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A proposed synthesis routine of akuammicine, one of the akuamma alkaloids from the seeds of the akuamma tree
Published in Binoy K. Saikia, Advances in Applied Chemistry and Industrial Catalysis, 2022
Yangyi Gu, Tianhe Zheng, Jiongchen Guo
The first step of the proposed retrosynthesis is to make a disconnection of the carbon-carbon bond between positions 10 and 18, which is based on the Heck cyclization reaction. The advantage of this disconnection is that the reaction of an alkene by alkylation or arylation can easily happen. The second step is to break the carbon-nitrogen single bond between positions 16 and 17. Then, the third step is also the breaking of the carbon-nitrogen single bond but between positions 12 and 16. This shows the electrophilic addition reaction between amines and alkenes. After that, the fourth step is the key to the whole retrosynthesis. It is shown that two carbon-carbon single bonds are connected at the same time, which is related to the Diels-Alder reaction. The final step is the electrophilic substitution of indole, so it is obvious that the raw material is indole. However, the indole molecule contains an amino group that could take participate in side reactions, so it is necessary to protect it at the beginning. (scheme 2)
Containers and Vessels for Supramolecular Catalysis
Published in Jubaraj Bikash Baruah, Principles and Advances in Supramolecular Catalysis, 2019
In addition to these, structurally rigid container molecules derived from zeolites are used as hosts for various organic compounds. Zeolites are aluminosilicate and they have porous structures. Due to intrinsic acid-base properties associated with aluminosilicate, they are good catalysts for selective organic transformations in heterogeneous conditions. Some of the metal ion-exchanged zeolites are active catalysts. The acidity of zeolites changes upon incorporation of zinc ions and acts as a catalyst for the Prin reaction. The Prin reaction refers to transformation of activated aldehyde; it is an electrophilic addition reaction and is generally catalysed by an acid. Such reactions in homogeneous conditions are nonspecific. Zinc-incorporated β-zeolite has high selectivity in the conversion of β-pinene upon reaction with formaldehyde to form nopol (Figure 3.44). The reaction proceeds when 0.31 mmol/g of zinc ion is loaded onto the H-beta zeolite with a turnover number of 138. In Brönsted acid-catalysed reactions of ß-pinene, it rearranges to α-pinene, limonene, camphene and terpinolenes, which is not the case in the confined media of zeolite. The incorporated zinc ions in the zeolite decrease the Brönsted acidity and enhance the reaction rate to form a specific product. This reaction is presumably through the stabilization of tertiary carbocation, which is held inside the cavity through the oxygen atom of the condensation product formed between the reactants.
Vinylcyclopropanes in the addition and polymerization reactions: a detailed review
Published in A. K. Haghi, Lionello Pogliani, Devrim Balköse, Omari V. Mukbaniani, Andrew G. Mercader, Applied Chemistry and Chemical Engineering, 2017
Abasgulu Guliyev, Rita Shahnazarli, Gafar Ramazanov
Now there are sufficiently many works devoted to the study of conducting of VCP in the electrophilic addition reaction.48−65 In these works, the monoaddition reactions of various addends to different alkyland aryl-substituted VCP,48−56 polycyclic compounds containing VCP fragment in its structure,57−61 to some functionally substituted VCP have been studied.62, 63
Multiple-color aggregation-induced emission-based Schiff base sensors for ultrafast dual recognition of Hg2+ and pH integrating Boolean logic operations
Published in Journal of Coordination Chemistry, 2019
Ani Wang, Ruiqing Fan, Yuze Zhou, Xubin Zheng, Xuesong Zhou, Sue Hao, Yulin Yang
As described above, L has a different response to pH under acidic conditions, which may be due to the different negative inductive effect of substituent groups in phenylamine moieties. Generally, in acid solution, the hydrolysis of Schiff base is attributed to an electrophilic addition reaction. The stability of Schiff base is dominated by the electron density of the C = N bond. The high electronegativity of the nitro-substituent will impair the charge density of the C = N bonds in Schiff base. Therefore, the hydrolysis of L7 requires higher hydrogen ion concentration. Compared with nitro-substituent, the methyl-substituent possessed inductive effect, which has a weaker negative inductive effect. Thus, the titration jump value of L2–L6 was observed at a higher pH than that of L7. For L1, in benzene moiety, there is no substituent group with negative inductive effect, thus, C = N double bond in L1 has the lowest stability.
Mercury removal performance and mechanism of biochar co-modified with HNO3 and NH4Br under oxy-combustion atmosphere
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Qingshan Zeng, Hui Wang, Hengyuan Ran, Jingmao Wu, Kang Yang
Figure 13 is a rice husk char model loaded with C-Br (RHC (C-Br)), and Figure 14 is an electrostatic potential analysis of the model before and after adsorption. Table S7 and S8 show the atomic bond distribution and Mulliken charge population before and after adsorption of the model. From the results of electrostatic potential analysis, it can be seen that the introduction of C-Br leads to the redistribution of charge on the carbonaceous surface, and the electron-rich region of the whole carbonaceous surface moves toward C7 and C14, indicating that these two may be the main sites of mercury adsorption. The electrostatic potential after adsorption shows that Hg0 is indeed adsorbed in this region. Combining the results of Table S7, the bond length of Hg-C14 is the shortest, only 2.365 Å, indicating that C14 is the main chemisorption site of Hg0. At this time, the adsorption energy is 135.913 kJ/mol, which belongs to the category of chemical adsorption. The C14 charge population continued to decrease after the reaction, which is consistent with the above analysis. The charge population of Br also maintained a significant downward trend, indicating that Br also received a large number of electrons in the adsorption process. By comparing the charge population of RHC (C-Br)-C6 and RHC-C6 before adsorption, it can be found that the former is much larger than the latter, because the embedding of Br is an electrophilic addition process (Liu, Qu, and Zheng 2013) Br and C6 formed a very stable covalent bond on the carbonaceous surface, which is also consistent with the XPS analysis. Comparing the changes of Hg charge population and Hg-C bond length before and after adsorption between O embedding and Br embedding, it can be concluded that O embedding can adsorb Hg0 more stably.
Novel drying and pretreatment methods for control of pesticide residues in fruits and vegetables: A review
Published in Drying Technology, 2023
Tiantian Tang, Min Zhang, Ronghua Ju, Arun S. Mujumdar, Dongxing Yu
Wen et al.[100] investigated the degradation of residual fungicide pentachloronitrobenzene (PCNB) in ginseng by γ-irradiation. The results showed that the concentration of PCNB was remarkably decreased by 60Co γ-irradiation, and the decomposition product of PCNB was pentachloroaniline under 5 kGy irradiation, and the PCNB (3.7 ppm) in ginseng was decreased to 0.2 ppm by 20 kGy irradiation. In addition, the degradation of PCNB by γ-ray might be due to the attack of free radicals on benzene rings and nitro groups of PCNB through electrophilic addition reaction. Armelim et al.[101] found that γ-irradiation (60Co) caused significant dissipation of thiamethoxam in beans, which decreased by 66% at 2 kGy and 44% at 1 kGy compared with non-irradiation treatment. However, irradiation did not affect imidacloprid residue. Chowdhury et al.[102] evaluated the removal efficiency of pesticides in capsicum (diazinon), cucumber (chlorpyrifos), and tomato (phosphamidon) by γ-irradiation (60Co). The results showed that gamma radiation decreased the level of pesticides proportionally with the increase of radiation dose. The degradation rates of phosphamidon, chlorpyrifos, diazinon at 1.0 kGy irradiation dose (90–95%, 80–91%, and 85–90%, respectively) were higher than 0.5 kGy (30–45%, 35–43%, and 40–48%, respectively). Similar results were found by Ciarrocchi et al.[104] The γ-irradiation doses of 1.5, 2.0 and 4.0 kGy degraded carbendazim in strawberry by 13.17%, 15.95%, and 27.99%, and azoxystrobin by 25.53%, 32.32%, and 56.70%, respectively. Basfar et al.[103] reported that 18% and 44.4% of pirimiphos-methyl residues in potatoes and dates were removed by 1 kGy γ-irradiation, while the removal rates of malathion, pirimiphos-methyl and cypermethrin in grapes were only 3.83%, 19.1%, and 2.6% at a dose of 7 kGy, respectively. Another study showed that the degradation of profenofos in peas increased with electron beam dose.[105] The removal efficiency of profenofos at 4.5, 12.2, and 30.4 kGy were 38.2%, 41.8%, and 47.9%, respectively. In conclusion, the elimination effect of both γ-irradiation and electron beam irradiation on pesticides mainly depends on the nature of food, irradiation dose, type and concentration of pesticides. It is a feasible way to degrade pesticide residues in fruits and vegetables by ionizing radiation.