Synthetic Studies toward 5,6,7,3',4'-Monomethoxytetrahydroxyflavones: Synthesis of Pedalitin.

During the synthetic studies toward 5,6,7,3',4'-monomethoxytetrahydroxyflavones, a concise pedalitin synthesis procedure was achieved. As previously reported, 6-hydroxy-2,3,4-trimethoxyacetophenone was prepared by Friedel-Crafts acylation of 1,4-dihydroxy-2,6-dimethoxybenzene with boron trifluoride diethyl etherate in acetic acid. When aldol condensation of 6-hydroxy-2,3,4-trimethoxyacetophenone 2b with vanillin was performed in basic conditions, it produced 2'-hydroxychalcone 3b, and, surprisingly, along with 3-hydroxyflavone 4 in a considerable amount. We propose that this oxidative cyclization is presumably due to the contribution of a quinone methide, likely to be subjected to aerobic oxidation. The chalcone was then subjected to oxidative cyclization with iodine in dimethyl sulfoxide to afford flavone 5 in good yield. To our delight, serial demethylation of the three methoxy groups at the 5-, 6-, and 3'-positions of 5 proceeded smoothly to produce pedalitin 1, under hydrogen bromide solution (30% in acetic acid). The crystal structures of 3-hydroxyflavone 4 and pedalitin tetraacetate 6 were unambiguously determined by X-ray crystallography.

Structural Requirements of 1-(2-Pyridinyl)-5-pyrazolones for Disproportionation of Boronic Acids.

We observed an unusual formation of four-coordinate boron(III) complexes from the reaction of 1-(2-pyridinyl)-5-pyrazolone derivatives with arylboronic acids in the basic media. The exact mechanism is not clear; however, the use of unprotected boronic acid and the presence of a bidentate ligand appeared to be the key structural requirements for the transformation. The results suggest that base-promoted disproportionation of arylboronic acid with the assistance of the [N,O]-bidentate ligation of 1-(2-pyridinyl)-5-pyrazolone should take place and facilitate the formation of pyrazole diarylborinate. Experiments to obtain a deeper understanding of its mechanism are currently underway.

Catalytic reaction system for rapid selective oxidation of alkyl sulphide.

Highly efficient catalytic reaction systems are developed to rapidly and selectively oxidize 2-chloroethyl ethyl sulfide (CEES). In the systems, precursors containing bromide(s) and nitrate anions are chosen for the development of cyclic catalytic loop and the effect of acids on the selective oxidation of CEES are investigated by the addition of several homogeneous acid catalysts. The experimental results reveal that addition of acid results in a higher concentration of tribromide, which is reported as a key component for the observed activity in the catalytic solution. As a consequence, a dramatic improvement in catalytic activity is observed, especially when the molar amount of acid is controlled to be more than twice the initial concentration of tribromide. For the efficient design of a catalytic system, heterogeneous acid catalysts possessing different ratios of Brønsted to Lewis acid sites are also considered. Compared to reaction systems catalysed by homogeneous acids, similar reaction behaviour is observed for the reaction with Amerlyst-15, while those with other heterogeneous catalysts, containing Lewis or mixed acid sites in their structure, exhibits an adverse effect of selective sulfoxidation, mainly due to the adsorption of anions onto Lewis sites and consequential deconstruction of the catalytic loop.

Adsorption of hydrocarbons commonly found in gasoline residues on household materials studied by inverse gas chromatography.

The adsorption of hydrocarbons present in gasoline residues on household materials was investigated via inverse gas chromatography (IGC). A series of hydrocarbons (n-heptane, n-octane, n-nonane, toluene, p-xylene, and 1,2,4-trimethylbenzene) and three household materials (carpet fibers, cotton fabric, and cardboard) were selected in this work. IGC measurements using columns packed with these household materials were conducted to obtain molar enthalpies of adsorption of the selected hydrocarbons over the temperature range of 40 to 70 °C. Adsorption isotherms and Henry's law solubility coefficients (S) were also determined at 40 °C. Results from our IGC measurements revealed that molar enthalpies of adsorption, adsorption isotherms, and solubility coefficients were largely dependent upon the structures and size of hydrocarbons and the choice of solid substrates. Measured molar enthalpies of adsorption became more exothermic with increasing size of hydrocarbons, ranging from -23.4 to -40.9 kJ/mol for carpet fibers, -36.2 to -48.2 kJ/mol for cotton fabric, and -30.1 to -52.5 kJ/mol for cardboard. From the adsorption isotherms and the measured retention times as a function of the injection amount, the adsorption affinity of hydrocarbons to the carpet fibers was found to be weaker than the affinity between hydrocarbon molecules, producing relatively lower solubility coefficients for all hydrocarbons than those measured on cotton fabric and cardboard. However, the adsorption affinities of hydrocarbons to both cotton fabric and cardboard were much stronger with increased solubility coefficients presumably due to the diffusion and dispersion of hydrocarbons through solid substrates. In particular, solubility coefficients of three aromatics on cardboard were significantly larger than those measured on carpet fibers and cotton fabric. This might be responsible for previously reported enhanced persistence of gasoline residues spiked on cardboard.

Mechanistic reaction model for oxidation of sulfur mustard simulant by a catalytic system of nitrate and tribromide.

A new metal-free catalytic reaction system is developed to selectively oxidize 2-chloroethyl ethyl sulfide (CEES), a surrogate of sulfur mustard. The combination of two catalytic precursors, tribromide and nitrate, allows a rapid sulfoxidation of CEES even at ambient conditions. The kinetic behaviours at various reaction conditions are investigated to identify the most probable reaction pathways of the development of catalytic loop and the overall reaction steps of CEES sulfoxidation. The mechanistic study demonstrates that the catalytic loop does not require an addition of mineral acid or water, which is common in most other reaction systems. Incomplete catalytic systems with one precursor are also examined to uncover the complex network of sulfoxidation in the catalytic reaction system. The results reveal that the complex between CEES and bromine is a reactive intermediate, bromosulfonium, which can be further catalysed and converted into sulfoxide by nitrate. Based on the proposed reaction mechanism, a predictive kinetic model fully describing most reaction behaviours is developed.

Synthesis of Mesoporous α-Fe2O3 Nanoparticles by Non-ionic Soft Template and Their Applications to Heavy Oil Upgrading.

This paper reports the synthetic route of 3-D network shape α-Fe2O3 from aqueous solutions of iron precursor using a non-ionic polymeric soft-template, Pluronic P123. During the synthesis of α-Fe2O3, particle sizes, crystal phases and morphologies were significantly influenced by pH, concentrations of precursor and template. The unique shape of worm-like hematite was obtained only when a starting solution was prepared by a weakly basic pH condition and a very specific composition of constituents. The synthesized nanocrystal at this condition had a narrow pore size distribution and high surface area compared to the bulk α-Fe2O3 or the one synthesized from lower pH conditions. The hydrocracking performance was tested over the synthesized iron oxide catalysts with different morphologies. The worm-like shape of iron oxide showed a superior performance, including overall yield of liquid fuel product and coke formation, over the hydrocracking of heavy petroleum oil.

Kinetics and reaction engineering of levulinic acid production from aqueous glucose solutions.

We have developed a kinetic model for aqueous-phase production of levulinic acid from glucose using a homogeneous acid catalyst. The proposed model shows a good fit with experimental data collected in this study in a batch reactor. The model was also fitted to steady-state data obtained in a plug flow reactor (PFR) and a continuously stirred tank reactor (CSTR). The kinetic model consists of four key steps: (1) glucose dehydration to form 5-hydroxymethylfurfural (HMF); (2) glucose reversion/degradation reactions to produce humins (highly polymerized insoluble carbonaceous species); (3) HMF rehydration to form levulinic acid and formic acid; and (4) HMF degradation to form humins. We use our model to predict the optimal reactor design and operating conditions for HMF and levulinic acid production in a continuous reactor system. Higher temperatures (180-200 °C) and shorter reaction times (less than 1 min) are essential to maximize the HMF content. In contrast, relatively low temperatures (140-160 °C) and longer residence times (above 100 min) are essential for maximum levulinic acid yield. We estimate that a maximum HMF carbon yield of 14% can be obtained in a PFR at 200 °C and a reaction time of 10 s. Levulinic acid can be produced at 57% carbon yield (68% of the theoretical yield) in a PFR at 149 °C and a residence time of 500 min. A system of two consecutive PFR reactors shows a higher performance than a PFR and CSTR combination. However, compared to a single PFR, there is no distinct advantage to implement a system of two consecutive reactors.

Investigations of chemical modifications of amino-terminated organic films on silicon substrates and controlled protein immobilization.

Fourier transform infrared spectroscopy by grazing-angle attenuated total reflection (FTIR-GATR), ellipsometry, atomic force microscopy (AFM), UV-visible spectroscopy, and fluorescence microscopy were employed to investigate chemical modifications of amino-terminated organic thin films on silicon substrates, protein immobilization, and the biological activity and hydrolytic stability of immobilized proteins. Amino-terminated organic films were prepared on silicon wafers by self-assembling 3-aminopropyltriethoxysilane (APTES) in anhydrous toluene. Surface amino groups were derivatized into three different linkers: N-hydroxysuccinimide (NHS) ester, hydrazide, and maleimide ester groups. UV-visible absorption measurements and fluorescence microscopy revealed that more than 40% of surface amino groups were chemically modified. Protein immobilization was carried out on modified APTES films containing these linkers via coupling with primary amines (-NH(2)) in intact monoclonal rabbit immunoglobulin G (IgG), the aldehyde (-CHO) of an oxidized carbohydrate residue in IgG, or the sulfhydryl (-SH) of fragmented half-IgG, respectively. FTIR spectra contain vibrational signatures of these functional groups present in modified APTES films and immobilized IgGs. Changes in the APTES film thickness after chemical modifications and protein immobilization were also observed by ellipsometric measurements. The biological activity and long-term hydrolytic stability of immobilized IgGs on modified APTES films were estimated by fluorescence measurements of an adsorbed antigen, fluorescein isothiocyanate (FITC)-labeled goat anti-rabbit IgG (FITC-Ab). Our results indicate that the FITC-Ab binding capacity of half-IgG immobilized via maleimide groups is greater than that of the oxidized IgG and the intact IgG immobilized via hydrazide and NHS ester groups, respectively. In addition, IgGs immobilized using all coupling chemistries were hydrolytically stable in phosphate-buffered saline (PBS).