Gopal L. Tembe

Bio: Gopal L. Tembe is an academic researcher from Reliance Industries. The author has contributed to research in topics: Catalysis & Polymerization. The author has an hindex of 13, co-authored 42 publications receiving 444 citations.

Catalytic oxidation by polymer-supported copper(II)-L-valine complexes

Abstract: Anchoring of an amino acid l -valine on cross-linked styrene–divinyl benzene was carried out in presence of a base. Reaction of cupric acetate with the polymeric ligand resulted in chelate formation with Cu(II) ion. The immobilized Cu(II) catalysts were characterized by elemental analyses, IR, UV-Vis, SEM, ESR and thermal analysis. Physico-chemical properties like surface area, apparent bulk density, pore volume, etc. have been determined. The supported Cu(II) complexes behave as versatile catalysts in the oxidation of various substrates such as benzyl alcohol, cyclohexanol and styrene in presence of t -butyl hydroperoxide as oxidant. The effect of reaction conditions on conversion and selectivity to products has been studied in detail. Preliminary kinetic experiments reveal that the Cu(II) complexes attached to polymer matrix can be recycled about four times with no major loss in activity.

Catalytic ring-opening polymerization of l-lactide by titanium biphenoxy-alkoxide initiators

Abstract: Six different titanium biphenolate complexes were synthesized and investigated as initiators for the ring opening polymerization of l -lactide in the bulk phase but typically below the degradation temperature of the monomer. All the titanium complexes are effective in forming polylactide with good conversions. The nature and steric bulk of the phenolic ligands coordinated to the central titanium greatly influence polymer properties. In all cases the PLA obtained display low molecular weights and narrow disperisities. Both 1H and 13C NMR spectra indicate the polymers to be essentially isotactic in nature. High crystallinity and controlled morphology of polylactides are uniquely different compared to conventional high molecular weight PLA obtained with tin based initiator.

Catalytic oxidation of alkanes and alkenes by polymer-anchored amino acid-ruthenium complexes

Abstract: A synthetic strategy was developed to anchor an amino acid, l -valine, on to chloromethylated styrene–divinyl benzene co-polymer beads with 6% and 8% cross-linking. The polymeric ligands containing bidentate N,O donor sites were treated with a solution of ruthenium(III)chloride to form the metal complex on the support. These immobilized Ru(III) complexes were characterized by elemental analyses, FT-IR, ESR, SEM and thermal analysis. Physico-chemical properties of the supported catalysts were also studied. The catalytic oxidation of cyclohexane and toluene were investigated using the catalysts in presence of tert -butyl hydroperoxide as the terminal oxidant at ambient and at 45 °C. In the case of cyclohexane the formation of cyclohexanol and cyclohexanone were observed. Benzaldehyde was selectively obtained with toluene as substrate. The catalysts are also active in the epoxidation of olefins such as styrene and norbornylene. Recycling studies indicate that the catalyst can be recycled three to four times without significant degradation of polymer matrix. The probable mechanistic pathway has been described.

Synthesis and catalytic activity of Fe(III) anchored to a polystyrene–Schiff base support

Abstract: Cross-linked styrene-divinylbenzene copolymer was functionalized into bidentate Schiff base bearing ligands. Immobilization of iron(III) on to the polymer matrix resulted in the synthesis of catalytically active metal complexes. These supported catalysts were found to be effective in the epoxidation of cis-cyclooctene and styrene in presence of tert-butylhydroperoxide under mild conditions. The influence of various reaction parameters on conversion and selectivity to products of epoxidation has been discussed.

Cyclohexane oxidation continues to be a challenge

Abstract: Many efforts have been made to develop new catalysts to oxidize cyclohexane under mild conditions. Herein, we review the most interesting systems for this process with different oxidants such as hydrogen peroxide, tert -butyl hydroperoxide and molecular oxygen. Using H 2 O 2 , Na-GeX has been shown to be a most stable and active catalyst. Mesoporous TS-1 and Ti-MCM-41 are also stable, but the use of other metals such as Cr, V, Fe and Mo leads to leaching of the metal. Homogeneous systems based on binuclear manganese(IV) complexes have also been shown to be interesting. When t -BuOOH is used, the active systems are those phthalocyanines based on Ru, Co and Cu and polyoxometalates of dinuclear ruthenium and palladium. Microporous metallosilicates containing different transition metals showed leaching of the metal during the reactions. Molecular oxygen can be used directly as an oxidant and decreases the leaching of active species in comparison to hydrogen peroxide and tert -butyl hydroperoxide. Metal aluminophosphates (metal: Mn, Fe, Co, Cu, Cr V) are active and relatively stable under such conditions. Mn-AlPO-36 yields directly adipic acid, but large amounts of carboxylic acids should be avoided, as they cause metal leaching from the catalysts. Rare earth exchanged zeolite Y also shows good selectivity and activity. In the last part of the review, novel alternative strategies for the production of cyclohexanol and cyclohexanone and the direct synthesis of adipic acid are discussed.