Anuj S. Sharma

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.

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.

Mesomorphic properties of liquid crystalline compounds with chalconyl central linkage in two phenyl rings

ABSTRACT In order to investigate the influence of the central linking group and the effect of flexibility on mesomorphism, we have synthesised a newly homologous series 3-(3-butoxyphenyl)-1-(4-n-alkoxy phenyl) prop-2-en-1-one (series-l) consisting of 13 homologues C1–C8, C10, C12, C14, C16 and C18. In the present series, mesophase commences from the C6 homologue. C1–C5 homologues did not exhibit liquid crystalline (LC) property, while C6–C12 homologues exhibited an enantiotropic nematic phase and the rest of the homologues C14–C18 displayed monotropic SmC and nematic mesophase. The transition temperatures of the synthesised compounds were determined by an optical polarising microscopy equipped with a heating stage. All newly synthesised compounds were confirmed by 1H-NMR, 13C-NMR, IR and elemental analysis.

Microwave assisted one pot three component synthesis of propargylamine, tetra substituted propargylamine and pyrrolo[1,2-a]quinolines using CuNPs@ZnO–PTh as a heterogeneous catalyst

The present work deals with the investigation and catalytic activity analysis of copper nanoparticles (CuNPs) supported on a zinc oxide–polythiophene (ZnO–PTh) nanocomposite. CuNPs@ZnO–PTh was prepared using a simple impregnation method and characterized using various techniques (XRD, XPS, FT-IR, SEM, ICP-AES, TEM, TEM-EDS and EDAX). HR-TEM indicates that CuNPs supported on ZnO–PTh were of spherical shape and distributed uniformly over the nanocomposite with a particle size of ∼2–8 nm. Further, the synthesized CuNPs@ZnO–PTh was used as a heterogeneous catalyst for the synthesis of propargylamine, tetra substituted propargylamine (A3 and KA2 coupling reactions) and pyrrolo[1,2-a]quinoline (A3 coupling reactions) using a microwave technique in ethylene glycol as a recyclable, green and biodegradable solvent with 98% yield. The high catalytic activity of CuNPs@ZnO–PTh was due to the high surface area and synergetic effect of both the CuNPs and ZnO–PTh nanocomposite, which makes it cost effective and environmentally benign with high atom economy. Considering all above facts, this protocol was found to be more efficient and sustainable as compared to the available commercial methods.

Synthetic pathway for a new calamitic series of liquid crystal: Comparison with corresponding linkage group

GRAPHICAL ABSTRACT ABSTRACT Two homologous series based on three linking groups have been synthesized and characterized by elemental analyses and spectroscopic techniques such as Fourier transform infrared [FT-IR] and protonmagnetic resonance magnetic resonance [1H-NMR] spectroscopy. The mesomorphic properties of these compounds were observed by optical polarized light microscopy (POM) and differential scanning calorimetry (DSC). In this present investigation, we have synthesized two homologous series viz. 4-(3-oxo-3-(4-((-3-phenylallylidene) amino) phenyl) prop-1-en-1-yl) phenyl 4-n-alkoxy benzoate) (series-1) and 4-(3-oxo-3-(4-((-3-phenylallylidene) amino) phenyl) prop-1-en-1-yl) phenyl 3-(4-n-alkoxy phenyl) acrylate (series-2). Both of the series are differing with respect to the first linking group. All the homologous in the following series exhibits LC phase on heating as well as cooling condition except first two homologue (C1, C2) in series-1 and three homologue (C1, C2, C3) in series-2.

Synthesis and mesomorphic properties of new chalconyl-ester based liquid crystals: The effect of tail group

GRAPHICAL ABSTRACT ABSTRACT A new homologous series viz. 4-(3-(3, 4-dioctadecyloxy) phenyl)-3-oxoprop-1-en-1-yl) phenyl-3-(4-n-alkoxy phenyl) cinnamate) based on two linking groups have been synthesized and characterized. The mesomorphic properties of these compounds were observed by optical polarized light microscopy (POM) and confirmed by differential scanning calorimetry (DSC). All synthesized compounds exhibited LC behaviour except compound C1. Thermal stability of smectic and nematic phase of present series are 79.0°C and 120.0°C whose temperature range is vary from 14 to 20°C and 24 to 56°C respectively. The mesomorphic properties of present series were compared with other structurally related mesogenic homologous series to evaluate the effects of tail group on mesomorphism.

Columnar self-assembly of bowl shaped fluorescent liquid crystals based on calix[4]arene with Schiff base units

A new family of bowl-shaped molecules with a calix[4]arene rigid core and appended on four-sides, that display a wide range of hexagonal columnar phases, has been synthesised and well characterized. The thermal behaviours of the present compounds were established using a combination of polarising optical microscopy (POM), differential scanning calorimetry (DSC) and a high-temperature powder X-ray diffraction method (XRD). It is found that all of the synthesised materials show an enantiotropic hexagonal columnar liquid crystal phase. The structural and conformation characterization of these newly synthesised compounds was achieved by FT-IR, 1H NMR, and 13C NMR spectroscopy. All of the synthesised compounds exhibited good blue luminescence in solution under long wavelength UV light. To explore the structure property correlations, the alkoxy side chain group was varied from a lower alkyl spacer to a higher alkyl spacer on the lower rim of the calix[4]arene. The present research specified that the introduction of linking groups on the lower rim with an n-alkoxy side group is an influential approach to obtaining a supramolecular bowl shape liquid crystal which has good thermal and photophysical behaviour.

New hockey stick shaped amino allylidene (‒N˭CH‒CH˭CH) based compounds: Effect of linkage group on mesomorphic properties

GRAPHICAL ABSTRACT ABSTRACT Two nonlinear hockey stick shaped homologous series based on three linking groups have been synthesized and characterized by elemental analyses and spectroscopic techniques. The mesomorphic properties of these compounds were observed by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). In this present investigation, we have synthesized two homologous series viz. 2-((3-phenyl allylidene) amino) phenyl 4-((4-n-alkoxy benzylidene) amino) benzoate (series-1) and 4-((2-((3-phenyl allylidene) amino) phenoxy) carbonyl) phenyl-4-n-alkoxy benzoate (series-2). Both the series are differing with respect to first linking group. In series-1, comp.C4–C18 shows nematic as well as smectic phase while in series-2, comp.C10–C16 shows smectic and nematic phase while comp.C4–C18 shows only nematic phase.

Synthesis and characterization of rigid rode shape homologous series: Effect of tail iodo group

GRAPHICAL ABSTRACT ABSTRACT In this study, the synthesis, structural characterization and mesomorphic properties of newly thirteen calamitic rod-shaped compounds derived from chalcone and 4-n-alkoxy benzoic acid. Here we present, chalcone as central group and terminal side substituted iodo (−I) group containing homologous series. Comp.C1 displayed nonmesogenic nature, while comp.C3 to comp.C18 shows enantiotropic smectic plus nematic property except comp.C2 which show only nematic phase. It is shown that chalcone as central linking unit favors a calamitic liquid crystalline behaviour in molecules. Phase transition temperatures of present synthesised compounds were determined by optical polarising microscopy (POM), differential scanning calorimetric (DSC). Thermal stabilities for smectic and nematic mesophases are 150.18 and 163.58 respectively.

Calamitic-rod-shaped mesogens based on chalcone esters comprising varying alkoxy and lauryl ester chains: Synthesis, mesomorphism and computational study

GRAPHICAL ABSTRACT ABSTRACT In this study we have synthesized a new class of compounds incorporating of chalconyl-ester and terminally substituted lauryl group. A series of new chalcones with three aromatic rings is synthesized and characterised by elemental analyses and spectroscopic techniques such as Fourier transform infrared [FT-IR] and proton magnetic resonance magnetic resonance [1H NMR] spectroscopy. The mesomorphic properties of these compounds were observed by optical polarized light microscopy (POM) and confirmed by differential scanning calorimetry (DSC). It is found that all the prepared materials display enantiotropic LCs phases except first two homologue in present series. The lower member comp. (C3 to C6) display only SmC phase while comp. (C7 to C12) shows smectic C as well as nematic phase. The higher member comp. (C14 to C18) display only nematic phase in heating and cooling condition. To get more insights, the HOMO, LUMO studies are carried out which supports intramolecular charge transfer interactions in this class of mesogens.