Triphenylmethane

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).Aug. Kekulé and A. Franchimont (1872) [https://babel.hathitrust.org/cgi/pt?id=uc1.b3481750&view=1up&seq=868 "Ueber das Triphenylmethan"] (On triphenylmethane), Berichte der deutschen chemischen Gesellschaft, 5 : 906–908.

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:{{cite journal |title= Triphenylmethane |author= J. F. Norris |journal= Organic Syntheses |year= 1925 |volume= 4 |page= 81 |doi= 10.15227/orgsyn.004.0081}}

: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.

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.{{cite journal |doi=10.1021/acs.chemrev.6b00664|title=The Essential Role of Bond Energetics in C–H Activation/Functionalization|year=2017|last1=Xue|first1=Xiao-Song|last2=Ji|first2=Pengju|last3=Zhou|first3=Biying|last4=Cheng|first4=Jin-Pei|journal=Chemical Reviews|volume=117|issue=13|pages=8622–8648|pmid=28281752}} Correspondingly, triphenylmethane is mildly acidic, with a pK_a of 33.297.{{cite journal|author=Ronald Breslow and William Chu|journal=Journal of the American Chemical Society|year=1969|doi=10.1021/ja00710a077|title=Electrochemical determinations of pK_a's. Triphenylmethanes and cycloheptatriene|volume=92|issue=7|pages=2165}}

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:

:frameless

Its sodium salt can be prepared from the chloride:{{OrgSynth | author = W. B. Renfrow Jr and C. R. Hauser | title = Triphenylmethylsodium | collvol = 2 | collvolpages = 607| year = 1943 | prep = CV2P0607}}

:(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.

{{Main|Triarylmethane dye}}

Examples of triarylmethane dyes are bromocresol green:

:File:Bromocresol green.svg

And the nitrogen-bearing malachite green:

:File:Malachite green structure.svg

The triphenylmethyl substituent, also called trityl after 1927 suggestion by Helferich et al.{{Cite journal |last=Helferich |first=B. |last2=Bredereck |first2=H. |last3=Schneidmüller |first3=A. |date=1927 |title=Acylwanderung an partiell acylierten Methyl‐glucosiden |url=https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/jlac.19274580108 |journal=Justus Liebigs Annalen der Chemie |language=de |volume=458 |issue=1 |pages=111–116 |doi=10.1002/jlac.19274580108 |issn=0075-4617}}, is widely used in organic chemistry. Trityl serves as a protecting group for alcohols.{{cite journal |doi=10.15227/orgsyn.022.0056|title=β-d-Glucose-1,2,3,4-Tetraacetate|journal=Organic Syntheses|year=1942|volume=22|page=56|author=Delbert D. Reynolds, William Lloyd Evans

}}

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

: deprotection: Ph₃COR + HBr → ROH + Ph₃CBr

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).{{cite journal |doi=10.1107/S0108270194004439|title=Molecules isoelectronic with 2,2,2-triphenylethanol: Multiple Hydrogen-Bonding Modes in the Structures of O-Tritylhydroxylamine, Ph₃CONH₂, and Triphenylmethanesulfenamide, Ph₃CSNH₂|year=1994|last1=Glidewell|first1=C.|last2=Ferguson|first2=G.|journal=Acta Crystallographica Section C Crystal Structure Communications|volume=50|issue=8|pages=1362–1366|bibcode=1994AcCrC..50.1362G }}

• Tetraphenylmethane
• Triphenylmethanol
• Triphenylmethyl chloride
• Triphenylmethyl hexafluorophosphate
• Triphenylmethyl radical

{{Reflist}}

Category:Aromatic hydrocarbons

Category:Phenyl compounds

Category:Substances discovered in the 19th century