One-Pot Synthesis of Dihydropyrimidinones Using Polyaniline-Bismoclite Complex. A Facile and Reusable Catalyst for the Biginelli Reaction

Abstract

Polyaniline-bismoclite complex was used as an efficient catalyst for the three-component condensation reaction of an aldehyde, β-ketoester, and urea in ethanol to afford the dihydropyrimidinones in excellent yields. Furthermore, after completion of reaction the catalyst could be easily recovered and reused without affecting its activity.

Key words

polyaniline-bismoclite - reusable catalyst - dihydropyrimidinones - one-pot condensation - Biginelli reaction

References

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23

(a) Typical Procedure for the Preparation of Polyaniline-Bismoclite Complex (i)Preparation of polyaniline-sulfate salt: In a typical experiment, 10 mL of aniline was added to an aqueous solution (700 mL) containing H₂SO₄ (30 mL) in a 2 L-round-bottomed flask. The solution was kept under constant stirring at 5-10 °C. To this solution, sodium persulfate (23.8 g) in water (250 mL) was added during 15-20 min. The reaction was allowed to continue for 4 h. The precipitated polyaniline-sulfate salt was filtered, washed with water (5 L) followed by acetone (500 mL). (ii) Preparation of polyaniline base: The obtained polyaniline-sulfate salt was dispersed in an aqueous solution of NaOH (1 L, 1 N) and stirred for 12 h at ambient temperature. The solution was filtered and washed several times with water to remove the excess NaOH. The product (polyaniline base) was dried at 100 °C until a constant mass was reached. (iii) Preparation of polyaniline-bismoclite complex: Polyaniline base (5 g) prepared by the above method was added to acetone (500 mL) containing 0.1 M of BiCl₃. The solution was stirred for 4 h under an N₂ atmosphere at ambient temperature. The solution was filtered and washed with acetone (1 L). The powder was dried at 100 °C until a constant mass was reached.
(b) Properties of PANI-BC complex The PANI-BC complex possesses useful properties,
(i) number of dopant groups(bismoclite) per aniline unit in the polymer chain, i.e., x = 0.38; (ii) amount of bismoclite present in polyaniline salt (51.5%); (iii) conductivity (0.004 S/cm); (iv) pellet density (1.85 g/cm³) and particle size from SEM analysis (0.8-3 µm with core shell morphology).