Application of fatty acid chlorides in the iron-catalyzed depolymerization of polyethers

Depolymerization by transition metal complexes: strategic approaches to convert polymeric waste into feedstocks

At present, plastic pollution is a global environmental catastrophe and a major threat to mankind. Moreover, the increasing manufacture of various plastic products is causing rapid depletion of precious resources. Thus, transforming plastic waste into feedstock, which can maintain a circular economy, has emerged as a significant technique for waste management and carbon resource conservation. Furthermore, the urgent development of effective depolymerization methods is vital to save our planet from man-made plastic pollution. Among various chemical depolymerization techniques developed thus far, cleavage of the polymeric skeleton by transition metal complexes is a highly emerging, effective and exciting strategy. In this context, herein, we have summarized mechanistic approaches for cleaving various polymeric bonds using organometallic catalysts. The recently developed strategies, catalyst design and mechanisms for depolymerization of synthetic and natural polymers with polar (C-N, C-O, C-Cl, and Si-O) and non-polar (C-C) skeletal bonds are systematically discussed in detail.

Application of surfactants in papermaking industry and future development trend of green surfactants

In this work, the application of chemical surfactants, including cooking aids, detergents, surface sizing agents, and deinking agents as core components, is introduced in the wet end of pulping and papermaking. This method for the combined application of enzymes and surfactants has expanded, promoting technological updates and improving the effect of surfactants in practical applications. Finally, the potential substitution of green surfactants for chemical surfactants is discussed. The source, classification, and natural functions of green surfactants are introduced, including plant extracts, biobased surfactants, fermentation products, and woody biomass. These green surfactants have advantages over their chemically synthesized counterparts, such as their low toxicity and biodegradability. This article reviews the latest developments in the application of surfactants in different paper industry processes and extends the methods of use. Additionally, the application potential of green surfactants in the field of papermaking is discussed. KEY POINTS: • Surfactants as important chemical additives in papermaking process are reviewed. • Deinking technologies by combined of surfactants and enzymes are reviewed. • Applications of green surfactant in papermaking industry are prospected.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Low-temperature depolymerization of polysiloxanes with iron catalysis

The easy accessibility and high adjustability of polymers mainly accounts for the great impact of such materials on modern society. Besides this great success, an important matter is the accumulation of large amounts of end-of-life polymers, which are mainly deposited in landfills or converted by thermal recycling or down-cycling to low-quality materials. In contrast to that, the depolymerization of end-of-life polymers to monomers, which can be applied as feedstock in polymerization chemistry for high-quality polymers, is only carried out for a small fraction of waste. Polysiloxanes are extensively used in a diverse array of technological applications. Based on intrinsic properties of polymers, depolymerization is challenging and only a few high-temperature or less environment-friendly processes have been reported. In this regard, we have set up a capable low-temperature protocol for the depolymerization of poly(dimethylsiloxane) in the presence of catalytic amounts of simple iron salts in combination with different depolymerization reagents. The application of benzoyl fluoride, benzoyl chloride/potassium fluoride, or benzoic anhydride/potassium fluoride as depolymerization reagents affords difluorodimethylsilane or 1,3-difluoro-1,1,3,3-tetramethyldisilxanes as products, which are interesting building blocks for the synthesis of new polymers and allow an overall recycling of polysiloxanes.

Zinc-catalyzed depolymerization of end-of-life polysiloxanes

Polymers occupy an important role in our current society. Besides their great success, an issue is the accumulation of huge amounts of end-of-life polymers. Currently, the waste management is based primarily on landfills, thermal recycling, and downcycling. Notably, only a small portion of end-of-life materials is recycled by depolymerization, which refers to the creation of synthetic precursors that can be polymerized to new polymers to close the cycle. Widely used polymers in modern times are silicones (polysiloxanes), the intrinsic properties of which make their depolymerization demanding; only a few high-temperature or less environmentally friendly processes have been reported. In this regard, we have established an efficient low-temperature protocol for the depolymerization of silicones with benzoyl fluoride in the presence of cheap zinc salts as precatalysts to yield defined products. Notably, the products can be useful synthetic precursors for the preparation of new polymers, so that an overall recycling process is feasible.

The first zinc-catalyzed oxidation of sulfides to sulfones using H2O2 as green oxidant

The first example of the zinc-catalyzed oxidation of sulfides to sulfones has been developed. By using a catalytic amount of zinc salt as the catalyst, DBU as the ligand, various sulfones were produced in good yields with hydrogen peroxide as the terminal green oxidant.