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Mineral Resources, Pollution Control, and Nanotechnology
Published in Stephen L. Gillett, Nanotechnology and the Resource Fallacy, 2018
Indeed, the direct synthesis of organic silicates—that is, silicon bonded directly to organic side groups—from minerals has been demonstrated, of alkoxides in particular.104 An “ alkoxide” can be visualized as compound of an alcohol with a metal, with the hydrogen in the −OH group of the alcohol replaced by a metal atom. Tetraethoxysilane (called tetraethyl silicate in the older literature), for example, with formula Si (OC2H5), consists of a silicon atom bonded to four ethoxy groups, which can be formally derived from ethanol (C2H5OH) by omitting the hydrogen on the -OH group. Furthermore, the resulting alkoxides largely reflect the structure of the original silicate anion; hence, the syntheses also provide unexpected control over the products obtained. In particular, a complex chain siloxane was synthesized directly from K2CuSi4O10, a “tube” chain silicate, with preservation of the intricate tubular silicate backbone. 105 Alkoxides are reactive compounds and so again are useful feedstocks for further syntheses. They can be used directly in sol-gel synthesis, for example, or further reduced to siloxanes. Sodium methoxide is used in the conventional synthesis of biodiesel (Box 5.12).
Halato-Telechelic Polymers: a New Class of Lonomers
Published in Eric J. Goethals, Telechelic Polymers: Synthesis and Applications, 2018
Alkoxides of most of the alkaline and alkaline-earth metals are easily prepared by reacting the metal with the related anhydrous alcohol. Where transition metals are concerned, the preparation of the derived alkoxides is much more difficult. For instance, Fe(III) and Cu(II) isopropoxides are insoluble and their synthesis requires several steps; therefore great care must be taken to obtain a pure reagent and to handle it in a quantitative way. When the transition metal alkoxides are not available, at least with a sufficient purity, they are advantageously replaced by the corresponding metal acetate.28 Proceeding in the same way as described for the alkoxides, this second pathway meets the requirements of reaction completeness and elimination of the reaction by-product as supported by the IR analysis of the carbonyl groups and the titration of the recovered acetic acid. This technique has been used to prepare the α,ω-dicarboxylato polymers derived from the divalent Hg, Cd, Ni, Co, and Mn cations.
Fabrication of Ceramic Membranes
Published in Chandan Das, Sujoy Bose, Advanced Ceramic Membranes and Applications, 2017
In sol-gel processing, the precursors for the preparation of sol consist of inorganic salt or metal-organic compounds (metal alkoxides). Metal alkoxides, a class of metal-organic compounds having the general formula M(OR)X, where M is a metal of valence X and R is an alkyl group, are the most common precursors used in the sol-gel method because they react readily with water. Depending upon the electronegativity of the metal, the methods for the preparation of metal alkoxides are divided into two groups: (1) reaction between metals and alcohols for more electropositive metals and (2) reaction including metal chlorides for relatively less electropositive metals. In addition to this, there are some other processes, such as transesterification, alcohol interchange, and esterification reaction.
Photodegradation of rhodamine-B and methyl orange employing nano-alumina developed from new aluminium(III) complex(es) associated with phenanthridine-salicylaldehyde derived ligands
Published in Journal of Coordination Chemistry, 2022
Sathish Thanigachalam, Madhvesh Pathak, Kulathu Iyer Sathiyanarayanan
Normally, all metal alkoxides are highly moisture sensitive and must be protected from exposure to avoid formation of corresponding metal hydroxides. But, after the metal center is chelated with β-diketone and ligand moieties, the moisture sensitivity is decreased considerably because of loss of -OPri species. Thus, in order to investigate stability in the new derivatives, comparison between 1H NMR spectra of 2a was carried out in protected and exposed samples. It is important to mention that despite exposing 2a for 3 weeks, there was no sign of variation in its 1H NMR spectrum at all (Figure 3). In a similar fashion, UV–VIS investigation also revealed that there was no relocation in characteristic absorption peak at 281 nm. Further, the UV–VIS spectrum of 2a was recorded twice within 36 h while using acetonitrile as solvent; the location of the band at 281 nm remained unaltered. Therefore, the aluminium complexes could be quite stable in the ambient conditions.
A review of production, properties and advantages of biodiesel
Published in Biofuels, 2018
Vijay Kumar Mishra, Rachna Goswami
The transesterification reaction is catalysed by alkaline metal alkoxides [39,53], hydroxides [41,54,55] and sodium or potassium carbonates [18,56,57]. Alkaline catalyst-based transesterifications show high conversions for obtaining vegetable oils with high quality, but the oils contain significant amounts of FFA which do not convert into biodiesels but into soap [58]. These FFA react with the alkaline catalyst to produce soaps which hinder the separation of biodiesel, glycerine and wash water [59]. Triglycerides are readily transesterified batchwise in the presence of an alkaline catalyst at atmospheric pressure and 60–70°C temperature with an excess amount of methanol [11]. The alkali (NaOH or KOH) catalytic transesterification reaction is a more time-consuming process. In addition, removal of these catalysts is technically difficult and brings extra costs to the final product [60,61]. Alkoxides of alkaline group element (as CH3ONa for the methanolysis) are the highly active catalysts, since they give very high yields (>98%) in short reaction times (30 min) even if they are applied at low molar concentrations (0.5 mole %). Hydroxides of alkaline elements (KOH and NaOH) are cheaper than metal alkoxides but comparatively less active. However, these are a good alternative since they can give the same high conversions of vegetable oils just by increasing the catalyst concentration to 1–2 mole % [62]. The most economic thing about this transesterification process is that some of the methanol can be recovered and that glycerine (used in pharmaceuticals and other applications) is produced as a by-product. In this process, the glycerin needs to be removed continuously otherwise it will convert to formaldehyde or acetaldehyde when burned; both are health hazards [18].