Design and Development of Zeolite-Based Catalytic Processes for Aromatics Production

Processes for the production of xylenes, which occur in an integrated aromatic complex, are discussed. A brief overview of the work carried out at Indian Petrochemicals Corporation Limited for the development of zeolite-based catalytic processes for the production of aromatics is presented. This includes xylene isomerization, transalkylation and disproportionation of C₇ and C₉ aromatics for maximization of xylenes, selective disproportionation of toluene and selective alkylation of mono-alkylaromatics to p-dialkylbenzene. Achievements in the commercialization of zeolite-based catalysts and processes for isomerization of m-xylene to p- and o-xylene along with dealkylation of ethylbenzene, and for selective ethylation of ethylbenzene to produce p-diethylbenzene are highlighted.     

Synthesis of chiral 4-hydroxy-2,3-unsaturated carbonyl compounds from 3,4-epoxy alcohols by oxidation: application in the formal synthesis of macrosphelide A

An interesting transformation during the oxidation of 3,4-epoxy alcohols 1a-d, derived from the corresponding homoallylic alcohols, led to the formation of 4-hydroxy-2,3-unsaturated carbonyls 2a-d in very good yields. One of these products 2c was transformed into the functionalised carboxylic acid 5, an advanced stage intermediate from which the total synthesis of macrosphelide A has been reported.     

Amino Acid based cationic surfactants in aqueous solution: physicochemical study and application of supramolecular chirality in ketone reduction

The present study provides a molecular understanding of the origin of the chirality in aqueous micelles and its correlation with the proficiency of stereoselective ketone reduction. The effects of varied headgroup architecture on the surface-active properties as well as on other microstructural parameters were studied and correlated to the structural differences of these naturally occurring amino acid containing surfactants (1-4). Micropolarity sensed by pyrene showed that the micelles prepared using 1-4 are mostly hydrated; particularly large headgroup size surfactant produces more polar environment. A theoretical study was done to quantify the varied spatial dissymmetry for all four surfactants. Asymmetric reduction of prochiral ketones was carried out at the aqueous micellar interface of these chiral amphiphiles by exploiting the supramolecular chirality as evidenced from a circular dichroism study. The enantioselectivity of the reduction process is rationally improved through increase in spatial dissymmetry and steric constraint imposed at the micellar interface by the polar head of surfactants.     

Reversed phase chromatographic separation of zirconium,niobium and hafnium tracers with HDEHP

Effective separation of the congeneric pair of elements, zirconium and hafnium and also niobium which was in admixtures with zirconium as daughter in its isotopic form were achieved through reversed phase column and paper extraction chromatographic procedures using di-(2-ethylhexyl)phosphoric acid (HDEHP) as the liquid exchanger. In reversed phase column chromatographic separation, the tracers,⁹⁵Zr,⁹⁵Nb and^175,181Hf, were extracted by HDEHP impregnated on kieselguhr and were sequentially eluted with 6N H₂SO₄+xN oxalic acid+H₂O₂(where x=0.1, 0.5 and 2). Similarly, in reversed phase paper chromatographic study in which a coating of HDEHP on Whatman No. 1 chromatographic paper was used as stationary phase, the mobile phase, 18N H₂SO₄+0.1N oxalic acid + H₂O₂, helped in separating the elements with favorable separation factors. Under the optimal conditions, the separation and decontamination of the elements in both methods were found to be quantitative, as verified by -spectrometric studies.     

Studies of carbazole-based polyarylates

A low temperature solution condensation method with pyridine as acceptor-catalytic reagent was applied to the synthesis of polyarylates from carbazole and bisphenol A/phenolphthalein. The polyarylates were classified with respect to their structure, thermal stability, and dielectric behavior.     

Determination of critical micelle concentration by hyper-rayleigh scattering

The critical micelle concentration (CMC) of several surfactants that contain an NLO chromophore, either at the hydrocarbon tail, or at the hydrophilic headgroup, or even as a counterion, was determined by hyper-Rayleigh scattering (HRS). In all cases, the HRS signal exhibited a similar variation with surfactant concentration, wherein the CMC is inferred from a rather unprecedented drop in the signal intensity. This drop is attributed to the formation of small pre-micellar aggregates, whose concentrations become negligible above CMC. In addition, a probe molecule, which upon protonation yielded a species with significantly enhanced HRS intensity, was developed and its utility for the determination of the CMC of simple fatty acids was demonstrated.     

Thermodynamics of silver—silver halide electrodes and thermodynamic solubility products of silver halides in glycerol + water mixtures at different temperatures

The standard potentials of silver—silver bromide and silver—silver iodide electrodes in glycerol+water mixtures containing 5, 10, 20 and 30 wt% glycerol were determined from electromotive force measurements of the cell Ag(s), AgX(s), KX(c)//KCl(c), AgCl(s), Ag(s), where X is Br or I, at seven different temperatures in the range 5–35°C. The standard potentials in each solvent are represented as a function of temperature. The standard thermodynamic functions for the electrode reactions, the primary medium effects of various solvents upon X⁻, and the standard thermodynamic quantities for the transfer of 1 g-ion of X⁻ from water to the respective glycerol + water media are evaluated and discussed in the light of ion—solvent interactions as well as the structural changes of the solvents. From the values of the Ag/Ag⁺ and Ag/AgX, X⁻ electrodes, the thermodynamic solubility product constants of silver chloride, silver bromide and silver iodide have been determined in glycerol + water solvent mixtures at different temperatures.     

Studies of vulcanization with tetramethylthiuram disulfide and sulfur vulcanization accelerated by tetramethylthiuram disulfide of styrene–butadiene rubber in presence and absence of dicumyl peroxide

The salient features of nonelemental sulfur vulcanization by tetramethylthiuram disulfide (TMTD) and elemental sulfur vulcanization promoted by TMTD both in presence and absence of ZnO and stearic acid have been studied. In stock containing TMTD, a higher rate constant value for dicumyl peroxide (DCP) decomposition was observed. TMTD decreases the crosslinking density due to DCP depending on its concentration. An entirely radical mechanism has been advanced in the absence of ZnO. ZnO or ZnO–stearic acid seems to alter the entire course of reaction. The rate of crosslinking increases in the presence of ZnO or ZnO–stearic acid. Moreover, crosslinks are formed additively (further supported from the activation energy data), and mixed crosslink formation has been confirmed by the methyl iodide test of the vulcanizates. Stearic acid has no effect on crosslink formation. An ionic chain mechanism has been postulated in the presence of ZnO, as suggested by British authors.     

Oscillation of higher order delay differential equations

A sufficient condition was obtained for oscillation of all solutions of theodd-order delay differential equation $$x^{(n)} (t) + \sum\limits_{i = 1}^m {p_i (t)} x(t - \sigma _{_i } ) = 0,$$ wherep _i (t) are non-negative real valued continuous function in [T ∞] for someT≥0 and σ_i,∈(0, ∞)(i = 1,2,…,m). In particular, forp _i (t) =p _i ∈(0, ∞) andn > 1 the result reduces to $$\frac{1}{m}\left( {\sum\limits_{i = 1}^m {(p_i \sigma _i^m )^{1/2} } } \right)^2 > (n - 2)!\frac{{(n)^n }}{e},$$ implies that every solution of (*) oscillates. This result supplements forn > 1 to a similar result proved by Ladaset al [J. Diff. Equn.,42 (1982) 134–152] which was proved for the casen = 1.     

Arsenic speciation in aqueous samples using a selective As(III)/As(V) preconcentration in combination with an automatable cryotrapping hydride generation procedure for monomethylarsonic acid and dimethylarsinic acid

Differentiation between As(III) and As(V) is accomplished using earlier developed selective preconcentration methods (carbamate and molybdate mediated (co)precipitation of As(III) and As(V) respectively) follewed by AAS detection of the (co)precipitates. Apart from this, separation of methylated arsenic species is performed by an automatable system comprising a continuous flow hydride generation unit in which monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) are converted into their corresponding volatile methylarsines, monomethylarsine (MMA) and dimethylarsine (DMA) respectively. These species are cryogenically trapped in a Teflon-line stainless stell U-tube packed with a gas chromatographic solid-phase and subsequently separated by selective volatilization. A novel gas drying technique by means of a Perma Pure dryer was applied successfully prior to trapping. Detection is by atomic absorption spectrometry (AAS). MMAA and DMAA are determined with absolute limits of detection of 0.2 and 0.5 ng, respectively. Investigation of the behaviour of the methylarsines in the system was conducted with synthesized⁷³As labeled methylated arsenic species. It was found that MMA is taken through the system quantitatively whereas DMA is recovered for about 85%. The opumized system combined with selective As(III)/As(V) preconcentration has been tested out for arsenic speciation of sediment interstitial water from the Chemiehaven at Rotterdam. The obtained concentrations are 28.5, 26.8 and 0.60 ng·ml^–1 for As(III), As(V) and MMAA, respectively, whereas the DMAA concentration was below 0.16 ng·ml^–1.