Department of Chemistry

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Curtius rearrangement is the elimination of N2 from carbonyl azides RC(O)N3 to form isocyanates RNCO. Two mechanisms, viz., stepwise and concerted have been proposed in the literature for this reaction. The stepwise mechanism involves the formation of a nitrene RC(O)N by elimination of N2 followed by an intramolecular rearrangement of the nitrene to form the isocyanate. The concerted mechanism is a single-step pathway forming the N2 + RNCO products directly. Previous experimental and theoretical studies have indicated that the mechanism is usually concerted for thermal reactions and both stepwise and concerted are preferred under photochemical conditions. In the present work, we investigated the mechanism of Curtius rearrangement of two carbonyl azides with different substituents (R = CH3 and F). Atomic level reaction mechanisms were studied using chemical dynamics simulations under thermal reaction conditions. Classical trajectories were generated on-the-fly at the density functional B3LYP/6-31+G∗ level of electronic structure theory with similar initial conditions for both the molecules. Simulation results showed a dominant concerted mechanism for CH3C(O)N3 and the operation of both the mechanisms for FC(O)N3. The fluorocarbonyl nitrene FC(O)N had an appreciable lifetime before undergoing intramolecular rearrangement to form the isocyanate. In a small number of trajectories, the product isocyanate produced via the concerted dissociation of FC(O)N3, isomerized back to the nitrene form. Copyright © 2020 American Chemical Society.

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Journal of Physical Chemistry A

Chemical Dynamics Simulations of Curtius Reaction of Acetyl-and Fluorocarbonyl Azides

For two-time scale systems, singular perturbation theory is often used for designing a controller based only on an approximate model of its slow dynamics, assuming the fast model to be stable. In this context, the authors investigate and implement a stabilising event-triggered feedback law for a networked singularly perturbed system, based only on an approximate model of its slow dynamics. Triggering rule guarantees the stability and the existence of a positive lower bound between two consecutive transmissions. The proposed approach has been validated for a laboratory-scale hardware setup of an active suspension system of a quarter-car model. The presence of fast and slow modes in a vehicle suspension system is utilised to model it as a singularly perturbed system. Experimental results indicate that in spite of the simplified structure of the controller and event-triggered feedback, its performance is comparable to that of the full-state feedback design with continuous feedback with the significant reduction in control execution events. © The Institution of Engineering and Technology 2020.

Department of Electrical Engineering

Fulltext

IET Control Theory and Applications

Reduced-order event-triggered controller for a singularly perturbed system: An active suspension case

Multifunctional carbon nanomaterials have attracted remarkable consideration for use in various energy conversion and storage devices because of their ultrahigh specific surface area, unique morphology, and excellent electrochemical properties. Herein, we report the synthesis of highly uniform and ordered nitrogen-enriched carbon nanospheres (CS) and nanobubbles (CNB) by a modified Stober reaction using resorcinol and formaldehyde in the presence of ethylenediamine as a nitrogen source. A comparative study of the prepared CS and CNB nanomaterials is presented here with potential use in a wide variety of applications involving large surface area and electrical conductivity. As counter electrode materials in solar cells, CNB and CS showed enhanced photoelectrochemical activity for catalytically reducing I-3(-) to I- and improved capacitive behavior with a low charge transfer resistance and remarkable power conversion efficiency (PCE) of 10.40\% with improved J(sc) (20.20 mA/cm(2)) and V-oc (0.73 V). The enhanced performance of the fabricated photoelectrochemical cell is due to the excellent point contact and good conductivity that offered better charge transportation of electrons with minimum recombination. The enhanced adsorption upon increasing the pressure without an apparent saturation level signified the large CO2 adsorption with 2 mmol/g for the CS. Additionally, the rectangular-shaped CV curve indicated the double-layer capacitive behavior, good electrochemical reversibility, and high-power characteristics, prerequisites for supercapacitor application. This study probes the practical possibility of nitrogen-enriched carbon nanostructures as a multifunctional material for prospective applications.

ACS APPLIED NANO MATERIALS

Nitrogen-Enriched Carbon Nanobubbles and Nanospheres for Applications in Energy Harvesting, Storage, and CO2 Sequestration

The current study describes cucurbit{[}6]uril and 4-tert-butylcalix{[}6]arene as high-performance multifunctional additives for polyol lubricant base oils. Cucurbit{[}6]uril is a macrocyclic compound with an aliphatic core, while 4-tert-butylcalix{[}6]arene has an aromatic core. The tribological properties of cucurbit{[}6]uril and 4-tert-butylcalix{[}6]arene in terms of the friction coefficient and average wear scar diameter were evaluated by the four-ball test (ASTM D4172). The antioxidant properties of these additives were assessed via a universal oxidation test (IP-306) and anticorrosion study by standard ASTM D664. Of the two additives, cucurbit{[}6]uril shows great promise for applications in industrial areas, maintains excellent tribological ability and exhibits a better load-bearing tribofilm as per morphologies observed by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy.

NEW JOURNAL OF CHEMISTRY

On the study of cucurbit{[}6]uril and 4-tert-butylcalix{[}6]arene as multifunctional lubricant additives

Carbon materials such as activated carbon, carbon nanotubes, carbon nanofibers, fullerenes, and graphene are used as support for heterogeneous catalysis because of their large specific surface area, good porosity, high electron conductivity, and relative chemical inertness. The composition of these materials with metal nanoparticles has attracted huge attention in catalytic hydrogenation because of their excellent electrical, thermal, optical, and mechanical properties as well as high surface-to-volume ratios. Specifically, metal-carbon nanotube-based nanocomposite has demonstrated extraordinary catalytic activity in hydrogenation reaction by virtue of the integration and synergetic effects between both materials. Highly valuable products applicable for pharmaceutical, biomedical, and agricultural industries are produced from the catalytic hydrogenation reactions. Consequently, the demand for metal nanocomposites has been increasing rapidly, and particular attention is required for advanced synthesis techniques and to understand the real factors responsible for high catalytic activity. This chapter includes the significant advances that have emerged in this field and aims to explore the catalytic-activity-dependent factors and their prospective application in the hydrogenation reaction. © 2020 American Chemical Society.

ACS Symposium Series

Recent Advances in Synthesis of Metal-Carbon Nanocomposites and Their Application in Catalytic Hydrogenation Reactions

Well-defined nano- and atomic-sized heterogeneous catalysts with extremely high catalytic activities and unique selectivities show promise in addressing the critical energy- and environment-related challenges of this century. The exceptional properties of these catalysts, such as their electronic and geometric structures and the effective interactions between metals and supports, give rise to unprecedented catalytic efficiency over that of conventional catalysts. The facile prospects for tuning the active sites of these catalysts pave the way to optimizing their activities, selectivities, and stabilities, thus offering extensive application possibilities in significant industry-related catalytic reactions. A prerequisite for synthesizing nano- and atomic-sized catalyst is to prepare extremely disperse nano- and subnanoscale atoms on suitable supports. This book chapter summarizes various synthesis methods employed to synthesize nano- and atomic-scale catalysts. © 2020 American Chemical Society.

Recent Progress in Synthesis of Nano- And Atomic-Sized Catalysts

Facile and robust technologies for efficient removal of uranium from effluent and groundwater is important for sustainability and environmental protection. Herein, we describe engineered surface fluorinated nano-hematite nanoparticles (F-α-Fe2O3) for the effective removal of uranium from aqueous media. The sorption of U(VI) from aqueous solution is investigated as a function of pH, contact time and concentration using batch technique. The adsorption capacity (qm) is found to be 79 mg/g using Langmuir adsorption isotherm within 60 min at pH 5. The isothermal data shows better fit with Langmuir than Freundlich equations and follow the pseudo-second-order kinetic model. The interactions between adsorbents and adsorbates are accounted for by the Temkin isotherm model. The surface charge of F-α-Fe2O3 is evaluated by the zeta potential curve. The results are best in terms of adsorption capacity and kinetics for hematite/modified hematite material. The results are significant for the application of surface fluorinated hematite in U(VI) removal from drinking water. © 2020 Elsevier Ltd.

Journal of Environmental Chemical Engineering

Surface fluorinated hematite for uranium removal from radioactive effluent

Syntheses, structures, and magnetic properties of two hexanuclear [5×1 + 1×1] lanthanide cocrystal complexes [Ln 5 (L) 4 (LH 2 ) 2 (tfa) 4 ]·[Ln(tfa) 4 ]·2CH 3 OH [Ln = Dy(1) and Tb(2)] derived from the polyhydroxy ligand 2-(hydroxymethyl)-6-carbaldehyde-4-methylphenol (LH 2 ) are reported. Compounds 1 and 2 crystallize in the triclinic system with space group P1. X-ray crystallography reveals that 1 and 2 are cocrystals comprising one cationic pentanuclear [Ln 5 (L) 4 (LH 2 ) 2 (tfa) 4 ] + unit and one anionic mononuclear [Ln(tfa) 4 ] – unit as well as two molecules of methanol as solvent of crystallization. Both complexes form a [2.2] spirocyclic topology fashioned core due to merging of two triangular geometries composed of Ln(III) ions through a common vertex. The central Ln(III) ion in the spirocyclic pentanuclear assembly is eight-coordinate with distorted square antiprism geometry. On the other hand, the peripheral eight-coordinate Ln(III) ions are in a distorted trigonal dodecahedron geometry. The comprehensive magnetic study reveals that compound 1 displays slow relaxation of magnetism. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

European Journal of Inorganic Chemistry

[5×1 + 1×1] Hexanuclear Lanthanide(III) Cocrystal Complexes: Syntheses, Structures, and Magnetic Properties

Pd-Catalyzed sequential reactions to afford skeletally diverse molecules are described. The reaction involved azomethine imine formation and a cyclocondensation reaction as individual steps. The methodology provides excellent regio- and stereocontrol. Skeletal diversity was ensured by changing the electrophilic counterpart of azomethine imine. Due to its broader diversity and complexity, the DOS methodology is likely to benefit drug discovery and development in the future. This journal is © 2019 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

New Journal of Chemistry

A diversity-oriented synthesis of polyheterocycles: Via the cyclocondensation of azomethine imine

Late stage functionalization (LSF) through direct X-H manipulations (X = C, N) enables synthetic chemists to accelerate the diversification of natural products, agrochemicals and pharmaceuticals allowing rapid access to novel bioactive molecules without resorting to arduous de novo synthesis. LSF does not only allow tapping of the hitherto unexplored chemical space but also renders the synthetic sequence more straightforward, atom economical and cost-effective. In this regard, the recent decade has witnessed the emergence of hypervalent iodine(iii) reagents as a powerful synthetic tool owing to their easy availability, mild reaction conditions, remarkable oxidizing properties and high functional group tolerance. Iodine(iii) reagents have tremendous applications in the regio- and chemo-selective late-stage functionalization of a diverse variety of heterocycles through an exciting range of transformations, such as oxidative amination, cross-dehydrogenative coupling (CDC), fluoroalkylation, azidation, halogenation and oxidation. The present review, classified according to the types of synthetic methods involved, encompasses all these recent developments in the field of transition-metal-free iodine(iii)-catalyzed/mediated direct functionalizations of heterocycles with representative examples and insightful mechanistic discussions. © The Royal Society of Chemistry.