Low‐Temperature Iron‐Catalyzed Depolymerization of Polyethers

Abstract

Iron will: The iron-catalyzed depolymerization of a range of polyethers is studied. The products of the depolymerization reactions are chloroesters, which can be used as starting materials for new polymers. In the presence of simple iron salts extraordinary catalyst activities and selectivities are feasible at low temperature.

Zinc(II)‐triflate as catalyst precursor for ring‐closing depolymerization of end‐of‐life polytetrahydrofuran to produce tetrahydrofuran

“…Noteworthy, the current system exhibits an excellent recyclability in comparison to the recently reported FeCl 3 system, because after ninth run a yield of 84% [Zn(OTf) 2 ] vs. 13% (FeCl 3 ) was observed. 37 Interestingly, a comparable performance was observed for catalytic amounts of TfOH, indicating once more the potential formation of TfOH with the Zn(OTf) 2 system (Figure 1). Moreover, the system (Zn(OTf) 2 , 180 C) was applied to other polyethers such as polyethylene oxide and polypropylene oxide.…”

“…Recently, we presented a low‐temperature depolymerization of artificial polyethers [e.g., polytetrahydrofuran (PolyTHF), polyethylene oxide, and polypropylene oxide] to generate suitable chemicals (chloroesters) as possible starting materials for polymerization chemistry. In more detail, in the presence of catalytic amounts of simple zinc or iron salts polyethers were easily depolymerized with acid chlorides under noninert and solvent‐free conditions . Importantly, stoichiometric amounts of acid chlorides were necessary to perform the cleavage of the carbon oxygen bonds, which creates additional synthetic steps and therefore further costs.…”

“…In more detail, in the presence of catalytic amounts of simple zinc or iron salts polyethers were easily depolymerized with acid chlorides under noninert and solvent-free conditions. [19][20][21] Importantly, stoichiometric amounts of acid chlorides were necessary to perform the cleavage of the carbon oxygen bonds, which creates additional synthetic steps and therefore further costs. In this regard, a depolymerization process without additional reagents will be more resourceful.…”

“…For realizing the ring-closing depolymerization of PolyTHF catalysis was necessary, for instance yttrium triflate, copper triflate, ytterbium triflate supported on silica-alumina, Kaolin, zeolite, aluminum silicate, sulfuric acid, or iron salts have been applied to generate THF. [30][31][32][33][34][35][36][37] Based on the reported procedures the selection of the catalyst is of significance to carry out the depolymerization with high productivity and reasonable costs. In this regard, the use of zinc salts can be of interest, due to abundance and low costs.…”

Iron‐Catalyzed Ring‐Closing Depolymerization of Poly(tetrahydrofuran)

“…In addition, the catalyst loading was reduced to 2.5, 1.0, and 0.25 mol % (Table 1, entries [13][14][15][16][17], and an elongation of the reaction time was necessary to obtain comparable yields. For instance, with 5.0 mol % loading, a yield of 68 % was realized after 5 min, whereas with 2.5 and 1.0 mol %, 20 and 30 min were required, respectively (Table 1, [18][19][20][21][22]. [30] However, no significant product formation was observed.…”