Selective Lanthanide‐Organic Catalyzed Depolymerization of Nylon‐6 to ϵ‐Caprolactam

Abstract

Nylon-6 is selectively depolymerized to the parent monomer ɛ-caprolactam by the readily accessible and commercially available lanthanide trisamido catalysts Ln(N(TMS) 2 ) 3 (Ln = lanthanide). The depolymerization process is solvent-free, near quantitative, highly selective, and operates at the lowest Nylon-6 to ɛcaprolactam depolymerization temperature reported to date. The catalytic activity of the different lanthanide trisamides scales with the Ln 3 + ionic radius, and this process is effective with post-consumer Nylon-6 as well as with Nylon-6 + polyethylene, polypropylene or polyethylene terephthalate mixtures. Experimental kinetic data and theoretical (DFT) mechanistic analyses suggest initial deprotonation of a Nylon terminal amido NÀ H bond, which covalently binds the catalyst to the polymer, followed by a chain-end back-biting process in which ɛcaprolactam units are sequentially extruded from the chain end.

Selective Lanthanide‐Organic Catalyzed Depolymerization of Nylon‐6 to ϵ‐Caprolactam

“…To further probe the Nylon-6 reaction mechanism and energetic landscape, a detailed solution-phase enthalpy profile was computed by DFT [37] for the (TMS 2 N) 3 La (La NTMS )-catalyzed Nylon-6 depolymerization. First, the DFT-derived structure of La NTMS was found to be in excellent agreement with the experimental X-ray structure, [38] validating the computational approach (Figure 4). The structure of La NTMS possesses similar structural characteristics as previously reported lanthanide analogues, [39] however, note that this is the first time that the structure of solvent-free La NTMS has been reported.…”

Mechanistic study of homoleptic trisamidolanthanide-catalyzed aldehyde and ketone hydroboration. Chemically non-innocent ligand participation

“…Due to the lack of an additional substrate heteroatom to engage in bidentate La(III) chelation, it will be seen that these mechanisms differ from those previously identied in the deoxygenative reduction of amides and esters. 43,44 In situ experimental mechanistic studies In pioneering work, La NTMS , the solid-state structure of which was recently published, 61 was previously reported to catalyze the Tishchenko reaction, producing esters from the cross-coupling of aldehydes at TOFs < 100 h −1 (Scheme 1, path (a)), 62,63 and as noted above, La NTMS is also an efficient ester hydroboration catalyst (Fig. 1c).…”

“…In pioneering work, La NTMS , the solid-state structure of which was recently published, 61 was previously reported to catalyze the Tishchenko reaction, producing esters from the cross-coupling of aldehydes at TOFs < 100 h −1 (Scheme 1, path (a)), 62,63 and as noted above, La NTMS is also an efficient ester hydroboration catalyst (Fig. 1c).…”

Hybrid Monomer Design Synergizing Property Trade‐offs in Developing Polymers for Circularity and Performance

“…[85] Very recently, Marks et al achieved CRM of nylon 6 to 7-LM at almost quantitative yield with lanthanide trisamido catalyst La[N(SiMe 3 ) 2 ] 3 , which underlines the ability of catalysis to enable selective and efficient depolymerization, although the catalyzed depolymerization still requires the reaction to be performed at temperatures as high as 240 °C. [86] Hence, the juxtaposition of LCT nylon 4's intrinsic recyclability and HCT nylon 6's robust material properties presents an excellent opportunity for applying the synergistic hybrid monomer design strategy to solve the above problems associated with nylons.…”