Synthesis of ε-caprolactam from ε-caprolactone and ammonia in supercritical water

Synthesis of epsilon -caprolactam from caprolactone with ammonia was carried out in supercritical water (SCW : T > 374 degreesC, P > 22.1 MPa). A main reaction pathway for the formation of E-caprolactam was elucidated on the basis of a series of reactions of 1) epsilon -caprolactone, 2) hexanol + ammonia, 3) hexanoic acid + ammonia, and 4) hexanoic acid + hexanamide in SCW. The results clearly showed the following three steps of reactions for the formation of epsilon -caprolactam. The first step is the ring cleavage of epsilon -caprolactone to yield 6-hydroxyhexanoic acid. The second step is the dehydration between 6-hydroxyhexanoic acid and ammonia to form 6-hydroxyhexanamide. The final step is the intramolecular dehydration of 6-hydroxyhexanamide to produce E-caprolactam. The effects of reaction temperature, water density, and ammonia concentration were also studied. At 380 degreesC and 38 MPa (water density 0.5 g/cm(3)), the yield of E-caprolactam from epsilon -caprolactone and ammonia at a ratio 1 : 5 increased with increasing reaction time and reached 79.2% in 60 min.