Triphenylmethane
Encyclopedia
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 has the basic skeleton of many synthetic dye
s called triarylmethane dye
s, many of them are pH indicator
s, and some display fluorescence
. A trityl group in organic chemistry is a triphenylmethyl group Ph3C, e.g. triphenylmethyl chloride
— trityl chloride.
from benzene
and chloroform
with aluminium chloride
catalyst:
Alternatively, benzene may react with carbon tetrachloride
using the same catalyst to obtain the trityl chloride-aluminium chloride
adduct, which is hydrolyzed with dilute acid:
Synthesis from benzylidene chloride, prepared from benzaldehyde
and phosphorus pentachloride, is used as well.
of the hydrogen on the central carbon is around 31. Triphenylmethane is significantly more acidic than most other hydrocarbons because the planar trityl anion is stabilized by extensive delocalization over three phenyl rings. However, delocalization does not occur simultaneously over all phenyl rings, due to sterics: each phenyl ring forces the other two out of coplanarity to form a three-vaned fan, such that delocalization only occurs if the sp2 orbital of the anionic carbon is properly aligned with one of the aromatic systems. The trityl anion absorbs strongly in the visible region, making it red. This colour can be used as an indicator when maintaining anhydrous conditions with calcium hydride
; the hydride reagent reacts with water to form solid calcium hydroxide
, while it is also a strong enough base to generate the trityl anion. If the hydride is used up then the solution will turn colourless. The sodium salt can be prepared also from the chloride:3CCl + 2 Na → (C6H5)3CNa + NaCl
Before the popularization of butyllithium and related strong bases, trityl sodium was often used as a strong, non-nucleophilic base.
:
or malachite green
:
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
(C6H5)3CH. This colorless solid is soluble in nonpolar organic solvents and not in water. Triphenylmethane has the basic skeleton of many synthetic dye
Dye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
s called triarylmethane dye
Triarylmethane dye
Triarylmethane dyes are synthetic organic compounds containing triphenylmethane backbones. As dyes, these compounds are intensely colored. Many of these dyes undergo reactions in response to acid and base, and thus serve as pH indicators....
s, many of them are pH indicator
PH indicator
A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions or hydrogen ions in the Arrhenius model. Normally, the indicator causes the...
s, and some display fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
. A trityl group in organic chemistry is a triphenylmethyl group Ph3C, e.g. triphenylmethyl chloride
Triphenylmethyl chloride
Triphenylmethyl chloride or trityl chloride is a white solid with the chemical formula C19H15Cl. It is an alkyl halide, sometimes used to introduce the trityl protecting group.-Preparation:Triphenylmethyl chloride is commercially available...
— trityl chloride.
Preparation
Triphenylmethane can be synthesized by Friedel-Crafts reactionFriedel-Crafts reaction
The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877. There are two main types of Friedel–Crafts reactions: alkylation reactions and acylation reactions. This reaction type is a form of electrophilic aromatic substitution...
from benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
and chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
with aluminium chloride
Aluminium chloride
Aluminium chloride is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron trichloride, giving it a yellow colour. The solid has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large...
catalyst:
- 3 C6H6 + CHCl3 → Ph3CH + 3 HCl
Alternatively, benzene may react with carbon tetrachloride
Carbon tetrachloride
Carbon tetrachloride, also known by many other names is the organic compound with the formula CCl4. It was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent...
using the same catalyst to obtain the trityl chloride-aluminium chloride
Aluminium chloride
Aluminium chloride is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron trichloride, giving it a yellow colour. The solid has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large...
adduct, which is hydrolyzed with dilute acid:
- 3 C6H6 + CCl4 + AlCl3 → Ph3CCl·AlCl3
- Ph3CCl·AlCl3 + HCl → Ph3CH
Synthesis from benzylidene chloride, prepared from benzaldehyde
Benzaldehyde
Benzaldehyde is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. This colorless liquid has a characteristic pleasant almond-like odor...
and phosphorus pentachloride, is used as well.
Acidity
The pKaPKA
PKA, pKa, or other similar variations may stand for:* pKa, the symbol for the acid dissociation constant at logarithmic scale* Protein kinase A, a class of cAMP-dependent enzymes* Pi Kappa Alpha, the North-American social fraternity...
of the hydrogen on the central carbon is around 31. Triphenylmethane is significantly more acidic than most other hydrocarbons because the planar trityl anion is stabilized by extensive delocalization over three phenyl rings. However, delocalization does not occur simultaneously over all phenyl rings, due to sterics: each phenyl ring forces the other two out of coplanarity to form a three-vaned fan, such that delocalization only occurs if the sp2 orbital of the anionic carbon is properly aligned with one of the aromatic systems. The trityl anion absorbs strongly in the visible region, making it red. This colour can be used as an indicator when maintaining anhydrous conditions with calcium hydride
Calcium hydride
Calcium hydride is the chemical compound with the formula CaH2. This grey powder reacts vigorously with water liberating hydrogen gas. CaH2 is thus used as a drying agent, i.e. a desiccant....
; the hydride reagent reacts with water to form solid calcium hydroxide
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...
, while it is also a strong enough base to generate the trityl anion. If the hydride is used up then the solution will turn colourless. The sodium salt can be prepared also from the chloride:3CCl + 2 Na → (C6H5)3CNa + NaCl
Before the popularization of butyllithium and related strong bases, trityl sodium was often used as a strong, non-nucleophilic base.
Triarylmethane dyes
Examples of triarylmethane dyes are bromocresol greenBromocresol green
Bromocresol Green is a dye of the triphenylmethane family , which is used as a pH indicator and as a tracking dye for DNA agarose gel electrophoresis. It can be used in its free acid form , or as a sodium salt...
:
or malachite green
Malachite green
Malachite green is an organic compound that is used as a dyestuff and has emerged as a controversial agent in aquaculture. Malachite green is traditionally used as a dye for materials such as silk, leather, and paper...
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