Current Catalysis - Volume 11, Issue 2, 2022

Photocatalytic transformation of small substrate molecules to useful products through an environmentally benign and economically viable pathway is a challenging area of research of continual importance. This review focuses on our perception of the application of ruthenium(III) complexes comprising ‘edta’ ligand (edta^4- = ethylenediaminetetraacetate) as a ‘redox mediator’ or ‘relay’ in photocatalytic electron transfer reaction pertaining to the conversion of small substrate molecules viz. hydrazine to ammonia, bicarbonate to formate, dioxygen to hydrogen peroxide. In this article, the prospect of [Ru^III(edta)(H2O)]^- and [Ru^III(edta)(pz)]^- to act as ‘redox mediator’ or ‘molecular catalysts’ in photocatalytic transformations of aforesaid small molecules are assessed systematically.

Background: Pyridine is one of the most ubiquitous hetero-aromatic moieties in pharmaceutical chemistry and it has enormous importance in a plethora of fields. From a synthetic chemistry standpoint, pyridine moiety has been used as a directing group in C-H activation strategies to functionalize various rings. However, this unique feature to participate as a directing group hinders developing methodologies to carry out C-H activation on the pyridine ring itself. One of the simplest solutions is to block the activity of ring nitrogen at the cost of two extra steps. Here, in this review, along with the blocking, we will briefly mention some interesting ways to get around this problem and the remaining challenges ahead. Objective: The coordinating ability of pyridine N poses a big challenge toward C-H functionalization on the pyridine ring. This review summarizes some of the recent methods towards this challenge. Methods: Some key ideas towards that goal have been described. Here, the C-H activation strategies are categorised as follows: (1) Pyridine N-oxide mediated C-H activation, (2) Dimerization of C-H activation of pyridine, (3) Direct Pyridine C2-H activation, (4) Direct Pyridine C3-H activation and (5) Direct Pyridine C4-H activation. Results: Several methods have been highlighted that can be utilised to prepare C-H functionalized products with regiospecificity that subsequently may be manipulated into interesting products which are difficult to attain easily. Conclusion: This review explores various new direct C-H activation methods on pyridine which attempts to fill the void of traditional synthetic protocols in regard to regioselective pyridine functionalization. This review also explores the limitations of current methodologies which must be wiped off to attain a mature state in need of the pharmaceutical industry.

Experimental values of ultrasonic velocity (u), density (ρ) and viscosity (η) for the binary mixtures of ethyl acetate with 1-alkanols have been measured at 303.15 K over the entire mole fraction range. Using these data, the excess isentropic compressibility (β^Es), excess intermolecular free length (L^Ef), excess molar volume (V^Em), excess free volume (V^Ef) and excess available volume (V^Ea) have been calculated. These parameters were used to study the nature and extent of intermolecular interaction between component molecules present in the binary mixtures. Excess values of isentropic compressibility, intermolecular free length, molar volume, free volume and available volume were plotted against the mole fraction of ethyl acetate over the whole composition range. From the properties of these excess parameters, the nature and strength of the interactions in these binary systems are discussed.

Background: An eco-friendly catalyst was synthesized in good yield and characterized by various physicochemical techniques. The catalytic performance of the environmentally benign complex was investigated via slurry synthesis of oximes. The catalytic studies were successfully carried out using a simple protocol. The fascinating advantage of this protocol is cost effectiveness, simple work up, good yield, short reactions time, and milder reaction conditions. Methods: The complex was prepared by reaction of vanadium pentoxide with hydrazone ligand in 1:1 molar ratios, and to this reaction mixture, potassium carbonate (0.14 g, 1 mmol) was added and ground till fine yellow colour powder appeared. Oximations were carried out by reacting the substrates, 15 % H2O2, ammonia and vanadium(V) complex. The reaction was taken in a mortar and ground till a fine powder appeared. After completion of the reaction, the crude product was extracted using dichloromethane/ water in 1:2, v/v, evaporated and dried under vacuum. Results: We synthesized different varieties of oximes using our newly synthesized complex as a catalyst. The products were characterized by ¹H NMR and ¹³C NMR spectroscopy. The completion of the reaction was monitored by checking the complete disappearance of the aldehyde proton and the appearance of oxime protons. We also grew some single crystals of the products to provide further supporting evidences about the formation of products. Conclusion: Oximation of various carbonyl compounds was prepared quantitatively under the slurry condition, using {[K(H-2O)3][V(O)2L]}2 as a catalyst. The catalytic reactions can be carried out under mild conditions, with ease of scalability, and straightforward work-up procedure, which makes the present protocols greener and better alternative methods for the synthesis of oximes.

Background: As a major source of pollutant, the effluents of dye based industries are mostly associated with several toxic heavy metals. Limited efforts have been made on simultaneous removal of both dyes and heavy metals from these effluents through adsorption/ photocatalysis processes. Spinel ferrites with narrow band gap and high stability are suitable for further exploitation in this regard. Objective: Synthesis and characterisation of manganese ferrite nanoparticle and to assess its efficiency towards removal of organic dyes and hexavalent chromium in single and binary component systems are the objectives of this study. Methods: Manganese ferrite nanoparticle (MF NPs), prepared by coprecipitation, was characterised systematically by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-Visible diffuse reflectance and magnetic measurement. Adsorptive and photocatalytic performances of the material under visible light were evaluated using aqueous solutions of different dyes and Cr(VI). Results: Characterisation by various techniques revealed the formation of cubic MF nanoparticles with narrow band gap (1.78 eV) and moderate saturation magnetization (38.5 emu/g). In comparison, the anionic dyes and Cr(VI) were better adsorbed on MF, while photoactivity was more pronounced in the case of cationic dye. Conclusion: MF NPs displayed potential for photo-degradation/reduction of different dyes and Cr(VI) individually or simultaneously under visible light. The catalyst can be recovered magnetically from the reaction mixture for recycling and further use.