Organocatalytic Synthesis of (Hetero)arylidene Malononitriles Using a More Sustainable, Greener, and Scalable Strategy

AIM AND OBJECTIVE: The establishment of a green and sustainable Knoevenagel con-densation reaction in organic chemistry is still crucial. This work aimed to provide a newly de-veloped metal-free and halogen-free catalytic methodology for the synthesis of CS and (het-ero-)arylidene malononitriles in the laboratory and industrial scale. The Knoevenagel condensa-tion reaction of various carbonyl groups with malononitrile was investigated in ethanol, an eco-friendly medium, in the presence of seven nitrogen-based organocatalysts.

MATERIALS AND METHODS: A comparative study was conducted using two as-obtained and four commercially available nitrogen-based organocatalysts in Knoevenagel condensation reactions. The synthesis of CS gas (2-chlorobenzylidene malononitrile) using a closed catalytic system was optimized based on their efficiency and greener approach.

RESULTS: The conversion of 100% and excellent yields were obtained in a short time. The products could be crystallized directly from the reaction mixture. After separating pure products, the resi-due solution was employed directly in the next run without any concentration, activation, purification, or separation. Furthermore, the synthesis of 2-chlorobenzylidenemahmonitrile (CS) was carried out on a large scale using imidazole as a selected nitrogen-based catalyst, afforded crys-talline products with 95±2% yield in five consecutive runs.

CONCLUSION: Energy efficiency, cost saving, greener conditions, using only 5 mol% of organo-catalyst, high recyclability of catalyst, prevention of waste, recycling extractant by a rotary evaporator for non-crystallized products, demonstrated the potential commercial production of CS using imidazole in ethanol as an efficient and highly recyclable catalytic system.