Acid-catalyzed isomerization of pivalaldehyde to methyl isopropyl ketone via a reactive protosolvated carboxonium ion intermediate

G A Olah; T Mathew; E R Marinez; P M Esteves; M Etzkorn; G Rasul; G K Prakash

doi:10.1021/ja011253a

Acid-catalyzed isomerization of pivalaldehyde to methyl isopropyl ketone via a reactive protosolvated carboxonium ion intermediate

J Am Chem Soc. 2001 Nov 28;123(47):11556-61. doi: 10.1021/ja011253a.

Authors

G A Olah¹, T Mathew, E R Marinez, P M Esteves, M Etzkorn, G Rasul, G K Prakash

Affiliation

¹ Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, California 90089-1661, USA.

PMID: 11716708
DOI: 10.1021/ja011253a

Abstract

Quantitative rearrangement of pivalaldehyde to methyl isopropyl ketone is observed in acids such as trifluoromethanesulfonic acid, anhydrous HF, and trifluoroethyl alcohol-BF3 but not in trifluoroacetic acid. Studies in a mixture of trifluoroacetic acid and trifluoromethanesulfonic acid show that acids with H(o) < or = -11 are able to carry out complete isomerization. These results and density functional theory calculations at the B3LYP/6-31G level suggest that protonated pivalaldehyde undergoes further protosolvation at higher acidities to a reactive superelectrophilic species resulting in rearrangement. A mechanism for the pivalaldehyde rearrangement to methyl isopropyl ketone in strong protic acids involving a reactive protosolvated superelectrophilic intermediate is suggested. Aspects of the related mechanism of the reaction with isobutane with CO in HF/BF3 medium leading to methyl isopropyl ketone are also discussed.