Knoevenagel Condensation uses a compound of the type X-CH2-Y as the carbanion source, where X and Y are the electron withdrawing groups such as –CN,-COOR,-COR, NO2, etc. These groups are capable of stabilizing an adjacent carbanion by resonance. So in this experiment, the Knoevenagel Condensation of diethyl malonate with aromatic aldehyde salicylaldehyde involves an initial aldol-type addition followed by a spontaneous dehydration. The final step forms a lactone ring, generating the heterocyclic ring system known as Coumarin. One of the best known synthetic coumarins is warfarin, which is a powerful blood anticoagulant that is used in medicine to control blood clotting and is also sold as a rat killer. [pic]
Physical Contants: mol.wt.(g/mol) bp((C) density(g/ml)
Salicylaldehyde 122.12 197 1.167 Diethyl malonate 160.17 199 1.055 Ethyl 3-coumarin- 218.21 mp 92-94 carboxylate
For 5mL reaction, 0.50g of salicylaldehyde, 0.72 g of diethyl malonate, 2.5 mL of absolute ethanol, 0.05mL of piperidine, o.002mL of glacial acetic acid, and a boiling chip were placed in a flask. The mixture was equipped with a water-cooled condenser plugged with a cotton plug to prevent evaporation. The mixture was allowed to reflux for two hours. Once the mixture was done refluxing, it was transferred to a 25mL Erlenmeyer flask. 3.5 mL of water was added and the solution was placed in an ice bath. Once crystallization was complete the crystals were removed by suction and washed twice with 0.5 mL of ice cold 50% aqueous ethanol. The crystals were allowed to dry and the weight and melting point was determined....