Triphenylmethane

From Wikipedia, the free encyclopedia
  (Redirected from Trityl)
Jump to: navigation, search
Triphenylmethane
Triphenylmethane.png
Triphenylmethane-3D-balls.png
Identifiers
CAS number 519-73-3 YesY
PubChem 10614
ChemSpider 10169 YesY
EC number 208-275-0
ChEBI CHEBI:76212
Jmol-3D images Image 1
Properties
Molecular formula C19H16
Molar mass 244.33 g/mol
Density 1.014 g/cm3
Melting point 92-94 °C
Boiling point 359 °C
Solubility in water insoluble
Solubility soluble in dioxane[1] and hexane
Acidity (pKa) 33
Hazards
MSDS External MSDS
R-phrases R36 R37 R38
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

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 triarylmethane dyes, many of them are pH indicators, and some display fluorescence. A trityl group in organic chemistry is a triphenylmethyl group Ph3C, e.g. triphenylmethyl chloride — trityl chloride.

Preparation[edit]

Triphenylmethane can be synthesized by Friedel-Crafts reaction from benzene and chloroform with aluminium chloride catalyst:

3 C6H6 + CHCl3 → Ph3CH + 3 HCl

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:[2]

3 C6H6 + CCl4 + AlCl3 → Ph3CCl·AlCl3
Ph3CCl·AlCl3 + HCl → Ph3CH

Synthesis from benzylidene chloride, prepared from benzaldehyde and phosphorus pentachloride, is used as well.

Acidity[edit]

The pKa of the hydrogen on the central carbon is 33.[3] Triphenylmethane is significantly more acidic than most other hydrocarbons because the trityl anion is stabilized by extensive delocalization over three phenyl rings. However, delocalization does not occur simultaneously over all phenyl rings due to steric effects: each phenyl ring forces the other two out of coplanarity to form a three-vaned fan, such that delocalization only occurs if the p-orbital of the anionic carbon is parallel to the p-orbitals of one of the phenyl rings. 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:[4]

(C6H5)3CCl + 2 Na → (C6H5)3CNa + NaCl

Before the popularization of butyllithium and related strong bases, tritylsodium was often used as a strong, non-nucleophilic base.

Triarylmethane dyes[edit]

Main article: Triarylmethane dye

Examples of triarylmethane dyes are bromocresol green:

Bromocresol green

or malachite green:

Malachite green

References[edit]

  1. ^ http://www.chemicalbook.com/ChemicalProductProperty_EN_CB5689132.htm
  2. ^ J. F. Norris (1941), "Triphenylmethane", Org. Synth. ; Coll. Vol. 1: 548 
  3. ^ Ronald Breslow and William Chu (1969). Journal of the American Chemical Society. doi:10.1021/ja00710a077 http://pubs.acs.org/doi/abs/10.1021/ja00710a077 |url= missing title (help). 
  4. ^ W. B. Renfrow Jr and C. R. Hauser (1943), "Triphenylmethylsodium", Org. Synth. ; Coll. Vol. 2: 607