Development of Elegant Methods for the Synthesis of Novel Heterocycles

Heterocyclic compounds have attracted much pharmacological and synthetic interest as they have been found in many biologically important scaffolds. Therefore, development of efficient and elegant methodologies for the synthesis of novel fused heterocycles of biological significance is a challenging task in organic chemistry. The research work embodied in this thesis describes efficient and elegant protocols for the synthesis of triazole fused benzoxazines, triazole fused benzodiazepines/benzodiazocines and pyrazole fused benzodiazepines applying palladium-copper catalyzed reactions and 1,3- dipolar cycloaddition. The work has been presented in three Chapters.Describes the efficient synthesis of 3-aryl substituted [1,2,3]triazolo[5,1- c][1,4]benzoxazines using palladium and copper catalysts in one-pot through Sonogashira coupling followed by azide-alkyne cycloaddition.Describes a facile and expedient general synthesis of novel tricyclic scaffolds 3-aryl substituted [1,2,3]triazolo[1,5-a][1,4]benzodiazepin-6-ones and[1,2,3]triazolo[1,5-a][1,5]benzodiazocin-7-ones through Sonogashira coupling followed by in situ diazotization, azidation and azide-alkyne cycloaddition reactions

Efficient Synthesis of [1,2,3]triazolo[5,1-c][1,4]Benzoxazines Through Palladium–copper Catalysis

A wide variety of [1,2,3]triazolo[5,1-c][1,4]benzoxazines were synthesized through palladium-copper catalyzed reactions of 1-azido-2-(prop-2-ynyloxy)benzene with aryl/vinyl iodides. A plausible reaction mechanism has also been propose

Totally Regio- and Stereoselective Synthesis of (E)-3-Arylidene-3,4- Dihydro-2H-1,4-benzoxazines Under Palladium Catalyst

A new, one-pot palladium catalyzed reaction has been developed for the general synthesis of (E)-3-arylidene- 3,4-dihydro-2H-1,4-benzoxazines at room temperature. The reaction procedure tolerates various functional groups. The method is characterized by regio- and stereoselectivity, operational simplicity, mild reaction conditions, and short reaction time

Surface Plasmon Effect of Cu and Presence of n–p Heterojunction in Oxide Nanocomposites for Visible Light Photocatalysis

In this paper, we report the design, synthesis, and characterization of three different composite nanomaterials (Cu-ZnO, Cu-Cu₂O-ZnO, and Cu₂O-ZnO) with surface plasmon resonance (SPR) effect and n–p heterojunction for visible light photocatalysis. We have accounted for the first time the SPR effect of Cu in photocatalysis for promotion of efficient electron–hole separation that further enhances visible light induced photocatalytic activity. To make the composite efficient we have judiciously introduced cheap and common Cu and Cu₂O in ZnO matrix individually and cojointly to make the composites visible light sensitizer. Furthermore, wide band gap barrier of ZnO crosses its UV limit in the composites and spreads over to visible region. By simply varying the complexing agents, here we achieve success to obtain three kinds of highly stable composite nanomaterials with three distinct structures from identical experimental condition. This synthetic strategy offers a radically different approach where oxidation of Cu is inhibited in the matrix and visible light induced photocatalytic performance remains unaltered for months. Interestingly, the combined effect of both Cu and Cu₂O in the as-synthesized ternary composite, Cu-Cu₂O-ZnO endorses highest photocatalytic activity than the other two composites. This activity attributed to extended light absorption, effective transfer of photogenerated carriers and presence of strong SPR effect. Finally, the comparative photocatalytic activity of all the nanocomposites has been accounted from methylene blue (MB) degradation in aqueous solution under visible light irradiation

Bond-Energy-Driven, Low- or High-Angle-Grain-Boundary-Movement-Mediated Synthesis of Porous Se–Te for Use in Water-Splitting Reactions

Herein, for the first time, we applied the metal–metal-bond-energy factor to the evolution of a porous Se–Te alloy. The porous Se–Te material has been prepared from the constituents’ elemental states, through only a heating–cooling process in silicone oil without the use of any reagent, surfactant, or capping agent. Surprisingly, the reaction occurred at a much lower temperature (240 °C) than the mp (450 °C) of Te⁰. The reaction’s nucleation and growth by means of varied bond energy have been clarified for the first time. A difference in the bond energies of a hetero metal–metal bond (Se–Te) and a homo metal–metal bond (Se–Se) directs nucleation and growth toward the fabrication of a porous structure, even from the constituents’ elemental states, in which low-angle-grain-boundary (LAGB) and high-angle-grain-boundary (HAGB) movements play governing roles. Proper band-gap alignment of Se and Te makes the alloy composite applicable to water-splitting reactions under Xe-arc-lamp illumination. PEC efficiency of Se–Te was found to be higher than those reported for Se and other composite materials

Modified hydrothermal reaction (MHT) for CoV₂O₆·4H₂O nanowire formation and the transformation to CoV₂O₆·2H₂O single-crystals for antiferromagnetic ordering and spin-flop

A modified hydrothermal protocol (MHT) has been adopted for the synthesis of a single-crystal of CoV₂O₆·2H₂O. The crystals grew as a result of prolonged hydrothermal reaction between precursor salts of CoCl₂ and ammonium vanadate. At first, the adopted reaction conditions resulted in nanowires of CoV₂O₆·4H₂O. Then with increased reaction time, nanowires changed to single crystals of molecular formula CoV₂O₆·2H₂O. The nanowires have lengths of several tens of micrometers and average diameter of 100 nm. The well defined structure crystallizes in the orthorhombic crystal system having space group Pnma and it displays a = 5.5647(2) Å, b = 10.6870(5) Å, c = 11.8501(5) Å, α = β = γ = 90.00°. Here, each vanadium atom is tetrahedrally connected to four oxygens where two oxygens are connected to vanadium atoms and another two connected to cobalt atoms. Magnetic moment measurement of the nanowires indicates that antiferromagnetic ordering is observed at around 14.9 K and 6.8 K and field induced antiferromagnetic to ferromagnetic (spin-flop-type) transitions have been observed at a low temperature (5–8.8 K) range while these are absent in the as-synthesized single crystals

Suitable Morphology Makes CoSn(OH)₆ Nanostructure a Superior Electrochemical Pseudocapacitor

Morphology of a material with different facet, edge, kink, etc., generally influences the rate of a catalytic reaction., Herein, we account for the importance of altered morphology of a nanomaterial for a supercapacitor device and employed CoSn­(OH)₆ as an electrode material. Suitable fabrication of a stable aqueous asymmetric supercapacitor (AAS) using metal hydroxide as positive electrode can be beneficial if the high energy density is derived without sacrificing the power density. Here we have synthesized an uncommon hierarchical mesoporous nanostructured (HNS) CoSn­(OH)₆ to fabricate a pseudocapacitor. In this endeavor, NH₃ is found to be a well-suited hydrolyzing agent for the synthesis. Serendipitously, HNS was transformed into favored cubic nanostructure (CNS) in NaOH solution. In solution, NaOH acts as a structure directing as well as an etching agent. Both the samples (HNS & CNS) were used as pseudocapacitor electrodes in KOH electrolyte independently, which is reported for the first time. The HNS exhibits very high specific capacitance value (2545 F/g at 2.5 A/g specific current) with better cyclic durability over CNS sample (851 F/g at 2.5 A/g specific current). To examine the real cell application, we used HNS sample as the positive electrode material with the activated carbon (AC) as the negative electrode material for the development of an aqueous asymmetric supercapacitor (AAS). The as-fabricated AAS exhibited very high specific capacitance value of 713 F/g at a specific current of 1.5 A/g and retained 92% specific capacitance value even after 10 000 charge–discharge cycles. A maximum energy density of 63.5 Wh kg^–1 and a maximum power density of 5277 W kg^–1 were ascertained from the as-fabricated AAS, HNS CoSn­(OH)₆//AC

Account of Nitroarene Reduction with Size- and Facet-Controlled CuO–MnO₂ Nanocomposites

In this work, we propose a systematic and delicate size- and shape-controlled synthesis of CuO–MnO₂ composite nanostructures from time-dependent redox transformation reactions between Cu₂O and KMnO₄. The parental size and shape of Cu₂O nanostructures are retained, even after the redox transformation, but the morphology becomes porous in nature. After prolonged reaction times (>24 h), the product shapes are ruptured, and as a result, tiny spherical porous nanocomposites of ∼100 nm in size are obtained. This method is highly advantageous due to its low cost, its easy operation, and a surfactant or stabilizing agent-free approach with high reproducibility, and it provides a facile but new way to fabricate porous CuO–MnO₂ nanocomposites of varied shape and size. The composite nanomaterials act as efficient recyclable catalysts for nitroarene reduction in water at room temperature. The time-dependent reduction kinetics can be easily monitored by using UV–vis spectrophotometer. The catalytic system is found to be very useful toward the reduction of nitro compounds, regardless of the type and position of the substituent(s). Furthermore, it is revealed that CuO–MnO₂ composite nanomaterials exhibit facet-dependent catalytic activity toward nitroarene reduction, where the (111) facet of the composite stands to be more active than that of the (100) facet. The results are also corroborated from the BET surface area measurements. It is worthwhile to mention that porous tiny spheres (product of 48 h reaction) exhibit the highest catalytic activity due to pronounced surface area and smaller size

Superb Dye Adsorption and Dye-Sensitized Change in Cu₂O–Ag Crystal Faces in the Dark

Hybrid Cu₂O–Ag is attractive because of its many applications in the fields of photocatalysis, surface-enhanced Raman scattering (SERS), and optical features. In this article, we have presented a newer application of Cu₂O–Ag. Cu₂O–Ag has been found to exhibit excellent anionic dye adsorption properties together with organic transformation for effective water remediation. Cu₂O–Ag was prepared through a facile but controlled galvanic reaction between cuprous oxide (Cu₂O) and silver nitrate (AgNO₃), rendering stability and porosity. The experimental results of adsorption showed that Cu₂O–Ag bears an exceptionally high adsorption capacity toward methyl orange (501.23 mg g^–1), which is higher than most reported results. The adsorption of MO on Cu₂O–Ag happens because of the definite chemical interaction between Cu­(I) and the SO₃^– functionality of MO. A kinetic study revealed that the MO adsorption on Cu₂O–Ag primarily followed the pseudo-second-order kinetic model. The kinetic model followed the Langmuir adsorption isotherm. A very significant feature that emerged during MO adsorption by Cu₂O–Ag is the transformation of the 3-D morphology of Cu₂O–Ag into 2-D nanosheets under ambient and dark conditions. This morphology change corroborates that the adsorption occurred through chemical interaction, i.e., the chemisorption process. This feature, a morphology change in the dark, presumably happened through the participation of the highly interactive exposed high-index facet of spherical Cu₂O–Ag nanoparticles. This unique recrystallization of Cu₂O–Ag due to the chemisorption of MO is reported for the first time. Cu₂O–Ag was also found to have a high adsorption capacity (976.30 mg g^–1) even for Congo red (an anionic azo dye), which is also higher than the reported adsorption capacities of various materials. In another water remediation aspect, Cu₂O–Ag has also been applied to the transformation of organic toxic pollutant, 4-nitrophenol (4-NP), into its nontoxic and medicinally important amino derivative through catalytic reduction. The catalysis of 4-NP reduction by Cu₂O–Ag in the presence of sodium borohydride (NaBH₄) exhibited a high rate constant value (<i>k</i> = 0.38 min^–1). Thus, two novel properties, adsorption and catalytic reduction on organic pollutants, of Cu₂O–Ag have been ascertained for water remediation

Serendipitous Synthesis of Ag_1.92Mo₃O₁₀·H₂O Nanowires from AgNO₃‑Assisted Etching of Ammonium Phosphomolybdate: A Material with High Adsorption Capacity

Ultralong Ag_1.92Mo₃O₁₀·H₂O nanowires have been serendipitously obtained due to selective etching of ammonium phosphomolybdate (APM) only by Ag⁺ ions in water under stirring conditions. The spherical yellow APM particle upon etching by Ag⁺ ions generates a hollow sphere, and PO₄^3– ions are expelled as a consequence of etching. The etching and hollowing disrupt the APM structure. Concentration of the etching agent and reaction time are crucial for the formation of Ag_1.92Mo₃O₁₀·H₂O nanowire. The growth of nanowires occurs probably due to etching followed by Ostwald ripening, oriented attachment, and splitting process. Finally, the as-synthesized nanowire exhibits a high capacity to adsorb cationic dyes on its surface. It shows superb adsorption properties, with maximum adsorption capacity of 110 mg g^–1, 175 mg g^–1, 160 mg g^–1 for Methylene Blue, Methyl Green, Crystal Violet, respectively. Moreover, the adsorption process of Methylene Blue on the nanomaterial was investigated taking it as a representative adsorbate. The selective adsorption capability of the nanomaterial toward cationic dye molecules makes it a competent candidate for water purification