Synthesis of 15N-labeled phthalimide

A new method for preparing 15N-labeled phthalimide from the reaction between phthalic anhydride and 15N-urea (99.34%15N) in the presence of ortho-xylene is described in this work. Reaction conditions were the mole ratio of phthalic anhydride to 15N-urea (99.34%15N) of 3–1 at 140 °C and under atmospheric pressure. Excessive phthalic anhydride reacted with ethanol for 90 min. The by-product of diethyl phthalate dissolving in ethanol was separated by filtration. The high yield of 96% of 15N-labeled phthalimide was obtained and the purity and abundance was 99.5% and 99.04%, respectively.