Formic Acid Molecules Research Articles

A Theoretical Study of the Photoisomerization of Glycolaldehyde and Subsequent OH Radical-Initiated Oxidation of 1,2-Ethenediol.

It has recently been discovered that carbonyl compounds can undergo UV-induced isomerization to their enol counterparts under atmospheric conditions. This study investigates the photoisomerization of glycolaldehyde (HOCH2CHO) to 1,2-ethenediol (HOCH═CHOH) and the subsequent (•)OH-initiated oxidation chemistry of the latter using quantum chemical calculations and stochastic master equation simulations. The keto-enol tautomerization of glycolaldehyde to 1,2-ethenediol is associated with a barrier of 66 kcal mol(-1) and involves a double-hydrogen shift mechanism to give the lower-energy Z isomer. This barrier lies below the energy of the UV/vis absorption band of glycolaldehyde and is also considerably below the energy of the products resulting from photolytic decomposition. The subsequent atmospheric oxidation of 1,2-ethenediol by (•)OH is initiated by addition of the radical to the π system to give the (•)CH(OH)CH(OH)2 radical, which is subsequently trapped by O2 to form the peroxyl radical (•)O2CH(OH)CH(OH)2. According to kinetic simulations, collisional deactivation of the latter is negligible and cannot compete with rapid fragmentation reactions, which lead to (i) formation of glyoxal hydrate [CH(OH)2CHO] and HO2(•) through an α-hydroxyl mechanism (96%) and (ii) two molecules of formic acid with release of (•)OH through a β-hydroxyl pathway (4%). Phenomenological rate coefficients for these two reaction channels were obtained for use in atmospheric chemical modeling. At tropospheric (•)OH concentrations, the lifetime of 1,2-ethenediol toward reaction with (•)OH is calculated to be 68 h.

From roaming atoms to hopping surfaces: mapping out global reaction routes in photochemistry.

The photodissociation of small molecules occurs upon irradiation by ultraviolet or visible light, and it is a very important chemical process in Earth's atmosphere, in the atmospheres of other planets, and in interstellar media. Photodissociation is an important method used to thoroughly investigate the fundamental issues of chemical reactivity. Photodissociation involves molecules and reaction fragments moving over ground- and excited-state potential surfaces (PESs). Molecules can move on a single PES (adiabatic pathway) or can cross over from one PES to another (nonadiabatic pathways). For a full theoretical understanding of a photodissociation mechanism, all of the important nonadiabatic and adiabatic pathways must be determined. This is not an easy task. We have developed an efficient computational method, called the global reaction route mapping (GRRM) strategy, that allows a theoretical exploration of ground- and excited-state PESs and their crossing seams in an automatic manner. In this Perspective, we summarize our approaches and present examples of their application together with newly determined chemical insights. These include the complex photodissociation mechanism of the formaldehyde molecule, the exclusive excited-state roaming dynamics of the nitrate radical, and all product channels and conformational memory in the photodissociation of the formic acid molecule. Finally, perspectives for the theoretical design of photofunctional molecules are discussed.

Hydroxyl radical initiated oxidation of formic acid on mineral aerosols surface: a mechanistic, kinetic and spectroscopic study

Environmental context The presence of air-borne mineral dust containing silicates in atmospheric aerosols should be considered in any exploration of volatile organic compound chemistry. This work reports the mechanisms, relative energies and kinetics of free-radical reactions with formic acid adsorbed on silicate surface models. We find that silicate surfaces are more likely to act as a trap for organic radicals than to have a catalytic effect on their reactions. Abstract Heterogeneous reactions of atmospheric volatile organic compounds on aerosol particles may play an important role in atmospheric chemistry. Silicate particles are present in air-borne mineral dust in atmospheric aerosols, and radical reactions can be different in the presence of these mineral particles. In this work, we use quantum-mechanical calculations and computational kinetics to explore the reaction of a hydroxyl free radical with a formic acid molecule previously adsorbed on several models of silicate surfaces. We find that the reaction is slower and takes place according to a mechanism that is different than the one in the gas phase. It is especially interesting to note that the reaction final products, which are the formyl radical attached to the cluster surface, and a water molecule, are much more stable than those formed in the gas phase, the overall reaction being highly exothermic in the presence of the surface model. This suggests that the silicate surface is a good trap for the formed formyl radical. In addition, we have noted that, if a second hydroxyl radical approaches the adsorbed formyl radical, the formation of carbonic acid on the silicate surface is a highly exothermic and exergonic process. The carbonic acid molecule remains strongly attached to the surface, thus blocking CO2 formation in the formic acid oxidation reaction. The spectroscopic properties of the systems involved in the reaction have been calculated, and interesting frequency shifts have been identified in the main vibration modes.

Catalytic effect of water, water dimer, or formic acid on the tautomerization of nitroguanidine

We have investigated the reaction mechanisms and kinetics of water, water dimer, or formic acid catalyzed gas-phase isomerization of α-nitroguanidine to β-nitroguanidine by means of high level theoretical methods and transition state theory. The potential energy surface profile has been characterized at the CCSD(T)/6-311++G(2df,2pd)//M06-2X-D3/6-311++G(3df,3pd) level with zero-point energy correction. The calculations indicate that incorporation of water, water dimer, or formic acid molecule into the reactant α-nitroguanidine can noticeably reduce the energy barrier. The reductions are found to be small for water and most significant for formic acid. Most importantly, the kinetics calculations show that the rate constants for the water, water dimer or formic acid assisted reactions are about 14, 14 or 19 orders of magnitude larger than those for the uncatalyzed reaction, respectively. These results suggest that formic acid should play a larger role than both water and water dimer on isomerization of α-nitroguanidine to β-nitroguanidine under tropospheric conditions.

Tandem mass spectrometric fragmentation behavior of lignans, flavonoids and triterpenoids in Streblus asper.

An unambiguous identification of compounds can be achieved by comparison of known fragmentation patterns. While the literature about fragmentation mechanisms of lignans, flavonoids and triterpenoids is few. So the present study analyses the fragmentation mechanisms of these compounds isolated from Streblus asper. Electrospray ionization ion trap mass spectrometry (ESI-ITMS) and atmospheric pressure chemical ionization ion trap mass spectrometry (APCI-ITMS) were used to obtain the MS(n) spectra of the compounds. By analyzing the differences between the ions, the fragmentation mechanisms of these compounds were explored. Of the 29 compounds detected, 17, 7, and 5 were lignans, flavonoids and triterpenoids, respectively. The majority of lignans were found to give [M - H](-) ions of sufficient abundance for MS(n) analyses. The flavonoids were prone to the loss of CO and H2O. The triterpenoids always lost one formic acid molecule and two hydrogens, or one H2O from [M - H](-) to form the most abundant product ion in the MS(n) spectrum. ESI/APCI-ITMS were demonstrated to be fast, effective and practical tools to characterize the structures of flavonoids, triterpenoids and lignans. Results of the present study can help identify the analogous constituents by analyzing their MS(n) spectra.

Formic Acid on TiO2–x (110): Dissociation, Motion, and Vacancy Healing

The adsorption and dissociation of a formic acid molecule (HCOOH) on a partially reduced rutile TiO2-x (110) surface and the subsequent transformations of the adsorbed fragments are studied via qua ...

Hydrolysis of glyoxal in water-restricted environments: formation of organic aerosol precursors through formic acid catalysis.

The hydrolysis of glyoxal involving one to three water molecules and also in the presence of a water molecule and formic acid has been investigated. Our results show that glyoxal-diol is the major product of the hydrolysis and that formic acid, through its ability to facilitate intermolecular hydrogen atom transfer, is considerably more efficient than water as a catalyst in the hydrolysis process. Additionally, once the glyoxal-diol is formed, the barrier for further hydrolysis to form the glyoxal-tetrol is effectively reduced to zero in the presence of a single water and formic acid molecule. There are two important implications arising from these findings. First, the results suggest that under the catalytic influence of formic acid, glyoxal hydrolysis can impact the growth of atmospheric aerosols. As a result of enhanced hydrogen bonding, mediated through their polar OH functional groups, the diol and tetrol products are expected to have significantly lower vapor pressure than the parent glyoxal molecule; hence they can more readily partition into the particle phase and contribute to the growth of secondary organic aerosols. In addition, our findings provide insight into how glyoxal-diol and glyoxal-tetrol might be formed under atmospheric conditions associated with water-restricted environments and strongly suggest that the formation of these precursors for secondary organic aerosol growth is not likely restricted solely to the bulk aqueous phase as is currently assumed.

Ion–ion coincidence imaging of dissociative ionization dynamics of formic acid in intense laser fields

We have studied the dissociative ionization dynamics of formic acid molecules with intense femtosecond laser pulses centered at 800nm, employing the ion–ion coincidence imaging technique. Fragmentation reactions originating from both singly and doubly charged parent formic acid ions are observed. In this paper the kinetic energy distributions of several different ionic fragments will be presented. A clear difference in the kinetic energy distributions is observed between ionic fragments originating from the dissociation of the singly charged parent ion and those from the Coulomb explosion of the doubly charged parent ion. Channels exhibiting the emission of neutral hydrogen and channels exhibiting intra molecular hydrogen migration will also be discussed. We present a combined theoretical and experimental study to get to an understanding of the hydrogen migration mechanism at the molecular level.

Pd-Catalyzed Reduction of Aldehydes to Alcohols Using Formic Acid as the Hydrogen Donor

Facile and selective reduction of aromatic aldehydes as well as aliphatic aldehydes to alcohols was achieved using formic acid as the hydrogen donor in the presence of a catalytic amount of Pd(OAc)2 and Cy3P. It was found that both hydrogen atoms in the formic acid molecule can serve as the hydride source. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]

Influences of aniline, carbazole, indole, and pyrrole monomers and polymers on formic acid oxidation at Pt electrodes

The effects of aniline, carbazole, indole, and pyrrole on formic acid oxidation at Pt electrodes are compared with those of their corresponding polymers. While thin films of polyaniline, polycarbazole, polypyrrole, and polyindole all promote the direct oxidation (i.e. the pathway that does not involve carbon monoxide as an intermediate) of formic acid at low potentials on Pt, only aniline exhibits a similar effect when added to the formic acid solution. At +0.25V vs. SCE, current enhancements over bare Pt by factors of 4.0, 3.0, 3.4, 5.2, 6.8, respectively, were observed. Interestingly, drop coating of a Pt electrode with carbazole also promoted the direct pathway, although adsorption of carbazole from solution only inhibited formic acid oxidation. The promotion of the direct pathway by aniline adsorbed from solution followed a dependence on surface coverage that suggests inhibition of poisoning by adsorbed carbon monoxide. It is argued that the diversity of these effects indicates that the mechanism by which the direct pathway becomes favoured does not involve any specific chemical functionality of the modifier. However, it must be dependent on the orientation of the modifier relative to the Pt surface. A recent literature model, in which the direct pathway is shown to be favoured by disruption of the H-bonding network of water at the water/metal interface, is invoked to explain this. According to this model, the reaction pathway is determined by the orientation of the formic acid molecule as it adsorbs, which can be changed by other adsorbed species (formate in the model) that create a local hydrophobic region. It is suggested that the modifiers used here can play a similar role.

Electron collisions with the HCOOH⋯(H2O)n complexes (n = 1, 2) in liquid phase: The influence of microsolvation on the π* resonance of formic acid

We report momentum transfer cross sections for elastic collisions of low-energy electrons with the HCOOH···(H2O)n complexes, with n = 1, 2, in liquid phase. The scattering cross sections were computed using the Schwinger multichannel method with pseudopotentials in the static-exchange and static-exchange plus polarization approximations, for energies ranging from 0.5 eV to 6 eV. We considered ten different structures of HCOOH···H2O and six structures of HCOOH···(H2O)2 which were generated using classical Monte Carlo simulations of formic acid in aqueous solution at normal conditions of temperature and pressure. The aim of this work is to investigate the influence of microsolvation on the π* shape resonance of formic acid. Previous theoretical and experimental studies reported a π* shape resonance for HCOOH at around 1.9 eV. This resonance can be either more stable or less stable in comparison to the isolated molecule depending on the complex structure and the water role played in the hydrogen bond interaction. This behavior is explained in terms of (i) the polarization of the formic acid molecule due to the water molecules and (ii) the net charge of the solute. The proton donor or acceptor character of the water molecules in the hydrogen bond is important for understanding the stabilization versus destabilization of the π* resonances in the complexes. Our results indicate that the surrounding water molecules may affect the lifetime of the π* resonance and hence the processes driven by this anion state, such as the dissociative electron attachment.

Chemical reactions induced in frozen formic acid by heavy ion cosmic rays

We studied the effects produced by the interaction of heavy ion cosmic rays with interstellar and cometary organic molecules in the solid phase. Formic acid (HCOOH) ice at 15 K was irradiated by 267-MeV 56Fe22+ ions and the chemical evolution was analysed using Fourier transform infrared spectroscopy. The destruction cross-section of HCOOH and the formation cross-sections of the produced molecular species have been determined; the sputtering yield values are also discussed. The most abundant chemical species formed by Fe ion irradiation are CO, CO2 and H2O. The half-life of frozen formic acid molecules in the interstellar medium, as a result of interaction with the different cosmic ray constituents, is evaluated to be 108 yr, considering that the destruction cross-section σd of heavy ions is ruled by a power law as a function of the electronic stopping power Se (i.e. σd ∼ S3/2e). Moreover, a complementary study based on mass spectrometry data from the literature has been performed, in order to understand the HCOOH molecule radiolysis, the desorption of its product and the chemical reaction pathways in ice.

Structural and magnetic characterization of the tridimensional network [Fe(HCO2)3]n·nHCO2H

In this work we report the structural and magnetic characterization of a new three-dimensional porous metal–organic framework (MOF) based on iron(III) and the formate anion, [Fe(HCO2)3]n·nHCO2H (1), which was obtained by solvothermal synthesis. The tridimensional structure crystallizes in the trigonal space group Rc and is formed by highly regular octahedral Fe(OHCO)6 units. These units contain six equal Fe–O distances, with angles slightly different from 90° or 180°. The packing of 1 corresponds to a 3D covalent network defined by face sharing between the parallelepipeds, which are formed by the interactions of Fe(OHCO)6 units through formate ligands, thus generating a 41263 topology. This topology contains channels in the three spatial directions, in which it is possible to find guest molecules of formic acid. The thermogravimetric analysis shows that 1 remains stable till 180 °C; after this temperature the decomposition of 1 begins. From a magnetic point of view, the reported MOF presents an antiferromagnetic behaviour in the 296 to 20 K range. The fit of the experimental data between room temperature and 50 K, using the high temperature series model (HTS model), permits us to estimate a J value of −1.01 cm−1, which is in agreement with the reported values for analogous systems based on transition metal ions and formate ligands. Below this temperature, a weak ferromagnetism as a product of spin canting was observed due to the anti–anti coordination mode of the bridging ligand, which satisfies the requirement for Dzyaloshinsky–Moriya antisymmetric interactions between the FeIII ions. The isothermal magnetization obtained at 2 K shows that the magnetization increases linearly with the applied magnetic field, reaching a value of 0.49Nβ at the highest applied field of 50 kOe, indicating the antiferromagnetic character of the ground state. DFT calculations using a dinuclear fragment confirm the magnitude and nature of the magnetic phenomena of this extended system at high temperatures.

Hollow palladium nanospheres with porous shells supported on graphene as enhanced electrocatalysts for formic acid oxidation

The hollow palladium nanospheres with the porous shell comprised of uniform 5 nm Pd nanoparticles (Pd NS-HP) have been synthesized successfully by employing a simple replacement process between PdCl4(2-) ions and Co with the assistance of a structure-directing agent, polyvinyl pyrrolidone (PVP). Then, the obtained Pd NS-HP is supported on graphene nanosheets (GN) to prepare Pd NS-HP/GN composites by a wet-impregnation method. As the catalyst towards formic acid electrooxidation, the Pd NS-HP/GN composite exhibits a larger electrochemically active surface area, better electrocatalytic activity and better stability compared with Pd nanoparticles/graphene (Pd NP/GN) and commercial Pd/C catalysts. The enhancement in electrocatalytic performance of Pd NS-HP/GN is attributed to the abundant connected pore channels in the inner and exterior surfaces of Pd nanospheres, which could provide a large contact surface for adsorption and transmission of reactants, facilitating the oxidation of formic acid molecules on its surface and also improving the utilization of Pd metal. Moreover, the support of graphene could enhance the stability of the catalyst.

AN AB INITIO MOLECULAR DYNAMICS STUDY ON THE SOLVATION OF FORMATE ION AND FORMIC ACID IN WATER

Formate ion and formic acid are linked in water by the equilibrium for the acidic dissociation of formic acid, which as the simplest carboxylic acid is an important model system. In this study, the microscopic details of the solvation around a formate ion and around a formic acid molecule in aqueous solution are explored by ab initio molecular dynamics simulations, at 300, 500, 700, and 900 K. The formate ion exerts a strong influence on the surrounding solvent molecules by hydrogen bonding, which restricts the access of other water molecules. With rising temperature, the hydrogen bonds are disrupted, and the space around formic acid becomes more accessible. Solvation of the formic acid is marked by its partial dissociation to produce a proton, and the hydrogen bond interaction around a formic acid is not as strong as that around a formate ion. The acidic dissociation becomes less favorable as temperature rises, which indicates a lesser catalytic role for the water molecules in the thermal dissociation of formic acid.

Methanol and formic acid electrooxidation on nafion modified Pd/Pt{1 1 1}: The role of anion specific adsorption in electrocatalytic activity

The electrooxidation of formic acid and methanol on Pt{111} in aqueous sulphuric and perchloric acid as a function of both palladium coverage and Nafion adsorption is reported. Nafion is a proton conducting polymer commonly used as a membrane electrolyte in fuel cells. Understanding the interaction of Nafion with platinum and other bimetallic electrocatalytic surfaces is therefore of crucial importance if one is to optimise fuel cell performance. Here, we demonstrate that for formic acid electrooxidation, Nafion behaves as a weakly adsorbing electrolyte exhibiting similar properties to aqueous perchloric acid. Adsorbed palladium is observed to promote formic acid electrooxidation on Pt{111} and a maximum in electrooxidation rate is found when a single monolayer of palladium on Pt{111} is formed in agreement with previous studies. In contrast, aqueous sulphuric acid strongly inhibits formic acid electrooxidation due to extensive specific adsorption of (bi-)sulphate anions on the palladium adlayer which compete successfully with molecules of formic acid for adsorption sites. In all electrolytes studied, unique electrooxidation peaks ascribable to formic acid electrooxidation occurring on first and second/third layer palladium islands are observed. We ascribe this behaviour to a strong coupling of formic acid adsorption with changes in the local potential of zero total charge as a function of palladium coverage. Hence, it is deduced that Pd/Pt electrocatalysts utilising Nafion membranes should not prove deleterious to electrocatalytic activity. In contrast, similar measurements but using methanol instead of formic acid indicated that methanol electrooxidation is inhibited significantly when Nafion is adsorbed relative to activity recorded in aqueous perchloric acid. In addition, palladium adlayers on Pt{111} are found to inhibit methanol electrooxidation in all electrolytes studied, presumably because the key CH methanol dissociation step is less favoured on palladium compared to platinum. It is concluded that the role of specifically adsorbed anions is crucial in order to afford optimal fuel cell performance and that for methanol at least, proton conducting membranes other than Nafion should be considered although for formic acid, Nafion appears to be ideal.

Theoretical–Experimental Study of Formic Acid Photofragmentation in the Valence Region

Photoionization and photofragmentation studies of formic acid (HCOOH) are performed for the valence shell electron ionization process. The total and partial ion yield of gaseous HCOOH were collected as a function of photon energy in the ultraviolet region, between 11.12 and 19.57 eV. Measurements of the total and partial ion yield of gaseous formic acid molecule are performed with a time-of-flight mass spectrometer at the Synchrotron Light Brazilian Laboratory. Density functional theory and time dependent density functional theory are employed to calculate the ground and excited electronic state energies of neutral and ionic formic acid as well as their fragments and normal vibration modes. The ionization potential energies, the stability of electronic excited states of HCOOH(+), and the energies of opening fragmentation channels are estimated from theoretical-experimental analysis. Additionally, the main formic acid photofragmentation pathways by exposition of photons within that energy range are determined experimentally. These produced ions primarily have the following mass/charge ratios: 46 (HCOOH(+)), 45 (COOH(+)), 29 (HCO(+)), and 18 (H(2)O(+)).

Aggregation of Benzene Molecules with Molecules of Methanol and Formic Acid

Calculations and experimental studies of Raman scattering spectra show that there is a dimeric aggregation of benzene molecules with the molecule of methyl alcohol with the use of π-electrons of the benzene ring. In this process, the H-active hydrogen atom of O–H group is oriented to the edge of the benzene ring (a distance along the normal to the plane of the benzene ring is 2.850 Å). The unusual position of the H-active hydrogen atom is conditioned by the interaction of two hydrogen atoms of the alcohol's methyl group with π-electrons of the benzene ring. In Raman scattering spectra, the aggregation of molecules in the liquid state of the substance leads to a broadening of the band of full-symmetric vibrations with the maximum at 992 cm–1, as well as to a shift of this band toward lower frequencies by ~1 cm–1. The band at 992 cm–1 is narrowed more than twice at the strong dilution of the benzene–methyl alcohol mixture by a large amount of heptane. The aggregation of benzene molecules takes place also with the molecules of formic acid with the use of π-electrons of the benzene ring. As in the case of the benzene–methyl alcohol mixture, the H-active hydrogen atom of O–H group of the acid is shifted toward the edge of the benzene ring. The energy of the benzene–formic acid dimerization is 9.2 kJ/mole.

Interaction Energies and Spectroscopic Effects in the Adsorption of Formic Acid on Mineral Aerosol Surface Models

Heterogeneous reactions of atmospheric volatile organic compounds (VOCs) on aerosol particles may play an important role in atmospheric chemistry. Silicate particles are present in airborne mineral dust in aerosols, and the atmospheric chemistry in general can be modified by their presence. In this work, the adsorption of a single formic acid molecule on different silicate surface models has been studied using quantum-mechanical methods. Both molecular clusters and a periodic crystal model of the (001) pyrophyllite surface have been employed, and all possible adsorption geometries have been considered. We find that silanol groups are always the most reactive formic acid adsorption sites. In the case of a periodic system, silanol groups at the crystal edges are favored. However, OH groups on the phyllosilicate octahedral sheet are also reactive sites through the tetrahedral cavities. The effect of formic acid adsorption on the spectroscopic properties of the whole system is also analyzed. Significant frequ...

Theoretical insights into the effects of the diameter and helicity on the adsorption of formic acid on silicon carbide nanotube

The anchoring of small organic molecules onto the semiconductor surface has a great application for developing various molecular devices, such as novel solar cells, fuel cells, hybrid systems, sensors, and so on. In the present work, by carrying out detailed density-functional theory calculations, we have investigated the adsorption of the formic acid (HCOOH) molecule on planar and various curved silicon carbide (SiC) nanotubes. By considering both the molecular and dissociative adsorptions of HCOOH on these SiC nanomaterials, we found that the HCOOH molecule prefers to dissociate into HCOO and H group. Interestingly, different adsorption modes were found for HCOOH on SiC nanotubes, i.e. dissociative monodentate or bidentate adsorption, which depends on the tube diameter and helicity. For (n, 0) SiC nanotube, the monodentate adsorption mode is energetically favorable when n is less than 10. However, HCOOH prefers to be adsorbed on other (n, 0) SiC nanotubes in a bridged bidentate mode, which is similar to those of on (n, n) SiC nanotubes or planar SiC sheet. Moreover, upon HCOOH adsorption, these SiC nanomaterials remain to be of the semiconducting nature and their band gaps are decreased to different degrees. In addition, we also explored the effects of HCOOH coverage on its adsorption on SiC nanotube.