Correlation analysis of reactivity in oxidation of substituted benzyl alcohols by tetrabutylammonium tribromide

• Published in: Journal of physical organic chemistry Vol. 15; no. 10; pp. 721 - 727
• Main Authors: Kumar, Ashok, Sharma, Pradeep K., Banerji, Kalyan K.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.10.2002
• Subjects: alcohols; correlation analysis; mechanism; oxidation; tribromide
• ISSN: 0894-3230; 1099-1395
• DOI: 10.1002/poc.541

Oxidation of benzyl alcohol and some ortho‐, meta‐ and para‐monosubstituted benzyl alcohols by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid leads to the formation of corresponding benzaldehydes. The reaction is first order each in TBATB and the alcohol. The oxidation of [1,1‐2H2]benzyl alcohol (PhCD2OH) exhibited a substantial kinetic isotope effect. Addition of tetrabutylammonium chloride or potassium bromide did not affect the rate. Tribromide ion has been postulated as the reactive oxidizing species. The reaction rate increases with increase in the polarity of the solvent. The rates of oxidation of meta‐ and para‐substituted benzyl alcohols showed excellent correlation in terms of Charton's triparametric LDR, equation whereas the oxidation of ortho‐substituted benzyl alcohols correlated best with the LDRS equation. The oxidation of para‐substituted benzyl alcohols is more susceptible to the delocalization effect than is the oxidation of ortho‐ and meta‐substituted compounds, which display a greater dependence on the field effect. The positive value of η suggests the presence of an electron‐deficient reaction centre in the rate‐determining step. The reaction is subject to steric acceleration by the ortho‐substituents. A suitable mechanism is proposed. Copyright © 2002 John Wiley & Sons, Ltd.