Infrared study of methyl formate and formaldehyde adsorption on reduced and oxidised silica-supported copper catalysts

Infrared spectra are reported of methyl formate and formaldehyde adsorbed at 300 K on silica, Cu/SiO2 reduced in hydrogen and Cu/SiO2 which had been oxidised by exposure to nitrous oxide after reduction. Silanol groups on silica form hydrogen bonds with carbonyl groups in weakly adsorbed methyl formate molecules. Methyl formate ligates via its carbonyl groups to Cu atoms in the surface of reduced copper. A low residual concentration of surface oxygen on copper promoted the slow reaction of ligated methyl formate to give a bridging formate species on copper and adsorbed methoxy groups. Methyl formate did not ligate to an oxidised copper surface but was rapidly chemisorbed to give unidentate formate and methoxy species. Formaldehyde slowly polymerises on silica to form trioxane and other oxymethylene species. The reaction is faster over Cu/SiO2 which, in the reduced state, also catalyses the formation of bridging formate anions adsorbed on copper. The reaction between formaldehyde and oxidised Cu/SiO2 leads to both unidentate and bidentate formate and adsorbed water.

Evidence for the adsorption of molecules at special sites located at copper/zinc oxide interfaces. Part 3. -- Fourier-transform infrared study of methyl formate adsorption on reduced and oxidised Cu/ZnO/SiO2 catalysts

FTIR spectra are reported of methyl formate adsorbed at 295 K on ZnO/SiO2, reduced Cu/ZnO/SiO2 and on Cu/ZnO/SiO2 which had been preoxidised by exposure to nitrous oxide. Methyl formate on ZnO/SiO2 gave adsorbed zinc formate species and strongly physisorbed molecular methanol on silica. The comparable reaction of methyl formate with reduced Cu/ZnO/SiO2 catalyst produced bridging formate species on copper and a diminished quantity of zinc formate relative to that formed on ZnO/SiO2 catalyst. This effect is explained in terms of site blockage on the ZnO surface by small copper clusters. Addition of methyl formate to a reoxidised Cu/ZnO/SiO2 catalyst produced a considerably greater amount of formate species on zinc oxide and methoxy groups on copper were detected. The increase in concentration of zinc formate species was rationalised in terms of rearrangement of unidentate copper formate species to become bonded to copper and zinc oxide sites located at the interface between these two components.

Oxidation and pyrolysis of methane and methyl formate in a plug flow reactor: computational and experimenal studies

Biodiesel represents a possible substitute to the fossil fuels; for this reason a good comprehension of the kinetics involved is important. Due to the complexity of the biodiesel mixture a common practice is the use of surrogate molecules to study its reactivity. In this work are presented the experimental and computational results obtained for the oxidation and pyrolysis of methane and methyl formate conducted in a plug flow reactor. The work was divided into two parts: the first one was the setup assembly whilst, in the second one, was realized a comparison between the experimental and model results; these last was obtained using models available in literature. It was started studying the methane since, a validate model was available, in this way was possible to verify the reliability of the experimental results. After this first study the attention was focused on the methyl formate investigation. All the analysis were conducted at different temperatures, pressures and, for the oxidation, at different equivalence ratios. The results shown that, a good comprehension of the kinetics is reach but efforts are necessary to better evaluate kinetics parameters such as activation energy. The results even point out that the realized setup is adapt to study the oxidation and pyrolysis and, for this reason, it will be employed to study a longer chain esters with the aim to better understand the kinetic of the molecules that are part of the biodiesel mixture.

Experimental and computational study of methane and methyl formate pyrolysis and oxidation in a flow reactor

A study of the pyrolysis and oxidation (phi 0.5-1-2) of methane and methyl formate (phi 0.5) in a laboratory flow reactor (Length = 50 cm, inner diameter = 2.5 cm) has been carried out at 1-4 atm and 300-1300 K temperature range. Exhaust gaseous species analysis was realized using a gas chromatographic system, Varian CP-4900 PRO Mirco-GC, with a TCD detector and using helium as carrier for a Molecular Sieve 5Å column and nitrogen for a COX column, whose temperatures and pressures were respectively of 65°C and 150kPa. Model simulations using NTUA [1], Fisher et al. [12], Grana [13] and Dooley [14] kinetic mechanisms have been performed with CHEMKIN. The work provides a basis for further development and optimization of existing detailed chemical kinetic schemes.

Infrared study of the adsorption of methanol on oxidised and reduced Cu/SiO2 catalysts

Infrared spectra are reported of methanol adsorbed at 295 K on reduced Cu/SiO2 and on Cu/SiO2 which had been preoxidised by exposure to excess nitrous oxide. Methanol was chemisorbed on reduced Cu/SiO2 to give methoxy species on both silica and copper, gave a trace of formate on copper via reaction with residual surface oxygen, and was weakly adsorbed at SiOH sites on the silica support. Heating the adsorbed species at 393 K led to the loss of methoxy groups on copper and the concomitant formation of a bidentate surface formate. Heating reduced Cu/SiO2 in methanol at 538 K initially gave both gaseous and adsorbed (on Cu) methyl formate which subsequently decomposed to CO and hydrogen. The reactions of methanol with oxidised Cu/SiO2 were similar to those for the reduced catalyst although surface oxygen promoted the formation of surface methoxy groups on copper. Subsequent heating at 393 K led first to unidentate formate before the appearance of bidentate formate.

The irradiation of pure CH3OH and 1:1 mixture of NH3:CH3OH ices at 30 K using low energy electrons

The results of an experimental investigation of 1 keV electron irradiation of ices (deposited at 30 K) of (i) pure methanol and (ii) of a 1:1 mixture of NH3:CH3OH are reported. Molecular products formed within the ice were detected and monitored using FTIR spectroscopy. The products observed were methyl formate (H3COHCO), methane (CH4), hydroxymethyl (CH2OH), formamide (HCONH2), formic acid (HCOOH), formaldehyde (H2CO), formyl radical (HCO), cyanate ion (OCN-), isocyanic acid (HNCO), carbon monoxide (CO) and carbon dioxide (CO2). The consequences of these results for prebiotic chemistry in the interstellar medium and star forming regions are discussed. Crown Copyright (C) 2012 Published by Elsevier B. V. All rights reserved.

Structure and reactivity of the Ru(0 0 0 1) electrode towards fuel cell electrocatalysis

The reactivity of the Ru(0 0 0 1) electrode towards the adsorption and electrooxidation of CO and methanol has been studied by variable-temperature in situ FTIR spectroscopy in both perchloric acid and sodium hydroxide solution, and the results interpreted in terms of the surface chemistry of the Ru(0 0 0 1) electrode. Both linear (CO) and threefold hollow (CO) binding CO adsorbates (bands at 1970-2040 and 1770-1820 cm, respectively) were observed on the Ru(0 0 0 1) electrode in both 0.1 M HClO and 0.1 M NaOH solutions from the CO adsorption. In the acid solution, CO was detected as the main adsorbed species on Ru(0 0 0 1) surface over all the potential region studied. In contrast, in the alkaline solution, more CO than CO was detected at lower potentials, whilst increasing the potential resulted in the transformation of CO to CO. At higher potentials, the oxidation of the adsorbed CO took place via reaction with the active (1 × 1)-O oxide/hydroxide. It was found that no dissociative adsorption or electrooxidation of methanol took place at the Ru(0 0 0 1) at potentials below 900 mV vs Ag/AgCl in perchloric acid solution at both 20 and 55°C. However, in the alkaline solution, methanol did undergo dissociative adsorption, to form linearly adsorbed CO (CO) with little or no CO adsorbed at threefold hollow sites (CO) at both 20 and 55°C. Increasing the temperature from 20 to 55°C clearly facilitated the methanol dissociative adsorption to CO and also enhanced the electrooxidation of the CO. At the higher potentials, significant oxidation of methanol to CO and methyl formate in acid solution and to bicarbonate and formate in alkaline solution, was observed, which was attributed to the formation of an active RuO phase on the Ru(0 0 0 1) surface, in agreement with our previous studies. © 2003 Elsevier Ltd. All right reserved.

On-line FTIR spectroscopic investigations of methanol oxidation in a direct methanol fuel cell

A real-time Fourier transform infrared spectroscopy (FTIRS) analysis of the products of methanol oxidation in a prototype direct-methanol fuel cell operating at high temperatures (150 to 185°C) is reported here. The methanol oxidation products on platinum black and platinum-ruthenium catalyst surfaces were determined as a function of the fuel cell operating temperature, current density, and methanol/water mole ratio. Neither formaldehyde nor formic acid was detected in anode exhaust gas at all cell operating conditions. The product distributions of methanol oxidation obtained by on-line FTIRS are consistent with our previous results obtained by on-line mass spectroscopy under similar conditions. With pure methanol in anode feed, methanaldimethylacetal was found to be the main product, methyl formate and CO were also found. However, when water was present in the anode feed, the main product was CO , and the formation of methanaldimethylacetal and methyl formate decreased significantly with increase of the water/methanol mole ratio. Increase of cell operating temperature enhanced the formation of CO and decreased the formation of methanaldimethylacetal and methyl formate. Pt/Ru catalyst is more active for methanol oxidation and has a higher selectivity toward CO formation than Pt-black. Nearly complete methanol oxidation, i.e., the product was almost exclusively CO , was achieved using a Pt/Ru catalyst and a water/methanol mole ratio of 2 or higher in the anode feed at a temperature of 185°C or above.

In situ FTIR studies on the effect of temperature on the electro-oxidation of small organic molecules at the Ru(0001) electrode

The adsorption and electro-oxidation of formaldehyde, formic acid and methanol at the Ru(0001) electrode in perchloric acid solution have been studied as a function of temperature, potential and time using in situ FTIR spectroscopy, and the results interpreted in terms of the surface chemistry of the Ru(0001) electrode and compared to those obtained during our previous studies on the adsorption of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at Ru(0001) at potentials 1000 mV, both the oxidation of formic acid to CO and the oxidation of formaldehyde to both CO and formic acid were significantly increased, and the oxidation of methanol to CO and methyl formate was observed, all of which were attributed to the formation of an active RuO phase on the Ru(0001) surface.

The electro-oxidations of methanol and formic acid at the Ru(0001) electrode as a function of temperature:In-situ FTIR studies

The electro-oxidations of methanol and formic acid at a Ru(0001) electrode in perchloric acid solution have been investigated as functions of temperature, potential and time using in-situ FTIR spectroscopy, and the results compared to those obtained during our previous studies on the adsorption and electro-oxidation of CO under the same conditions. It was found that no dissociative adsorption or electro-oxidation of methanol takes place at the Ru(0001) at potentials 1000 mV, the oxidation of formic acid to CO was significantly increased, and the oxidation of methanol to CO and methyl formate was observed, both of which were attributed to the formation of an active RuO phase on the Ru(0001) surface.

A high resolution study of complex organic molecules in hot cores

We present the results of a line identification analysis using data from the IRAM Plateau de Bure Inferferometer, focusing on six massive star-forming hot cores: G31.41+0.31, G29.96-0.02, G19.61-0.23, G10.62-0.38, G24.78+0.08A1 and G24.78+0.08A2. We identify several transitions of vibrationally excited methyl formate (HCOOCH$_3$) for the first time in these objects as well as transitions of other complex molecules, including ethyl cyanide (C$_2$H$_5$CN), and isocyanic acid (HNCO). We also postulate a detection of one transition of glycolaldehyde (CH$_2$(OH)CHO) in two new hot cores. We find G29.96-0.02, G19.61-0.23, G24.78+0.08A1 and 24.78+0.08A2 to be chemically very similar. G31.41+0.31, however, is chemically different: it manifests a larger chemical inventory and has significantly larger column densities. We suggest that it may represent a different evolutionary stage to the other hot cores in the sample, or it may surround a star with a higher mass. We derive column densities for methyl formate in G31.41+0.31, using the rotation diagram method, of $\times$10$^{17}$ cm$^{-2}$ and a T$_{rot}$ of $\sim$170 K. For G29.96-0.02, G24.78+0.08A1 and G24.78+0.08A2, glycolaldehyde, methyl formate and methyl cyanide all seem to trace the same material and peak at roughly the same position towards the dust emission peak. For G31.41+0.31, however, glycolaldehyde shows a different distribution to methyl formate and methyl cyanide and seems to trace the densest, most compact inner part of hot cores.

Síntese e transformação de 4-quinolonas e quinolinas

Compostos do tipo quinolin-4(1H)-ona e quinolina estão presentes em diversas moléculas biologicamente ativas, desde alcalóides naturais a fármacos sintéticos disponíveis comercialmente, sendo que, as quinolin-4(1H)-onas destacam-se essencialmente pela sua atividade antibiótica de largo espectro. Este tipo de compostos têm sido alvo de intensa pesquisa na procura de novas moléculas com potencial aplicação na indústria farmacêutica. Nesta dissertação estabeleceram-se novos métodos de síntese de quinolin-4(1H)- onas e quinolinas e estudou-se a sua reatividade em algumas transformações químicas. No primeiro capítulo apresenta-se uma breve revisão bibliográfica sobre a ocorrência natural, atividade biológica e métodos de síntese de (E)-2- estirilquinolin-4(1H)-onas e acridin-9(10H)-onas. Seguidamente, descreve-se a síntese de novas (E)-2-estirilquinolin-4(1H)-onas a partir da ciclização de (E)- N-(2-acetilfenil)-3-arilacrilamidas, que são obtidas através da reação da 2’- aminoacetofenona com derivados do ácido cinâmico. Neste capítulo estão também descritas as transformações das (E)-2-estirilquinolin-4(1H)-onas em acridin-9(10H)-onas através de reações de Diels-Alder com a Nmetilmaleimida. No entanto, antes de se proceder ao estudo da reação de Diels-Alder foi necessário efetuar a proteção do grupo amina da 4-quinolona para evitar reações secundárias na reação de cicloadição. O estudo da proteção direta do grupo amina das (E)-2-estirilquinolin-4(1H)-onas conduziu à sintese de derivados da 2-estiril-4-metoxiquinolina como produtos secundários. A falta de regiosseletividade na reação de proteção levou a uma alteração da estratégia e as (E)-2-estiril-1-metilquinolin-4(1H)-onas foram sintetizadas a partir da reação de metilação das (E)-N-(2-acetilfenil)-3-arilacrilamidas seguida de ciclização in situ. As reações foram efetuadas também sob irradiação com micro-ondas e verificou-se que a principal vantagem desta tecnologia está relacionada com a diminuição drástica do tempo de reação. O segundo capítulo centra-se no estudo de reações catalisadas por paládio. Apresenta-se uma breve revisão bibliográfica sobre a ocorrência, propriedades biológicas e métodos de síntese de (E)-3-estirilquinolin-4(1H)-onas e furo[3,2- c]quinolinas. Seguidamente, descreve-se a síntese da 3-iodoquinolin-4(1H)- ona a partir da reação da 2’-aminoacetofenona com o formato de metilo, seguida de iodação na posição 3. A 3-iodoquinolin-4(1H)-ona será usada como precursor de novas (E)-3-estirilquinolin-4(1H)-onas através de reações de Heck com derivados do estireno. Verificou-se, no entanto, que a reação conduzia a baixos rendimentos e a estratégia utilizada para contornar esta situação foi a proteção do grupo amina da quinolona de partida, levando assim à sintese de novas (E)-3-estiril-1-metilquinolin-4(1H)-onas em bons resultados. Em alguns casos, as reações de Heck deram origem a derivados do produto secundário ramificado, verificando-se que a reação procede por duas vias mecanísticas. Este estudo foi também efetuado sob irradiação com microondas, no entanto, verificou-se que neste caso esta tecnologia conduz a uma diminuição do tempo, mas também a uma diminuição dos rendimentos. Estudou-se também a reatividade da 3-iodoquinolin-4(1H)-ona com derivados de arilacetileno em reações de Sonogashira, tendo-se estabelecido novas rotas de síntese de 2-arilfuro[3,2-c]quinolinas e, em alguns casos, de 2-aril-3- (feniletinil)furo[3,2-c]quinolinas como produtos secundários. A 3-iodo-1- metilquinolin-4(1H)-ona foi também usada como reagente de partida em reações de Sonogashira com o fenilacetileno levando à formação de novas 2- fenil-5-metilfuro[3,2-c]quinolin-4(5H)-onas. No terceiro capítulo apresenta-se uma breve revisão bibliográfica sobre a ocorrência natural, atividade biológica e métodos de síntese de pirrolo[3,2- c]quinolinas e descreve-se a síntese de novos derivados destes compostos usando a 4-cloro-3-iodoquinolina como sintão. Assim, fez-se reagir a 4-cloro-3- iodoquinolina, preparada a partir da 3-iodoquinolin-4(1H)-ona, em reações de Sonogashira, levando ao estabelecimento de novas rotas de síntese de 3- (ariletinil)-4-cloroquinolinas. Seguidamente estudou-se a reatividade das 3- (ariletinil)-4-cloroquinolinas em reações de substituição nucleofílica com várias aminas, levando à formação das intermediárias aminoquinolinas que após ciclização conduzem à síntese das novas pirrolo[3,2-c]quinolinas. Em alguns casos estes compostos foram também sintetizados num só passo usando como precursor as 3-(ariletinil)-4-cloroquinolinas, embora em piores rendimentos. Neste capítulo é também testada a reatividade da 3-(ariletinil)-4- cloroquinolina e da 4-cloro-3-iodoquinolina com a azida de sódio, tendo-se obtido as 4-aminoquinolinas correspondentes. Todos os novos compostos sintetizados foram caracterizados estruturalmente recorrendo a estudos de espectroscopia de ressonância magnética nuclear (RMN), incluindo espectros de 1H e 13C e estudos bidimensionais de correlação espectroscópica homonuclear e heteronuclear e de efeito nuclear de Overhauser (NOESY). Foram também efectuados, sempre que possível, espectros de massa (EM) e análises elementares ou espectros de massa de alta resolução (EMAR) para todos os novos compostos sintetizados.

N-H...S=C hydrogen bond in O-alkyl N-methoxycarbonyl thiocarbamates, ROC(S)N(H)C(O)O)CH(3) (R = CH(3)(-), CH(3)CH(2)-)

Pure O-methyl N-methoxycarbonyl thiocarbamate CH(3)OC(S)N(H)C(O)OCH(3) (I) and O-ethyl N-methoxycarbonyl thiocarbamate, CH(3)CH(2)OC(S)N(H)C(O)OCH(3) (II), are quantitatively prepared by the addition reaction between the CH(3)OC(O)NCS and the corresponding alcohols. The compounds are characterized by multinuclear ((1)H and (13)C) and bi-dimensional ((13)C HSQC) NMR, GC-MS and FTIR spectroscopy techniques. Structural and conformational properties are analyzed using a combined approach involving crystallographic data, vibration spectra and theoretical calculations. The low-temperature (150 K) crystal structure of II was determined by X-ray diffraction methods. The substance crystallizes in the monoclinic space group P2(1)/n with a = 4.088(1)angstrom. b = 22.346(1)angstrom, c = 8.284(1)angstrom, beta = 100.687(3)degrees and Z = 4 molecules per unit cell. The conformation adopted by the thiocarbamate group -OC(S)N(H)- is syn (C=S double bond in synperiplanar orientation with respect to the N-H single bond), while the methoxycarbonyl C=O double bond is in antiperiplanar orientation with respect to the N-H bond. The non-H atoms in II are essentially coplanar and the molecules are arranged in the crystal lattice as centro-symmetric dimeric units held by N-H center dot center dot center dot S=C hydrogen bonds Id(N center dot center dot center dot S) = 3.387(1)angstrom, <(N-H center dot center dot center dot S) = 166.4(2)degrees]. Furthermore, the effect of the it electronic resonance in the structural and vibrational properties is also discussed. (C) 2009 Elsevier Ltd. All rights reserved.