6-Aminohexanoic Acid → 6-Maleimidohexanoic acid

A solution of maleic anhydride (0.05 mole) in acetic acid (20 mL) was mixed with a solution of ε-Amino-n-caproic acid (0.05 mole) in acetic acid (50 mL) and stirred at room temperature for 2 hours. An additional amount of acetic acid (150 mL) was added and the reaction mixture refluxed for 16 hours. The reaction mixture was evaporated under vacuo to an oil and chloroform was then added (50 mL). The solution was left to stand for 16 hours at room temperature whereupon impurities were precipitated out of the solution. The precipitate was filtered and the filtrate was collected, evaporated under vacuo and chromatographed on silica gel using chloroform:acetic acid (95:5) to give 6-Maleimidocaproic acid 23 (8 g).