Harjinder Kaur

Selective oxidation of alcohols by supported gold nanoparticles: recent advances

Industrially, oxidation of alcohols is very important as they are starting materials for a variety of ketones, aldehydes, acids, etc. required to produce plastics, detergents, paints, cosmetics, food additives and drug intermediates. The potential of gold nanoparticles (AuNPs) in oxidation, in general, is immense owing to its tendency to dissociate dioxygen. Supports play a vital role not only in the synthesis and stabilization of nanoparticles, but can also look after the issues of sustainability by facilitating separation, recycling and recovery of catalyst. In the oxidation of alcohols, supports also control the outcome of the reaction. This review aims to systematically discuss the recent developments in the selective oxidation of alcohols catalyzed by supported gold nanoparticles. We draw attention to the impressive progress that has taken place in the oxidation of alcohols in the last thirteen years, leading to several green, sustainable and highly efficient protocols. The effect of a support on the remarkable properties of gold nanoparticles in terms of its catalytic activity, selectivity, recyclability, and stability is discussed at length. Mechanistic aspects of these conversions are discussed in brief.

Poly(styrene-p-hydroxamic acids) : synthesis, and ion exchange separation of rare earths

Six new poly(styrene-p-hydroxamic acids) have been synthesised, characterised and their physico-chemical properties have been determined. These polymers are used as chelating ion-exchange resins for the separation and determination of rare earths. The method is used for the determination of lanthanum, cerium, neodymium and yttrium in the synthetic, standard and environmental samples.

Gold nanoparticles supported on dendrimer@resin for the efficient oxidation of styrene using elemental oxygen

Highly dispersed AuNPs of sizes 2–5 nm were deposited onto third generation PAMAM dendrimers attached to XAD-4. The nanocatalyst thus prepared was characterised by SEM, TEM, BET etc. The catalyst showed remarkable stability and activity towards the oxidation of styrene. Reaction parameters such as the nature of the oxidant, solvent, catalyst concentration, temperature and reaction time were investigated and the reaction conditions were optimized. Furthermore, the recyclability and stability of the AuNPs supported on dendrimers@resin was established. The results demonstrate that epoxidation can be carried out using molecular oxygen and the prepared heterogeneous gold nanocatalyst possesses potential applications for green and sustainable development of epoxides.

Synthesis, characterization and applications of poly(β-styryl) hydroxamic acids

The synthesis and properties of poly(β-styryl) hydroxamic acids as ion exchange resins are described. The chelating properties of the resins are determined. The chromatographic separation of uranium(VI) from lanthanides is also described.

A chromogenic calixarene hydroxamic acid for the sequential separation of Ti(IV) and Zr(IV)

A new chromogenic calixarene with hydroxamic acid as chelating agent was synthesized by partial reduction of nitrocalixarene which was subsequently coupled with coumarin chloride. The reagent showed selective and quantitative extraction of Ti(IV) into chloroform at 6 M HCl and that of Zr(IV) at 0.5 M HCl. A facile liquid-liquid extraction method for the separation and spectrophotometric determination of Ti(IV) and Zr(IV) has been proposed. The validity of the method was checked by separating several synthetic mixtures. The method was successfully applied to the analysis of piezoelectric lead-zirconium-titanate (PZT) samples. The method shows remarkable simplicity and selectivity. The method can also be used for the determination of Ti(IV) and Zr(IV) in various environmental samples.

A Study on Complexation and Transport of Cr(III) Through a Chromogenic Aza Crown Liquid Membrane

A new chromogenic aza-crown-ether N-(8-hydroxyquinoline-7-methylene)-4-azadibenzo-18-crown-6-ether (HQMADCE) was synthesized through the condensation reaction of 4-azadibenzo-18-crown-6-ether, 8-hydroxy quinoline and formaldehyde. The synthesized chromogenic crown was characterized by various spectroscopic techniques and its complexation with Cr(III) was studied. The parameters like extraction constant (Kex), stability constant (β), free energy change (ΔG), enthalpy change (ΔH) and change in entropy (ΔS) were calculated. Subsequently transport of Cr(III) through a bulk liquid membrane containing HQMADCE as carrier was studied. The permeation of metal was investigated as a function of various experimental variables viz. pH, carrier concentration, metal concentration and time. Furthermore, interference by other ions was also studied.

A PLA–TiO2 particle brush as a novel support for CuNPs: a catalyst for the fast sequential reduction and N-arylation of nitroarenes

The present study describes the synthesis and characterization of dispersible copper nanoparticles on a PLA–TiO2 particle brush and their catalytic efficiency in conducting sequential reactions. The prepared CuNP@PLA–TiO2 was characterized using various techniques like SEM, TEM, EDAX, FT-IR, TGA, XRD and UV-vis spectroscopy. The support controlled the size of the nanoparticles between 2–6 nm and prevented their agglomeration during catalysis. A zeta potential of −70.3 mV was measured for the dispersed catalyst, which indicated its high stability in solution. The nanoparticles were effectively used for the synthesis of biphenyl amines from nitro arenes by sequentially carrying out reduction and N-arylation in a single pot. The short reaction time of N-arylation and recyclability are the hallmark of the developed catalytic system.

Microwave Assisted Hydrogenation of Olefins by PdNPs@Polystyrene Resin using Gas Addition Kit: A Robust & Sustainable Protocol

Polystyrene (PS) resin bead supported palladium nanoparticles (Pd NPs@PS resin) were prepared and their catalytic activity for the hydrogenation of olefins was investigated under microwave heating. The hydrogenation of styrene was effectively carried out in EtOH/H2O, in the presence of 0.00035 mmol of the catalyst to afford the corresponding ethylbenzene in high yield within 20 min under microwave heating. The catalyst efficiency measured in terms of turn over number (TON) and turn over frequency (TOF) was found to be 2829 and 8573 (h−1), respectively. The encapsulated palladium nanoparticles were easily recovered by a simple filtration method and reused several times without significant loss in their catalytic activity. Further, the method showed a wide substrate scope under mild reaction conditions, making it a green versatile and highly sustainable protocol.

Polymer Resins as Nanoreactors for the Synthesis of Nanoparticles and Their Catalytic Application in C-C Coupling

Abstract In the last two decades nanoparticles have emerged as sustainable alternatives to conventional materials—as robust, high surface area heterogeneous catalysts. The nanosize of the particles increases the exposed surface area of the active component of the catalyst, thereby dramatically enhancing the contact between reactants and catalyst, thus mimicking homogeneous catalysis. At the same time their insolubility in reaction solvents renders them easily separable from the reaction mixture like heterogeneous catalysts, which in turn makes the product isolation stage effortless. Macroporous and gel-type resins are available in the market, and the latter can be synthesized in the lab. They are widely used as ion exchangers and solid-phase support in organic synthesis. The micropores of the resin can act as templates for the synthesis of nanoparticles without any additional capping agents. The nanoparticles that are intimately embedded in the porous network can resist agglomeration and provide excellent recyclability. This chapter discusses the research and development in the field of resin supported metal nanoparticle catalyzed carbon-carbon coupling reactions such as Suzuki, Heck, Sonogashira, Hiyama etc., that are routinely used in the synthesis of complex organic molecules. Besides this, general methods of synthesis, characterization, recyclability, and mechanistic aspects are briefly discussed.