National Chemical Laboratory

About: National Chemical Laboratory is a facility organization based out in Pune, Maharashtra, India. It is known for research contribution in the topics: Catalysis & Enantioselective synthesis. The organization has 8891 authors who have published 14837 publications receiving 387600 citations.

Hydrogenation of diene elastomers, their properties and applications : A critical review

Abstract: This chemistry and technology of hydrogenation of diene elastomers have substantially grown during the past decade. New applications of hydrogenated elastomers have emerged. Homogeneous hydrogenation has several advantages over heterogeneous hydrogenation because of its higher selectivity, faster rate and cleaner end products. However, separation of catalysts and recycle/reuse of expensive metals still poses problems. The preferred alternative for the hydrogenation of elastomers in solution is the use of Zeigler type catalyst which are less expensive than the noble metal catalysts like Rh, Pd etc. However, such catalysts are not effective when strongly coordinating groups are present in the elastomer. One approach would be to use transition metals, which have less tendency to coordinate with polar monomers in the elastomer. Research is also warranted in the use of less expensive metals for elastomer hydrogenation (Ni, Co, Ru). Use of large quantities of solvent (to keep the solution viscosity low) is another significant cost center in elastomer hydrogenation. Novel agitator systems/reactor configuration to handle higher concentration of rubber in solution, yet provide adequate heat and mass transfer in gas-liquid hydrogenation reaction, needs to be explored. Hydrogenation of diene elastomers in the latex form using water soluble catalyst appear to be hold great promise at the present time since many diene elastomers (like SBR, CR and NBR etc.) are commercially produced directly in the form of latex. Creative exploitation of biphasic catalysts for hydrogenation is expected to gain momentum since early results look promising. This would require greater fundamental understanding of the aqueous-organic interphase in a latex process and the mechanism of transport of catalytic reagent across this interphase. More studies are needed to achieve homogeneous chemical reaction inside of each individual latex particles.

2,5-dioxido-1,4-benzoquinonediimine (H2L2 ), A hydrogen-bonding noninnocent bridging ligand related to aminated topaquinone: Different oxidation state distributions in complexes [{(bpy)2Ru} 2(μ-H2L)]n (n = 0, + ,2 + ,3 + ,4+) and [{(acac)2Ru}2(μ-H2L)]m (m = 2-, -,0, + ,2 + )

Abstract: The symmetrically dinuclear title compounds were isolated as diamagnetic [(bpy) 2 Ru(μ-H 2 L)Ru(bpy) 2 ]-(ClO 4 ) 2 (1-(ClO 4 ) 2 ) and as paramagnetic [(acac) 2 Ru(μ-H 2 L)Ru(acac) 2 ] (2) complexes (bpy=2,2'-bipyridine; acac - =acetylacetonate = 2,4-pentane-dionato; H 2 L =2,5-dioxido-1,4-benzo-quinonediimine). The crystal structure of 2.2H 2 O reveals an intricate hydrogen-bonding network: Two symmetry-related molecules 2 are closely connected through two NH(H 2 L 2 - )O-(acac - ) interactions, while the oxygen atoms of H 2 L 2 - of two such pairs are bridged by an (H 2 O) 8 cluster at half-occupancy. The cluster consists of cyclic (H 2 O) 6 arrangements with the remaining two exe-H 2 O molecules connecting two opposite sides of the cyclo-(H 2 O) 6 cluster, and oxido oxygen atoms forming hydrogen bonds with the molecules of 2. Weak antiferromagnetic coupling of the two ruthenium(m) centers in 2 was established by using SQUID magnetometry and EPR spectroscopy. Geometry optimization by means of DFT calculations was carried out for 1 2 + and 2 in their singlet and triplet ground states, respectively. The nature of low-energy electronic transitions was explored by using time-dependent DFT methods. Five redox states were reversibly accessible for each of the complexes; all odd-electron intermediates exhibit comproportionation constants K c > 10 8 . UV-visible-NIR spectroelectrochemistry and EPR spectroscopy of the electrogenerated paramagnetic intermediates were used to ascertain the oxidation-state distribution. In general, the complexes 1 n + prefer the ruthenium(n) configuration with electron transfer occurring largely at the bridging ligand (μ-H 2 L n - ), as evident from radical-type EPR spectra for 1 3 + and 1 + . Higher metal oxidation states (III, IV) appear to be favored by the complexes 2 m ; intense long-wavelength absorption bands and Ru I I I -type EPR signals suggest mixed-valent dimetal configurations of the paramagnetic intermediates 2 + and 2.

Genetic diversity across natural populations of three montane plant species from the Western Ghats, India revealed by intersimple sequence repeats.

Abstract: We analysed genetic diversity across the natural populations of three montane plant species in the Western Ghats, India; Symplocos laurina, Gaultheria fragrantissima and Eurya nitida using intersimple sequence repeat (ISSR) markers. These markers revealed genetic diversity within the populations of these plants from Nilgiri and also between two populations of S. laurina from Nilgiri and Amboli. Genetic variation within and between populations was analysed using various parameters such as total heterozygosity (HT), heterozygosity within population (HS), diversity between populations (DST), coefficient of population differentiation (GST), genetic distance (D) and gene flow (Nm). Total heterozygosity (HT) was higher for S. laurina (0.238) than for G. fragrantissima (0.172) and E. nitida (0.182). Two populations of S. laurina, separated by > 1000 km, showed a high within-population variation (53.7%) and a low gene flow (Nm = 0.447). upgma phenograms depicted a tendency of accessions to group according to their geographical locations in all the three plant species. The insight gained into the genetic structure of these plant populations might have implications in developing in situ and ex situ conservation strategies.