Formohydroxamic Acid Research Articles

Optimization of conventional hydroxamic acid for cassiterite flotation: Application of structural modification under principle of isomerism

In this paper, through the structural modification of N-phenyl formohydroxamic acid (NPFHA), an isomer of benzohydroxamic acid (BHA), we designed and synthesized a series of N-phenyl hydroxamic acids (NPHA), including N-phenyl acetohydroxamic (NPHA-2), N-phenyl butyrohydroxamic acid (NPHA-4), N-phenyl hexanohydroxamic acid (NPHA-6) and N-phenyl octanohydroxamic acid (NPHA-8), and first introduced them as flotation collectors for selectively separating cassiterite from quartz and feldspar. Micro-flotation tests indicated that with increase of non-polar carbon chain length, the collecting ability to cassiterite improved dramatically. More to the point, compared to BHA, NPHA-6 and NPHA-8 possessed superior flotation performances to cassiterite and enabled the separation of cassiterite and quartz/feldspar over a wide pH range, with no application of frother or activator, providing a new insight into the development of cassiterite collector. Zeta potential experiments indicated that NPHA-8 chemisorbed onto cassiterite surfaces, with no significant adsorption to quartz or feldspar detected. DFT calculations, FT-IR and XPS analyses further demonstrated that NPHA-8 chemisorbed on cassiterite surfaces by forming C–O–Sn and N-O–Sn bonds, accompanied by proposing two interaction geometries, first with the same Sn atom of cassiterite surface, leading to a five-membered chelating ring, second with two different Sn atoms, resulting in constituting an irregular complex.

Mechanistic insight into the methanol selective catalytic reduction of NO reaction over Cu-containing perovskites

The selective catalytic reduction (SCR) of NO by methanol was studied on LaFe0.8Cu0.2O3, and compared with that on an Ag/Al2O3 reference catalyst. A detailed characterization of the catalyst’s physicochemical properties was carried out by X-ray diffraction, N2 physisorption, H2 temperature-programmed reduction, isotopic exchange experiments, NOads + O2ads temperature-programmed desorption, and X-ray photoelectron spectroscopy. Materials reactivity was investigated in the CH3OH-SCR of NO. The LaFe0.8Cu0.2O3 catalytic system, modified using reactive grinding (Cu-RG), exhibits the best catalytic performance in terms of both NO conversion (95% at 450 °C) and N2 yield (YN2 ≈ 93%). Activity is related to low-temperature Cu2+ redox activation, and a strong improvement of structural Fe3+ reducibility occurs with substitution of the structure. In contrast, Ag/Al2O3 was confirmed to be close to inactive in the studied temperature range. To elucidate the main reaction pathways over the two catalysts, in situ diffuse reflectance infrared Fourier transform spectroscopy was performed to determine the nature of the adsorbed species and surface intermediates involved. Over Cu-containing perovskite, CH3OH is observed to form methoxy species (OCH3). The surface adNOx species observed over Cu-RG are mainly reactive nitrite/nitrate species, which further reacted with OCH3 species to form formohydroxamic acid and carboxylate. In the case of Ag/Al2O3, nitrate species continuously accumulated over the alumina surface, on which dehydration of CH3OH indubitably occurs. Therefore, no enolic intermediate of SCR can be observed over Ag/Al2O3. A reaction mechanism over LaFe0.8Cu0.2O3 was finally proposed, supported by density functional theory calculations, in which CN bond coupling accompanied by the first H transfer step is identified as the crucial step for N2 production in the CH3OH-SCR process over Cu-containing perovskites.

Covalency-Driven Dimerization of Plutonium(IV) in a Hydroxamate Complex.

The reaction of formohydroxamic acid [NH(OH)CHO, FHA] with Pu(III) should result in stabilization of the trivalent oxidation state. However, slow oxidation to Pu(IV) occurs, which leads to formation of the dimeric plutonium(IV) formohydroxamate complex Pu2(FHA)8. In addition to being reductants, hydroxamates are also strong π-donor ligands. Here we show that formation of the Pu2(FHA)8 dimer occurs via covalency between the 5f orbitals on plutonium and the π* orbitals of FHA(-) anions, which gives rise to a broad and intense ligand-to-metal charge-transfer feature. Time-dependent density functional theory calculations corroborate this assignment.

Demonstration of the Use of Formohydroxamic Acid in the UREX Process

The Uranium Extraction (UREX) process was developed to separate U and Tc from the transuranic elements and the remaining fission products. To prevent the extraction of Np and Pu, a dilute nitric acid scrub stream containing acetohydroxamic acid (AHA) is used in the process. When the AHA contacts nitric acid, the complexant begins to decompose producing acetic acid and hydroxylamine nitrate (HAN). The HAN decomposes to gaseous products and water; however, the acetic acid is relatively stable and will contaminate nitric acid recovered from waste streams. To address this issue, formohydroxamic acid (FHA) was evaluated as a replacement for AHA. Formohydroxamic acid prevents the extraction of Np and Pu and its decomposition products (formic acid and HAN) readily decompose. Neptunium and Pu distribution coefficient measurements demonstrated that FHA was an acceptable replacement for AHA. Additional extraction experiments performed with the addition of uranyl nitrate to the aqueous phase showed that its presence had little effect on the distribution coefficients. A steady increase in distribution coefficients with increasing nitrate concentrations was consistent with a salting-out effect. When the actinides were back-extracted into the aqueous phase, the Np and Pu distribution coefficients were larger than the distribution coefficients measured in an extraction mode potentially due to kinetic limitations. These data imply that a greater number of scrub stages would be required in the first bank of the UREX process contactors than would be calculated based on the Pu and Np distribution data generated in the extraction experiments.

Ab initio study on transition states of formohydroxamic acid tautomerization in the presence of water molecules

Keto-iminol transformation of formohydroxamic acid in the presence of water molecules is investigated using ab initio quantum mechanics calculations. Calculations revealed that the proton transfer energy barriers are significantly lowered in the presence of water molecules. The proton transfer in Z-keto form occurs via a pathway involving two transition states and a charge separated intermediate. The proton transfer in E-keto tautomer occurs via a single transition state. A third pathway, which is not feasible in the absence of water, becomes feasible when there are hydrogen bonded water molecules. The stability order of formohydroxamic acid tautomers was found to be E-keto>Z-keto>Z-iminol>E-iminol and remains the same even after hydrogen bonded to water.

Hydrogen bonding ability and acid–base behavior of formylphosphinous acid: an isostere of formohydroxamic acid

The conformational isomerism, relative stabilities of isomeric forms, acid–base behavior, and hydrogen bonding of formylphosphinous acid (FPA), an isostere of formohydroxamic acid (FHA) and its tautomer formylphosphine oxide have been analyzed in the present study. Molecular orbital and density functional theory methods in conjunction with 6-31+G* basis set have been employed. The protonation, deprotonation, and hydrogen bonding abilities of FHA and FPA have been compared. FPA has P as preferred site of deprotonation like N in FHA, but they differ in their preferred site of protonation. With similar nature and orientation of H-bond donor and acceptor atoms, stabilization energy of most stable aggregate of FHA with water is 0.99 kcal/mol higher than that of similar aggregate of FPA with water. In addition, FPA is more stable than its corresponding oxide form in gas phase as well as on H-bonding interaction with single water molecule.

Thermal Stability of Formohydroxamic Acid

The thermal stability of formohydroxamic acid (FHA) was evaluated to address the potential for exothermic decomposition during storage and its use in the uranium extraction process. Accelerating rate calorimetry showed rapid decomposition at a temperature above 65°C; although, the rate of pressure rise was greater than two orders of magnitude less than the lower bound for materials which have no explosive properties with respect to transportation. An FHA solution in nitric acid did not reach runaway conditions until 150°C. Water appeared to temper the FHA decomposition. Analysis by differential scanning calorimetry showed that FHA melted at 67°C and thermally decomposed at 90°C with an enthalpy of −1924 J/g. The energics of the FHA thermal decomposition are comparable to those measured for aqueous solutions of hydroxylamine nitrate. Solid FHA should be stored in a location where the temperature does not exceed 20–25°C. As a best practice, the solid material should be stored in a climate-controlled environment such as a refrigerator or freezer. FHA solutions in water are not susceptible to degradation by acid hydrolysis and are the preferred way to handle FHA prior to use.

Hydrolysis of Hydroxamic Acid Complexants in the Presence of Non-Oxidizing Metal Ions

ABSTRACTSimple Hydroxamic acids (XHAs) are salt free, organic compounds with affinities for hard cations such as Fe3+, Np4+, Pu4+ and have been identified as suitable reagents for the control of Pu and Np in advanced nuclear fuel reprocessing. Building upon previous work on the neptunium(IV)-formohydroxamic(FHA) acid system [1], a model that describes the hydrolysis of the acetohydroxamate moiety has been extended to include hydrolysis of bishydroxamatoneptunium(IV) complex. The model has been used to determine the rate constants for hydrolysis of mono- and bis-acetohydroxamatoneptunium(IV) at 25 °C, which were found to be 1.0×10-5 dm3 mol-1 s-1 and 5.0×10-5 dm3 mol-1 s-1, respectively.

Hydrogen bond cooperativity in dimers of hydroxamic acids

AbstractMolecular orbital calculations are performed on various dimeric forms of four tautomers each of thioformohydroxamic acid and formohydroxamic acid. The analysis of stabilization energies associated with the dimerization and their correlation to proton affinities and deprotonation enthalpies of different potential sites present in the molecules indicate that the highest stabilization results when the most basic, site of the molecule acts as hydrogen bond acceptor but combination of the most acidic and the most basic site does not result in the largest stabilization when dimerization occurs. The presence of hydrogen bond cooperativity is indicated and the reasons for the observed cooperativity are explored in this study. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Mechanistic aspects of the selective catalytic reduction of NO x by dimethyl ether and methanol over γ-Al 2O 3

High catalytic activity for selective catalytic reduction of NO x with dimethyl ether and methanol (DME- and methanol-SCR) has been found over a γ-alumina catalyst. The surface species involved in the DME-SCR reaction were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in combination with mass spectrometry and compared to the corresponding species observed during methanol-SCR. Dimethyl ether adsorbs mainly as methoxy groups ( O CH 3) on the catalyst surface, while methanol adsorbs as methoxy groups and molecularly. With increasing temperature, DME desorbs in two steps, whereas methanol desorbs first as methanol and at higher temperatures as DME. At higher temperatures, the two reducing agents display similar DRIFTS spectra showing first formaldehyde-like species and then formates on the surface. In the presence of NO or NO 2, reactions between NO x species and carbon-containing species occur. Formohydroxamic acid (CHO N(H)OH) forms isocyanates (NCO), and both are observed at temperatures relevant for DME-SCR. Since these species are likely intermediates for hydrocarbon-SCR over Ag/Al 2O 3, a partly similar reaction mechanism may be operational for DME-SCR over γ-Al 2O 3 despite the fact that Ag/Al 2O 3 does not catalyze DME-SCR efficiently. The difference is thus due to the reaction steps leading to the formation of formohydroxamic acid that with DME follow a more efficient route over γ-Al 2O 3 than over Ag/Al 2O 3.

ChemInform Abstract: Molecular Orbital Study of the Structures of Hydroxamic Acids

Semiempirical (AM1 and PM3) and ab initio Hartree-Fock and Moeller-Plesset (MP2) calculations using the 3-21G, 3-21G(d), 6-31G(d,p), 6-311G(d,p) basis sets are reported for the E and Z conformations of both the keto and iminol tautomers of formohydroxamic acid. Semiempirical and Hartree-Fock calculations are also reported for several substituted hydroxamic acids. The HF calculations tend to favor the non-hydrogen-bonding E forms, while the MP2 calculations predict both of the Z forms to be close in energy

Gas phase and solution state stability of complexes L…M, where M = Cu 2+, Ni 2+, or Zn 2+ and L = R−C( [dbnd]O)NHOH (R = H, NH 2, CH 3, CF 3, or Phenyl)

The structure and gas-phase metal affinities (M = Cu 2+, Ni 2+, and Zn 2+) of formohydroxamic acid derivatives R–C( O)NHOH (R = H, NH 2, CH 3, CF 3 and Phenyl) were studied using the B3LYP/6-311+G(d,p) method of DFT theory. In order to evaluate the conformational behavior of these systems in water, we carried out CPCM-SCRF optimization calculations at the B3LYP/6-311+G(d,p) levels of theory. The obtained optimized geometries and interaction affinities of the gas and solution phase were compared. The following order of stability was found for ionic complexes of the transition metals: Cu 2+ > Ni(t) 2+ > Zn 2+. The same stability order would be expected according to the Irving–Williams order of stability constants. The high-spin complexes of the Ni 2+ were more stable than the low-spin complexes. The solvent effect reduced the observed relative stability of individual metallic complexes of substituted hydroxamic acids.

C [sbnd]N rotational barrier, MP4 and CCSD(T) energies of formohydrazide and formohydroxamic acid and vibrational spectral analysis of the hydrazide

The C N internal rotations in formohydrazide OHC NH NH 2 and formohydroxamic acid OHC NH OH were investigated at the B3LYP/6-311+G** and MP2/6-311+G** levels of theory. The C N rotational barrier in the molecules was calculated to be about 28–30 kcal/mol. The energies of the molecules were calculated at the B3LYP, MP2, MP4(SDTQ) and CCSD(T) levels of theory with both 6-311G** and 6-311+G** basis sets. From the calculations at all the levels formohydroxamic acid was predicted to exist predominantly in a non-planar near- cis conformation at ambient temperature. From all the calculations formohydrazide was predicted to have a planar cis–syn (C O and N N bonds eclipse each other and NH 2 moiety is syn to C N bond) conformation as the lowest energy structure. The NH 2 inversion barrier in formohydrazide was predicted to be about 5–7 kcal/mol. The vibrational frequencies of the cis–syn formohydrazide were computed at the B3LYP/6-311+G** level and normal coordinate calculations were carried out. Complete vibrational assignments were made on the basis of normal coordinate analyses and experimental infrared and Raman data of the molecule.

A comparative study on hydrogen bonding ability of thioformohydroxamic acid and formohydroxamic acid

The presence of intra and intermolecular hydrogen bonding interactions has been explored in six tautomeric forms of thioformohydroxamic acid and its 1:1 aggregates with water employing MP2/Aug-cc-pVDZ theoretical level. The intramolecular hydrogen bonding interactions are observed to be present in both the most stable forms of thione and thiol tautomeric forms (1Z and 2Z, respectively). The stabilization energy resulting from aggregation of TFHA with H 2O in 1:1 ratio for all the tautomeric forms has been evaluated for different orientations of H 2O relative to TFHA. The most stable aggregate has orientation similar to the most stable aggregate of FHA with H 2O and the stabilization energy for TFHA is only 0.79 kcal/mol less than the value for FHA at MP2/Aug-cc-pVDZ theoretical level.

Stability of hydroxamate ions in aqueous medium

Hydroxamic acids form a class of compounds which display interesting chemical and biological properties. They act as chelating agents for many metal ions. They find applications as functionalizing agents for carbon nanotubes and polymer bound chelating agents. Properties of hydroxamic acids strongly depend on the mode of ionization. N-unsubstituted hydroxamic acids have two protons that can be ionized to form hydroxamate ions. The stability of hydroxamate ions has been the topic of many recent scientific investigations, as it is fundamental to the understanding of their properties. Experimental and theoretical studies in gas phase suggest that hydroxamic acids ionize via N–H bond dissociation. Experimental evidence shows that hydroxamic acids ionize via O–H bond dissociation in solution. Aqueous phase HF/6-31+G(D) and CBS-QB3 calculations performed on bare ions generated from formohydroxamic acid and aceto hydroxamic acid employing the solvation model CPCM do not correctly identify the stable ionic forms in aqueous medium. In this work we present an ab initio cluster model that accurately predicts the stable ionic forms in aqueous solution. In the cluster model, the first hydration shell is treated explicitly and outer shells are treated as a continuous dielectric medium. Results of cluster calculations show that the O–H bond dissociation is favored in aqueous medium. The results are also supported by a molecular dynamics simulation.

Intra and intermolecular hydrogen bonding in formohydroxamic acid

AbstractThe presence of hydrogen bonding interactions in several tautomeric forms of formohydroxamic acid (FHA) and 1:1 association among the tautomeric forms and water‐coordinated tautomeric forms of FHA is explored theoretically. Out of the seven equilibrium structures, four tautomeric forms have been selected for aggregation with single water molecule and dimer formation. Fifteen aggregates of FHA with H2O have been optimized at MP2/AUG‐cc‐PVDZ level and analyzed for intramolecular and intermolecular H‐bond interactions. Twenty‐seven dimers of the four tautomeric forms have been obtained at MP2/6‐31+G* level. The stabilization energies associated with dimerization and adduct formation with water are the result of H‐bond interactions and range from very weak to medium. The atomic charges and NBO analysis indicate that the electrostatic and the charge transfer are the important components favoring H‐bond formation. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Keto–iminol tautomerism in acetohydroxamic and formohydroxamic acids: Experimental and theoretical study

Full Xe arc irradiation of acetohydroxamic (AHA) and formohydroxamic acids (FHA) isolated in argon matrixes was used to study the keto–iminol tautomerism of these molecules. The energies and spectra of the most stable isomers were calculated at the MP2 level using the 6-311++G(2d,2p) basis set. The relative abundances of the 1 Z, 2 Z, and 1 E isomeric structures in the AHA/Ar matrixes, obtained by deposition of the vapour over solid AHA sample heated to 301 K, are equal to 95.1%, 3.7%, and 1.2%, respectively. The results of calculations are in accord with the experimentally determined order of stability of the AHA isomers. The calculated stabilization energies of AHA structures (Δ E ZPE) indicate that 1 Z is 1.31, 1.35, and 5.75 kcal mol −1 more stable than the 2 Z, 1 E, and 2 E isomers, respectively. The theoretical relative abundances of the studied structures calculated from the Gibbs free energies at 301.15 K are 92.2%, 4.05%, 3.73%, and 0.0162% for 1 Z, 2 Z, 1 E, and 2 E isomers of AHA, respectively. The results obtained for formohydroxamic acid indicate that in the FHA/Ar matrixes, obtained by deposition of the vapour above solid FHA kept at room temperature, the relative abundances of the 1 Z, 2 Z, and 1 E isomeric structures are 94.3%, 2.5%, and 3.1%, respectively. The calculated Δ E ZPE energy differences show that 1 Z FHA isomer is 1.43, 1.25, and 5.29 kcal mol −1 more stable than the 2 Z, 1 E, and 2 E structures, respectively. The theoretical relative abundances of FHA isomers calculated from the Gibbs free energies at 298.15 K are 85%, 3.99%, 11%, and 0.0062% for 1 Z, 2 Z, 1 E, and 2 E, respectively.

Molecular interaction study of formohydroxamic acid (FHA) with water

Ab initio and dft theoretical methods have been used to study the hydrogen bonding in the complexes formed between formohydroxamic acid (FHA) and water molecules. Eight reasonable geometries on the potential energy surface of formohydroxamic acid and water systems have been considered; four structures with three water molecules FHA-(H 2O) 3 and four structures with two water molecules FHA-(H 2O) 2. In all the complexes, the formohydroxamic acid has cis-keto form. The most stable complexes were found with cyclic double hydrogen bonds. The results of chemical hardness indicate that it does not obey maximum hardness principle (MHP) for the above hydrogen bonded systems. Two-body, three-body interaction energies and relaxation energies have been calculated by applying many-body analysis to know their role in the total interaction energy of the molecule. The results of many body analysis indicate that two-body interaction energy contribute more to the total interaction energy when compared to three-body interaction energies. Topological analysis has been performed for the complexes using Bader's Atoms in molecule theory. The topological parameters electron density and Laplacian of electron density show excellent linear correlation with the hydrogen bond length. NBO analysis have been carried out to study the charge transfer between proton acceptor to the antibonding orbital of the X-H bond in the complexes.

Intra- and intermolecular hydrogen bonding in formohydroxamic acid complexes with water and ammonia: infrared matrix isolation and theoretical study

Abstract The complexes of formohydroxamic acid with water and ammonia have been studied using FTIR matrix isolation spectroscopy and MP2 calculations with a 6-311++G(2d,2p) basis set. The analysis of the experimental spectra of the HCONHOH/H 2 O(NH 3 )/Ar matrixes indicates formation of strongly hydrogen-bonded complexes in which the NH group of formohydroxamic acid acts as a proton donor toward the oxygen atom of water or the nitrogen atom of ammonia. The NH stretching vibration of formohydroxamic acid exhibits 150 cm −1 red shift in the complex with water and 443 cm −1 red shift in the complex with ammonia as compared to the NH stretch of the HCONHOH monomer. The theoretical calculations indicate stability of five isomers for the water complex and three isomers for the ammonia complex. The most stable are the cyclic structures in which the water or ammonia molecules are inserted within the intramolecular hydrogen bond of the formohydroxamic acid molecule and act as proton donors for the CO group and proton acceptors for the OH group of the formohydroxamic acid molecule. In spite of their stability the cyclic structures have not been observed in the matrixes which indicates high energy barrier for their formation, the reaction of complex formation is under kinetic and not thermodynamic control.

The interaction of formohydroxamic acid with nitrogen: FTIR matrix isolation and ab initio studies

Argon matrix infrared spectra of the complexes formed between formohydroxamic acid, HCONHOH (FHA) and nitrogen have been recorded. The experimental results indicate formation of two isomeric complexes in which the nitrogen atom of the N 2 molecule is attached to the NH or OH groups of FHA. Theoretical studies of the structure and spectral characteristics of the complexes were carried out on the MP2 level with the 6-311++G(2d,2p) basis set. The calculated vibrational frequencies for the complexes present in the matrices are in good agreement with the experimental data.