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Alkyl Halides and Substitution Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
The ether oxygen is basic in the presence of the powerful acid. Therefore, the reaction occurs by protonation of the ether oxygen to give an oxonium ion such as A. The nucleophilic iodide counterion attacks the less sterically hindered carbon in a SN2 reaction, displacing ethanol as a leaving group to give iodoethane.
Sustainable Production of Biofuels—A Green Spark: Technology, Economics, and Environmental Issues
Published in V. Sivasubramanian, Bioprocess Engineering for a Green Environment, 2018
Rajarathinam Ravikumar, Muthuvelu Kirupa Sankar, Manickam Nareshkumar, Moorthy Ranjithkumar
Waste oils contain FFAs that cannot be converted to biodiesel using an alkaline catalyst. These FFAs produce soap that inhibits the separation of the ester, glycerin, and ash water when reacted with an alkaline catalyst. Hence, liquid acid-catalyzed transesterification is proposed in order to overcome challenges posed by liquid base catalysts. Sulfuric acid, sulfonic acid, hydrochloric acid, organic sulfonic acid, and ferric sulfate are the acids most commonly used as catalysts in transesterification. In the production of biodiesel, hydrochloric acid and sulfuric acid are favored as catalysts. Despite its insensitivity to FFA in the feedstock and its ability to catalyze esterification and transesterification simultaneously, acid catalyst has been less popular in transesterification reactions because it has a relatively slower reaction rate. Thus, the alcohol to oil molar ratio is the main factor influencing the reaction. Addition of excess alcohol can speed up the reaction and favors the formation of biodiesel product. The steps involved in acid-catalyzed transesterification are initial protonation of the acid to give an oxonium ion followed by the oxonium ion and an alcohol undergoing an exchange reaction to give the intermediary, which later loses a proton to become an ester (López et al., 2005).
Polysaccharides
Published in Stanislaw Penczek, H. R. Kricheldorf, A. Le Borgne, N. Spassky, T. Uryu, P. Klosinski, Models of Biopolymers by Ring-Opening Polymerization, 2018
The polymerization of 1,4-anhydro-2,3-di-O-benzyl-α-d-ribopyranose 31 forms almost exclusively (1→5)-α-d-ribofuranan structure under a wide variety of conditions. This fact implies that since in the di-O-benzylated monomer the 1,5-linked (O5) oxygen has higher basicity and less steric hindrance than the O4 oxygen, the initiation reaction starts from the coordination of a Lewis acid to the O5 oxygen, as illustrated in Scheme 14. Then the oxonium ion 31b is formed on the O5 oxygen. The O5 oxygen of an approaching monomer attaches to the C-l carbon of 31b from the direction opposite to the C-1-O5 oxygen bond to cause Walden inversion at an instance when the 1,5-scission occurs.
3D-VAT printing of nanocomposites by photopolymerisation processes using amino-meta-terphenyls as visible light-absorbing photoinitiators
Published in Virtual and Physical Prototyping, 2023
Filip Petko, Emilia Hola, Magdalena Jankowska, Alicja Gruchała-Hałat, Joanna Ortyl
Studied 2-(diethylamino)-4,6-diphenyl-benzene-1,3-carbonitrile derivatives were investigated in the role of photosensitisers of iodonium salt for cationic polymerisation. Ring opening photopolymerisation of epoxy monomer was performed with irradiation of LED 405, 420 and 455 nm during 800 s. Photopolymerisation profiles for epoxy monomer CADE under air at 455 nm are presented in Figure 4A,B (profiles at 405 and 420 nm are gathered in Figures S34–S37). The CADE monomer was chosen because of its relatively low reactivity. After protonation of oxirane ring (and secondary oxonium ion formation) the hydrogen bond is formed between protonated oxirane ring and carbonyl bond in monomer structure [20]. Such stabilisation effect make it easier to compare the activity of photoinitiating systems. Final conversions for all photosensitisers and wavelengths are summarised in Table 2.
Synthesis and characterization of Pd supported on methane diamine (propyl silane) functionalized Fe3O4 nanoparticles as a magnetic catalyst for synthesis of α-aminonitriles and 2-methoxy-2-phenylacetonitrile derivative via Strecker-type reaction under ambient and solvent-free conditions
Published in Inorganic and Nano-Metal Chemistry, 2021
Mingzhe Sun, Wei Liu, Wei Wu, Qun Li, Di Song, Li Yan, Majid Mohammadnia
Acetals act as powerful electrophiles toward different nucleophiles under acidic conditions owing to the generation of an oxonium ion intermediate. Several Lewis acids, such as trimethylsilyl triflate CoCl2,[44] BF3-Et2O,[44] and SnCl2,[45] could improve the cyanation of acetals with trimethylsilyl cyanide (TMSCN). Moreover, tetracyanoethylene (TCNE) also catalyzed the reaction of acetals with TMSCN. However, conventional procedures must be performed under severely anhydrous conditions, which are hard to handle on a specifically large scale. Hence, the development of low expensive, biocompatibility, and easily handled improvers for the synthesis of C–C bond under neutral, mild, and comfortable conditions is quiet very worthwhile.[46]
Oxidation-precipitation of magnetic Fe3O4/AC nanocomposite as a heterogeneous catalyst for electro-Fenton treatment
Published in Chemical Engineering Communications, 2020
Pegah Nazari, Neda Askari, Shahrbanoo Rahman Setayesh
The activity of the hydrogen peroxide and hydroxyl radical is highly depended on the reaction system pH. To study the impact of pH, a set of experiments was carried out at pH = 1 to 10 (Figure 4(a)). It can be seen that the increase of pH from 1 to 3 caused improving in the catechol removal. The results showed that pH = 3 is the optimum pH for the EF system. By increasing pH to 10, the efficiency of the EF system diminished. At pH = 1, H2O2 reacts with H+ to produce oxonium ion (H3O2+) (Equation 4). At very low pH values, magnetite NPs dissolve and Fe2+ from the dissolution of Fe3O4 NPs reacts with hydroxyl radical (Equation 5) and inhibits the degradation reaction (Huang et al., 2017). When pH raises to values more than 5, Fe2+ and H2O2 produce Fe (IV) species, for example, FeO2+. However, in our work, the probability of this reaction was eliminated, since the heterogeneous catalyst was utilized. The low rate of reaction (Equation 2) in comparison to reactions (Equations 3 and 6), at high pH value, might cause the decrease in the degradation efficiency (Heidari et al., 2015).