Continuous production of benzylideneacetophenone via gas phase reaction of benzaldehyde and acetophenone: Mechanism and reaction kinetics

The continuous gas phase condensation of acetophenone (A) with benzaldehyde (B) into valuable (chalcone) benzylideneacetophenone (P = 1 atm, 498 K < T < 573 K; Eapp = 58 +/- 4 kJ mol-1) has been performed over an array of commercial oxides (i.e. SiO2, ZnO, ZrO2, CeO2 and MgO) with modified crystal size (18-50 nm, from XRD), specific surface area (8-176 m2 g-1) and total surface basicity (based on carbon dioxide temperature programmed desorption (CO2-TPD)). Reaction operation under chemical controlled regime has been expressly established by parameter estimation and experimental variation of contact time and catalyst/reactant ratio. Full selectivity to target benzylideneacetophenone was achieved over ZnO, ZrO2 and MgO, while benzaldehyde disproportionation to benzyl alcohol and benzoic acid (Cannizzaro reaction) was promoted using SiO2 and CeO2. A direct correlation between activity and specific (per m2) Lewis catalyst basicity has been presented, where MgO delivered the highest chalcone production rate. The reaction orders with respect to acetophenone and benzaldehyde have been estimated, while the experimentally determined benzylideneacetophenone production rates/ PA/PB profiles were subjected to a Langmuir-Hinshelwood type kinetic modelling. The best fit was obtained with a model involving non-competitive adsorption of A and B with the surface -C-C- bond formation as ratedetermining. Our results demonstrate, for the first time, the sole formation of benzylideneacetophenone over extended reaction time (28 days on-stream) through an alternative continuous gas phase route involving acetophenone + benzaldehyde condensation using MgO to deliver an order of magnitude greater productivity relative to conventional batch liquid systems.

Automated summary

The study demonstrated successful synthesis of benzylideneacetophenone through the reaction of acetophenone and benzaldehyde using different commercial oxide catalysts under specific conditions, with high selectivity achieved. MgO showed the highest chalcone production rate and a novel continuous gas phase route was used to efficiently produce benzylideneacetophenone over 28 days using an alternative approach.