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Alkyl Halides and Substitution Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Most commonly, solvolysis is by defined as the nucleophilic displacement of a leaving group by the electron rich atom of a solvent such as the oxygen atom in water or an alcohol. As a practical matter and in the presence of water, tertiary alkyl halides slowly ionize to an intermediate carbocation, which reacts with water to give an alcohol. What is the product when 2-methyl-2-bromopentane is heated in water for an extended period of time, say a week?
Substitution reactions of cis-platinum(II) complexes containing bidentate N,N-donor pyridinecarboxamide ligands with different substituents
Published in Journal of Coordination Chemistry, 2022
Tshephiso R. Papo, Deogratius Jaganyi, Allen Mambanda
Substitutions of the coordinated chloride ligands from five Pt(II) complexes by three thiourea nucleophiles were studied as a function of concentration of the nucleophiles and temperature of the reaction medium. The concentration of the nucleophiles was kept at least 20-fold greater than that of the Pt(II) complexes to ensure pseudo first order kinetic conditions. The ionic strength of the reaction media was maintained at 0.10 M with sodium perchlorate (0.09 M) and lithium chloride (0.01 M) in methanol. The complexes were dissolved in 0.10 M methanol solution. The solvolysis stability of the complexes in methanol was established by monitoring spectral changes of their solutions over a 20-h period using the UV-visible spectrophotometer. Figure 2 shows the spectral changes for PtCl2; the complex is stable over the time period since no changes in absorbance are observed.
Biodegradability and ecotoxicity of polyurethane foams: A review
Published in Critical Reviews in Environmental Science and Technology, 2022
Kateřina Skleničková, Sabina Abbrent, Martin Halecký, Vladimír Kočí, Hynek Beneš
Chemical recycling of PUF via solvolysis such as glycolysis (Beneš et al., 2007; Jutrzenka Trzebiatowska et al., 2019), hydrolysis, hydroglycolysis, degradation by natural oil-derivates (Beneš et al., 2012; Horak & Benes, 2015; Paruzel et al., 2017; etc.) are well described techniques of depolymerization producing recycled polyols (Beneš et al., 2018) or other low molecular weight compounds suitable for use as starting monomers for production of novel PUF (Behrendt & Naber, 2009). Even if chemical recycling is less demanding on purity than physical processing, it still requires certain level of the pretreatment. On the other hand, for feedstock recovery (thermal conversion) there are only low demands on purity of the input. Feedstock recovery includes pyrolysis and gasification. The first thermally decomposes PUF in the absence of air into a wide range of low molecular weight compounds (aromatic and aliphatic hydrocarbons) and gases (CO2, CO, CH4, etc.), while the latter involves the presence of a gasification agent (oxygen, air, etc.) to convert PUF into synthesis and fuel gas (Artham & Doble, 2008). Although feedstock recovery and chemical recycling are currently not economically attractive and therefore not explored at industrial scale, the shift to circular economy may change the situation in the near future (Simón et al., 2018).
Upcycling textile wastes: challenges and innovations
Published in Textile Progress, 2021
Zunjarrao Kamble, Bijoya Kumar Behera
The use of polymeric composites in disparate fields such as aerospace, automotive, construction, and energy generation is increasing due to their high strength to weight ratio (Pakdel et al., 2021). The USA and UK are generating around 3 kilotonnes of carbon fibre waste per year within their composite industry. In 2030, around 6000–8000 commercial planes will be decommissioned in Europe alone (Pakdel et al., 2021). Different composite recycling techniques are depicted in Figure 10. Mechanical recycling is a mature recycling technique (Meng et al., 2018). The re-cyclate obtained after composite milling consists of short fibres along with matrix which could be used as filler in short fibre composites (Zhang et al., 2020). Pyrolysis is a commercially used carbon fibre recovery process from waste composites, in which the composite is subjected to high temperature under an inert gas atmosphere (Zhang et al., 2020). In the fluidized bed technique, the re-cyclate obtained after shredding (typically 6–20mm in size) is fed to a silica sand bed. The silica bed is fluidized by air heated to 450 and 550 °C and 10–25 kPa pressure (Meng, McKechnie, Turner, & Pickering, 2017). The temperature is chosen to ensure complete matrix degradation. This technique has health hazards due to pollutant gas, organic solvents, usage of high energy (Zhang et al., 2020). The solvolysis technique uses a solvent to dissolve away the thermoset matrix to separate it from fibres (Meng et al., 2018). A wide variety of solvents, such as water, ethanol, acetone or methanol can be used for solvolysis.