Current Catalysis - Volume 10, Issue 1, 2021

Background: During the last two decades, horizon of research in the field of Nitrogen Heterocyclic Carbenes (NHC) has widened remarkably. NHCs have emerged as ubiquitous species having applications in a broad range of fields, including organocatalysis and organometallic chemistry. The NHC-induced non-asymmetric catalysis has turned out to be a fruitful area of research in recent years. Methods: By manipulating structural features and selecting appropriate substituent groups, it has been possible to control the kinetic and thermodynamic stability of a wide range of NHCs, which can be tolerant to a variety of functional groups and can be used under mild conditions. NHCs are produced by different methods, such as deprotonation of N-alkylhetrocyclic salt, transmetallation, decarboxylation and electrochemical reduction. Results: The NHCs have been used successfully as catalysts for a wide range of reactions making a large number of building blocks and other useful compounds accessible. Some of these reactions are: benzoin condensation, Stetter reaction, Michael reaction, esterification, activation of esters, activation of isocyanides, polymerization, different cycloaddition reactions, isomerization, etc. The present review includes all these examples published during the last 10 years, i.e., from 2010 till date. Conclusion: The NHCs have emerged as versatile and powerful organocatalysts in synthetic organic chemistry. They provide the synthetic strategy which does not burden the environment with metal pollutants and thus fits in the Green Chemistry.

Among the porous organic polymers, Covalent Triazine Polymers (CTPs) have emerged as an important class of materials with versatile applications such as energy storage and conversion, gas adsorption and separation, photocatalysis and heterogeneous catalysis. Particularly, CTPs have been often used as catalyst/catalyst support due to their excellent thermal and chemical stability, as well as recyclability in catalytic reactions. Moreover, the expanding methods available for the synthesis of CTPs, convenient functionalization and presence of nitrogen sites in the framework make them a suitable candidate to develop catalysts for organic transformations. In this review, the methods of synthesis, characterization of CTPs and mainly their applications as catalyst/ catalyst support in organic transformations are summarized.

Background: Betti base derivatives were employed as chiral ligands or as chiral auxiliaries in asymmetric transformations. In particular, N-alkyl Betti base derivatives are gaining importance as excellent ligands in asymmetric reactions. However, no appropriate method exists for regioselective N-alkylation of Betti base. Therefore, there is an urgent need to develop a new protocol for the regioselective N-alkylation of chiral Betti-base. Methods: An efficient method has been developed for one-pot synthesis of chiral N-alkyl Bettibase ligands from (S)-(+)-Betti base, arylglyoxals and cyclic 1,3-C,N-binucleophiles under catalyst- free conditions. Results: The chiral N-alkyl Betti-base ligands were obtained in good yields with excellent enantioselectivities. This method is rapid, clean and does not require a catalyst or chromatographic purification. Conclusion: We have developed an efficient one-pot three component strategy for the synthesis of new chiral N-alkyl Betti-base ligands from (S)-(+)-Betti base, arylglyoxals and cyclic 1,3-C,Nbinucleophiles in the absence of a catalyst.

Background: Benzyl cinnamate is widely used in many fragrance compounds. The traditional methods to obtain benzyl cinnamate, including chemical synthesis or extraction from leaves, have many drawbacks. Recently, lipase-catalyzed synthesis of benzyl cinnamate has provided us with a promising alternative due to its high catalytic efficiency, mild reaction conditions, and green and environmentally friendly process. In this work, the purpose is to investigate the kinetics and thermodynamics of enzymatic synthesis of benzyl cinnamate. Objective: The objective of the current study was to investigate the kinetics and thermodynamics of the enzymatic synthesis of benzyl cinnamate. Results: The results showed that the reaction followed the Ping-Pong mechanism leading to substrate inhibition. Furthermore, the kinetic and thermodynamic parameters were estimated. The inhibition constant Ki^B decreased with temperature enhancement, implying that the inhibition of benzyl alcohol on lipase could be depressed at high temperatures. Moreover, the activation energy of the first-step reaction (52.46 kJ/mol) was much higher than that of the second-step reaction (12.97 kJ/mol), demonstrating that the first-step reaction was the rate-limiting reaction. The esterification process was found to be endothermic, with an enthalpy value (ΔH) of +55.7 kJ/mol and entropy value (ΔS) of +170.2 J/mol K, respectively. Based on the change of Gibbs free energy (ΔG), enzymatic esterification of cinnamic acid changed from non-spontaneous to spontaneous reaction when temperature was raised to above 53ºC. Conclusion: This obtained information could be utilized to optimize the biosynthesis of benzyl cinnamate.

Background: Increasing environmental pollution generated by fossil fuel consumption has intensified the consumption and development of renewable fuels. Objective: Thus, the aim of this work was to investigate the use of heterogeneous catalysts (SBA- 15 and Al-SBA-15) for the transesterification of soybean oil to produce biodiesel. Methods: The pore size and surface acidity of SBA-15 were modified by the addition of heterogeneous Al atoms. Samples were characterized by X-ray diffraction, Nitrogen adsorption, Scanning electron microscopy, Infrared Spectroscopy, and Thermogravimetry. Results: Results of the characterization study evidenced that a large amount of mesopore and surface acidity can significantly improve the transesterification reaction with the incorporation of aluminum into the SBA-15 framework. The best results were obtained with a 24 h reaction time and Al-SBA-15. The transesterification reaction of soybean oil with ethanol during 24 h showed in this work presented an efficient conversion of 85.5% with SBA-15 catalyst and 96.5% with the Al- SBA-15 catalyst.