Communications
Scheme 2. Synthesis of 1,3-dioxane in a solvent-free approach using very
low catalyst loadings.
In addition to the biomass-derived diols, a set of these diols
can also be derived from the recycling of polymeric plastic
waste.[4c,8a,e] Two specific examples of the latter case are repre-
sented by ethylene glycol and propylene glycol, which can be
obtained from waste polyethylene terephthalate (PET) and pol-
ylactic acid (PLA).[4c] Moreover, the expected cyclic acetal prod-
ucts of these glycol substrates have already been introduced
(mainly 1,3-dioxolane) as commercial solvents for polar poly-
mers, in paint stripping formulations, and as a general clean-
up solvent for epoxy and urethane systems, as well as for the
synthesis of selected pharmaceutical intermediates.[13] Remark-
ably, when ethylene glycol and propylene glycol were em-
ployed in the reaction with POM substrate, the corresponding
cyclic acetal products, 1,3-dioxolane and 4-methyl-1,3-dioxo-
lane, were obtained in 66% and 93% yield, respectively
(Scheme 3), clearly validating the versatility and substrate flexi-
bility of the developed concept.
Figure 2. Upcycling of POM plastic wastes as a C1 building block in the
Bi(OTf)3-catalyzed synthesis of 1,3-dioxane by using 1,3-propanediol.
ditions with 1,3-propanediol. Astonishingly, the waste material
selectively forms the envisaged 1,3-dioxane products in very
good yield (Figure 2 and Table S10 in the Supporting Informa-
tion). Interestingly, the POM polymer content of these plastics
was fully converted, whereas the dyes and additives could be
precipitated and removed by filtration. More specifically, 1,3-di-
oxane was formed in 87, 90, 88, 92, and 88% yield, starting
from baggage clips, joint clips, disposable lighters, and plastic
gears, respectively, using only 0.2 mol% of Bi(OTf)3 catalyst.
Finally, a scale-up of the reaction starting from approximate-
ly 6 g of a mixture of commercial POM waste under neat con-
ditions was performed. After product distillation, 91% yield of
pure 1,3-dioxane product could be isolated. The detailed steps
of the straightforward recycling concept on a larger scale are
shown in Figure 3, clearly corroborating the potential of the
facile approach. Moreover, the performance of the reaction
under neat conditions and the ease of separation of the prod-
uct disclose the future potential of this method.
In the last decade, market demand for POM polymer has
doubled, leading to an increase of the production capacity to
1.7 million tons per annum in 2015. POM polymers are widely
used in the production of a variety of commercial plastic prod-
ucts, including consumer goods such as toys, zippers, clips,
cosmetic containers, and pens, which are typical items found
in contaminated shore and sea areas. Moreover, POM has also
been used for complicated engineering applications, mainly in
the automotive industry for production of around 3000 differ-
ent components used for external & internal auto parts. Conse-
quently, in a final set of experiments, our approach of utilizing
POM polymer as an alternative C1 source for the synthesis of
cyclic acetals was applied on some commercial consumer
products, such as small gears, baggage clips, and disposable
lighters, as well as old laboratory joint clips (Figure 2). These
commercial POM plastic wastes were shredded to small frag-
ments (<3 mm in size) and treated under the developed con-
The efficiency of this recycling approach of POM plastic
waste can be evaluated by the converted carbon content of
the used plastic waste. Interestingly, the complete carbon con-
tent of the POM homopolymer is efficiently converted into the
acetal unit of the cyclic product driven by the excellent yields
obtained for these products. Moreover, the addressed recycling
method of POM is associated with a very low E-factor,[14] where
water is produced as the only byproduct of the acetalization
reaction.
In the present work, the development of a sustainable con-
cept for effective polymer recycling was targeted, focusing on
the transformation of polyoxymethylene waste materials. The
basic concept was grounded on a combined catalytic
processing of polymer waste material and biomass
derived diols. The respective integrated concept ena-
bled a selective cascade reaction, encompassing ef-
fective depolymerization and condensation, leading
to cyclic acetals. The robustness of this approach al-
lowed the flexible formation of various cyclic prod-
ucts in high yield by facile modification of biomass-
derived diol. Based on this approach, an efficient
open-loop recycling of these waste materials can be
envisaged, paving the way to unprecedented possi-
bilities within a circular economy of polyoxymethy-
lene plastic polymers.
Scheme 3. Synthesis of 1,3-dioxolane or 4-methyl-1,3-dioxolane starting from POM poly-
mer in the presence of ethylene or propylene glycol.
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ChemSusChem 2020, 13, 1 – 6
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ꢁ 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!