Triphenylmethane

Triphenylmethane
Names
Preferred IUPAC name
1,1′,1″-Methanetriyltribenzene
Other names
Triphenylmethane
1,1′,1″-Methylidynetrisbenzene
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.007.524 Edit this at Wikidata
EC Number
  • 208-275-0
UNII
  • InChI=1S/C19H16/c1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18/h1-15,19H checkY
    Key: AAAQKTZKLRYKHR-UHFFFAOYSA-N checkY
  • InChI=1/C19H16/c1-4-10-16(11-5-1)19(17-12-6-2-7-13-17)18-14-8-3-9-15-18/h1-15,19H
    Key: AAAQKTZKLRYKHR-UHFFFAOYAF
  • c1c(cccc1)C(c2ccccc2)c3ccccc3
Properties
C19H16
Molar mass 244.337 g·mol−1
Appearance Colorless solid
Density 1.014 g/cm3
Melting point 92 to 94 °C (198 to 201 °F; 365 to 367 K)
Boiling point 359 °C (678 °F; 632 K)
Insoluble
Solubility Soluble in dioxane[1] and hexane
Acidity (pKa) 33.3
−165.6×10−6 cm3/mol
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H315, H319, H335
Safety data sheet (SDS) External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Triphenylmethane or triphenyl methane (sometimes also known as Tritan), 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) and the triphenylmethyl radical (trityl radical).

Preparation

Triphenylmethane was first synthesized in 1872 by the German chemist August Kekulé and his Dutch student Antoine Paul Nicolas Franchimont (1844–1919) by heating diphenylmercury (Hg(C6H5)2, Quecksilberdiphenyl) with benzal chloride (C6H5CHCl2, Benzylenchlorid).[2]

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 triphenylmethyl chloride–aluminium chloride adduct which is then treated with diethyl ether for 24 hours at room temperature and hydrolyzed with concentrated hydrochloric acid:[3]

3 C6H6 + CCl4 + AlCl3 → Ph3CCl·AlCl3
Ph3CCl·AlCl3 + Et2O + HCl → Ph3CH

It can also be synthesized from benzylidene chloride, which is prepared from benzaldehyde and phosphorus pentachloride.

Reactions of C-H bond

The Ph3C-H bond is relatively weak, with a bond dissociation energy (BDE) of 81 kcal/mol, or about 24 kcal/mol less than methane.[4] Correspondingly, triphenylmethane is mildly acidic, with a pKa of 33.297.[5]

Triphenylmethane is significantly more acidic than most other hydrocarbons because the charge is delocalized over three phenyl rings. Steric effects however prevent all three phenyl rings from achieving coplanarity simultaneously. Consequently diphenylmethane is even more acidic, albeit only slightly, because in its anion the charge is spread over two phenyl rings at the same time.

The trityl anion is isolable in crown ethers:

Its sodium salt can be prepared from the chloride:[6]

(C6H5)3CCl + 2 Na → (C6H5)3CNa + NaCl

The use of tritylsodium as a strong, non-nucleophilic base has been eclipsed by the popularization of butyllithium and related strong bases.

The unmodified anion is red, and can be used as an indicator in acid–base titrations. Derived substances have proven useful as chemical dyes.

Triarylmethane dyes

Main article: Triarylmethane dye

Examples of triarylmethane dyes are bromocresol green:

Bromocresol green

And the nitrogen-bearing malachite green:

Malachite green

Trityl group

Protecting group

The triphenylmethyl substituent, also called trityl after 1927 suggestion by Helferich et al.[7], is widely used in organic chemistry. Trityl serves as a protecting group for alcohols.[8]

protection (requires proton acceptor): Ph3CCl + ROH → Ph3COR + HCl
deprotection: Ph3COR + HBr → ROH + Ph3CBr

Platform for unusual functional groups

Trityl derivatives of reactive functional groups are often crystalline and in some cases sterically stabilized relative to less bulky derivatives. Three such derivatives are S-nitrosotriphenylmethanethiol (Ph3CSNO), tritylsulfenyl chloride (Ph3CSCl), and trityl sulfenamide (Ph3CSNH2).[9]

See also

References

  1. ^ "Triphenylmethane | 519-73-3".
  2. ^ Aug. Kekulé and A. Franchimont (1872) "Ueber das Triphenylmethan" (On triphenylmethane), Berichte der deutschen chemischen Gesellschaft, 5 : 906–908.
  3. ^ J. F. Norris (1925). "Triphenylmethane". Organic Syntheses. 4: 81. doi:10.15227/orgsyn.004.0081.
  4. ^ Xue, Xiao-Song; Ji, Pengju; Zhou, Biying; Cheng, Jin-Pei (2017). "The Essential Role of Bond Energetics in C–H Activation/Functionalization". Chemical Reviews. 117 (13): 8622–8648. doi:10.1021/acs.chemrev.6b00664. PMID 28281752.
  5. ^ Ronald Breslow and William Chu (1969). "Electrochemical determinations of pKa's. Triphenylmethanes and cycloheptatriene". Journal of the American Chemical Society. 92 (7): 2165. doi:10.1021/ja00710a077.
  6. ^ W. B. Renfrow Jr and C. R. Hauser (1943). "Triphenylmethylsodium". Organic Syntheses; Collected Volumes, vol. 2, p. 607.
  7. ^ Helferich, B.; Bredereck, H.; Schneidmüller, A. (1927). "Acylwanderung an partiell acylierten Methyl‐glucosiden". Justus Liebigs Annalen der Chemie (in German). 458 (1): 111–116. doi:10.1002/jlac.19274580108. ISSN 0075-4617.
  8. ^ Delbert D. Reynolds, William Lloyd Evans (1942). "β-d-Glucose-1,2,3,4-Tetraacetate". Organic Syntheses. 22: 56. doi:10.15227/orgsyn.022.0056.
  9. ^ Glidewell, C.; Ferguson, G. (1994). "Molecules isoelectronic with 2,2,2-triphenylethanol: Multiple Hydrogen-Bonding Modes in the Structures of O-Tritylhydroxylamine, Ph3CONH2, and Triphenylmethanesulfenamide, Ph3CSNH2". Acta Crystallographica Section C Crystal Structure Communications. 50 (8): 1362–1366. Bibcode:1994AcCrC..50.1362G. doi:10.1107/S0108270194004439.

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