Thomas, John Meurig and Raja, Robert
Design of a ‘‘green’’ one-step catalytic production
of caprolactam (precursor of nylon-6)
Proceedings of the National Academy of Sciences of the United States of America, 102, (39), . (doi:10.1073/pnas.0506907102).
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The ever-increasing industrial demand for nylon-6 (polycaprolactam) necessitates the development of environmentally benign methods of producing its precursor, E-caprolactam from cyclohexanone. It is currently manufactured in two popular double-step processes, each of which uses highly aggressive reagents and each generates substantial quantities of largely unwanted ammonium sulfate as by-product. Here we describe a viable laboratory-scale, single-step, solvent-free process of producing E-caprolactam using a family of designed bifunctional, heterogeneous, nanoporous catalysts containing isolated acidic and redox sites, which smoothly convert cyclohexanone to E-caprolactam with selectivities in the range 65 to 78 percent in air and ammonia at 80 C. The catalysts are microporous (pore diameter 7.3 Å) aluminophosphates (AlPOs) in which small fractions of the AlIIIO45- and PVO43- tetrahedra constituting the 4-connected open framework are replaced by CoIIIPO45- and SiIVO44- tetrahedra which become the loci of the redox and acidic centers respectively. The catalysts may be further optimized, and already may be so designed as to generate selectivities of ca 80 percent for the intermediate oxime, formed from NH2OH which is produced in situ within the pore system. The advantages of such designed heterogeneous catalysts, and their application to a range of other chemical conversions, are also adumbrated.
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