Electrochemical oxidation of oxalic acid and hydrazinium nitrate on platinum in nitric acid media

Several studies in the literature have investigated the electrochemical effects of oxalic acid and hydrazine on various materials in neutral (pH buffered to 7), basic or weakly acidic media (pH 6). The present work proposes electrochemical techniques that allow for the study of the electrochemical behavior, on a Pt electrode, of oxalic acid and hydrazinium nitrate to better understand their oxidation mechanisms in a nitric acid medium at a pH below 1; in addition, some experiments were carried out to define an electrochemical method that would allow for the simultaneous detection of these species when present within process effluent in very acidic solutions. Some physical data regarding oxalic acid and hydrazinium nitrate were also determined: anodic oxidation of hydrazinium nitrate and oxalic acid were observed at 0.2 V and 0.7 V (vs. Ag/AgCl), respectively. The diffusion coefficients of hydrazinium nitrate and oxalic acid were found to be 5.2 × 10−6 and 2.9 × 10−7 cm2 s−1, respectively. An experimental design approach demonstrated the influence of nitric acid concentrations on the diffusion coefficients of these species

Voltammetric behavior of triethylamine trihydrofluoride and anisole in acetonitrile as a first approach of studies for electro-fluorination of some adducts

This work focuses on kinetic studies of anisole and triethylamine trihydrofluoride (fluorinating agent) on platinum electrode and acetonitrile as solvent, in order to get a better understanding of their anodic behavior. Results show that both compounds can be oxidized and some kinetic parameters are calculated: the diffusion coefficient within the working media, the anodic electronic transfer coefficient and the apparent intrinsic heterogeneous electronic transfer constant. An unusual variation of these parameters occurs within the chosen reaction conditions, particularly by varying the triethylaminetrihydrofluoride concentration. Preliminary experiments for anodic fluorination of dimethoxy ethane (DME) and anisole were carried out and even if results show a possible electrofluorination for the DME (classically used as solvent), there is no fluorination of anisole when electrochemical microreactor was used

Scalable synthesis of ionic liquids: comparison of performances of microstructured and stirred batch reactors

A range of alkylpyridinium bromide ionic liquids have been synthesized in a stirred reactor at multigram scale and characterized by physical methods (viscosity, conductivity, melting point, electrochemical window, and water content). One ionic liquid, octylpyridinium bromide, was chosen to be synthesized in both macro and reduced scale reactors, in order to compare its performance and to afford evidence of the advantages of a cross channel micro reactor (channel width = 1 mm) compared to a stirred reactor

Effects of Soils on the Holocene History of Forest Communities, Cape Cod, Massachusetts, U.S.A.

Palynological evidence from a sediment sequence in Owl Pond, Cape Cod, Massachusetts, documents the persistence of an area of oak-white pine dominated vegetation through most of the Holocene. The small size of the basin (1.6 ha) and its small catchment area suggest that it receives most pollen from nearby vegetation and consequently its pollen record can be used to study the history of the surrounding forests. The 10,500-year pollen record showed three main phases of relative vegetational stability. A late-glacial spruce-jack pine forest phase, followed by an early Holocene phase when white pine dominated the landscape while oak and pitch pine became increasingly important. After 9000 yr BP, an oak-dominated forest was established. White pine continued to be an important component of the forest. This pattern is similar to vegetational changes elsewhere in southern New England, except for the relatively high values of pine pollen, which reflect the influence of the sandy glacial soils on Cape Cod. The pollen record from Owl Pond is compared with that from another site on Cape Cod, Duck Pond. Oak pollen values are higher at Owl Pond, but values of pitch pine pollen are higher at Duck Pond for the past 8000 years. Soil type (composition, texture) is judged to be the most important factor in maintaining the differences between the two sites. The results from Owl Pond suggest that mainly through the local control of the substrate, a mosaic of oak-dominated patches of vegetation existed at places on Cape Cod during the Holocene, interspersed within a pitch pine-dominated landscape.Les données palynoiogiques tirées d'une séquence sédimentaire dans le OwI Pond, à Cape Cod, atteste de la persistance d'une zone de végétation dominée par le pin blanc et le chêne pendant la plus grande partie de l'Holocène. Les petites superficies de la cuvette (1,6 ha) et de son bassin versant indique que la plus grande partie du pollen qui s'y dépose provient de la végétation des alentours; conséquemment, l'inventaire palynologique peut servir à étudier l'évolution des forêts environnantes. L'inventaire palynologique de 10 500 ans montre trois phases principales de stabilité relative de la végétation. La phase tardiglaciaire de forêts d'épinettes et de pins gris a été suivie, au début de l'Holocène, par une phase durant laquelle le pin blanc dominait le paysage et le chêne blanc et le pin rigide prenaient de plus en plus d'importance. Après 9000 ans BP, la forêt dominée par le chêne régnait, mais le pin blanc continuait à être un élément important. Ce patron ressemble aux changements de végétation survenus ailleurs dans le sud de la Nouvelle-Angleterre, sauf en ce qui a trait aux valeurs relativement élevées de pollen du pin qui reflète l'influence des sols glaciaires sablonneux du Cape Cod. On compare les données palynoiogiques du OwI Pond avec ceux du Duck Pond, également du Cape Cod. Les valeurs polliniques du chêne sont plus élevées au OwI Pond, mais les valeurs polliniques du pin rigide sont plus élevées au Duck Pond depuis 8000 ans. On considère que le type de sol (composition, texture) est le facteur le plus important dans les différences observées dans les deux sites. Les résultats tirés du site du Old Pond semblent indiquer que l'influence locale du substrat a permis, pendant l'Holocène, l'établissement de parcelles de végétation dominées par le chêne réparties ça et là au Cape Cod dans un paysage lui-même dominé par le pin rigide.Pollen- und Fossilbelege einer AbIa-gerungssequenz in Owl Pond, Cape Cod, Massuchsetts, dokumentieren das Fortbestehen eines von Eiche und WeiBkiefer dominierten Vegetationsgebietes wàhrend des grôBten Teils des Holozàns. Die geringe GrôBe des Beckens (1.6 ha) und sein kleines Einzugsgebiet legen nahe, daB es den meisten Pollen von der umliegenden Vegetation erhâlt, und so kann sein Polleninventar fur das Studium der Geschichte der umliegenden Wàlder genutzt werden. Das Pollen-lnventar von 10 500 Jahren zeigte drei Hauptphasen relativer Vegetationsstabilitàt. Eine spàtglaziale Rottanne- und Graukiefer-Waldphase, gefolgt von einer Frûhholozànphase, in der WeiBkiefer die Landschaft beherrschte, wàhrend Eiche und Pechkiefer zunehmend wichtig wurden. Nach 9000 Jahren v.u.Z. hatte sich ein von Eiche beherrschter WaId angesiedelt. Die WeiBkiefer blieb ein wichtiger Bestandteil des Waldes. Dieses Muster àhnelt den Vegetationswechseln anderswo in Neu-england, mit Ausnahme der relativ kohen Kiefernpollenwerte, welche den EinfluB der sandigen glazialen Bôden auf Cape Cod spie-geln. Der Poiienbeieg von OwI Pond wird mit dem eines anderen Platzes auf Cape Cod, Duck Pond, verglichen. Die Eichenpoilenwerte sind bei OwI Pond hôher, aber die Pechkief-erpollenwerte sind fur die letzten 8000 Jahre am Duck Pond hôher. Man hàlt den Boden-Typus (Zusammensetzung, Textur) fur den wichtigsten Faktor fur die Aufrechterhaltung der Unterschiede zwischen den zwei Plàtzen. Die Ergebnisse von OwI Pond legen nahe, daB hauptsàchlich durch die ôrtliche Kontrolle des Substrats auf Cape Cod ein von Eiche beherrschtes Mosaik von Vegetationsflecken hier und da im Holozàn existierte, welches in eine von Pechkiefer beherrschte Landschaft fein verteilt war

Reconciling diverse lacustrine and terrestrial system response to penultimate deglacial warming in southern Europe

Unlike the most recent deglaciation, the regional expression of climate changes during the penultimate deglaciation remains understudied, even though it led into a period of excess warmth with estimates of global average temperature 1–2 °C, and sea level ∼6 m, above pre-industrial values. We present the first complete high-resolution southern European diatom record capturing the penultimate glacial-interglacial transition, from Lake Ioannina (northwest Greece). It forms part of a suite of proxies selected to assess the character and phase relationships of terrestrial and aquatic ecosystem response to rapid climate warming, and to resolve apparent conflicts in proxy evidence for regional paleohydrology. The diatom data suggest a complex penultimate deglaciation driven primarily by multiple oscillations in lake level, and provide firm evidence for the regional influence of abrupt changes in North Atlantic conditions. There is diachroneity in lake and terrestrial ecosystem response to warming at the onset of the last interglacial, with an abrupt increase in lake level occurring ∼2.7 k.y. prior to sustained forest expansion with peak precipitation. We identify the potentially important role of direct input of snow melt and glacial meltwater transfer to the subterranean karst system in response to warming, which would cause rising regional groundwater levels. This explanation, and the greater sensitivity of diatoms to subtle changes in temperature, reconciles the divergent lacustrine and terrestrial proxy evidence and highlights the sensitivity of lakes situated in mountainous karstic environments to past climate warming

Similar millennial climate variability on the Iberian margin during two early Pleistocene glacials and MIS 3

Although millennial-scale climate variability (<10 ka) has been well studied during the last glacial cycles, little is known about this important aspect of climate in the early Pleistocene, prior to the Middle Pleistocene Transition. Here we present an early Pleistocene climate record at centennial resolution for two representative glacials (marine isotope stages (MIS) 37–41 from approximately 1235 to 1320 ka) during the “41 ka world” at Integrated Ocean Drilling Program Site U1385 (the “Shackleton Site”) on the southwest Iberian margin. Millennial-scale climate variability was suppressed during interglacial periods (MIS 37, MIS 39, and MIS 41) and activated during glacial inceptions when benthic δ^18O exceeded 3.2‰. Millennial variability during glacials MIS 38 and MIS 40 closely resembled Dansgaard-Oeschger events from the last glacial (MIS 3) in amplitude, shape, and pacing. The phasing of oxygen and carbon isotope variability is consistent with an active oceanic thermal bipolar see-saw between the Northern and Southern Hemispheres during most of the prominent stadials. Surface cooling was associated with systematic decreases in benthic carbon isotopes, indicating concomitant changes in the meridional overturning circulation. A comparison to other North Atlantic records of ice rafting during the early Pleistocene suggests that freshwater forcing, a s proposed for the late Pleistocene, was involved in triggering or amplifying perturbations of the North Atlantic circulation that elicited a bipolar see-saw response. Our findings support similarities in the operation of the climate system occurring on millennial time scales before and after the Middle Pleistocene Transition despite the increases in global ice volume and duration of the glacial cycles.This work was made possible by a DAAD scholarship and NERC Grant NE/K005804/1.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1002/2015PA00286

Electrochemical study in both classical cell and microreactors of flavin adenine dinucleotide as a redox mediator for NADH regeneration

The electrochemical reduction of flavinadeninedinucleotide (FAD) is studied in a classical electrochemical cell as well as in two types of microreactors: the first one is a one-channel reactor and the other one, a multichannel filter-press reactor. The ultimate goal is to use the reduced form of flavin (FADH2), in the presence of formate dehydrogenase (FDH), in order to continuously regenerate the reduced form of nicotinamide adeninedinucleotide (NADH) for chiral syntheses. Various voltammetric and adsorption measurements were carried out for a better understanding of the redox behavior of the FAD as well as its adsorption on gold. Diffusivity and kinetic electrochemical parameters of FAD were determined

Coupled ocean-land millennial-scale changes 1.26 million years ago, recorded at Site U1385 off Portugal

While a growing body of evidence indicates that North Atlantic millennial-scale climate variability extends to the Early Pleistocene, its impact on terrestrial ecosystems has not been established. Here we present ultra-high resolution (70–140 year) joint foraminiferal isotopic and pollen analyses from IODP Site U1385 off Portugal, focusing on a short glacial section of Marine Isotope Stage 38, ~ 1.26 million years ago. Our records reveal the presence of millennial-scale variability in the coupled ocean–atmosphere–land system in the North Atlantic and provide the first direct evidence for the response of western Iberian vegetation to abrupt climate changes in the Early Pleistocene. The magnitude and pacing of changes bear significant similarities to Dansgaard–Oeschger variability of the last two glacials

Can we predict the duration of an interglacial?

Differences in the duration of interglacials have long been apparent in palaeoclimate records of the Late and Middle Pleistocene. However, a systematic evaluation of such differences has been hampered by the lack of a metric that can be applied consistently through time and by difficulties in separating the local from the global component in various proxies. This, in turn, means that a theoretical framework with predictive power for interglacial duration has remained elusive. Here we propose that the interval between the terminal oscillation of the bipolar seesaw and three thousand years (kyr) before its first major reactivation provides an estimate that approximates the length of the sea-level highstand, a measure of interglacial duration. We apply this concept to interglacials of the last 800 kyr by using a recently-constructed record of interhemispheric variability. The onset of interglacials occurs within 2 kyr of the boreal summer insolation maximum/precession minimum and is consistent with the canonical view of Milankovitch forcing pacing the broad timing of interglacials. Glacial inception always takes place when obliquity is decreasing and never after the obliquity minimum. The phasing of precession and obliquity appears to influence the persistence of interglacial conditions over one or two insolation peaks, leading to shorter (~ 13 kyr) and longer (~ 28 kyr) interglacials. Glacial inception occurs approximately 10 kyr after peak interglacial conditions in temperature and CO2, representing a characteristic timescale of interglacial decline. Second-order differences in duration may be a function of stochasticity in the climate system, or small variations in background climate state and the magnitude of feedbacks and mechanisms contributing to glacial inception, and as such, difficult to predict. On the other hand, the broad duration of an interglacial may be determined by the phasing of astronomical parameters and the history of insolation, rather than the instantaneous forcing strength at inception