (supernatural), magical ele ...
s mainly used as
pH indicator
A pH indicator is a halochromism, halochromic chemical compound added in small amounts to a Solution (chemistry), solution so the pH (acidity or Base (chemistry), basicity) of the solution can be determined visually or spectroscopically by chang ...
s, due to their ability to change colors depending on pH.
They are formed by the reaction of
phthalic anhydride
Phthalic anhydride is the organic compound with the formula C6H4(CO)2O. It is the anhydride of phthalic acid. Phthalic anhydride is a principal commercial form of phthalic acid. It was the first anhydride of a dicarboxylic acid to be used commer ...
with various
phenols
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (− O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds ar ...
. They are a subclass of
triarylmethane dye
Triarylmethane dyes are synthetic organic compounds containing triphenylmethane backbones. As dyes, these compounds are intensely colored. They are produced industrially as dyes.
Families
Triarylmethane dyes can be grouped into families accordin ...
s.
Common phthalein dyes include:
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Bromothymol blue
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Bromocresol green
Bromocresol green (BCG) is a dye of the triphenylmethane family ( triarylmethane dyes). It belongs to a class of dyes called sulfonephthaleins. It is used as a pH indicator in applications such as growth mediums for microorganisms and titrations ...
*
Bromocresol purple
Bromocresol purple (BCP) or 5′,5″-dibromo-''o''-cresolsulfophthalein, is a dye of the triphenylmethane family (triarylmethane dyes) and a pH indicator. It is colored yellow below pH 5.2, and violet above pH 6.8. In its cyclic sulfonate ester f ...
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Cresol Red
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''o''-Cresolphthalein
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Chlorophenol red
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Dixylenolphthalein
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Guaiacolphthalein
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α-Naphtholphthalein
α-Naphtholphthalein (C28H18O4) is a phthalein dye used as a pH indicator with a visual transition from colorless/reddish to greenish blue
''Icaricia saepiolus'', the greenish blue, is a butterfly of the family Lycaenidae. It is found from th ...
*
Phenolphthalein
Phenolphthalein ( ) is a chemical compound with the chemical formula, formula carbon, C20hydrogen, H14oxygen, O4 and is often written as "HIn", "HPh", "phph" or simply "Ph" in shorthand notation. Phenolphthalein is often used as an indicator in ...
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Phenolsulfonphthalein
Phenol red (also known as phenolsulfonphthalein or PSP) is a pH indicator frequently used in cell biology laboratories.
Chemical structure and properties
Phenol red exists as a red crystal that is stable in air. Its solubility is 0.77 grams per ...
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Tetrabromophenolphthalein
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Thymol blue
Thymol blue (thymolsulfonephthalein) is a brownish-green or reddish-brown crystalline powder that is used as a pH indicator. It is insoluble in water but soluble in alcohol and dilute alkali
In chemistry, an alkali (; from the Arabic word , ...
*
Thymolphthalein
Thymolphthalein is a phthalein dye used as an acid– base ( pH) indicator. Its transition range is around pH 9.3–10.5. Below this pH, it is colorless; above, it is blue. The molar extinction coefficient
In chemistry, the molar absorption c ...
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Xylenolphthalein
See also
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Triarylmethane dye
Triarylmethane dyes are synthetic organic compounds containing triphenylmethane backbones. As dyes, these compounds are intensely colored. They are produced industrially as dyes.
Families
Triarylmethane dyes can be grouped into families accordin ...
References
Triarylmethane dyes
Phthalides
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