video tutorial Synthesis of parabanic acid

Parabenic acid synthesis (summary)

• Objective: prepare parabenic acid, a five-membered lactam, from urea and thymethyloxylate.
• Reagents: crystalline urea (6.5 g) and thymethyloxylate (12.8 g) in equal molar amounts.
• Setup: 250 mL flask with stirring and condenser; dry methanol used to generate a strongly basic medium; cooling water available.
• Base formation: 5 g sodium metal reacted with 70 mL dry methanol to form sodium methoxide in situ; vigorous reaction with methanol.
• Reaction: add urea to the sodium methoxide solution, then dissolve dimethoxylate in methanol (40 mL) and add slowly; stir at room temperature for about 1 hour after addition.
• Workup: acidify with 20 mL concentrated HCl to form the free acid; add slowly to control heat; test pH to ensure strongly acidic; precipitate forms and settles as sodium chloride salt; parabenic acid remains in solution.
• Isolation: filter the mixture; distill filtrate under vacuum to remove methanol; collect two-thirds of distillate for recycling; continue until methanol is gone.
• Purification: crystallize from warm water; recrystallize to obtain pure product; yield of 9 g (73% based on starting urea/dimethyloxylate).
• Product notes: parabenic acid is a cyclic amide (lactam) with an equilibrium between two forms; forms salts with alkalis; unlike barbiturates, it has no known physiological or medicinal use; the reaction is an interesting demonstration.