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PubMed1998

[Studies on the oxidation reaction of octanol-2 with nitric acid by infrared spectroscopy].

In this paper, the reaction process of oxidation of octanol-2 with nitric acid has been studied by IR spectroscopy. It is found that the main components of non-sapoifiable matter are different in different oxidation degrees. The relation between oxidation products and the amount of nitric acid are investigated,the reaction mechanism has also been studied. Experimental results show that the oxidation process of octanol-2 is as follows: first, octanol-2 is oxidated to octanone-2, or to nitrate, nitrite and nitrile copmpounds, then these compounds are reoxidated to caproic acid in the meantime some by-products, such as valeric, enanthic acids are also found in oxidated products.

English Abstract↗
PubMed1992

Detection of neuromuscular junctions on isolated branched muscle fibers: application of nitric acid fiber digestion method for scanning electron microscopy.

Three-dimensional morphology and neuromuscular junctions of the branched muscle fibers of the rat skeletal muscles isolated from the rat were examined by application of the nitric acid digestion method for scanning electron microscopy. Treatment with fifteen percent nitric acid and a supersonic wave bath were effective in isolating the branched muscle fibers and for detecting their innervations by scanning electron microscopy. Mean numbers of total and branched fibers in the rat plantaris muscles were 11,130 +/- 314 and 32.4 +/- 4.8 (n = 12), respectively. Bifurcation of these fibers resembled either the letter X (X type) or letter Y (Y type). The Y type fibers were most frequently seen (84% of total branched fibers), and X types accounted for 14%. The remaining 2% of the fibers were subtypes of X and Y with overlapping bifurcation. These branched fibers were differentiated by their length from the bifurcated point, i.e., short, medium and long branches. Neuromuscular junctions on these branched fibers were located almost at the center of their length. The number of innervations was decided by the number of bifurcating fibers across the central part of the length.

Animals↗
PubMed2006

Reactive uptake of nitric acid onto sodium chloride aerosols across a wide range of relative humidities.

Reactive uptake coefficients for nitric acid onto size-selected (d(ve) = 102 and 233 nm) sodium chloride aerosols are determined for relative humidities (RH) between 85% and 10%. Both pure sodium chloride and sodium chloride mixed with magnesium chloride (X(Mg/Na) = 0.114, typical of sea salt) are studied. The aerosol is equilibrated with a carrier gas stream at the desired RH and then mixed with nitric acid vapor at a concentration of 60 ppb in a laminar flow tube reactor. At the end of the reactor, the particle composition is determined in real time with a laser ablation single particle mass spectrometer. For relative humidities above the efflorescence relative humidity (ERH), the particles exist as liquid droplets and the uptake coefficient ranges from 0.05 at 85% RH to >0.1 near the ERH. The droplet sizes, relative humidity and composition dependencies, are readily predicted by thermodynamics. For relative humidities below the ERH, the particles are nominally "solid" and uptake depends on the amount of surface adsorbed water (SAW). The addition of magnesium chloride to the particle phase (0.114 mole ratio of magnesium to sodium) facilitates uptake by increasing the amount of SAW. In the presence of magnesium chloride, the uptake coefficient remains high (>0.1) down to 10% RH, suggesting that the displacement of chloride by nitrate in fine sea salt particles is efficient over the entire range of conditions in the ambient marine environment. In the marine boundary layer, displacement of chloride by nitrate in fine sea salt particles should be nearly complete within a few hours (faster in polluted areas)-a time scale much shorter than the particle residence time in the atmosphere.

Journal Article↗
PubMed2001

Kinetic behaviour investigations and crystal structure of nitric acid dihydrate.

X-ray powder diffraction experiments are performed to prove the possible crystallization of nitric acid dihydrate (HNO(3).2H(2)O, further denoted NAD) and to determine the best thermal conditions for growing a single crystal. It is shown that the kinetic behaviour of NAD strongly depends on the preliminary thermal treatment. One good single crystal obtained by an in situ adapted Bridgman method procedure enabled determination of the crystal structure. The intensities of diffracted lines with h odd are all very weak. The H atom of nitric acid is delocalized to one water molecule leading to an association of equimolar nitrate (NO(3)(-)) and an H(5)O(2)(+) ionic group. The asymmetric unit contains two such molecules. These two molecules are related by a pseudo a/2 translation (with a 0.3 A mean atomic distance difference), except for one H atom of the water molecules (0.86 A) because of their different orientations in the two molecules. The two molecules, linked by very strong hydrogen bonds, are arranged in layers. Two layers which are linked by weaker hydrogen bonds are approximately oriented along the c axis. The structure may be described by translations of this set of two layers along the c axis without hydrogen bonds leading to a two-dimensional hydrogen-bond network. The structures of the monohydrate (NAM) and trihydrate (NAT) are re-determined for comparisons. These structures may be described by one- and three-dimensional hydrogen-bond networks, respectively.

Journal Article↗
PubMed2005

Formation of microcrystals, micropuddles, and other spatial inhomogenieties in surface reactions under ambient conditions: an atomic force microscopy study of water and nitric acid adsorption on MgO(100) and CaCO3(104).

In this study, atomic force microscopy (AFM) is used to image freshly cleaved MgO(100) and CaCO3(104) as these surfaces undergo reaction with water and nitric acid under ambient conditions of temperature, pressure, and relative humidity. The reaction of water and nitric acid results in the formation of hydroxylated and nitrated surfaces, respectively. It is clear from the AFM images that there are spatial inhomogenieties and surface features that form on micrometer and nanometer length scales as these reactions proceed. These features, which include hillocks, patches, microcrystallites, and micropuddles, are due to surface and phase segregation as a result of facile ion mobility in the presence of adsorbed water. In addition, instabilities and oscillations in the AFM images provide an indication of liquid formation and the deliquescence (i.e., a solid to liquid-phase transition) of nitrate salts as a function of relative humidity.

Adsorption↗
PubMed1993

Rapid partial digestion of biological tissues with nitric acid for the determination of trace elements by atomic spectrometry.

Determination of Cu, Fe, Mn and Zn in fresh bovine liver and BCR bovine liver and pig kidney reference materials, after digestion at 105 degrees C with nitric acid for various times, showed that the trace elements were completely released after heating for only 20 min. Centrifugation of the samples after digestion improved the separation from undigested fat. This partial-digestion method, based on heating about 0.2 g of sample with 2 ml of nitric acid for 20 min, was tested on a range of biological reference materials and on fresh bovine liver for the four elements. Comparison was made with results obtained after digestion by a recommended hydrogen peroxide--sulfuric acid digestion procedure. Results obtained by inductively coupled plasma atomic emission spectrometry or by flame and graphite-furnace atomic absorption spectrometry showed good agreement between the two digestion procedures, and results for the reference materials agreed well with the certified values. Between-batch precision was better than 4% for Cu, Fe and Zn at levels of 30 to 190, 210 to 320 and 100 to 140 micrograms g-1, respectively. For Mn, the precision varied between 7 and 14% for measured concentrations of 8 to 12 micrograms g-1. The partial-digestion procedure offers simplicity, speed, low cost and the ability to handle a large number of samples at the same time.

Animals↗
PubMed1993

Effects of nitric acid gas alone or in combination with ozone on healthy volunteers.

Nitric acid (HNO3) is the most prevalent acid air pollutant in the western United States and has the potential to cause adverse respiratory effects through both acidification and oxidation reactions. To study this potential, we measured physiologic (specific airway resistance, SRaw, FEV1, and FVC) and bronchoalveolar lavage (total and differential cell counts, LDH, fibronectin, and total protein) end points in a group of 10 healthy, athletic subjects who were exposed to 500 micrograms/m3 of HNO3 gas or filtered air for 4 h during moderate exercise (ventilatory rate, 40 L/min) and underwent bronchoscopy 18 h later. Under an identical protocol, 10 healthy subjects were exposed to 500 micrograms/m3 of HNO3 gas plus 0.20 ppm ozone (O3) or 0.20 ppm O3 alone to determine if HNO3 might enhance the toxicity of O3. In addition to bronchoalveolar lavage (BAL), we employed the techniques of isolated left mainstem bronchial lavage and bronchial biopsy to determine if proximal airway injury was caused by pollutant exposure and whether there was any correlation with the degree of distal lung injury as assessed by BAL. We found no significant differences in pulmonary function tests or in the cellular or biochemical constituents in either the BAL or the left mainstem lavage fluids between the HNO3 and the air exposures. Similarly, there were no differences in these end points between the HNO3/O3 and the O3 exposures. Furthermore, there were no significant differences in the bronchial biopsy specimens between the HNO3 and air exposures or between the HNO3/O3 and O3 exposures.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2005

The effect of active carbon on the reduction of concentrated nitric acid by HCOOH.

In nuclear industry, removal of nitric acid from solutions is required in the course of chemical separation and waste treatment procedure as well as in chemical conversion steps. The reduction of HNO3 by HCOOH to gaseous products such as nitrogen, nitrogen oxides, and carbon dioxide is an attractive way to accomplish the denitration. A typical problem for the denitration is the existence of the induction period. The induction period has been explained as the time necessary to increase the concentration of HNO2, which is an important reaction intermediate, above a threshold value. In this study, adsorption sites on the surface of active carbon were found to promote HNO2 formation and efficiently suppress the induction period. Induction time was shortened by increasing the amount of active carbon in the solution. When the solution contains 3 M HNO3 and 1 M HCOOH, 10 g/L of active carbon was enough to eliminate the induction period at 50 degrees C. The catalytic effect exhibited by active carbon was similar to that reported for Pt/SiO2. Therefore, on the surface of active carbon, there is a redox cycle, where HNO3 is reduced to HNO2 and then the oxidized surface site will be reduced by HCOOH.

Journal Article↗
PubMed1979

[Behaviours of trinitratonitrosyl complexes of ruthenium in dilute nitric acid solutions (author's transl)].

This study aimed to elucidate the protolysis and condensation processes of the Ru complexes in relation to the concentration of nitric acid. The compositions of the dissociated and undissociated complexes were determined by the extraction with tributyl phosphate (TBP) and absorption spectroscopy in order to follow the rather rapid protolysis reaction of the complexes. The test solutions were prepared by dissolving the freshly obtained complexes into 0.50-0.001 M nitric acid solutions. The amounts of the undissociated complexes were determined at different elapses of time in the test solutions. The protolysis became significant when the concentration was below 0.15 M, and the dissociation rate suddenly increased at this concentration. At the concentrations above 0.2 M, the absorption peak of the complexes at 480 nm survived even after 144 hours. But below 0.15 M, the formation of dissociation products by protolysis was observed after the disappearance of the absorption peak. The amount of dissociation products rapidly increased after the preparation of the test solution as the concentration decreased below 0.15 M.

Chemical Phenomena↗
PubMed2003

Accurate quantification and transformation of arsenic compounds during wet ashing with nitric acid and microwave assisted heating.

Arsenous acid, dimethylarsinic acid (DMA), methylarsonic acid (MA), arsenic acid, arsenobetaine bromide (AB), trimethylarsine oxide (TMAO), arsenocholine iodide (AC), and tetramethylarsonium iodide (TETRA) were heated in a microwave autoclave with nitric acid to 100-300 degrees C. The arsenic compounds in the digests were separated with anion- and cation-exchange chromatography and determined with an inductively coupled plasma mass spectrometer as arsenic-specific detector. Arsenous acid was completely oxidized to arsenic acid at 100 degrees C. For a complete oxidation of MA and DMA to arsenic acid temperatures > 220 degrees C and > 280 degrees C were necessary. AB decomposed to arsenic acid via TMAO. Complete conversion was only obtained after heating the sample for 90 min to 300 degrees C. For a complete conversion of TMAO similar harsh conditions were necessary. AC was already substantially degraded to TMAO, TETRA and two unknown compounds at 100 degrees C. The unknown arsenic compounds were found only in the digests up to 160 degrees C. Quantitative conversion of AC to arsenic acid went also via TMAO. At temperatures above 220 degrees C TETRA started to convert to TMAO, which then was further converted to arsenic acid. To investigate whether the results obtained for the arsenic standards are transferable to real samples, the certified reference material DORM-2 was also heated in nitric acid with variable digestion temperatures and times. For an almost complete conversion of the AB present in DORM-2 90 min at 300 degrees C were necessary. Total organic carbon (TOC) was less < 0.2% when DORM-2 was heated at temperatures > or = 260 degrees C for 60 min. UV photo-oxidation of DORM-2 was investigated as an alternative sample decomposition. Only 6% of AB was converted to arsenic acid when DORM-2 was irradiated for 2 h at 1000 W. In contrast to microwave heating substantial amounts of MA were observed as degradation product.

Journal Article↗
PubMed2000

Nitric acid trihydrate (NAT) in polar stratospheric clouds.

A comprehensive investigation of polar stratospheric clouds was performed on 25 January 2000 with instruments onboard a balloon gondola flown from Kiruna, Sweden. Cloud layers were repeatedly encountered at altitudes between 20 and 24 kilometers over a wide range of atmospheric temperatures (185 to 197 kelvin). Particle composition analysis showed that a large fraction of the cloud layers was composed of nitric acid trihydrate (NAT) particles, containing water and nitric acid at a molar ratio of 3:1; this confirmed that these long-sought solid crystals exist well above ice formation temperatures. The presence of NAT particles enhances the potential for chlorine activation with subsequent ozone destruction in polar regions, particularly in early and late winter.

Journal Article↗
PubMed2005

Heterogeneous uptake of gaseous nitric acid on dolomite (CaMg(CO3)2) and calcite (CaCO3) particles: a Knudsen cell study using multiple, single, and fractional particle layers.

In this study, the heterogeneous uptake of gaseous nitric acid on dolomite, CaMg(CO3)2, and calcite, CaCO3, particles under dry conditions at 296 K was investigated. A Knudsen cell reactor was used to measure heterogeneous uptake coefficients for these reactions. Several different experiments were performed including those on many, single, and fractional layers of particles. For experiments using multiple particle layers, the Knudsen cell data were modeled to take into account gas diffusion into the underlying layers of the sample. From this analysis, initial heterogeneous uptake coefficients, gamma(o,t), were determined to be (5 +/- 2) x 10(-4) and (2 +/- 1) x 10(-3), for dolomite and calcite, respectively, at a nitric acid concentration of 6.5 x 10(10) molecules cm(-3). For experiments that employed single or fractional particle layers, the initial heterogeneous uptake coefficient was analyzed using a recent method described in the literature. Values of the initial heterogeneous uptake coefficient using this analysis were in agreement with the above analysis and determined to be (7 +/- 4) x 10(-4) and (2 +/- 0.4) x 10(-3) for CaMg(CO3)2 and CaCO3, respectively. In addition, these results are compared to previous literature values.

Journal Article↗
PubMed2005

Oxidation of hydroxylamine by nitrous and nitric acids. Model development from first principle SCRF calculations.

Ab initio molecular orbital calculations have been performed to develop an elementary reaction mechanism for the autocatalytic and scavenging reactions of hydroxylamine in an aqueous nitric acid medium. An improved understanding of the titled reactions is needed to determine the "stability boundary of hydroxylamine" for safe operations of the plutonium-uranium reduction extraction (PUREX) process. Under the operating conditions of the PUREX process, namely, 6 M nitric acid, the reactive forms of hydroxylamine are NH2OH, NH3OH+, and the complex NH3OH.NO3, and those of nitrous acid are NO+, H2ONO+, N2O4, N2O3, NO2, and NO. High-level CBSQB3/IEFPCM and CBSQB3/COSMO calculations were performed using GAUSSIAN03 to investigate the energy landscape and to explore a large number of possible ion-ion, ion-radical, ion-molecule, radical-radical, radical-molecule, and molecule-molecule pathways available to the reactive forms of the reactants in solution. It was found that in solution the autocatalytic generation of nitrous acid proceeds through free radical pathways at low-hydroxylamine concentrations from unprotonated NH2OH via hydrogen abstraction. At high [NH3OH+], we suggest a possible involvement of the NH3ONO+ intermediate via the reaction NH2ONO + NO2 --> HNO + HONO + NO. The NH3ONO+ intermediate, in turn, is formed favorably via the ion-ion reactions of NH3OH+ with NO+ and/or the reaction between NO+ and hydroxylammonium nitrate (HAN). The intermediates involved in the scavenging reaction of nitrous acid by hydroxylamine are NH3ONO+, NH2ONO, NH2(NO)O, NH(NO)OH, and HONNOH and the rate-determining step is the 1,2-NO migration in NH2ONO leading to NH2(NO)O. Reactions NH2ONO --> NH2(NO)O and NH2(NO)O --> NH(NO)OH were studied with two explicit water molecules and the results are discussed in the context of the importance of the explicit treatment of solvent in the determination of the energetics and mechanism of these processes. The rate constants for the reactions were estimated using transition-state theory and other traditional techniques. The kinetic parameters obtained at the B3LYP/CBSB7/IEFPCM level are in reasonable agreement with the limited experimental value. IEFPCM results on free energy of undelocalized polar ions such as NO3-, NO2-, and NH3OH+ are not very accurate and have difficulties in predicting the right direction of acid dissociation equilibrium of HONO2, HONO, and NH3OH+. Explicit incorporation of a solvation shell to these ions improves the theoretical descriptions of acid ionization equilibria as it captures some of the nonlocal effects of these ions. Additional work is needed to correctly describe the solvation shell and to introduce consistency in the theoretical treatment involving explicit solvent molecules. Nevertheless, this systematic exploration of reactions in solution and mechanism development for a solution phase process based on self-consistent reaction field (SCRF) results is likely to be one of the first of its kind.

Journal Article↗
PubMed2006

Infrared overtone spectroscopy and vibrational analysis of a Fermi resonance in nitric acid: Experiment and theory.

High resolution infrared spectra of nitric acid have been recorded in the first OH overtone region under jet-cooled conditions using a sequential IR-UV excitation method. Vibrational bands observed at 6933.39(3), 6938.75(4), and 6951.985(3) cm(-1) (origins) with relative intensities of 0.42(1), 0.38(1), and 0.20(1) are attributed to strongly mixed states involved in a Fermi resonance. A vibrational deperturbation analysis suggests that the optically bright OH overtone stretch (2nu1) at 6939.2(1) cm(-1) is coupled directly to the nu1 + 2nu2 state at 6946.4(1) cm(-1) and indirectly to the 3nu2 + nu3 + nu7 state at 6938.5(1) cm(-1). Both the identity of the zero-order states and the indirect coupling scheme are deduced from complementary CCSD(T) calculations in conjunction with second-order vibrational perturbation theory. The deperturbation analysis also yields the experimental coupling between 2nu1 and nu1 + 2nu2 of -6.9(1) cm(-1), and that between the two dark states of +5.0(1) cm(-1). The calculated vibrational energies and couplings are in near quantitative agreement with experimentally derived values except for a predicted twofold stronger coupling of 2nu1 to nu1 + 2nu2. Weaker coupling of the strongly mixed states to a dense background of vibrational states via intramolecular vibrational energy redistribution is evident from the experimental linewidths of 0.08 and 0.25 cm(-1) for the higher energy and two overlapping lower energy bands, respectively. A comprehensive rotational analysis of the higher energy band yields spectroscopic parameters and the direction of the OH overtone transition dipole moment.

Journal Article↗
PubMed2004

Photochemistry of molecules relevant to the atmosphere: photodissociation of nitric acid in the gas phase.

This Minireview gives an account of the photochemical decay of nitric acid HNO3 in the gas phase, which has been well investigated under bulk and molecular-beam conditions. Due to the importance of this molecule in atmospheric chemistry, attention was paid to the irradiation regions around 300 and 200 nm, where solar photolysis of HNO3 is expected to be particularly efficient. While the low-energy region is characterized by the products OH and NO2, the high-energy region gives rise to a variety of photochemical decay pathways, dominated by channels which lead to the products HONO + O in different electronic states.

Atmosphere↗
PubMed2006

Comparison of systemic and local effects of nitric acid and hydrochloric acid: an experimental study in a rat model.

BACKGROUND: We aimed to determine the local and systemic effects of widely available household cleaners, namely 45% nitric acid (NHO(3)), and 18% hydrochloric acid (HCl), in a rat model. METHODS: This prospective, experimental, placebo-controlled trial was carried out in the Animal Research Laboratory of Akdeniz University hospital. Commonly available solution of 45% NHO(3) and 18% HCl were tested against normal saline. Each solution was administrated orally to groups consisting of ten rats. The metabolic changes were determined by measuring the pH and calcium (Ca) levels before and after the administration of solutions. In addition, the pathological changes and mortality rates were determined for each group. RESULTS: There was a statistically significant increase in the post-ingestion (30 minutes later) Ca levels and a decrease in the post-ingestion pH levels after the administration of test solution in the NHO(3) (p=0.006 for Ca increase, p=0.001 for pH decrease) and HCl (p=0.007 for Ca increase, p=0.023 for pH decrease) groups. There was also a statistically significant difference between groups for Ca increase (p=0.000) and pH decrease (p=0.006). In post hoc analysis, the difference between the groups was found to be originated from the placebo group. In the pathological evaluation of esophagus and stomach, there was a statistically significant difference between groups (p=0.009 (E) and p=0.016 (S)) and the difference was found to be originated from the control group (p=0.543 (E), p=0.244 (S) for NHO(3) and HCl). The 30-minute mortality rates were 0,2 in the NHO(3) group, 0,6 in the HCl group and 0 in the control group. CONCLUSION: Serious metabolic and mild local pathological changes can occur after the ingestion of household NHO3 and HCl solutions. Further studies should be performed to elucidate the causes of death following oral ingestion of these compounds and appropriate public health warnings should be taken.

Administration, Oral↗
PubMed2006

Orientation effects on nitric acid dihydrate films.

An investigation of orientation effects in films of nitric acid dihydrate (NAD) is presented, based on a systematic study of transmission and reflection-absorption infrared (RAIR) spectra of samples of varying thickness. The samples are prepared by vapor deposition on Ge (for transmission spectroscopy) and on Al substrates (for RAIR spectroscopy) at 175 K to produce crystalline alpha-NAD films. Transmission spectra were recorded at normal incidence, and RAIR spectra were recorded at a grazing angle of 75 degrees, with polarized radiation. The observed spectra are compared with predictions of a classical Fresnel model, to test the available optical indices of NAD, which are of great importance for the accurate interpretation of data from remote sensing measurements. Whereas the procedure yields satisfactory results for transmission and s-polarized RAIR spectra, it is found that the agreement is not acceptable for p-polarized RAIR spectra. An explanation is suggested in terms of a preferential alignment of the films, with the (10-1) crystallographic plane of the crystal situated parallel to the substrate. The infrared activity of a band at approximately 1170 cm(-1) is explained in terms of a preferential orientation of the crystal domains in the film.

Journal Article↗