ADVERTISEMENT
2 /3 FREE ARTICLES LEFT THIS MONTH Remaining
Chemistry matters. Join us to get the news you need.

If you have an ACS member number, please enter it here so we can link this account to your membership. (optional)

ACS values your privacy. By submitting your information, you are gaining access to C&EN and subscribing to our weekly newsletter. We use the information you provide to make your reading experience better, and we will never sell your data to third party members.

ENJOY UNLIMITED ACCES TO C&EN

Synthesis

Greener Nylon

Route to nylon-6 caprolactam precursor eliminates unwanted by-product

by Bethany Halford
September 19, 2005 | APPEARED IN VOLUME 83, ISSUE 38

ONE STEP
[+]Enlarge
The Cambridge group's catalyst converts cyclohexanone to -caprolactam in a single step.
8338notw7caprolactam.gif
The Cambridge group's catalyst converts cyclohexanone to -caprolactam in a single step.

CATALYSIS

With the help of a cleverly designed catalyst, chemists at the University of Cambridge, in England, have developed a one-step procedure for making -caprolactam from cyclohexanone (Proc. Natl. Acad. Sci. USA, published online, www.pnas.org/cgi/doi/10.1073/pnas.0506907102). Because the new route is solvent-free and doesn't generate any unwanted ammonium sulfate by-products, it could offer industry an environmentally benign process for preparing -caprolactam--the immediate precursor to nylon-6.

Each year, chemical companies make several billion pounds of -caprolactam. All but a fraction of the material is polymerized to make nylon-6, a popular polymer used in carpets, automotive parts, sporting goods, films, and packaging. The standard method for synthesizing -caprolactam involves conversion of cyclohexanone to its corresponding oxime, followed by a Beckmann rearrangement to generate the cyclic amide. This route has one major drawback: It produces immense quantities of unwanted ammonium sulfate--as much as 2.3 lb for every pound of -caprolactam.

BY DESIGN
[+]Enlarge
Credit: COURTESY OF ROBERT RAJA
Nanoporous catalyst has both redox-active sites (blue cobalt atoms) and acidic sites (pink magnesium atoms).
8338notw7acatalystsm.jpg
Credit: COURTESY OF ROBERT RAJA
Nanoporous catalyst has both redox-active sites (blue cobalt atoms) and acidic sites (pink magnesium atoms).

John Meurig Thomas and Robert Raja thought they could eliminate this by-product with judicious use of a bifunctional catalyst. They designed a nanoporous aluminophosphate catalyst with redox-active cobalt sites and acidic silicon, magnesium, or zinc sites integrated into the catalyst's framework.

The cobalt redox centers generate hydroxylamine in situ from ammonia and air. After hydroxylamine and cyclohexanone form the intermediate oxime, the acidic centers nudge the Beckmann rearrangement along via acid catalysis. The nanoporous nature of the catalyst allows products and reactants to move freely throughout the system, a strategy that's been evolving in Thomas' lab for 15 years.

"We're proud of the fact that we've been able to tackle an environmentally harmful process using genuinely benign reagents and catalysts," Thomas says.

Advertisement
X

Article:

This article has been sent to the following recipient:

Leave A Comment

*Required to comment