Green and mild retro-aldol synthesis of natural benzaldehyde from cinnamaldehyde over Li-doped MgO catalysts

Abstract

A green and efficient method for the selective synthesis of natural benzaldehyde (BA) from cinnamaldehyde (CA) was developed using Li-doped MgO (Li/MgO) catalysts under mild conditions. Catalysts were systematically characterized via SEM, XRD, CO₂-TPD, and NH₃-TPD to investigate their structural and surface properties. Reaction parameters, including solvent composition, water content, catalyst dosage, reaction temperature, and stirring speed, were optimized. Among the tested materials, 0.25 Li/MgO delivered the highest benzaldehyde yield of 40.65% within 3 hours under optimal conditions: 0.01 mole CA, CA/H₂O molar ratio of 1 : 83, CA/EtOH ratio of 1 : 25, catalyst loading of 0.006 g mL⁻¹, 343 K, and 600 rpm. Catalyst reusability tests demonstrated stable performance over four cycles without significant loss of activity. Kinetic analysis followed a pseudo-first-order model, yielding a rate constant of 0.0032 min⁻¹ and an activation energy of 22.73 kJ mol⁻¹. A retro-aldol reaction mechanism involving active surface sites on the catalyst was proposed. Importantly, scale-up experiments using 10-fold reactant quantities maintained comparable yields, underscoring the catalyst's scalability and industrial relevance. This work presents a sustainable and selective approach for natural benzaldehyde production, with both the catalytic system and mild operational conditions offering significant advantages in green chemistry.