August 8, 2011
This “green” route to nylon begins with sugar. As oil prices rise, biobased routes to conventional petrochemicals are under intense investigation. Rather than developing completely new polymers and plastics, however, the market seems to prefer so-called “drop-in” polymers—well-known resins made from biobased instead of oil and gas–based feedstocks. This strategy has the advantages that the properties and manufacturing techniques of the polymers are well established in the marketplace, and end users can claim that their products are “green”.
To this end, inventor J. W. Frost discloses a biobased route to ε-caprolactam, the monomer used to produce nylon-6. Among the many petrochemical-based routes to caprolactam, all of the major ones start with benzene and proceed through cyclohexane oxidation to cyclohexanone or through phenol. The inventor’s method begins with L-lysine, an amino acid produced commercially by the microbial fermentation of sugars and used in large quantities as an animal feed additive. According to the patent, lysine is first converted to α-amino-ε-caprolactam, which is then deaminated to caprolactam.
In one example, 30 mmol L-lysine hydrochloride is neutralized with 30 mmol NaOH and then treated with 120 mL 1-pentanol. The mixture is heated at 137 °C for 60 h to give a 93% yield of α-amino-ε-caprolactam.
To deaminate the aminocaprolactam, 20 mmol is placed in a reaction chamber. The temperature is lowered to ~–20 °C, and then 160 mmol KOH and 80 mmol of hydroxylamine-O-sulfonic acid are added sequentially. The byproduct amine is removed with a H2O–EtOH mixture . The product ε-caprolactam is purified by sublimation. The yield based on lysine is 70%. (Board of Trustees of Michigan State University [East Lansing]. US Patent 7,977,450, July 12, 2011; Jeffrey S. Plotkin)