Excess Of Nitric Acid Research Articles

Study of finely divided aqueous systems as an aid to understanding the surface chemistry of polar stratospheric clouds: Case of HCl/H2O and HNO3/HCl/H2O systems

The conditions under which a liquid (quasi‐liquid) or glassy overlayer could form around solid polar stratospheric cloud (PSC) particles have been studied with differential scanning calorimetry (DSC) on nanometer‐size binary HCl/H2O and ternary HNO3/HCl/H2O systems obtained on voluminous powder of fumed silica (SiO2). A HCl/H2O nanosystem of 32 wt % HCl froze heterogeneously, because of the presence of the silica surface, between −70°C and −85°C (203 and 188 K). This suggests that in the absence of any heterogeneous nuclei, a liquid or quasi‐liquid overlayer can exist around solid particles if HCl concentration in the surface layer can reach about 30%. Experiments also showed that the ternary nanosystem freezes more readily (between −52 and −93°C, 221 and 180 K) than the binary HCl/H2O system of similar HCl concentration, except for ternary solutions with excess nitric acid. This finding indicates that in the stratosphere, complex HNO3/HCl/H2O hydrates could be formed within a supercooled liquid overlayer of suitable composition if heterogeneous nuclei, for instance, meteoritic smoke silica particles, are available. A relatively warm glass‐transition temperature region (between −80 and −100°C) observed in one of the ternary samples suggests that in principle, a glassy overlayer could also form from a supercooled liquid overlayer of appropriate composition.

Fully automated quantitative analysis of chloroaniline in personal cleansing liquid finished products

This presentation addresses an automated quantitative analysis designed for determination of chloroanilines (CA) in personal cleansing (PC) liquid products containing trichlorocarbonilide (TCC). These materials may be present as impurities in the germicides as used, or they may be formed from the germicides during processing. This is a fully automated analysis which covers everything from sample preparation to determination of CA at the parts per million level. The CA is diazotizated by addition of sodium nitrite. After a prescribed reaction time, the excess nitrous acid is destroyed with ammonium sulfamate. The diazotizated CA is derivatized with naphthylethylene diamine and the level determined by difference in the UV-VIS absorption at approximately on peak (555 nm) and background (660 nm). Linearity, accuracy, and precision ensure the validity of the robotics method. The method has a linearity working range from 0 to 100 ppm (correlation coefficient, R = 0.9995). The method gives acceptable recoveries: R = 102% for liquid soap. Relative standard deviation is 1.14%. These results demonstrate that the system can determine the concentration of CA in PC products. This automated CA analysis frees up analysts from routine laboratory work for more technically difficult projects. The robot is capable of managing 36 samples per day, which is more than three times higher capacity than the manual procedure. © 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:282–285, 2000

Determination of impurity elements in high purity graphite by inductively coupled plasma atomic emission spectrometry after microwave decomposition

A high purity graphite powder was completely decomposed with a mixture of nitric and sulfuric acids using an open microwave digestion system. The excess nitric acid remaining in the solution was evaporated off using the same system. The sample solution was diluted with water and analyzed for the determination of impurity elements (Li, Na, K, Mg, Ca, Sr, Al, Fe, Ni, Cr, Ti, V) by inductively coupled plasma atomic emission spectrometry (ICP-AES). The analytical results for the elements in standard samples agreed well with those by other methods.

Generation of Nitric Oxide and Possibly Nitroxyl by Nitrosation of Sulfohydroxamic Acids and Hydroxamic Acids

Diazeniumdiolates (NONOates) and sulfohydroxamic acids are chemical entities that spontaneously generate nitric oxide (NO) and nitroxyl (HNO), respectively, at physiological pH and temperature. By combining the functional aspects of the NONOates with the hydroxamic acids and sulfohydroxamic acids, hybrid NONOate-type compounds that could theoretically generate nitroxyl or nitric oxide can be rationalized. Although the instability of these compounds, viz., the N-nitrosohydroxamic acids and the N-nitrososulfohydroxamic acids, precluded their chemical characterization by actual isolation, their transient existence was deduced by identification of the products of their decomposition. Thus, treatment of benzohydroxamic acid (BHA) with limiting or excess nitrous acid (from NaNO2 and H3PO4) gave rise to quantitative generation of N2O, possibly via HNO, based on the limiting reactant. Nitrosation of N-t-butyloxycarbonyl hydroxylamine gave similar results. The organic acid produced from BHA was identified as benzoic acid. No nitric oxide was detected from these reactions. In contrast, treatment of Piloty's acid (benzenesulfohydroxamic acid) and methanesulfohydroxamic acid (MSHA) with nitrous acid under the same conditions as above gave 36% of the theoretical quantity of NO from Piloty's acid and 47% of NO from MSHA, although finite quantities of HNO (measured as N2O) were also formed. The organic acid produced from Piloty's acid was identified by reverse-phase HPLC as the redox product, benzenesulfinic acid.

Spectrophotometric Estimation of Nimesulide and its Formulations

Four simple and sensitive visible spectrophotometric methods (A–D) have been described for the assay of nimesulide (NMD) either in pure form or in pharmaceutical formulations. Methods A and B are based on the oxidative coupling between the reduced product of NMD (RNMD) and p-N,N-dimethyl phenylenediamine dihydrochloride (DMPD) in presence of chloramine – T (CAT) or 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in presence of ferric chloride (Fe III) to form coloured products with λmax at 540 nm and 600 nm respectively. Method C is based on the diazotization of RNMD with excess nitrous acid (HNO2) and estimating the consumed HNO2 with cresyl fast violet acetate (CFVA). Method D is based on the formation of the coloured charge-transfer complex, when RNMD is treated with metol (p-methyl aminophenol sulphate, PMAP) in presence of potassium dichromate. All variables have been optimized and the reaction sequence is presented. The concentration measurements are reproducible within a relative standard deviation of 1.0%. Recoveries are 98.6–100.2%.

Spectrophotometric determination of azathioprine in pharmaceutical formulations

Four simple and sensitive visible spectrophotometric methods (A–D) have been described for the assay of azathioprine (ATP) either in pure form or in pharmaceutical formulations. Methods A and B are based on the oxidation of ATP with excess N-bromosuccinimide (NBS) or chloramine-T (CAT) and determining the consumed NBS or CAT with a decrease in colour intensity of celestine blue (CB) (method A) or gallocyanine (GC) (method B), respectively. Methods C and D are based on the diazotisation of reduced azathioprine (RATP) with excess nitrous acid and estimating either the consumed nitrous acid (HNO 2) with cresyl fast violet acetate (CFVA) (method C) or by coupling reaction of the diazonium salt formed with N-1-naphthyl ethylene diamine dihydrochloride (NED) (method D). All of the variables have been optimized and the reactions presented. The concentration measurements are reproducible within a relative standard deviation of 1.0%. Recoveries are 99.2–100.3%.

Antimicrobial and antineoplastic activities of new 4-diazopyrazole derivatives

Several new 4-diazopyrazole derivatives were prepared by the reaction of 3-methyl-5(substituted-benzamido)pyrazoles with an excess of nitrous acid in acetic acid solution. The compounds were tested for antiretroviral activity in HIV-1 infected MT-4 cells and antiproliferative effects against a panel of human leukemia, lymphoma and solid tumor cell lines. They were also tested for activity against representative gram-negative ( Shigella, Salmonella) and gram-positive ( S. aureus, D group Streptococcus) bacteria as well as fungi ( C. albicans, C. paratropicalis, C. neoformans and A. fumigatus). Compounds were devoid of anti HIV-1 and antimicotic activities, whereas they were active against tumor cell lines, with inhibitory activity (IC 50) in the range 2.4–20 μM and bacteria. The highest microbial susceptibility was shown by gram-positive bacteria, with minimum inhibitory concentrations in the range 0.8–12.5 μM.

Kinetics and mechanism of the reaction of nitrous acid with 2,4-dinitrophenylhydrazine

Arylhydrazines react with excess nitrous acid to form mixtures of the diazonium ion and aryl azide. By use of the weakly basic 2,4-dinitrophenylhydrazine (DNP), pKa= 1.55, information about the mechanism of the diazotisation reaction has been obtained. Three successive stages can be observed. The initial reaction consists of parallel nitrosations by N2O3 and NO+ of the free base DNP at the terminal nitrogen. This is followed by a stage with the rate independent of [HNO2], almost certainly a tautomerisation, probably to form ArNNNHOH and ArNHNNOH. The former is converted to ArN3 while the latter undergoes a further electrophilic nitrosation by NO+ of a conjugate base species to yield a di-N,N′-nitrosoarylhydrazine, a precursor to the diazonium ion.

Method development and validation for the determination of mineral elements in food and botanical materials by capillary electrophoresis

A capillary electrophoresis (CE) procedure was developed and validated for the determination of K +, Na +, Ca 2+, Mg 2+ and Mn 2+ in solid natural products. Closed-vessel microwave acid digestion [HNO 3H 2O 2 (2:0.5)] was used for the sample preparation. Digests of these samples were diluted with deionized water and the resulting solutions injected for CE. The excess of nitric acid in the samples was found to influence the analytical performance, so its effect was investigated in detail. Direct calibration with aqueous standard solutions was applicable for the analysis of all sample types. To evaluate the bias of the proposed procedure, reference materials were analysed. The results agreed well with the certified or recommended values. The precision of the procedure was evaluated with a two-level nested analysis of variance. This allows one to estimate separately the variance due to three factors (the CE measurement, the sample preparation and time) that are expected to contribute to the variability of the measurement results. For all the elements determined, the CE system repeatability (R.S.D.) was smaller than 4%, method repeatability smaller than 6% and the within-laboratory reproducibility smaller than 9%, The limit of detection (LOD) and limit of quantification (LOQ) in solution are below 600 μg/l, except for K +, for which the LOQ is about 2 mg/l.

Facile Synthesis of 5-Benzamido-4-Diazopyrazole Derivatives, a Class of Biologically Active Agents and Key Intermediates

Abstract By reacting l-R1-3-R2-5-(R3-substituted)benzamidopyrazoles with a great ex-cess of nitrous acid in acetic acid media, the related 4-diazoderivatives in 65–80% yields were obtained.

Is hydrazoic acid (HN3) an intermediate in the destruction of hydrazine by excess nitrous acid?

The kinetics of the decomposition of NH2NNOH, the intermediate absorbing at 225 nm formed in the nitrous acid–hydrazine reaction have been studied by stopped-flow spectrophotometry at acidities up to 1 mol dm–3 H+. A substantial amount of protonation occurs at high acidities, and the pKa of NH3+NNOH is 0.57. In excess hydrazine decomposition occurs to form hydrazoic acid (HN3), but in excess nitrous acid a rapid second nitrosation occurs by a diffusion-controlled reaction between NO+ and NH2NNOH which can bypass this pathway, though the possibility of some hydrazoic acid formation cannot be ruled out. Spectrophotometric evidence has been obtained for the formation of a relatively stable species, probably a very minor component, a product of the double-nitrosation reaction.

Iron control in nitrate hydrometallurgy by (auto) decomposition of iron (II) nitrate

Iron removal from hydrometallurgical sulphate or chloride systems has not, to date, provided a lowcost route to a saleable iron product. Regeneration of the Fe 3+ ion as an oxidant still relies on slow gas/liquid transfer. The present work evaluates the possibilities in the nitrate system. Iron(III) nitrate leaching of metallic iron or reactive iron sulphides would yield iron(II) nitrate, which in this work was found to decompose spontaneously into iron(III) nitrate and iron(III) oxides in the temperature range 63–103°C, depending on the excess of nitric acid (HNO 3) present. An increase in nitric acid lowers the decomposition temperature. Stirring may have the opposite effect. (Auto) decomposition of Fe(NO 3) 2 involves reduction of nitrate and the gaseous end product was found to contain at least 95% NO in the absence of nitric acid. The iron(III) oxides formed were extremely fine (approximately 1 μm). Hydrolysis of the iron(III) nitrate formed above 120°C gave good filterable iron oxides. Hydrolysis at 160°C or 180°C gave a remarkable increase in particle size. In the more concentrated solutions, hematite spheroids of approximately 25 μm were produced. When sufficient nitric acid is present, only iron(III) nitrate is formed in the (auto)decomposition. A process possibility is proposed where iron(II) nitrate is first (auto)decomposed to iron(III) nitrate, from which a bleed stream is hydrolyzed to Fe 2O 3 and HNO 3. The bulk of the iron(III) nitrate is directly returned to the leaching operation. Air is used for oxidation of the NO evolved during (auto)decomposition of iron(II) nitrate.

Studies on the preparation and isomeric composition of 186Re- and 188Re-pentavalent rhenium dimercaptosuccinic acid complex

The preparative conditions for 186Re(V)DMSA and 188Re(V)DMSA (DMSA = meso-dimercaptosuccinic acid), beta-emitting radiopharmaceuticals that have been shown to localize in medullary thyroid carcinoma, require modification depending on the amount of carrier rhenium and the chemical form and medium in which the rhenium is supplied. Preparative conditions are described for use with carrier-free 188ReO4- in saline, and for use with 186ReO4- in saline, sodium hydroxide or nitric acid. Preparation of 186Re(V)DMSA (carrier present up to 2 mg per 2.5 ml reaction volume) requires a DMSA:SnCl2:Re ratio of 10:5:1 at 100 degrees C for 30 min. Addition of excess nitric acid or hydrochloric acid up to a concentration of 155 mM does not reduce the yield from 100%. A commercial DMSA kit vial (e.g. Amerscan DMSA) can be used for preparation of 188Re(V)DMSA (carrier free) provided the required activity is in a volume of less than 1 ml per vial. A convenient method of concentrating the 188Re generator eluate to the required volume is described.

Nitrosation of 4-amino-1-phenacyl-1,2,4-triazolium bromides and ?-(1,2,4-triazol-1-yl)acetophenones

The reaction of 4-amino-1-phenacyl-1,2,4-triazolium bromides with an excess of nitrous acid leads to a mixture of the corresponding ω-(1,2,4-triazol-1-yl)-acetophenones and ω-hydroximino-ω-(1,2,4-triazol-1-yl)acetophenones. Products of the latter type are formed during nitrosation at the methylene group of both the intermediate ω-triazolylacetophenones, and the starting 4-amino-1-phenacyl-1, 2,4-triazolium bromides. The role of Br− as a catalyst is significant for both nitrosation paths. In the reaction of ω-(1,2,4-triazol-1-yl)acetophenones with HNO2, SCN− is a more active catalyst than Br−. During the nitrosation of para-substituted 4-amino-1-phenacyl-1,2,4-triazolium bromides, the yield of ω-hydroximino-ω-(1,2,4-triazol-1-y1)acetophenones increases with increase in the acceptor properties of the aryl substituent, which is explained by the increase in the CH-acidity of the nitrosation substrates.

ChemInform Abstract: REVISED STRUCTURE FOR THE PRODUCT FROM THE REACTION OF 3‐HYDRAZINOCARBONYLMETHYLENE‐2‐OXO‐1,2,3,4‐TETRAHYDROQUINOXALINE WITH NITROUS ACID

AbstractAbhängig von den eingesetzten Molverhältnissen entstehen aus (I) durch Diazotierung und anschließendes Verkochen die Verbindungen (II) und (III).mit unterschiedlichen Ausbeuten.

ChemInform Abstract: PRODUCTS OF THE NITRATION OF 2‐THIAZOLYLUREAS AND 2‐THIAZOLYLTHIOUREAS

AbstractDie Thiazol‐Derivate (I), (IV) und (VII) werden in Schwefelsäure mit rauchender Salpetersäure umgesetzt.

Products of the nitration of 2-thiazolylureas and 2-thiazolylthioureas.

Products of the nitration of 2-thiazolylurea and 2-thiazolylthiourea derivatives with fuming nitric acid in concentrated sulfuric acid are described. The urea derivatives studied were 3-(4-methyl-2-thiazoly) urea and -thiourea (7), and their l-methyl (1 and 2, respectively) and 1, 1-dimethyl analogs. The products were the compounds nitrated at the 5-position of the thiazole moiety. With an excess of nitric acid, 1-methyl-3-(4-methyl-5-nitro-2-thiazolyl)-1-nitrourea was obtained from 1, while the corresponding 1-nitrosourea was formed from 2. A pale yellow compound was obtained from the nitration of 7. Unlike other nitrated thioureas, it did not form a colored Cu (II) chelate and was stable to acid, alkali, and heat. It was concluded to be 6-methyl-2-nitroiminothiazolo [3, 2-b] [1, 2, 4] thiadiazole from studies of its physicochemical properties, chemical reactions, and the results of X-ray crystallography. Corresponding compounds were obtained from other N-(4-alkyl-2-thiazolyl) thioureas.

Revised structure for the product from the reaction of 3-hydrazinocarbonylmethylene-2-oxo-1,2,3,4-tetrahydroquinoxaline with nitrous acid.

The structure of the compound 2, 2, 4-dioxo-3-nitroso-1, 2, 4, 5-tetrahydropyrazolo [1, 5-a]-quinoxaline, which was previously obtained from the reaction of 3-hydrazinocarbonyl-methylene-2-oxo-1, 2, 3, 4-tetrahydroquinoxaline (1a) with an excess of nitrous acid, was revised to 3-(1, 2, 4-oxadiazolin-5-on-3-yl)-2-oxo-1, 2-dihydroquinoxaline (7) on the basis of comparison with an authentic sample prepared from 3-cyano-2-oxo-1, 2-dihydroquinoxaline (8) via an unambiguous route.

Determination of selenium in zinc ore with high concentrations of lead and copper by the hydride generation-atomic absorption technique

For the AAS-determination of Se in zinc ore with high concentrations of lead and copper, the sample is dissolved in a nitric-hydrochloric acid mixture. Excess nitric acid is removed by heating with perchloric acid and hydrochloric acid is added to reduce Se(VI) to Se(IV). Thiourea is added to the sample aliquotes taken for hydride generation to minimize the interference from copper. The result for selenium agreed well with that found by NAA. Total standard deviation of the method is 5–10 %.

The bacterial mutagenicity of three naturally occurring indoles after reaction with nitrous acid

Three naturally occurring indoles were evaluated for potential nitrosatability using the Nitrosation Assay Procedure (NAP test) as recommended by the World Health Organisation. All three indoles i.e. tryptophan, tryptamine and 5-hydroxytryptamine were nitrosated to products which were directly mutagenic for S. typhimurium TA1537. In addition, the products of nitrosation of tryptamine and 5-hydroxytryptamine were also mutagenic for strains TA1538, TA98 and TA1535 without the need for metabolic activation. The sensitivities of the frameshift-detecting strains TA1537, TA1538 and TA98 were of particular interest, since nitroso compounds are characteristically base-substution mutagens. The mutagenic effects of the products formed after nitrosation of each indole at pH 3.6, were eliminated in the presence of S9 mix. This was not the case when the nitrosation assay was carried out at pH 2.6. At this pH the mutagenicity of the nitrosated products varied in the presence of S9 mix and depended upon the nature of the indole undergoing nitrosation, and the bacterial test strain utilised for the mutagenicity assay. This indicated that more than one mutagenic product was responsible for the observed effects. As well as pH, a number of other factors influenced the formation of mutagenic nitroso products. Most notably, the concentrations of precursor compounds (sodium nitrite, and indole) present in the NAP test were of critical importance. As the sodium nitrite concentration was reduced from that recommended by the W.H.O. (40 mM), so the mutagenicity decreased. For all three compounds significant mutagenic effects were lost at sodium nitrite concentrations below 15 mM. In conclusion the data presented in this paper clearly demonstrates that individuals are chronically exposed to naturally occurring substances which readily nitrosate in excess nitrous acid and yield bacterial mutagens.