Efficient cyclization of 1,5-dienes to industrially important terpenes using amorphous metal aluminophosphate catalyst: A continuous flow approach

Amorphous metal aluminophosphate was used for the first time in a continuous flow process for the cyclization of pseudoionones. A series of metal aluminophosphates was synthesized by a simple coprecipitation method and characterized using various techniques to determine the physico-chemical properties of the materials. The synthesized metal aluminophosphates were evaluated as catalysts in the cyclization of pseudoionone via a continuous flow process utilizing a coil flow reactor. All catalysts facilitated the formation of α- and β-isomers of ionones through the cyclization of pseudoionone. Calcium aluminophosphate demonstrated a higher catalytic efficiency of 96 % compared to other reported methods, which is attributed to its large surface area, surface acid sites, and reduced by-product inhibition. The reaction was optimized by varying parameters such as catalyst amount, reaction temperature, pressure, and retention time and compared with a batch process. The scope of the reaction was investigated by employing a variety of terpene ketones. A suitable reaction mechanism was proposed which highlights the role of the surface acidity of the catalyst in the formation of a cyclized ring. The catalyst exhibited excellent reusability, maintaining its efficiency over three consecutive cycles with minimal degradation. • First use of amorphous metal aluminophosphates in pseudoionone flow cyclization. • Calcium aluminophosphate showed 96 % conversion, highlighting good efficiency. • Coil flow system drives diene cyclization for key industrial terpene ketones. • Reaction mechanism reveals surface properties are key to pseudoionone cyclization. • Catalyst is highly reusable with low degradation, showing green, industrial promise.