The Persian Gulf Calcined Coral, Acropora Species: An Efficient Catalyst for Aldol Condensation

Abstract

Background: Coral, a marine organism, is known for its unique solid, natural, and efficient catalyst in organic reactions. Calcium carbonate (CaCO 3 ), the main component of marine coral, is an efficient, basic, and natural solid for catalytic aldol condensation reaction of aldehydes and ketones having α-hydrogens to produce β-hydroxy carbonyl compounds with good yields at room temperature. Objectives: The purpose of this research was to study using calcined coral as an efficient catalyst for aldol reaction at room temperature. Materials and Methods: Marine coral (Acropora sp.) was washed several times using methanol-ethyl acetate and deionized water and then dried in an oven at 80°C for 48 hours. The dried coral was ground to get fine powder. For preparation of calcined coral, its powder was put in an oven at 800°C for 2 hours. Calcined coral and sodium nitrate (1:1) were well stirred in sufficient water for about 5 hours. Then, the mixture was calcined in an oven at 800°C for 2 hours. In general experiment, the reaction was carried out by mixing aldehyde (150 mmol), ketone (50 mmol), 0.1 g of calcined coral/sodium nitrate, 5 mL water-ethanol (1:1) as a solvent. Finally, the mixture was stirred at room temperature for the appropriate time. Results: The best conditions for condensation reaction are using the calcined coral/sodium nitrate, as a catalyst in the presence of ethanol/water at room temperature. Aldol condensation reaction of nitro-substituted benzaldehydes with ketones has greater yields than benzaldehydes. Electron-withdrawing groups such as NO 2 on benzaldehyde ring activate aldol condensation reaction. In comparison, 4-methoxybenzaldehyde reacts more slowly with ketones and decreases the yield of products. Conclusions: Calcined coral/sodium nitrate as a new, efficient, and natural heterogeneous catalyst used in aldol condensation reaction of ketones and aldehydes led to β-hydroxyketones in good to high yields in appropriate condition.