Triarylmethane dyes are synthetic

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

s containing

triphenylmethane Triphenylmethane, or triphenyl methane, is the hydrocarbon with the formula (C6H5)3CH. This colorless solid is soluble in nonpolar organic solvents and not in water. Triphenylmethane is the basic skeleton of many synthetic dyes called triarylmeth ...

backbones. As

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

s, these compounds are intensely colored. They are produced industrially as dyes.

Families

Triarylmethane dyes can be grouped into families according to the nature of the substituents on the aryl groups. In some cases, the

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s associated with the cationic dyes (say crystal violet) vary even though the name of the dye does not. Often it is shown as chloride.

Methyl violet dyes

Methyl violet dyes have dimethylamino groups at the ''p''-positions of two aryl groups. Image:Methyl Violet 2B.png,

Methyl violet Methyl violet is a family of organic compounds that are mainly used as dyes. Depending on the number of attached methyl groups, the color of the dye can be altered. Its main use is as a purple dye for textiles and to give deep violet colors in pai ...

2B Image:Methyl Violet 6B.png,

6B Image:Methyl Violet 10B.png, Methyl violet 10B

Fuchsine dyes

Fuchsine dyes have primary or secondary amines (NH₂ or NHMe) functional groups at the ''p''-positions of each aryl group. File:Pararosaniline.png,

Pararosaniline Pararosaniline, Basic Red 9, or C.I. 42500 is an organic compound with the formula H2NC6H4)3Cl. It is a magenta solid with a variety of uses as a dye. It is one of the four components of basic fuchsine. (The others are rosaniline, new fuchsine ...

File:Rosaniline hydrochloride.svg, Fuchsine (hydrochloride salt) Neofuchsin.svg, New fuchsine (As chloride) Fuchsine acid vector.svg, Fuchsine acid

Phenol dyes

Phenol dyes have hydroxyl groups at the ''p'' positions of at least two aryl groups. File:Phenolphthalein-low-pH-2D-skeletal.svg,

Phenolphthalein Phenolphthalein ( ) is a chemical compound with the formula C20 H14 O4 and is often written as "HIn", "HPh", "phph" or simply "Ph" in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations. For this applica ...

File:Phenol-red-zwitterionic-form-2D-skeletal.png,

Phenol red 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 ...

File:Chlorophenol red.png,

Chlorophenol red Chlorophenol red is an indicator dye that changes color from yellow to violet in the pH range 4.8 to 6.7. The pH of a substance is determined by taking the negative logarithm of the Hydronium ion concentration and the indictor changes color due ...

File:Structure of cresol red.png,

Cresol red Cresol red (full name: ''o''-cresolsulfonephthalein) is a triarylmethane dye frequently used for monitoring the pH in aquaria. Molecular biology Cresol red can be used in many common molecular biology reactions in place of other loading dyes. ...

File:Structure of Bromocresol purple.png,

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 ...

File:Bromocresol green.svg,

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. ...

Malachite green dyes

Malachite green dyes are related to the methyl violet dyes, except that they contain one phenyl (C₆H₅) group. Image:Malachite green structure.svg ,

Malachite green Malachite green is an organic compound that is used as a dyestuff and controversially as an antimicrobial in aquaculture. Malachite green is traditionally used as a dye for materials such as silk, leather, and paper. Despite its name the dye is ...

Image:Structure of the dye brilliant green.png,

Brilliant green (dye) Brilliant green (also known as or ) is one of the triarylmethane dyes. It is closely related to malachite green. Uses Brilliant green has been used to color silk and wool. It is indicated for disinfection of fresh postoperative and post-traum ...

Image:Brilliant Blue FCF(2).svg,

Brilliant blue FCF Brilliant blue FCF (Blue 1) is a synthetic organic compound used primarily as a blue colorant for processed foods, medications, dietary supplements, and cosmetics. It is classified as a triarylmethane dye and is known under various names, such ...

, a common food colorant

Victoria blue dyes

Victoria blue dyes are related to the methyl violet dyes, except they contain one naphthylamino group. Variation is found is dimethylamine vs diethylamino substituents on the phenyl rings and variations of the secondary amine on the naphthyl group. File:Victoria blue B with charge.svg, Victoria blue B File:Victoria blue FBR revised.svg , Victoria blue FBR File:Victoria blue BO.svg, Victoria blue BO File:Victoria pure blue FGA revised.svg, Victoria blue FGA File:Victoria blue 4 R revised.svg, Victoria blue 4 R File:Victoria blue R revised.svg, Victoria blue R

Xanthene dyes

Xanthene dyes feature a

xanthene Xanthene (9''H''-xanthene, 10''H''-9-oxaanthracene) is the organic compound with the formula CH2 6H4sub>2O. It is a yellow solid that is soluble in common organic solvents. Xanthene itself is an obscure compound, but many of its derivatives are us ...

core. They are not widely used as textiles, but for other applications. File:EosinB.png, Eosin B File:EosinY.png,

Eosin Y Eosin Y, also called C.I. 45380 or C.I. Acid Red 87, is a member of the triarylmethane dyes. It is produced from fluorescein by bromination. Use Eosin Y is commonly used as the red dye in red inks. It is commonly used in histology, most notabl ...

File:rhodamine B.svg,

Rhodamine B Rhodamine B is a chemical compound and a dye. It is often used as a tracer dye within water to determine the rate and direction of flow and transport. Rhodamine dyes fluoresce and can thus be detected easily and inexpensively with fluorometers. ...

File:Rhodamine 123.svg,

Rhodamine 123 Rhodamine 123 is a chemical compound and a dye. It is often used as a tracer dye within water to determine the rate and direction of flow and transport. Rhodamine dyes fluoresce and can thus be detected easily and inexpensively with instrument ...

File:Fluorescein 2.svg ,

Fluorescein Fluorescein is an organic compound and dye based on the xanthene tricyclic structural motif, formally belonging to triarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol. It is widely used ...

Bridged arenes

Where two of the aryl groups are bridged by a

heteroatom In chemistry, a heteroatom () is, strictly, any atom that is not carbon or hydrogen. Organic chemistry In practice, the term is usually used more specifically to indicate that non-carbon atoms have replaced carbon in the backbone of the molecula ...

, these triarylmethane compounds may be further categorized into

acridine Acridine is an organic compound and a nitrogen heterocycle with the formula C13H9N. Acridines are substituted derivatives of the parent ring. It is a planar molecule that is structurally related to anthracene with one of the central CH groups re ...

s (nitrogen-bridged),

s (oxygen-bridged), and

thioxanthene Thioxanthene is a chemical compound in which the oxygen atom in xanthene is replaced with a sulfur atom. It is also related to phenothiazine. Several of its derivatives are used as typical antipsychotics in the treatment of schizophrenia and othe ...

s (sulfur-bridged).

Synthesis

The amine-containing dyes are often prepared from

Michler's ketone Michler's ketone is an organic compound with the formula of CH3)2NC6H4sub>2CO. This electron-rich derivative of benzophenone is an intermediate in the production of dyes and pigments, for example Methyl violet. It is also used as a photosensitize ...

or its diethylamino analogue. In this way, the third aryl group is readily differentiated. The Friedel–Crafts alkylation reaction is a popular method to prepare many of the phenolic derivatives: : ThymolphthaleinSynthesis

Applications

In addition to their dominant use as dyes, many of these dyes react reversibly with acid and base, and thus serve as

pH indicator A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hence, ...

s. :

References

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