• Praveen Kumar

      Articles written in Journal of Chemical Sciences

    • Formation of phosphonates and pyrophosphates in the reactions of chlorophosphate esters with strong organic bases

      K V P Pa Van Kumar K Praveen Kumar M Vijjulatha K C Kumara Swamy

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      The compounds S(6-t-Bu-4-Me-C6H2O)2P(O)Cl (1), CH2(6-t-Bu-4-Me-C6H2O)2P(O)Cl (2) and (2,2′-C20H12O2)P(O)Cl (3) react with diazabicycloundecene (DBU) to give rise to, predominantly, the phosphonate compounds [S(6-t-Bu-4-Me-C6H6O)2P(O)(DBU)]+[Cl] (4), [CH2(6-t-Bu-4-Me-C6H2O)2P(O) (DBU)]+[Cl] (5) and [(2,2′-C20Hi2O2)P(0)(DBU)]+[Cl]- (6). The first two compounds could be isolated in the pure state. In analogous reactions of 1 and 2 with diazabicyclononene (DBN) or N-methyl imidazole, only the pyrophosphates [S(6-t-Bu-4-Me-C6H2O)2P(O)]2O (7) and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)]2O (8) could be isolated, although the reaction mixture showed several other compounds in the phosphorus NMR. A possible pathway for the formation of phosphonate salts is proposed. The X-ray crystal structures of4,7 and8 are also discussed.

    • Unusual products in the reactions of phosphorus(III) compounds with N=N, C≡C or conjugated double-bonded systems

      K C Kumara Swamy E Balaraman M Phani Pavan N N Bhuvan Kumar K Praveen Kumar N Satish Kumar

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      The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated acetylenes with PIII compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC6H3O)P (μ-N-t-Bu)2P+[(NH-t-Bu)N[(CO2]-i-Pr)(HNCO2-i-Pr)]](Cl-)(2-t-Bu-4-MeC6H3OH)(23)and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)C(CO2Me)C-(CO2Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction.

    • Controlling dynamics in diatomic systems

      Praveen Kumar Harjinder Singh

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      Controlling molecular energetics using laser pulses is exemplified for nuclear motion in two different diatomic systems. The problem of finding the optimized field for maximizing a desired quantum dynamical target is formulated using an iterative method. The method is applied for two diatomic systems, HF and OH. The power spectra of the fields and evolution of populations of different vibrational states during transitions are obtained.

    • Co-catalyst free Titanate Nanorods for improved Hydrogen production under solar light irradiation

      N LAKSHMANA REDDY D PRAVEEN KUMAR M V SHANKAR

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      Harnessing solar energy for water splitting into hydrogen $ (H_{2})$ and oxygen $(O_{2})$ gases in the presenceof semiconductor catalyst is one of the most promising and cleaner methods of chemical fuel $ (H_{2})$ production.Herein, we report a simplified method for the preparation of photo-active titanate nanorods catalystand explore the key role of calcination temperature and time period in improving catalytic properties. Bothas-synthesized and calcined material showed rod-like shape and trititanate structure as evidenced from crystalstructure and morphology analysis. Notably, calcination process affected both length and diameter of thenanorods into shorter and smaller size respectively. In turn, they significantly influenced the band gap reduction,resulting in visible light absorption at optimized calcination conditions. The calcined nanorods showedshift in optical absorption band edge towards longer wave length than pristine nanorods. The rate of hydrogengeneration using different photocatalysts was measured by suspending trititanate nanorods (in the absence ofco-catalyst) in glycerol-water mixture under solar light irradiation. Among the catalysts, nanorods calcined at$250^{0}C$ for 2 hours recorded high rate of H2 production and stability confirmed for five cycles. Photocatalyticproperties and plausible pathway responsible for improved H2 production are discussed in detail.

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