Triphenylmethane
| Triphenylmethane | |
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Triphenylmethane |
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Other names
1,1',1"-Methylidynetrisbenzene |
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| Identifiers | |
| CAS number | 519-73-3  |
| PubChem | 10614 |
| ChemSpider | 10169 |
| EC number | 208-275-0 |
| Jmol-3D images | Image 1 |
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| 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 |
| Hazards | |
| MSDS | External MSDS |
| R-phrases | R36 R37 R38 |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| 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 has 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.
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[edit] Preparation
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:[1]
- 3 C6H6 + CCl4 + AlCl3 → Ph3CCl·AlCl3
- Ph3CCl·AlCl3 + HCl → Ph3CH
Synthesis from benzylidene chloride, prepared from benzaldehyde and phosphorus pentachloride, is used as well.
[edit] Acidity
The pKa of the hydrogen on the central carbon is 33[2] . 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:[3]
- (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.
[edit] Triarylmethane dyes
Examples of triarylmethane dyes are bromocresol green:
or malachite green:
[edit] References
- ^ J. F. Norris (1941), "Triphenylmethane", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0548; Coll. Vol. 1: 548
- ^ Journal of the American Chemical Society. 1969. doi:10.1021/ja00710a077. http://pubs.acs.org/doi/abs/10.1021/ja00710a077.
- ^ W. B. Renfrow Jr and C. R. Hauser (1943), "Triphenylmethylsodium", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV2P0607; Coll. Vol. 2: 607
