Study on the Pyrolysis behavior of some monoterpenes and monoterpenoids: a mechanistic and kinetic overview

Die vorliegende Doktorarbeit beschäftigt sich mit der Umlagerung von Verbindungen mit Pinanskelett in der Gasphase. Die Technik der Trägergaspyrolyse wurde für die Experimente verwendet, wobei Stickstoff als Fluid eingesetzt wurde. Innerhalb der großen Klasse von Verbindungen des Pinantyps wurden diejenigen für die Versuche ausgewählt, deren thermische Umlagerung von industriellem Interesse ist: cis-Pinan, trans-Pinan, a-Pinen, b-Pinen, cis-2-Pinanol und Nopinon. Neben der Untersuchung des thermischen Verhaltens dieser Verbindungen in Bezug auf gebildete Umlagerungsprodukte, wurden kinetische Pyrolysestudien durchgeführt, um einen tieferen Einblick in den Reaktionsmechanismus und die durchlaufenen Übergangszustände bei derartigen Reaktionen zu erhalten. Berechnung der Aktivierungsparameter nach Arrhenius und Eyring führte zu der Schlussfolgerung, dass der geschwidigkeitsbestimmende Schritt die Bildung eines Biradikals umfasst. Dieses resultiert aus der Öffnung des gespannten Cyclobutanringes im bizyklischen Pinansystem, wobei die Art der Substituenten in Nachbarstellung die kinetische und thermodynamische Stabilität der biradikalischen Zwischenstufe beeinflusst. Daneben hat die Zwischenstufe auch Einfluss auf die gebildeten Isomerisierungsprodukte. Im Falle von gesättigten Systemen (cis-Pinan, trans-Pinan, cis-2-Pinanol) entstehen zwei offenkettige Produkte, die aus konkurrierenden Reaktionspfaden herrühren. Die thermische Umlagerung von ungesättigten Systemen (a-Pinen, b-Pinen, Nopinon) hat neben der Bildung eines azyklischen Isomers die Entstehung von zyklischen Verbindungen mit p-Menthanstruktur (z.B. Limonen) zur Folge. Pyrolyseexperimente, die mit den offenkettigen Umlagerungsprodukten (b-Citronellen, Isocitronellen, Ocimen, Alloocimen, Myrcen, Linalool) durchgeführt wurden, haben gezeigt, dass diese leicht Folgereaktionen eingehen, wobei hauptsächlich zyklische Produkte gebildet werden.The present thesis covers the topic of thermal rearrangement of monoterpenes with pinane-skeleton in the gas-phase. Experiments were performed using carrier-gas pyrolysis technique with nitrogen as the inert fluidizing medium. Amongst the wide class of compounds with pinane-skeleton, the most abundant and important ones from industrial point of view were chosen for the experiments: cis-pinane, trans-pinane, a-pinene, b-pinene, cis-2-pinanol, and nopinone. Beside the investigation of the thermal behavior of these compounds regarding the types of isomerization products formed, kinetic pyrolysis experiments were conducted in order to gain a deeper insight into the reaction mechanism and the transition states the reactions pass through. Calculation of activation parameters according to Arrhenius and Eyring theory of activation, allows for the unequivocal conclusion that the thermal rearrangements of those compounds pass through biradical intermediates. Initial ring-opening of the rigid cyclobutane-ring in the bicyclic pinane-systems afforded the formation of a biradical, whereby the substituents in a-position to the initial bridge-head carbon atoms determine the stability and reactivity of the biradical transition state. Additionally the biradicals determine the type of products resulting from their rearrangement. In general pyrolysis of pinane-type compounds afforded at least one acyclic isomer. In case of saturated systems (cis-pinane, trans-pinane, cis-2-pinanol) two open-chained isomers are formed, yielding from competing reaction pathways. Thermal treatment of unsaturated compounds (a-pinene, b-pinene, nopinone) additionally leads to the formation of monocyclic products with p-menthane-skeleton (e.g. limonene). Pyrolysis experiments performed with the acyclic main isomerization products (b-citronellene, isocitronellene, ocimene, alloocimene, myrcene, and linalool) revealed that those willingly undergo rearrangement mainly yielding cyclized products

Using Principal Component Analysis of Satellite and Ground Magnetic Data to Model the Equatorial Electrojet and Derive Its Tidal Composition

The intensity of the equatorial electrojet (EEJ) shows temporal and spatial variability that is not yet fully understood nor accurately modeled. Atmospheric solar tides are among the main drivers of this variability but determining different tidal components and their respective time series is challenging. It requires good temporal and spatial coverage with observations, which, previously could only be achieved by accumulating data over many years. Here, we propose a new technique for modeling the EEJ based on principal component analysis (PCA) of a hybrid ground-satellite geomagnetic data set. The proposed PCA-based model (PCEEJ) represents the observed EEJ better than the climatological EEJM-2 model, especially when there is good local time separation among the satellites involved. The amplitudes of various solar tidal modes are determined from PCEEJ based tidal equation fitting. This allows to evaluate interannual and intraannual changes of solar tidal signatures in the EEJ. On average, the obtained time series of migrating and nonmigrating tides agree with the average climatology available from earlier work. A comparison of tidal signatures in the EEJ with tides derived from neutral atmosphere temperature observations show a remarkable correlation for nonmigrating tides such as DE3, DE2, DE4, and SW4. The results indicate that it is possible to obtain a meaningful EEJ spectrum related to solar tides for a relatively short time interval of 70 days

Microwave-Assisted Azide-Alkyne Cycloaddition in Water Using a Heterogeneous Cu-Catalyst

<div><p></p><p>Several triazoles have been synthesized. They were obtained by a Cu-catalyzed cycloaddition of azides and alkynes. The reaction takes place in aqueous media under microwave irradiation using a copper catalyst based on porous glass. The products have been characterized by infrared, gas chromatography–mass spectrometry, ¹H NMR, and ¹³C NMR in addition to melting = point determination. Furthermore the in situ building of some azides and alkynes and the influence of the used metal species was investigated.</p> </div

Sustainable synthesis of high-surface-area graphite oxide via dry ball milling

A sustainable route to produce graphite oxide (GO) is presented using dry ball milling. The production method was based on pristine graphite flakes in a planetary ball mill. The prepared GO was characterized using UV–vis spectroscopy, BET surface area analysis, thermal analysis, SEM-EDX, TEM, XPS, elemental analysis, and Raman spectroscopy. The degree of graphite oxidation was controllable by the milling time and milling material, and the carbon-based yields ranged from 86 to 97%. The maximum oxygen/carbon ratios of the produced GOs were 0.16 and 0.15 after 24 h of ball milling with steel and zirconia balls, respectively. The BET surface area increased with increasing milling time from 1 m2 g–1 for pristine graphite up to 730 m2 g–1 for the ball-milled samples. Furthermore, the intensity ratios of the D and G bands (ID/IG) from the Raman spectra were 0.84 and 0.77 for GO produced with the steel and zirconia balls, respectively. The in-plane sp2 crystallite sizes (La) of graphite (168 nm) decreased to 20 (steel balls) and 22 nm (zirconia balls). Additionally, the produced GO was tested as an adsorbent for methylene blue dye removal

Sustainable Synthesis of High-Surface-Area Graphite Oxide via Dry Ball Milling

A sustainable route to produce graphite oxide (<b>GO</b>) is presented using dry ball milling. The production method was based on pristine graphite flakes in a planetary ball mill. The prepared <b>GO</b> was characterized using UV–vis spectroscopy, BET surface area analysis, thermal analysis, SEM-EDX, TEM, XPS, elemental analysis, and Raman spectroscopy. The degree of graphite oxidation was controllable by the milling time and milling material, and the carbon-based yields ranged from 86 to 97%. The maximum oxygen/carbon ratios of the produced <b>GOs</b> were 0.16 and 0.15 after 24 h of ball milling with steel and zirconia balls, respectively. The BET surface area increased with increasing milling time from 1 m² g^–1 for pristine graphite up to 730 m² g^–1 for the ball-milled samples. Furthermore, the intensity ratios of the D and G bands (<i>I</i>_<i>D</i>/<i>I</i>_<i>G</i>) from the Raman spectra were 0.84 and 0.77 for <b>GO</b> produced with the steel and zirconia balls, respectively. The in-plane sp² crystallite sizes (<i>L</i>_a) of graphite (168 nm) decreased to 20 (steel balls) and 22 nm (zirconia balls). Additionally, the produced <b>GO</b> was tested as an adsorbent for methylene blue dye removal