A “Green” Approach to Synthesis of trans -4-Methoxycinnamic acid in the Undergraduate Teaching Laboratory

A green Knoevenagel reaction is described utilizing microwave irradiation. Students prepare trans-4-methoxycinnamic acid from malonic acid and 4-methoxybenzaldehyde (p-anisaldehyde) with ammonium acetate as a catalyst under solvent-free conditions. The product is purified by recrystallization and analyzed by proton NMR. The proton NMR spectrum allows students to determine the substitution pattern of the benzene ring and relative stereochemistry of the double bond through examination of the splitting pattern and coupling constants. The principles of green chemistry are demonstrated through use of low hazard reactants and reagents. The solvents used in purification of the product are derived from renewable resources and are biodegradable. Furthermore, the use of solvent-free conditions and microwave heating demonstrate resource conservation and waste reduction techniques.