Gy. Pokol

The effect of tetramethylammonium hydroxide in comparison with the effect of sodium hydroxide on the slow pyrolysis of cellulose

Abstract The effect of two bases, tetramethylammonium hydroxide (TMAH) used in thermally assisted hydrolysis and methylation (THM) analysis of biopolymers and NaOH generally used in cellulose and textile industry, was compared in the pyrolysis of cotton cellulose at very low concentrations using differential thermal analysis, data obtained from thermogravimetry/mass spectrometry and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) to get more information about the reactive decomposition of cellulose. Highly purified cotton cellulose was impregnated with NaOH or TMAH to various weight levels up to 5%, immediately dried and pyrolysed in He atmosphere. The interaction with cellulose has a stabilizing effect on TMAH. Both bases decrease the temperature of the decomposition with increasing concentration, however, the decomposition patterns are different. The differences in the pyrolysis are enhanced by the methylating effect of TMAH.

Characterization of Oil Shales by High Pressure DSC

Pressurised differential scanning calorimeter (PDSC) has been used to obtain information on the pyrolysis and combustion characteristics of oil shales. Two distinct exothermic peaks were identified in combustion experiments known as low temperature oxidation (LTO) and high temperature oxidation (HTO) reaction regions. The pyrolysis process of all studied oil shale samples showed one exothermic effect at each total pressure studied. Kinetic data were analysed by Roger & Morris and Arrhenius methods and the results are discussed.

Spectroscopic and thermal studies of [Fe(dioximato)2(amine)2] mixed chelates

A number of mixed complexes of the type [Fe(DioxH)2(amine)2] (DioxH2 = glyoxime, dimethylglyoxime, methylethylglyoxime and benzylmethylglyoxime; amine = imidazole, benzimidazole, 2-methylimidazole, β- and γ-picoline, pyridine, p-toluidine, p-Cl-aniline, α-naphthylamine) have been prepared and characterised by FTIR, Mössbauer and mass spectroscopy. The structural and vibrational characteristics of the title complexes were modelled by quantum chemical (DFT) computations on [Fe(methylglyoximato)2(pyridine)2]. All the methods support strong Fe–N donor acceptor interactions and O–H · · · O hydrogen bonding in the complexes. The thermal behaviour of these non-electrolytic compounds was studied by TG, DTA and DTG measurements indicating a decomposition mechanism of [Fe(DioxH)2(amine)2] → [Fe(DioxH)2(amine)] → [Fe(DioxH)2] → [Fe(DioxH)] → alkyl-, aryl-nitriles and hydrocarbon decomposition products.

Enantiomeric enrichment of partially resolved N-methyl-amphetamine

The enantiomeric enrichment of N-methyl-amphetamine (MA) was tried by eight different preparative separation methods. The enrichment process was also studied by thermoanalitical methods (DSC,TG). There is no enantiomeric enrichment during fractional distillation and selective extraction of the liquid base. The enantiomeric mixture of MA·HCl can be enriched by crystallization or by sublimation. The most effective enrichment can be achieved by fractional crystallization or distillation of the reaction mixture after partial salt formation with hydrochloric acid. The separation is less effective in case of fractional steam distillation and selective extraction when the enantiomer and the racemate are distributed between two liquid phases. This supports the general experience that having a solid phase in the system makes enantiomer separation more efficient.

Studies on the thermal reactions of aluminium oxides and hydroxides

The gibbsite →χ-alumina decomposition (in air) and theχ-alumina → boehmite transformation (under hydrothermal conditions) were investigated isothermally. Reaction products were characterized by TG and X-ray diffraction.The rate of the gibbsite →χ-alumina reaction below 250 °C appears to be nucleation and growth controlled. That of the hydrothermal transformation ofχ-alumina to boehmite depends on the time of grinding and the particle size of the gibbsite from which theχ-oxide has been prepared. During this reaction, partial re-formation of gibbsite was observed at lower temperatures, but the final product was always boehmite.ZusammenfassungDie Zersetzung von Hydrargillit zuχ-Aluminiumoxid in Luft und die Umwandlung vonχ-Aluminiumoxid zu Böhmit unter hydrothermalen Bedingungen bei isothermer Versuchsführung wurden untersucht. Die Reaktionsprodukte wurden mittels Thermogravimetrie und Röntgenbeugung charakterisiert. Die Geschwindigkeit der Umsetzung von Hydrargillit zuχ-Aluminiumoxid unterhalb 250 °C wird durch Keimbildung und Wachstum bestimmt. Die Geschwindigkeit der hydrothermalen Umsetzungχ-Al2O3→Böhmit hängt von der Mahldauer und der Teilchengrössen des Hydrargillits ab, aus dem dasχ-Al2O3 präpariert worden war. Während letztere Reaktion wird bei tieferer Temperatur partiell Hydrargillit gebildet, das Endprodukt war stets Böhmit.РезюмеИзотермически иссле довано разложение гиббсита доχ-окиси а люминия в атмосфере воздуха и превращени е его до боэмита в гидротермических ус ловиях. Методом ТГ и рентгенофазового ан ализа охарактеризов аны продукты реакции. Скорость реа кции разложения гиббсита доχ-окиси а люминия ниже 250° соотве тствует механизму образован ия центров кристаллизации и их к онтролируемому рост у. Гидротермическое пр евращениеχ-окиси алюминия до боэмита з ависит от времени изм ельчения и размера частиц гиббс ита, из которых был полученχ-оксид а люминия. Во время этой реакции при более низкой темп ературе вновь наблюдалось образов ание гиббсита, но коне чным продуктом реакции во всех случаях был боэмит.

The role of binary phase diagrams in separation of stereoisomeric mixtures

Crystallization from the melt was applied to separate components of stereoisomeric mixtures. Binary phase diagrams were determined by DSC and used in the design of the crystallization process. The method is illustrated by the separation of diastereoisomeric (cis-trans) permethrinic acid and by that of the enantiomeric excess and racemic fraction of the Corey-lacton.ZusammenfassungZur Abtrennung von Komponenten aus stereoisomeren Mischungen wurde die Kristallisation aus der Schmelze verwendet. Die binären Schmelzdiagramme wurden mittels DSC untersucht und zur Festlegund der Parameter des Kristallisations-prozesses genutzt. Die Methode wird-erläutert an den Beispielen (1) Trennung der Diastereomeren (cis/trans) Permethrinsäuren, (2) Abtrennung des Enantiomeren-überschusses von racemischem Corey-Lacton.РЕжУМЕДль РАжДЕлЕНИь стЕРЕ ОИжОМЕРНых сМЕсЕИ НА ОтДЕльНыЕ кОМпОНЕНт ы БылА ИспОльжОВАНА кРИстАллИжАцИь Иж РА сплАВА. МЕтОДОМ Дск Бы лИ ОпРЕДЕлЕНы ДВОИНыЕ Ф АжОВыЕ ДИАгРАММы, ИспОльжОВАННыЕ жАтЕ М пРИ ВыБОРЕ пРОцЕссА кРИстАллИжАцИИ. МЕтО Д пОкАжАН НА пРИМЕРЕ Р АжДЕлЕНИь ДИАстЕРЕОИжОМЕРНОИ (цИс-тРАНс) пЕРМЕтРИНО ВОИ кИслОты И РАжДЕлЕНИь ИжБытОЧ НОгО жНАНтИОМЕРА И РАцЕМИЧЕскОИ ФРАкц ИИ лАктОНА кОРЕь.

Mechanism of Optical Resolutions via Diastereoisomeric Salt Formation. Part 7 Role of the solvents in the optical resolution of α-phenylethylamine by 2R,3R-tartaric acid

The optical resolution of α-phenylethylamine (1) by 2R,3R-tartaric acid (2) was studied in different solvents, the precipitated salts were subjected to thermoanalytical measurements and X-ray powder diffraction. The most efficient resolution can be accomplished by using methanol, the precipitate, an unsolvated salt containing the S-(-)-1⋅2R,3R-(+)-2 salt in abundance, is not a simple mixture of the diastereoisomeric salt pair, but a new modification. In water, ethanol and acetonitrile a reversed, but less effective resolution can be accomplished by precipitation of a hydrate which contains the R-(+)-1 in abundance. The precipitates from water and ethanol also proved to be new modifications. Only the precipitate from acetonitrile is the mixture of the diastereoisomeric salt pair, which can be expected in fractional crystallization of an eutectic forming diastereoisomeric salt pair. The number of different modifications found by changing the solvent in case of this particular salt pair seems surprisingly high, but may occur for other diastereoisomeric salt pairs, too. The existing but not investigated polymorphism can be the explanation for the sometimes very poor reproducibility of the preparative resolutions.

Can a rate constant independent of sample size be obtained from the rate equation generally used in thermal analysis

Some consequences of using the rate equation dα/dt=ktf(α) are shown on a simple example. It is demonstrated thatkt usually depends on the sample size, and that it is usually incorrect to assume that if mass and heat transport effects are avoided bothα and dα/dt — as functions of time — are independent of the initial mass. Rate equations should be based on real local quantities.

Comparative spectral and thermal studies of [Pt(DioxH)2] chelates

Eleven [Pt(DioxH) complexes with various symmetric and asymmetric α-dioximes: R1−C(=NOH)−C(=NOH)−R2 (R1 = R2, R1 ≠ R2, R1, R2 = H, alkyl-, aryl-, alicyclic, heterocyclic groups) are characterized by IR, NMR, and mass spectrometry. The thermal behaviors of these complexes are studied with thermoanalytical methods (TG, DTA, and DSC). The complexes with serial number: 4, 5, 6, 7, and 10 are new compounds. The IR and 1H NMR-spectra prove the coplanar structure of the [Pt(DioxH)2] complexes stabilized by two very short O–H···O hydrogen bonds. The thermal studies show that the chelates of this type are anhydrous and decompose without well-defined, reproducible melting points. The lack of weight loss and endothermal peaks on the TG and DTA curves, respectively, between 120 and 220°C, proves this phenomenon. The thermal stability of the complexes with symmetrical ligands is higher than with asymmetrical ones. The appearance of the main peaks in the mass spectra (MS) of the complexes shows, generally, an identical decomposition mechanism for all Pt-derivatives studied.

COMPARISON OF ENANTIOMER SEPARATION BY INCLUSION CHROMATOGRAPHY AND BY RESOLUTION VIA DIASTEREOISOMERIC SALT FORMATION.

Abstract Enantiomers of 6,7-dihydroxy-(3,4,5-trimethoxybenzyl)-1,2,3,4-tetrahydroisoquinoline hydrochloride were separated via diastereoisomeric salt formation using optically active tartaric acid, by inclusion-complex formation using water-soluble cyclodextrin polymer, and by inclusion chromatography on β-cyclodextrin bead polymer. On a microscale, the chromatographic resolution has significant advantages over the traditional methods.