Aldol condensation of butan-2-one and pentan-3-one on an activated alumina as monitored via in-situ carbon-13 nuclear magnetic resonance spectroscopy

Conventional 13C nuclear magnetic resonance spectroscopy is used to monitor the reactions of butan-2-one and pentan-3-one adsorbed on alumina. Both reaction sequences proceed via successive aldol condensations. The products observed for butan-2-one (5-methyl-4-hepten-3-one and 4-hydroxy-4-methylpentan-2-one) are those expected for homogeneous base catalysis. A J-modulated spin–echo sequence demonstrates that 5-ethyl-4-methyl-5-hepten-3-one, the β, γ condensation product, is obtained using pentan-3-one. The results demonstrate that conventional 13C n.m.r. can be effectively used to distinguish reaction pathways and products for surface-catalysed reactions.