A high yielding, one-pot synthesis of S,S-dialkyl dithiocarbonates through the corresponding thiols using Mitsunobu’s reagent

A novel Mitsunobu-based technique has been developed for the synthesis of a variety of symmetrical and unsymmetrical S,S-dialkyl dithiocarbonates from various corresponding primary, secondary and tertiary thiols using gaseous carbon dioxide, in good to excellent yields.     

Mode coupling analysis of coherent quasi-elastic neutron scattering from fluorite-type materials approaching the superionic transition

Summary Neutron scattering experiments on SrCl₂, CaF₂ and PbF₂ have shown that intensity and width of the coherent diffuse quasi-elastic spectrum increase rapidly with temperature into the fast-ion conducting phase, the main feature in the integrated quasi-elastic intensity being a peak just beyond the (200) point along the [100] direction in scattering wave vector space. The Zwanzig-Mori memory function formalism is used in this work to analyse the quasi-elastic scattering cross-section from charge density fluctuations in terms of anharmonic couplings between the vibrational modes of the crystal. The two- and three-mode channels are examined for compatibility with the quasi-elastic neutron scattering evidence, on the basis of i) energy and momentum conservation and van Hove singularity arguments and ii) measured phonon dispersion curves along the main symmetry directions in SrCl₂, CaF₂, SrF₂ and BaF₂. The analysis identifies a specific microscopic role for the Raman-active optic branches. The eigenvectors of the relevant Raman-active and partner modes in the three-mode channel describe relative displacements of the two halogens in the unit cell superposed on relative displacements of the halogen and alkaline-earth components. This microscopic picture is thus consistent with the superionic transition being associated with the onset of dynamic disorder in the anionic component of the crystal.

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Riassunto Questo lavoro esamina la sezione d’urto per diffusione quasi elastica di neutroni da fluttuazioni di carica in cristalli di tipo fluorite in prossimità della transizione ad uno stato superionico, in relazione alle caratteristiche sperimentalmente osservate per lo spettro di diffusione quasi elastica da SrCl₂, CaF₂ e PbF₂. Si usa il formalismo della funzione di memoria di Zwanzig e Mori nell’ambito di un’approssimazione di accoppiamento anarmonico tra modi vibrazionali del cristallo. I processi di decadimento a due modi e tre modi sono analizzati mediante argomenti basati su leggi di conservazione e singolarità di van Hove, usando curve di dispersione per vibrazioni reticolari misurate in SrCl₂, CaF₂, SrF₂ e BaF₂. L’analisi attribuisce un ruolo specifico ai modi Raman nella dinamica ionica precorrente la transizione. Gli spostamenti atomici associati ai modi dominanti sono correlati all’attivazione di disordine dinamico nel sottoreticolo anionico che porta alla transizione.

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Резюме Эксперименты по рассеянию нейтронов на SrCl₂, CaF₂ и PbF₂ показывают, что интенсивность и ширина когерентного квази-упругого спектра быстро ывеличиваются с температурой причем основная особенность в проинтегрированной квази-упругой интенсивности представляет пик выше точки (200) вдоль направления [100] в пространстве волновых векторов рассеяния. В этой работе используется формализм функции памяти Цванцига-Мори для анализа поперечного сечения квази-упругого рассеяния на флуктуациях плотности заряда в терминах ангармонических связей между колебательными модами кристалла. Исследуются каналы двух- и трех-мод для подтверждения квази-упругого рассеяния неитронов, основываясь на 1) сохранении энергии и импульса и аргументах сингулярности ван Хова и на 2) измеренных фононных диспеионных кривых вдоль главных направлений симметрии в SrCl₂, CaF₂, SrF₂ и BaF₂. Проведенный анализ определяет микроскопическую роль Раман-активных оптических ветвей. Собственные векторы соответствующих мод в трех-модовых каналах описывают относительные смещения двух галогенов в элементарной ячейке, наложенные на относительные смещения галогенной и щелочно-земельной компонент. Эта микроскопическая картина согласется с суперионным переходом, который связан с началом динамического беспорядка в анионной компоненте кристалла.

     

Determination of lanthanides with m-toluidinyloxamic acid

m-Toluidinyloxamic acid is shown to be about as efficient as the para isomer as a gravimetric reagent for La, Pr and Nd. Conditions have been established for the determination of these lanthanides in presence of a number of metal ions.     

Cluster approaches to random alloys: An appraisal

Some of the cluster extensions of the coherent potential approximation (CPA) based on the effective medium theory have been critically studied with respect to the decoupling schemes involved in them. Their computational tractability has been examined and it has been found that theself-consistent calculations in three-dimensional systems are immensely difficult to perform. A self-consistent calculation has been reported for simple cubic lattices with diagonal and off-diagonal disorder using a pair-CPA method. A significant finding of the paper is that it has been shown thatnon-analyticities are a general feature of extensions of CPA within multiple scattering framework. The non-analyticities were reported several times but a general proof of their existence was not noticed. It was also believed that the so-called molecular—CPA is analytic, this has been shown to be wrong here. The density of states results with off-diagonal randomness have been qualitatively understood to yield some information about the influence of off-diagonal randomness on Anderson localisation of an electron.     

Equilibrium studies on some heteroligand hydroxo complexes of lanthanons with iminodiacetic acid and citraconic or maleic acid

Mixed-ligand ternary complexes of La(III), Pr(III), Nd(III), Gd(III), and Dy(III) with iminodiacetic acid (IMDA) and citraconic (CCA) or maleic acid (MIA), have been studiedpH-metrically. Their formation takes place through the stepwise addition of the secondary ligand (IMDA) to the initially formed 1:1, Ln(III)—CCA/MIA binary species. The resulting ternary complexes undergo hydrolysis to form their hydroxo derivatives simultaneously. The stability constants of the hydroxo species are calculated for constant temperature (27 ± 1°C) and ionic strength (I=0.1M KNO₃). The relative order of stability is: La(III)

Gleichgewichtsuntersuchungen an einigen Heteroliganden-Hydroxo-Komplexen von Lanthanid-Ionen mit Iminodiessigsäure und Citracon- oder Maleinsäure

Zusammenfassung Es wurden ternäre Komplexe von La(III), Pr(III), Nd(III), Gd(III) und Dy(III) mit gemischten Liganden [Iminodiessigsäure (IMDA) und Citraconsäure (CCA) oder Maleinsäure (MIA)] mittelspH-metrischer Methoden untersucht. Diese Komplexe werden über die stufenweise Addition des Sekundärliganden (IMDA) zu den primär gebildeten 1:1 Ln(III)—CCA/MIA Spezies gebildet. Zugleich erleiden die resultierenden ternären Komplexe Hydrolyse und gehen in die entsprechenden Hydroxo-Komplexe über. Die Stabilitätskonstanten der Hydroxo-Komplexe wurden für konstante Temperatur (27 ± 1°C) und Ionenstärke (I=0.1M KNO₃) berechnet. Die relative Reihung bezüglich der Stabilitäten ergab sich folgendermaßen: La(III)     

A high yielding one-pot, novel synthesis of carbamate esters from alcohols using Mitsunobu's reagent

A novel process for the one-step conversion of primary alcohols into carbamates as protected amines has been developed using Mitsunobu's reagent in the presence of gaseous carbon dioxide. Thus, carbamate esters of the different amines were prepared in very good to excellent yields.     

Heterogenous solar photocatalysis of two commercial reactive azo dyes

Two commercial reactive azo dyes--Reactive Black 5 (RB5) and Reactive Orange 16 (RO 16) have been treated by titanium dioxide and Zinc oxide photocatalysts separately under presence of sunlight. It is observed that solar photocatalytic treatment is effective in terms of colour and COD. The photodegradation efficiency of zinc oxide is comparable with TiO2 at pH 5-6 for RO16. The extent of decolourization and degradation of RB5 is greater in presence of zinc oxide photocatalyst than TiO2 at pH 5- 6. Zinc oxide undergoes <1% photodissolution after 6 hours of solar irradiation at working pH.     

A High Yielding, One-Pot, Triton-B Catalyzed Synthesis of Dithiocarbamates Using Alcoholic Tosylates

Summary. A novel process for the one-step chemoselective conversion of alcoholic tosylates into dithiocarbamates as protected amines was developed using benzyltrimethylammoniumhydroxide (Triton-B) in presence of carbon disulfide. Thus, dithiocarbamates of different amines were prepared in very good to excellent yields. This protocol is mild, chemoselective, and efficient compared to other reported methods. Present address: Institute of Organic and Biomolecular Chemistry, Georg-August University, D-37077, G?ttingen, Germany