One-Step Synthesis of Siloxanes from the Direct Process Disilane Residue

Me3SiSiMe2(O n Bu): a disilane reagent for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement

Herein, a readily available disilane Me₃SiSiMe₂(OⁿBu) has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement. This protocol enables the incorporation of a silylene into different starting materials, including acrylamides, alkene-tethered 2-(2-iodophenyl)-1H-indoles, and 2-iodobiaryls, via the cleavage of Si–Si, Si–C, and Si–O bonds, leading to the formation of spirobenzosiloles, fused benzosiloles, and π-conjugated dibenzosiloles in moderate to good yields. Preliminary mechanistic studies indicate that this transformation is realized by successive palladium-catalyzed bis-silylation and Brook- and retro-Brook-type rearrangement of silane-tethered silanols.

A readily available disilane Me₃SiSiMe₂(OⁿBu) as a silylene source has been developed for the synthesis of diverse silacycles via Brook- and retro-Brook-type rearrangement.

Microplastics in the environment: Occurrence, perils, and eradication

Microplastics (MPs) with sizes < 5 mm are found in various compositions, shapes, morphologies, and textures that are the major sources of environmental pollution. The fraction of MPs in total weight of plastic accumulation around the world is predicted to be 13.2% by 2060. These micron-sized MPs are hazardous to marine species, birds, animals, soil creatures and humans due to their occurrence in air, water, soil, indoor dust and food items. The present review covers discussions on the damaging effects of MPs on the environment and their removal techniques including biodegradation, adsorption, catalytic, photocatalytic degradation, coagulation, filtration and electro-coagulation. The main techniques used to analyze the structural and surface changes such as cracks, holes and erosion post the degradation processes are FTIR and SEM analysis. In addition, reduction in plastic molecular weight by the microbes implies disintegration of MPs. Adsorptive removal by the magnetic adsorbent promises complete elimination while the biodegradable catalysts could remove 70-100% of MPs. Catalytic degradation via advanced oxidation assisted by S O 4 • - or O H • radicals generated by peroxymonosulfate or sodium sulfate are also adequately covered in addition to photocatalysis. The chemical methods such as sol-gel, agglomeration, and coagulation in conjunction with other physical methods are discussed concerning the drinking water/wastewater/sludge treatments. The efficacy, merits and demerits of the currently used removal approaches are reviewed that will be helpful in developing more sophisticated technologies for the complete mitigation of MPs from the environment.

Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts

The industry-scale production of methylchloromonosilanes in the Müller-Rochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes Me_n Si₂ Cl_6-n (n=1-6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into mono- and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride.

Making Use of the Direct Process Residue: Synthesis of Bifunctional Monosilanes

The industrial production of monosilanes Me_n SiCl_4-n (n=1-3) through the Müller-Rochow Direct Process generates disilanes Me_n Si₂ Cl_6-n (n=2-6) as unwanted byproducts ("Direct Process Residue", DPR) by the thousands of tons annually, large quantities of which are usually disposed of by incineration. Herein we report a surprisingly facile and highly effective protocol for conversion of the DPR: hydrogenation with complex metal hydrides followed by Si-Si bond cleavage with HCl/ether solutions gives (mostly bifunctional) monosilanes in excellent yields. Competing side reactions are efficiently suppressed by the appropriate choice of reaction conditions.

A new approach for the agglomeration and subsequent removal of polyethylene, polypropylene, and mixtures of both from freshwater systems - a case study

Based on a new concept for the sustainable removal of microplastics from freshwater systems, a case study for a pH-induced agglomeration and subsequent removal of polyethylene and polypropylene particles from water is presented. The two-step-based process includes firstly a localization and secondly an aggregation of microplastic particles (250-350 μM) in a physicochemical process. The research describes a strong increase in the particle size independent of pH of the aquatic milieu induced by the addition of trichlorosilane-substituted Si derivatives. The resulting Si-based microplastic aggregates (particle size after aggregation is 2-3 cm) could be easily removed by use of, e.g., sand traps. Due to the effect that microplastic particles form agglomeration products under every kind of process conditions (e.g., various pH, various polymer concentrations), the study shows a high potential for the sustainable removal of particles from wastewater.