S.B. Halligudi

Zeolite encapsulated ruthenium and cobalt schiff base complexes catalyzed allylic oxidation of α-pinene

Abstract The allylic oxidation of α-pinene to its oxygenated products has been investigated using bis-salicylaldehyde- o -phenylenediimine (Saloph) and substituted (Cl, Br and NO 2 ) Salophs of ruthenium and cobalt in zeolite-Y. The oxidation of α-pinene resulted in various products like camphene, 2,7,7-trimethyl SS pinene (3-oxatricyclo-4,1,1,02,4-octane), 2,3-epoxy (epoxy), campholene aldehyde and d -verbenone. Ru(III)Saloph-Y showed higher catalytic activity than Co(II)Saloph-Y with a turn over frequency >18xa0000 (mole of α-pinene oxidized per mole of Ru per hour) at 100xa0°C and 30xa0atm air. The selectivity for epoxy and d -verbenone was found to be higher in α-pinene oxidation with both Ru and Co catalyst systems. The catalytic performance of the encapsulated complexes was better than the neat complexes. Air was a more convenient oxidant than H 2 O 2 and TBHP. No leaching of the metal complex in encapsulated systems were observed in the oxidation reaction. X-ray diffraction (XRD), thermogravimetric and X-ray photoelectron spectroscopy (XPS) studies supported the fact that the metal complexes were entrapped inside zeolite cages and not on its surface. Electronic spectra of the reaction mixture indicated that the oxidation of α-pinene proceeds through a free radical mechanism involving peroxoruthenium species as an active intermediate.

Oxidation by molecular oxygen using zeolite encapsulated Co(II)saloph complexes

Abstract Co(II) Schiff base complexes encapsulated in zeolite-Y having the general formula Co(II)L-Y (where L=salicylaldehyde-o-phenylenediimine (saloph), chloro-salicylaldehyde-o-phenylenediimine (Cl-saloph), bromo-salicylaldehyde-o-phenylenediimine, (Br-saloph) and nitro-salicylaldehyde-o-phenylenediimine, (nitro-saloph) and Y=zeolite Na-Y) have been synthesized and characterized for their physicochemical and spectroscopic properties. The neat and encapsulated catalysts were tested for their catalytic activities in the oxidation of β-isophorone (BIP) to keto-isophorone (KIP) using air as an oxidant at ambient conditions of pressure and temperature. It was found that the catalytic activities of encapsulated catalysts were higher than their homogeneous analogues in the oxidation reaction. Among the catalysts, however, Co(II)Cl-saloph neat and its encapsulated forms were comparatively more active than other catalysts tested in the oxidation reaction. The catalytic activities of neat and their encapsulated forms followed the same trend and the order of reactivities were: Co(II)Cl-saloph>Co(II)Br-saloph>Co(II)nitro-saloph>Co(II)saloph. Kinetics of Co(II)Cl-saloph-Y catalyzed aerial oxidation of BIP was investigated and the rates of oxidation have been obtained for variations made in catalyst, substrate and oxidant concentrations. Mechanism of oxidation involving Co(III)ue5f8Oue5f8O superoxo intermediate species in the oxidation of BIP has been established by UV–VIS using Co(II)saloph neat complex. Effect of temperature on the rates of oxidation of BIP was also studied and from Arrhenius plot, thermodynamic activation parameters estimated have been reported.

Oxidation of adamantane by urea hydroperoxide using vanadium complex anchored onto functionalized Si-MCM-41

Abstract A tetradentate complex 3-[ N , N ′-bis-3-(salicylidenamino)ethyltriamine] vanadium(IV), VO(Salten) was grafted onto MCM-41 through a covalently linked organic moiety. This covalently anchored complex was characterized by FTIR, X-ray diffraction, thermogravimetric and differential thermogravimetric (TG–DTA) and BET measurements. The structure of the support was retained after anchoring the complex. Based on the spectroscopic evidences it was envisaged that the complex retains its structure inside the channels and it hangs like a pendant inside MCM-41. This anchored complex allowed the catalytic oxidation of adamantane using urea hydroperoxide (UHP) as the oxidizing agent at 60xa0°C and atmospheric pressure. The reaction conditions have been optimized towards maximum conversion by varying different parameters. No leaching of the complex was observed after the reaction.

Au and Au-Pt bimetallic nanoparticles in M CM-41 materials: applications in co preferential oxidation

Abstract Nanosized Au and Au-Pt bimetallic particles of different atomic ratios were synthesized from HAuCl 4 and HPtCl 6 inside the channels of amine functionalized MCM-41. These were characterized through chemical analysis, XRD and TEM. The size of the bi-metallic particles was found to be in the range of 2-4 nm. Their catalytic activities were evaluated in simulated gas mixtures that typically contain 0.5 and 0.96% CO in presence of large proportions (≈74%) of H 2 . The catalysts that contain higher concentrations of Pt were found to be active and offer good CO preferential oxidation activity. Catalysts that contain an optimum amount of Au along with Pt have shown highest activities at lower temperatures.

Hydroamination of Terminal Alkynes by Amines Catalyzed by Copper Heteropoly Salts: A Simple Approach Towards Imine Synthesis

The hydroamination reaction offers a very attractive route for the synthesis of alkylated amines and their de- rivatives with no byproduct formation. Heterogeneous intermolecular hydroamination reactions of alkynes with aromatic amines using different inexpensive copper salts of hetropolyacid catalysts were investigated. Among heteropoly salts, copper salts of silicotungstic acid showed highest activity. Reactivity of aromatic amines increased with increase in its ba- sicity. Acidity in heterogeneous catalyst can act as promoter in hydroamination of alkynes.

Immobilized Molybdovanadophosphoric Acid for Selective Oxidations

In this review, we have summarized our work on the immobilization of molybdovanadophosphoric acids onto mesoporous silica and mesoporous carbon by different approaches such as amine functionalization and ionic liquid functionalization. All catalyst materials were well characterized by various ex-situ and in situ techniques for their structural integrity and physico-chemical properties. These materials were tested in different selective oxidation processes to develop environmentally benign protocols for the synthesis of fine chemicals and tried to study their mechanisms.

Supported Heteropoly Acids and Multicomponent Polyoxometalates as Eco-Friendly Solid Catalysts for Bulk and Fine Chemicals Synthesis

Supported heteropoly acids are an important class of eco-friendly solid catalysts which offer strong acidity or redox properties. Part 1 of this chapter gives the detailed description of Keggin heteropoly acids such as silicotungstic acid (STA) and phosphotungstic acid (PTA) supported on zirconia as thermally stable, reusable solid catalysts which can be used for variety of organic transformations such as alkylation, acylation, and allylation. The catalysts are characterized by various techniques such as X-ray diffraction, N2 sorption measurements, DTG–DTA, UV–Vis spectroscopy, FTIR pyridine adsorption, NH3-TPD, FT-Raman, and 31P MAS NMR. These supported HPA catalysts found to be highly active and selective with a long catalytic lifetime in the discussed reactions. Part 2 of this chapter describes the preparation of inorganic–organic hybrid materials by immobilization of molybdo-vanadophosphoric acids onto mesoporous silicas such as MCM-41, MCM-48, and SBA-15. The study has been further extended to mesoporous carbon and ethane-bridged SBA-15. All catalyst materials were characterized by elemental analysis, FTIR, N2 physisorption measurements, XRD, UV/Vis, XPS, CP-MAS-NMR, SEM, and TEM for their structural integrity and physicochemical properties. These materials were applied for various selective and controlled oxidation processes to develop environmentally benign protocols for synthesis of fine chemicals and tried to study their mechanisms. Further, a simple cation exchanged form of H5[PMo10V2O40]·32.5H2O supported on ionic liquid-modified SBA-15 (V2ILSBA) and its application in catalyzed aerobic oxidation of primary and secondary alcohols to corresponding aldehydes and ketones with no trace of over oxidation has been discussed.