Mahasweta Nandi

Highly ordered acid functionalized SBA-15: a novel organocatalyst for the preparation of xanthenes.

Post-synthesis modification of SBA-15 has been carried out to design highly ordered acid functionalized hybrid mesoporous organosilica, AFS-1. This material has been used as an efficient heterogeneous organocatalyst for the syntheses of xanthenes under mild conditions in the absence of any other metal co-catalyst.

Functionalized mesoporous silica supported copper(II) and nickel(II) catalysts for liquid phase oxidation of olefins

Highly ordered 2D-hexagonal mesoporous silica has been functionalized with 3-aminopropyltriethoxysilane (3-APTES). This is followed by its condensation with a dialdehyde, 4-methyl-2,6-diformylphenol to produce an immobilized Schiff-base ligand (I). This material is separately treated with methanolic solution of copper(II) chloride and nickel(II) chloride to obtain copper and nickel anchored mesoporous materials, designated as Cu-AMM and Ni-AMM, respectively. The materials have been characterized by Fourier transform infrared (FT-IR) and UV-vis diffuse reflectance (DRS) spectroscopy, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), N(2) adsorption-desorption studies and (13)C CP MAS NMR spectroscopy. The metal-grafted mesoporous materials have been used as catalysts for the efficient and selective epoxidation of alkenes, viz. cyclohexene, trans-stilbene, styrene, α-methyl styrene, cyclooctene and norbornene to their corresponding epoxides in the presence of tert-butyl hydroperoxide (TBHP) as the oxidant under mild liquid phase conditions.

An improved high yielding immobilization of vanadium Schiff base complexes on mesoporous silica via azide―alkyne cycloaddition for the oxidation of sulfides

Azide–alkyne [3+2] cycloaddition “click reaction” was found to be a simple yet improved approach for the efficient immobilization of oxo–vanadium(IV) tridentate Schiff base complexes to mesoporous silica via covalent attachment as it occurred under mild reaction conditions and provided high catalyst loading compared to the direct immobilization of oxo–vanadium(IV) tridentate Schiff base complex to 3-chloropropylsilyl functionalized silica support.

Four μ4-oxo-bridged copper(II) complexes: magnetic properties and catalytic applications in liquid phase partial oxidation reactions

Four copper(II) complexes, [Cu(4)(O)(L(n))(2)(CH(3)COO)(4)] with N(2)O-donor Schiff-base ligands, where HL(1) = 4-methyl-2,6-bis(cyclohexylmethyliminomethyl)phenol for complex 1, HL(2) = 4-methyl-2,6-bis(phenylmethyliminomethyl)phenol for complex 2 x CH(3)CN, HL(3) = 4-methyl-2,6-bis(((3-tri-fluoromethyl)phenyl)methyliminomethyl)phenol for complex 3, HL(4) = 4-methyl-2,6-bis(((4-tri-fluoromethyl)phenyl)methyliminomethyl)phenol for complex 4, were synthesized and characterized by elemental analysis, FT-IR, UV-vis spectroscopy and finally by single crystal X-ray diffraction study. X-Ray analysis reveals that all of these are mu(4)-oxo-bridged tetrameric copper(II) complexes. Four copper atoms arrange themselves around an oxygen atom tetrahedrally. Magnetic susceptibility measurements show the existence of very strong antiferromagnetic coupling among these ions (J = -210.1 to -271.3 cm(-1)), mediated by the oxygen atoms. Catalysis of the epoxidation of cyclohexene, styrene, alpha-methylstyrene and trans-stilbene by these complexes has been carried out homogeneously as well as heterogeneously by immobilizing the metal complexes over 2D-hexagonal mesoporous silica. The results obtained in both the catalytic conditions show that the olefins are converted to the respective epoxides in good yield together with high selectivity.

Synthesis of mesoporous hollow silica nanospheres using polymeric micelles as template and their application as a drug-delivery carrier

Mesoporous hollow silica nanospheres with uniform particle sizes of 31-33 nm have been successfully synthesized by cocondensation of tetramethoxysilane (TMOS) and alkyltrimethoxysilanes [RSi(OR)3], where the latter also acts as a porogen. ABC triblock copolymer micelles of poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) with a core-shell-corona architecture have been employed as a soft template at pH 4. The cationic shell block with 2-vinyl pyridine groups facilitates the condensation of silica precursors under the sol-gel reaction conditions. Phenyltrimethoxysilane, octyltriethoxysilane, and octadecyltriethoxysilanes were used as porogens for generating mesopores in the shell matrix of hollow silica and the octadecyl precursor produced the largest mesopore among the different porogens, of dimension ca. 4.1 nm. The mesoporous hollow particles were thoroughly characterized by small-angle X-ray diffraction (SXRD), thermal (TG/DTA) and nitrogen sorption analyses, infra-red (FTIR) and nuclear magnetic resonance ((13)C-CP MAS NMR and (29)Si MAS NMR) spectroscopies, and transmission electron microscopy (TEM). The mesoporous hollow silica nanospheres have been investigated for drug-delivery application by an in vitro method using ibuprofen as a model drug. The hollow silica nanospheres exhibited higher storage capacity than the well-known mesoporous silica MCM-41. Propylamine functionalized hollow particles show a more sustained release pattern than their unfunctionalized counterparts, suggesting a huge potential of hollow silica nanospheres in the controlled delivery of small drug molecules.

Triazine functionalized ordered mesoporous organosilica as a novel organocatalyst for the facile one-pot synthesis of 2-amino-4H-chromenes under solvent-free conditions

A highly ordered 2D-hexagonal mesoporous material functionalized with a triazine moiety has been synthesized via post-synthetic modification of mesoporous SBA-15 with thiols followed by a thiol–ene click reaction using 2,4,6-triallyloxy-1,3,5-triazine. A facile one-pot three-component condensation reaction of aromatic aldehyde, malononitrile and activated phenols for the synthesis of a diverse range of 2-amino-4H-chromenes has been efficiently catalyzed over this novel mesoporous metal-free heterogeneous organocatalyst under solvent-free reaction conditions. Further, this organocatalytic reaction is waste-free, easy to work-up and efficiently reused. The organic products have been isolated from the reaction mixture by using easily disposable solvents and can be easily purified by re-crystallization.

Hybrid porous tin(IV) phosphonate: an efficient catalyst for adipic acid synthesis and a very good adsorbent for CO2 uptake.

A new porous organic-inorganic hybrid tin phosphonate material has been synthesized hydrothermally, which shows a Brunauer-Emmett-Teller surface area of 723 m(2) g(-1) and it adsorbs 4.8 mmol g(-1) CO(2) at 273 K and 5 bar pressure. The material also shows remarkable catalytic activity in one-pot liquid phase oxidation of cyclohexanone to adipic acid under eco-friendly conditions.

Organic–inorganic hybrid porous sulfonated zinc phosphonate material: efficient catalyst for biodiesel synthesis at room temperature

A new porous zinc phosphonate material (HZnP-1) has been synthesized via the reaction between p-xylenediphosphonic acid and anhydrous ZnCl2 under hydrothermal and mildly acidic conditions (pH ∼ 5) in the absence of any structure directing agent. The phenyl group of this material has been sulfonated with concentrated sulfuric acid to obtain sulfonic acid functionalized material HZnPS-1. Powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE SEM), N2 sorption, solid state 13C CP MAS and 31P MAS NMR, and FT IR spectroscopic tools are employed to characterize these materials. The crystal structures of both the materials are indexed corresponding to the new orthorhombic phases with unit cell parameters a = 11.00, b = 8.74, c = 14.62 A, α = β = γ = 90° for HZnP-1, and a = 10.65, b = 13.52, c = 15.30 A and α = β = γ = 90° for HZnPS-1. HZnPS-1 showed outstanding catalytic activity and high recycling efficiency for the synthesis of different biodiesel compounds via esterification of long chain fatty acids by using methanol as both reactant and solvent at room temperature. The green and eco-friendly catalytic system described herein can overcome the problem faced by the existing catalytic systems known in biodiesel synthesis, such as drastic conditions (high reaction temperature) and requirement of hazardous organic solvents.

Organic–inorganic hybrid tinphosphonate material with mesoscopic void spaces: an excellent catalyst for the radical polymerization of styrene

A new porous tinphosphonate HSnP-1 has been synthesized through the reaction of butylene-1,4-diphosphonic acid and SnCl4·5H2O under hydrothermal conditions at 453 K for 3 days in the absence of any structure directing agent. Powder X-ray diffraction, transmission and scanning electron microscopies (TEM and SEM), N2 sorption, solid state 13C CP MAS and 31P MAS NMR, UV-vis and FT IR spectroscopic tools are used to characterize the material. The crystallinity of HSnP-1 is sufficiently high under mildly acidic pH conditions and the crystal structure of the material has been indexed to the tetragonal phase with unit cell parameters a = b = 11.52 A, c = 15.84 A, α = β = γ = 90°. The surface area and the pore volume of the material were 338 m2 g−1 and 0.54 cc g−1, respectively. HSnP-1 showed outstanding catalytic activity in the radical polymerization of styrene at room temperature in the presence of aqueous H2O2 as an initiator under solvent-free conditions, whereas in the presence of aprotic solvent it facilitates partial oxidation of styrene to phenylacetaldehyde and acetophenone.

Synthesis of Hierarchical Mesoporous Mn–MFI Zeolite Nanoparticles: A Unique Architecture of Heterogeneous Catalyst for the Aerobic Oxidation of Thiols to Disulfides

An efficient procedure for aerobic oxidation of thiols to disulfides catalyzed by new self‐assembled hierarchical mesoporous Mn–MFI in the presence of air under solvent‐free conditions as well as in aqueous medium is reported. The mesoporosity and Mn4+ loading, together with a highly crystalline microporous pore wall structure of the MFI framework were achieved through a newly designed hydrothermal process. This hydrothermal approach leads to hierarchical self‐assembled mesoporous zeolite structures through isomorphous substitution of Si by Mn and Al. It is shown that Mn‐containing mesoporous zeolites are capable to form disulfide bonds from thiols in the presence of air. The zeolitic materials were characterized by XRD, field‐emission scanning electron microscopy, high‐resolution TEM, X‐ray photoelectron spectroscopy, 29Si NMR, 27Al NMR, and EPR spectroscopy, as well as AAS analysis and N2 sorption studies. N2 sorption analysis revealed high surface areas and narrow pore size distributions (1.2–6.0 nm) for different samples. The mesoporous Mn–ZSM‐5 acted as an efficient heterogeneous catalyst with maximum catalytic activity in the benzenethiol conversion to diphenyldithiol.