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Chemistry Matrices of Biotransformation
Published in Shrikaant Kulkarni, Neha Kanwar Rawat, A. K. Haghi, Green Chemistry and Green Engineering, 2020
All traditional synthetic routes to the hydroxy nitrile product (HN) require a standard SN2 substitution of halide with cyanide ion in alkaline medium at higher temperatures. As substrate and product both are sensitive to base reasonably, more amount by-product is likely to be formed. Further, the product exists as high-boiling oil, which demands a cumbersome high-vacuum fractional distillation to recover a qualitative product, leading to further losses in yield. The key in designing an economically and environmentally acceptable process for HN was to design a process for carrying out the cyanation reaction under mild conditions such as neutral pH, by using the enzyme, HHDH. Table 4.4 shows the evolution of the HHDH Biocatalyst. Coupling this with the chlorohydrin substrate synthesis using enantioselective KRED-catalyzed reduction of the respective keto ester, and cofactor regeneration with glucose/GDH, allowed an elegant two-step, three-enzyme process. However, the KRED and GDH are characterized by low activities and more enzyme loadings to maintain an economically viable reaction rate and are accompanied by cumbersome emulsion formation in downstream processing. Therefore, the analytical yield is >99% though, the practical yield is 85%.
The Condensation Reactions Of 1-Chloro-2,3,4,6-Tetra-O-Acetyla-D-Gluco (Galacto) Pyranose With Heterocyclic Amines
Published in A. K. Haghi, Lionello Pogliani, Devrim Balköse, Omari V. Mukbaniani, Andrew G. Mercader, Applied Chemistry and Chemical Engineering, 2017
N. Sidamonidze, R. Gakhokidze, R. Vardiashvili
The condensation reaction of a-chloro-2,3,4,6-tetra-0-acetyl-a-Dgluco(galacto)pyranose with 4,4,8,8-tetramethyl-2,3,6,7-dibenzo-9-oxabicyclo-(3,3,1)-nonan-1-N-(4-methyltiazolylethylamino)-5-ol in the presence of the silver carbonate is nucleophilic substitution reaction that occurs through an SN2 mechanism. The direction of the reaction depends on the relative configuration of C1 and C2 in the initial acylated chloroglucose and chlorogalactose and on the acceptor of the released HCI. Condensation of 1,2-cz’s-acylglycosylhalides with alcohols in the presence of Ag2CO3 occurred mainly with C1 configuration inversion, resulting in formation of 1,2-trans -glycosides.
An analysis of the influence of affordable housing system on price
Published in Dawei Zheng, Industrial, Mechanical and Manufacturing Science, 2015
In aqueous solution, anionic surfactants are ionized to negatively charged hydrophilic radical on the end. There is a strong electrostatic repulsion between the anionic surfactant hydrophilic radical. To promote the surfactant molecules self-assemble into an anionic surfactant wormlike micelles, we need to add the appropriate counterion suppression molecular electrostatic repulsion between the molecules. [7] In the given condition, three hydroxyethyl benzyl ammonium chloride can engage by SN2 type nucleophilic substitution reaction. Potassium erucic and organic counterion three hydroxyethyl benzyl ammonium chloride were mixed at different ratios, the purpose is to get the best ratio to compose wormlike micelles.
Reaction probability and defluorination mechanisms of a potent greenhouse gas SF5CF3 attacked by CH3 radical: a theoretical study
Published in Molecular Physics, 2018
Yan Liu, Yue-tian Huang, Wen-liang Wang
The type of inserting and breaking mechanism will undergo complex muti-channel processes to decompose three HF molecules successively and produce an alkyne derivative, as shown in Figure 3(b). It is found that there are three entrance paths to form product Dp10 (SF5 + CH3CF3) via TS14 and TS15 (two different mechanisms) or Dp11 (CH3SF5 + CF3) via TS16 firstly. In TS14, the CH3 radical attacked and extracted the –CF3 group directly from the back side of CF3SF5 molecule, as shown in Figure 1. The process would result in the breaking of the old C–S bond and the forming of a new C–C bond, which is defined as the mechanism of bimolecular nucleophilic substitution (SN2 mechanism). But the SN2 mechanism has a higher energy barrier of 335.7 kJ mol−1. Another path to form Dp10 will go through the transition state TS15 with the energy barrier of 301.3 kJ mol−1, which is 34.4 kJ mol−1 lower than that of TS14. In TS15, the CH3 radical would insert in the C–S bond of CF3SF5 and also lead to the breaking of C–S bond to decompose a SF5 molecule. Meanwhile, CH3 and CF3 groups will combine together to form CH3CF3 molecule. Alternatively, the CH3 radical could combine –SF5 group and decompose the –CF3 group to form the product Dp11 via the transition state TS16 with the barrier of 332.4 kJ mol−1. It is noted that the products Dp10 and Dp11 could convert to each other via TS17 by through the –CH3 group swinging between –CF3 and –SF5 groups. The barrier from Dp10 to Dp11 is 414.7 kJ mol−1 and that of reverse reaction is 275.7 kJ mol−1. The decomposing products CH3SF5 and CF3 would eliminate a HF molecule and form intermediate IM1 via TS18 with an energy barrier of 383.9 kJ mol−1. In IM1, one of H atom could shift from the inside C atom to the end and form IM2 via TS19 with barrier of 140.7 kJ mol−1. IM2 would then dissociate a HF molecule in the –CF2H group to produce IM3 with a moderate barrier of 218.7 kJ mol−1. Competing to the two-step reactions, IM1 also could break its C–F and C–H bonds directly to produce IM3 + HF via TS21 with a slightly higher barrier of 222.1 kJ mol−1.