Synthesis of ω9-tetracosynoic and ω9-octacosynoic acids as entries into tritiated metabolic precursors ofcis-9-tricosene andcis-9-heptacosene in the housefly

The syntheses of 15-tetracosynoic acid (ω9-tetracosynoic acid) and 19-octacosynoic acid (ω9-octacosynoic acid) are described. These alkynoic acids are to be tritiated to the corresponding alkenoic acids, which will be used as metabolic precursors of housefly pheromone components. The final step in each synthesis involved the coupling of 1-decyne to the lithio-salt of the appropriate ω-bromoacid. Homologation of dibromoalkanes was accomplished with triphasic catalytic displacement of bromide by cyanide ion. Oxidation of a bromo-alcohol to a bromoacid was performed in benzene with KMnO₄ and 18-crown-6 ether. Mention of a company name or product in this paper does not imply endorsement by the U.S. Department of Agriculture.     

One-pot purification and functionalization of single-walled carbon nanotubes in less-corrosive poly(phosphoric acid)

As-received commercial single-walled carbon nanotubes (SWCNTs) were treated in mild, inorganic polyacid, viz. polyphosphoric acid (PPA) with or without additional phosphorous pentoxide (P₂O₅) at 130, 160, and 190 °C. Unlike the treatment in strong acids such as nitric acid/sulfuric acid mixtures, nitric acid and hydrochloric acid, PPA with or without additional P₂O₅ could selectively remove the tenacious carbonaceous and metallic impurities with little or no damage to the basic frameworks of SWCNTs and crystalline carbon materials. Since the medium PPA/P₂O₅ is known for an efficient “direct” Friedel-Crafts acylation using a carboxylic acid instead of a carboxylic acid chloride, it provides the advantage of combining both purification and functionalization steps into a one-pot process in manufacturing of functionalized SWCNTs.     

In Situ Reflection–Absorption Infrared Spectroscopy at the Liquid–Solid Interface: Decomposition of Organic Molecules on Polycrystalline Platinum Substrates

The room-temperature adsorption and surface chemistry of several categories of organic molecules used as reactants or solvents in liquid-phase catalysis, of carboxylic acids, esters, aldehydes, acetone, alcohols and ethers in particular, were characterized in situ on polycrystalline Pt in the presence of the liquid phase by reflection-absorption infrared spectroscopy (RAIRS). For carboxylic acids and esters it was found that the propensity for decomposition and CO formation follows a formic acid ? methyl formate, ethyl formate > acetic acid, propionic acid, acrylic acid, ethyl acetate sequence. For aldehydes and acetone, the observed trend is formaldehyde ? acetaldehyde > acrolein, crotonaldehyde > propionaldehyde, acetone. Virtually no adsorbed CO was detected when Pt surfaces were exposed to liquid solutions of either alcohols or ethers. The observed trends could be correlated with the corresponding molecular structures. They are discussed in the context of previous results obtained from studies under ultrahigh vacuum (UHV) and under electro-oxidation conditions.     

The interaction of sulfur with Cu/Pt(111) and Zn/Pt(111) surfaces: copper-promoted sulfidation of platinum

The interaction of sulfur with Pt(111), Zn/Pt(111) and Cu/Pt(111) has been examined using X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), and thermal desorption mass spectroscopy (TDS). At temperatures between 300 and 600 K, the exposure of Pt(111) to S₂ gas produces a chemisorbed layer of sulfurwithout the formation of bulk sulfides. Exposure of S₂ to a Zn/Pt(111) alloy, at room temperature, results in a breakdown of the alloy and formation of a zinc-sulfide film on Pt(111). Further S₂ exposure at 550 K sulfidizes the remaining metallic zincwithout affecting platinum. For the Cu/Pt(111) surface alloy, on the other hand, exposure to S₂2 at 550 K leads to sulfidation of the platinum. Platinum can effectively compete for sulfur atoms bonded to copper but not for those bonded to zinc. The reaction of S₂ gas with Cu/Pt(111) surfaces produces copper sulfides that promote the sulfidation of Pt by providing surface sites for the dissociation of S₂, and by favoring the diffusion of S into the bulk of the system.     

Synthesis of long-chain (E)-3-alkenoic acids by the Knoevenagel condensation of aliphatic aldehydes with malonic acid

Knoevenagel condensation of aliphatic aldehydes with malonic acid in equimolar ratio in triethylamine, which served the dual purpose of the solvent as well as the base, gave alkenoic acids in 80–88% yield as determined by acid values of the products and by gas-liquid chromatography with methyl heptadecanoate as the internal standard. The alkenoic acids were converted to methyl esters, purified by column chromatography and characterized by proton nuclear magnetic resonance, infrared and mass spectral analyses. The spectral data clearly established that the acids formed were (E)-3-alkenoic acids. The purified methyl esters were also subjected to the oxymercuration-demercuration reaction, and the mass spectra of the resulting methoxy esters confirmed the exclusive formation of 3-alkenoic acids.     

Generation of carbon dioxide from glycerol: Evidences of massive production on polycrystalline platinum

In this work we investigate the glycerol electrooxidation reaction on polycrystalline platinum in acid media. Cyclic voltammetry shows the existence of multiple oxidation peaks, which are related with a complex electrooxidation mechanism. We follow the voltammetric response of Pt in the presence of glycerol by using FTIR in situ. Results show that during glycerol electrooxidation massive amounts of CO₂ are produced. The production of CO₂ begins at low potentials and depends on the previous formation of adsorbed CO. This pathway is accelerated at high potentials and seems to be the main responsible for the rising of the currents observed in the cyclic voltammogram for potentials up to 1.0 V. Moreover, there is a parallel pathway involving the production of a carboxylic acid (probably glyceric acid), but the relative magnitudes of CO₂ bands and acid bands makes clear that the production of CO₂ is the dominant feature of the spectra, suggesting that glycerol can be a suitable candidate for use in direct alcohol fuel cells.     

Mechanistic pathways during oxidation of cyanate on platinum single crystal faces

Adsorption and oxidation processes of cyanate (OCN⁻) were studied on polycrystalline platinum and Pt(1 0 0), Pt(1 1 0) and Pt(1 1 1) surfaces in alkaline solution (pH 9). On Pt(poly), Pt(1 0 0) and Pt(1 1 0), it has been found that cyanate chemisorbs dissociatively, with production of adsorbed CO. Oxidation of cyanate thus follows a pathway involving CO_ad on polycrystalline Pt and these single crystal faces. CO_ad has not been observed during oxidation of cyanate on Pt(1 1 1); thus another pathway, involving direct oxidation of OCN⁻, has been identified for cyanate oxidation on platinum surfaces.     

Electrochemical degradation of clofibric acid in water by anodic oxidation: Comparative study with platinum and boron-doped diamond electrodes

Aqueous solutions containing the metabolite clofibric acid (2-(4-chlorophenoxy)-2-methylpropionic acid) up to close to saturation in the pH range 2.0-12.0 have been degraded by anodic oxidation with Pt and boron-doped diamond (BDD) as anodes. The use of BDD leads to total mineralization in all media due to the efficient production of oxidant hydroxyl radical (OH). This procedure is then viable for the treatment of wastewaters containing this compound. The effect of pH, apparent current density, temperature and metabolite concentration on the degradation rate, consumed specific charge and mineralization current efficiency has been investigated. Comparative treatment with Pt yields poor decontamination with complete release of stable chloride ion. When BDD is used, this ion is oxidized to Cl₂. Clofibric acid is more rapidly destroyed on Pt than on BDD, indicating that it is more strongly adsorbed on the Pt surface enhancing its reaction with OH. Its decay kinetics always follows a pseudo-first-order reaction and the rate constant for each anode increases with increasing apparent current density, being practically independent of pH and metabolite concentration. Aromatic products such as 4-chlorophenol, 4-chlorocatechol, 4-chlororesorcinol, hydroquinone, p-benzoquinone and 1,2,4-benzenetriol are detected by gas chromatography-mass spectrometry (GC-MS) and reversed-phase chromatography. Tartronic, maleic, fumaric, formic, 2-hydroxyisobutyric, pyruvic and oxalic acids are identified as generated carboxylic acids by ion-exclusion chromatography. These acids remain stable in solution using Pt, but they are completely converted into CO₂ with BDD. A reaction pathway for clofibric acid degradation involving all these intermediates is proposed.     

Self-assembled fabrication of a polycrystalline boron-doped diamond surface supporting Pt (or Pd)/Au-shell/core nanoparticles on the (111) facets and Au nanoparticles on the (100) facets

Modified boron-doped diamond (BDD) surfaces supporting different, carefully selected types of metal nanoparticles on different types of crystal facets were fabricated via a self-assembly method. A hydrogen plasma-treated BDD surface was treated with UV/ozone for 10 s followed by immersion in a Au nanoparticle (AuNP) solution to fabricate a BDD surface selectively and densely supporting AuNPs on the (111) facet (AuNP₁₁₁-BDD). The AuNP₁₁₁-BDD sample was then immersed in H₂PtCl₆/ascorbic acid or H₂PdCl₄/sodium citrate to cover the AuNP surface with Pt or Pd (Pt/AuNP₁₁₁-BDD or Pd/AuNP₁₁₁-BDD). These samples were treated with UV/ozone for 40 s followed by re-immersion in the AuNP solution to immobilize AuNPs on the (100) facets (Pt/AuNP₁₁₁-AuNP₁₀₀-BDD or Pd/AuNP₁₁₁-AuNP₁₀₀-BDD). The metal nanoparticles supported on the BDD surface were confirmed by cyclic voltammetry to be electrochemically active. The crystal-facet-selective support of the metal nanoparticles was also confirmed by two-dimensional elemental mapping via field emission Auger electron spectroscopy. The macro procedures used for the crystal-facet-selective immobilization of the AuNPs was reproducible, and this technique should be applicable to the creation of a new class of advanced materials in such fields as optics, electronics, sensing, and (electro)catalysis.     

Quantitative analysis of hydrogen adsorbed on Pt particles on SiO2 in the presence of coadsorbed CO by means of L3-edge X-ray absorption near-edge structure spectroscopy

X-ray absorption near-edge structure (XANES) spectra at the Pt L₃-edge for Pt particles supported on SiO₂ under CO adsorption and CO+H₂ coadsorption were recorded to analyze the amount of adsorbed hydrogen in the coadsorbed state on the Pt particles. Adsorbed CO on the Pt particles revealed a new peak at 6 eV above the Pt L₃-edge in the difference spectra before and after CO adsorption in the coverage range 0.10-0.51. Subsequent adsorption of hydrogen at various coverages on the CO-preadsorbed Pt particles broadened and shifted the peak to the higher energy side. The peak was deconvoluted to two components due to adsorbed hydrogen and CO by a linear least-squares fitting technique. It was found that the fitting coefficient with respect to adsorbed hydrogen was proportional to the amount of adsorbed hydrogen. The XANES difference spectra provide a quantitative analysis method for adsorbed hydrogen on supported Pt particles in the presence of coadsorbates like CO. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural effects in electrocatalysis: electrooxidation of carbon monoxide on Pt3Sn single-crystal alloy surfaces

The kinetics of the electrochemical oxidation of carbon monoxide (CO) and CO/hydrogen mixtures (0.1 and 2% CO) in sulfuric acid electrolyte at 25–62°C was studied on different surfaces of the ordered single crystal Pt₃Sn alloy. Characterization of the surface composition and structure was determined in UHV using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and low energy ion scattering (LEIS) prior to determining the electrode kinetics using the classical rotating disk method (RDE) with CO dissolved in the electrolyte. Clean annealed and sputtered-cleaned but not-annealed surfaces of (110) and (111) orientation were studied. A remarkable difference in activity was observed between the annealed (111) surface and the sputtered but not-annealed (110) surface, with both surfaces having the same nominal surface composition, 20–25 at% Sn, but different local structures. The onset potential for CO oxidation on the (111) surface was shifted cathodically by 0.13 V relative to that for the sputtered (110) surface, and the onset comes remarkably close to 0 V on the reversible hydrogen potential scale. Relative to pure Pt surfaces (of any crystal structure), the potential shift is more than 0.5 V, corresponding to a catalytic activity that is higher by more than four orders of magnitude. Comparable shifts were observed for the oxidation of CO/H₂ mixtures. Both the structure sensitivity and the high catalytic activity of the Pt₃Sn surface are attributed to an adsorbed state of CO unique to this alloy and occurs at relatively high coverage on the (111) surface.     

129Xe NMR study of 12-tungstophosphoric heteropoly acid supported on silica

The structure of 12-tungstophosphoric heteropoly acid (H₃PW₁₂O₄₀) supported on silica has been studied by¹²⁹Xe NMR of adsorbed xenon. The¹²⁹Xe NMR spectra are found to depend on the surface HPA concentration. The¹²⁹Xe NMR data provide evidence for the presence of an organized microporous structure within HPA overlayers. These results are in agreement with nitrogen adsorption and capillary condensation (77 K) measurements. The high sensitivity of the¹²⁹Xe NMR method and its applicability for testing of silica-based HPA catalysts are demonstrated.A preliminary report of this work was presented to the Second European Congress on Catalysis EUROPACAT-II, Maastricht, The Netherlands, 3–8 September 1995.Deceased.     

Copolymerization of sulfur dioxide with some alkenoic acids

The copolymerization of sulfur dioxide with some alkenoic acids such as acrylic, 3-butenoic, 4-pentenoic, and 10-undecenoic acid was carried out using organic and aqueous media in the presence of (CH₃)₃ COOH/SO₂ redox system. Elemental analysis, IR, and ¹³C-NMR revealed that the copolymers synthesized from the acrylic acid/SO₂ system were of variable composition in organic media, but only polyacrylic acid homopolymer was formed in the presence of water. The other three alkenoic acid/SO₂ systems gave always polysulfone copolymers of alternating structure regardless of the experimental conditions employed. Thermal analysis (TGA and DTA) of selected samples gave T_g in the 73–101°C, range T_m between 160 and 228°C, and the total weight loss in air from 31 to 97%. Flammability decreased as the S:C mole ratio increased. NMR shows that the complexation of SO₂ with the C?C part of all alkenoic acids is low.     

Poly(p‐phenylene benzoxazole) fiber chemically modified by the incorporation of sulfonate groups

Two kinds of modified poly(p‐phenylene benzoxazole) (PBO), the copolymer of TPA (SPBO) and p‐SPBO, containing ionic groups in the macromolecular chains were obtained by copolymerization from 1,3‐diamino‐4,6‐dihydroxybenzene dihydrochloride (DAR) and terephthalic acid (TPA), with the addition of selected amounts (1.5–5.0% molar ratio over DAR) of 5‐sulfoisophthalic acid monosodium salt or sulfoterephthalic acid monopotassium salt in place of the TPA, respectively, in poly(phosphoric acid) (PPA). The resultant PBO/PPA, SPBO/PPA, and p‐SPBO/PPA lyotropic liquid‐crystalline solutions were spun into fibers by a dry‐jet wet‐spinning technique. Chemically modified PBO fibers with sulfonate salt pendants in the polymer chains were obtained for the first time. The surface wetting behavior and interfacial shear strength between the fiber and epoxy resin were investigated. The interference of sulfonate salt pendants on the crystalline morphology was measured. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Estimating vibrational and thermodynamic properties of adsorbates with uncertainty using data driven surrogates

In this work, we propose a strategy to develop data driven local surrogate models of ab initio potential energy functions describing the interaction of adsorbates on heterogeneous catalytic materials. We show that these multivariable surrogate models, based on orthogonal polynomial expansion and trained on sampled ab-initio energies/forces, can be used to compute harmonic vibrational frequencies and the entropy of adsorbates. Further, we show that the errors in our surrogate model can be estimated and propagated to calculate the uncertainty in the computed properties. We show proof-of-concept illustrations of our method to calculate the vibrational frequencies of ethene on 1D edges of molybdenum sulfide (MoS₂), (b) 2D surfaces of Pt(111), and (c) 3D micropores of a HZSM-5 zeolite; the entropy of ethane adsorbed on Pt(111); and the associated uncertainties in all the cases.     

Unprecedented Reductive Esterification of Carboxylic Acids under Hydrogen by Reusable Heterogeneous Platinum Catalysts

Supported metal catalysts have been tested for an unprecedented reductive dimerization of carboxylic acids to esters under 8 bar hydrogen in solvent‐free conditions. Among various metal‐loaded tin oxide catalysts, platinum‐loaded tin dioxide (Pt/SnO₂) shows the highest ester yield for the reaction of dodecanoic acid. Among Pt catalysts on various supports, Lewis acidic oxides, especially SnO₂, show high activity. The most active catalyst, 5 wt% Pt/SnO₂ reduced at 100 °C, is effective for the reductive esterification of various carboxylic acids, and the catalyst is reusable for nine cycles, demonstrating the first successful example for the title reaction. Infrared (IR) studies of a model compound (formic acid) on some metal oxides indicate a strong Lewis acid‐base interaction between SnO₂ and the carbonyl oxygen. For Pt/SnO₂ catalysts with different Pt particle sizes, the activity increases with decreasing size of Pt metal. A cooperative catalysis of the Pt metal nanoparticles and the Sn⁴⁺ Lewis acid sites is proposed.

     

ATR-FTIR Study of the Decomposition of Acetic Anhydride on Fosfotungstic Wells–Dawson Heteropoly Acid Using Concentration-Modulation Excitation Spectroscopy

The decomposition of acetic anhydride in liquid phase on a fosfotungstic Wells–Dawson heteropoly acid (HPA) was investigated by in situ ATR-FTIR spectroscopy. Transient and concentration-modulation excitation spectroscopy (MES) experiments in combination with phase-sensitive detection (PSD) were used to monitor the solid–liquid interface. The MES method is based on the periodic variation of a parameter of the reaction media such as, the reactant concentration. That periodic alteration causes varying infrared signals of the surface adsorbed species that are subsequently demodulated with the PSD methodology. Thus, the separation of the static signals from the changing ones is achieved, and species with different response can be observed in the spectra. Using MES-PSD coupled with ATR-FTIR, acetic anhydride was observed to decompose to acetic acid, acetate and acyl [CH₃C(O)⁺] species, involving Brønsted acid sites of the HPA catalyst. The CH₃C(O)⁺ is a very unstable intermediate species and it is the key intermediate in the Friedel–Crafts acylation reactions. Moreover, the acetate groups are spectator species since remain strongly adsorbed on the catalyst surface and do not further react.     

IR spectroscopy study of cyclic anhydride as intermediate for ester crosslinking of cotton cellulose by polycarboxylic acids. V. Comparison of 1,2,4-butanetricarboxylic acid and 1,2,3-propanetricarboxylic acid

In recent years extensive efforts have been made to use multifunctional carboxylic acids as formaldehyde-free crosslinking agents for cotton to replace the traditional formaldehyde-based N-methylol reagents. In our previous research we found that a polycarboxylic acid esterifies cellulose through the formation of a five-membered cyclic anhydride intermediate by dehydration of two adjacent carboxyl groups. In this research we used Fourier transform IR (FTIR) spectroscopy to study the formation of cyclic anhydride intermediates and crosslinking of cotton by 1,2,4-butanetricarboxylic acid (BTA) and 1,2,3-propanetricarboxylic acid (PCA). BTA and PCA form five-membered cyclic anhydrides in the same temperature range. Both acids form the anhydrides at lower temperatures when a catalyst is present. When an acid molecule is bonded to cotton through an ester linkage, only PCA is able to form a second anhydride intermediate. We found that PCA is a more effective crosslinking agent, and it imparts higher levels of wrinkle resistance to the cotton fabric than BTA. Therefore, the formation of a five-membered cyclic anhydride by a polycarboxylic acid accelerates the esterification of cotton by the acid. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2142–2150, 2001     

Benzyl coupling on bismuth-modified Pt(111)

It has been found that adsorbed benzyl (Ø-CH₂(a)), produced from methylcyclohexane, can undergo dimerisation to adsorbed bibenzyl (Ø-CH₂-CH₂-Ø) on a bismuth-modified Pt(111) surface. In this case, the bismuth was postdosed to the benzyl adlayer, as in bismuth postdosing thermal desorption mass spectroscopy (BPTDS). The bibenzyl product desorbs to give bibenzyl gas in good yield with respect to the starting benzyl or the reacted methylcyclohexane. This reaction competes poorly with simple hydrogenation of the benzyl species to toluene when adsorbed hydrogen is also present on the bismuth-dosed surface. In the absence of hydrogen, dimerization dominates the chemistry of this intermediate, although some direct desorption of benzyl radical also occurs. The dependence of the activation energy for benzyl coupling on the thickness of the bismuth film suggests that the bismuth resides between the Pt surface and the benzyl adlayer. Benzyl coupling and desorption occurs on Bi/Pt, whereas only its decomposition occurs on clean Pt. This is attributed to two effects: the weakness of C-Bi bond leads to a low barrier for benzyl coupling or desorption; and, (2) bismuth blocks Pt sites needed to stabilize the fragments of decomposition. Both D₂-BPTDS and this bismuth-induced coupling reaction in simple BPTDS were used to monitor the coverage of benzyl during its thermal decomposition on bismuth-free Pt(111), and the temperature dependence of the rate of its decomposition. Estimates of the bismuth-carbon bond strengths are also presented.     

Theoretical Prediction and Experimental Verification of Stability of Pt–3d–Pt Subsurface Bimetallic Structures: From Single Crystal Surfaces to Polycrystalline Films

In this paper we will provide a review of our recent studies on the general stability of the Pt–3d–Pt (3d = Ti, V, Cr, Mn, Fe, Co and Ni) subsurface structures, which are the desirable structural configurations in several applications in heterogeneous catalysis and electrocatalysis. We will first provide a review of density functional theory (DFT) predictions of the thermodynamic stability of Pt–3d–Pt(111) and Pt–3d–Pt(100) in vacuum and with adsorbed hydrogen and oxygen. The DFT results predict that the Pt–3d–Pt subsurface structures are stable in vacuum and with adsorbed hydrogen, while with adsorbed oxygen the 3d atoms should segregate to the surface to produce the 3d–Pt–Pt surface structures. The DFT predictions are verified experimentally on selected Pt–3d–Pt(111) systems. The experimental efforts are further expanded by bridging the materials gap form single crystal Pt(111) to polycrystalline Pt to incorporate multiple crystal facets and to determine their effects on the kinetic barriers for the segregation of the subsurface 3d atoms. In order to further correlate DFT calculations with experimental results, a Brønsted–Evans–Polanyi relationship is derived to correlate thermodynamic stability from DFT calculations with kinetic barriers from experimental measurements for the Pt–3d–Pt systems. Finally, empirical equations have been developed for predicting the thermodynamic stability of other bimetallic systems both in vacuum and with adsorbed hydrogen and oxygen.