Triphenylmethanol

Structure and properties

Triphenylmethanol features three phenyl (Ph) rings and an alcohol group bound to a central tetrahedral carbon atom. All three C–Ph bonds are typical of sp3-sp2 carbon-carbon bonds with lengths of approximately 1.47 Å, while the C–O bond length is approximately 1.42 Å.

The presence of three adjacent phenyl groups confers special properties manifested in the reactivity of the alcohol. For example it reacts with acetyl chloride, not to give the ester, but triphenylmethyl chloride: :Ph3COH + MeCOCl → Ph3CCl + MeCO2H

The three phenyl groups also offer steric protection. Reaction with hydrogen peroxide gives an unusually stable hydroperoxide, Ph3COOH.

Acid-base properties

As a derivative of methanol, triphenylmethanol is expected to have a pKa in the range of 16–19. Typical of alcohols, resonance offers no stabilization of the conjugate base due to being bonded to a sp3 carbon atom. Stabilization of the anion by solvation forces is largely ineffective due to the steric influence of the three phenyl groups.

The basicity of triphenylmethanol is enhanced due to the formation of a resonance-stabilized carbocation upon breaking of the C–O bond. After protonation of the oxygen under strongly acidic conditions, triphenylmethanol loses water to form the triphenylmethyl ("trityl") cation: :Ph3COH + H+ → Ph3C+ + H2O The trityl cation is one of the easiest carbocations to isolate, although it quickly reacts with water.

Triphenylmethyl hydroperoxide is prepared from by treating triphenylmethanol with hydrogen peroxide in the presence of acid: :

Synthesis

The Russian doctoral student Walerius Hemilian (1851–1914) first synthesized triphenylmethanol in 1874 by hydrolysis of triphenylmethyl bromide as well as by chromate oxidation of triphenylmethane.{{cite journal|last1= Hemilian|first1= W.|title= VII. Synthese des Triphenylmethans und des Methylphenyl-Diphenylmethans|journal= Berichte der Deutschen Chemischen Gesellschaft|date= 1874|volume= 7|issue= 2|pages= 1203–1210|doi= 10.1002/cber.18740070284}}

The preparation of triphenylmethanol from methyl benzoate or benzophenone and phenylmagnesium bromide is a common laboratory experiment for illustrating the Grignard reaction. An alternative starting material is diethyl carbonate.

:[[File:Synthesis of triphenylmethanol.png|500px|Synthesis of triphenylmethanol]]

Applications

Although not of major industrial importance, triphenylmethanol is a useful reagent in the research laboratory. Substituted derivatives of triphenylmethanol are intermediates in the production of the commercially useful triarylmethane dyes.

References

References

1. (2019). "Deciphering the Hydrogen-Bonding Scheme in the Crystal Structure of Triphenylmethanol: A Tribute to George Ferguson and Co-workers". Acta Crystallographica Section C: Structural Chemistry.
2. W. E. Bachmann. "Triphenylchloromethane".
3. Bryant E. Rossiter and Michael O. Frederick "Triphenylmethyl Hydroperoxide" E-EROS Encyclopedia of Reagents for Organic Synthesis, 2013. {{doi. 10.1002/047084289X.rt363m.pub2
4. (2013). "Encyclopedia of Reagents for Organic Synthesis".
5. W. E. Bachmann and H. P. Hetzner. "Triphenylcarbinol".
6. Latimer, Devin. (2007). "The GC–MS Observation of Intermediates in a Stepwise Grignard Addition Reaction". [[J. Chem. Educ.]].
7. (2000). "Triarylmethane and Diarylmethane Dyes".