Further improvements in the 2,4-xylenol spectrophotometric method for nitrate

Improvements are described for the 2,4-xylenol spectrophotometric method for nitrate that reduce the elapsed and working time. Diluted (22 + 3) sulfuric acid is added quickly to the sample solution while the flask is immersed in tap water. 2,4-xylenol solution is added, the 6-nitro-2,4-xylenol formed is steam-distilled into a composite ammonia—isopropanol reagent, and the absorbance of the ammonium salt of 6-nitro-2,4-xylenol is measured. Further possible interferences are described. Br₂, I₂, ClO^-, CIO₃^-, BrO₃^-, and I0₄^-, cause low results by deactivating or destroying the 2,4-xylenol. Azide, hydrazine, and elemental carbon cause low results by reducing the nitrate in the strong sulfuric acid solution. Se⁺ causes low results because 2,4-xylenol is consumed in reducing Se⁴⁺ to the element. Pt⁴⁺ and Os⁸⁺ cause high results. Interferences from Br₂, I₂, ClO^-, ClO₃^- lO₃^-, and I0₄^- can be eliminated by reduction to the halide with sulfurous acid and precipitation with silver sulfate. Sulfurous acid reduction also eliminates interferences from V⁵⁺. Mn⁷⁺, Cr⁶⁺, S₂O₈^2-, and H₂0₂. Interferences from N₃^-, Br₂, I₂, and S₂0₈^2- are eliminated merely by boiling a 0.5% sulfuric acid solution for 30 min (and precipitating any residual halide with silver sulfate).     

An improved technique for the spectrophotometric determination of nitrate with 2,4-xylenol

An improved method is proposed for the spectrophotometric determination of nitrate with 2,4-xylenol. The sample in aqueous (1.7 + 1 ) sulfuric acid is treated with 2,4-xylenol to produce 6-nitro-2,4-xylenol which is distilled into an ammoniacal water—isopropanol mixture. The intense yellow color of the ammonium salt of 6-nitro-2,4-xylenol is measured at 455 nm. The distillation is done in a Parnas—Wagner Kjeldahl Semimicro distillation apparatus. The isopropanol keeps the excess of 2,4-xylenol in solution. Two procedures are described. In the first (applicable to samples containing alkali nitrates but no chloride, alkaline earth, or ammonium salts), the solution is evaporated to dryness, and (1.7 + 1) sulfuric acid and 2,4-xylenol in acetone are added. In the second (applicable to samples containing chloride, alkaline earth, or ammonium salts), concentrated sulfuric acid is added dropwise to a cooled aliquot and the 2,4-xylenol reagent is then added; if chloride is present, it must be removed by prior precipitation with silver sulfate. Nitrite shows a slight interference which depends on the amount of nitrate and nitrite present.     

Inorganic interferences in the 2,4-xylenol spectro-photometric method for nitrate and their elimination

A study of inorganic interferences with the 2,4-xylenol spectrophotometric method for nitrate and their elimination is reported. Fifty-three substances do not interfere with the original method. Nitrite interferes somewhat by producing a faint yellow color. Certain reducing agents (Fe²⁺, S^2-, S₂O₃^2-, and SCN^-) cause low results by reducing the nitrate in the strong sulfuric acid solution, while some oxidizing agents (Mn⁷⁺, Cr⁶⁺, V⁵⁺, and ClO₃^-) cause low results by inactivating or destroying the 2,4-xylenol. Persulfate and small amounts of H₂O₂ produce a slight deepening of the color; larger amounts of H₂O₂; cause low results, as do Cl^-, Br^-, I^-, and metals. The recommended maximum permissible limits (mg per 10-ml aliquot) for the original method are NO₂^--N, Fe²⁺, S^2-, SCN^-, V⁵⁺, ClO₃^-, Cl^-, I^-, 0.2; Mn⁷⁺, Cr⁶⁺, S₂O₈^2-, 5; H₂O₂, 0.02; S₂O₃^2-, Br^-, 0.1; metals, none. Procedures for the elimination of most of the interferences are described. Nitrite is destroyed with sulfamic acid. The interferences of reductants (Fe²⁺, S^2-, S₂O₃^2-, and SCN^-) and oxidants (Mn⁷⁺ and Cr⁶⁺) are eliminated with hydrogen peroxide, the excess of which (and S₂O₈^2-) is destroyed by boiling in the presence of Fe³⁺. The interference of Cl^-, Br^-, and I^- is eliminated by precipitation with silver sulfate. An alternative to the sulfamic acid procedure is to oxidize nitrite to nitrate with peroxide and deduct NO₂^--N from the total NO₃^--N. After elimination of interferences, a 10-ml aliquot of sample solution is treated with 17.0 ml of sulfuric acid and 2,4-xylenol, the 6-nitro-2,4-xylenol is steam-distilled into an ammonia—water—isopropanol mixture, and the yellow color is measured.     

Semimicro spectrophotometric determination of nitroglycerine in propellants by use of 2,4-xylenol

A semimicro spectrophotometric method using 2,4-xylenol is proposed for the determination of nitroglycerine in propellants. The propellant is extracted with methylene chloride, the extract is diluted, and a 10-ml aliquot is evaporated just to dryness. Then 2,4-xylenol reagent and 63% v/v sulphuric acid are added to hydrolyse the nitroglycerine to nitrate and form 6-nitro-2,4-xylenol which is steam-distilled in a Parnas-Wagner Kjeldahl distillation apparatus into a water-ammonia-isopropyl alcohol mixture. The absorbance of the yellow solution of the anion of the 6-nitro-2,4-xylenol is measured. The calibration curve is prepared from potassium nitrate and an empirical factor (5.50) is used to convert from nitrogen content to nitroglycerine (the theoretical factor is 5.40). The 2,4-xylenol should be added before the sulphuric acid in order to prevent interference from diphenylamine and ethyl centralite. The method is designed for the usual nitrocellulose double-base propellants containing 8-50% of nitroglycerine.     

Molecular emission cavity analysis: Part 23. Determination of Nitrite and Nitrate after Conversion to Nitrogen Monoxide

Molecular emission cavity analysis is applied to the determination of nitrite and nitrate after their reduction to nitrogen monoxide by iodide or zinc. The white emission stimulated from nitrogen monoxide in an oxy-cavity placed in a hydrogen—nitrogen diffusion flame is measured at 526 nm. Calibration graphs are linear up to 300 μg N ml^-1; the detection limit is 0.5 μg N ml^-1 for nitrite and 2 μg N ml^-1 for nitrate. There are few interferences. Procedures for the determination of nitrite and nitrate in admixture are described.     

Synthesis of new derivatives of 4-amino-2,4-dihydro-1,2,4-triazol-3-one as potential antibacterial agents

Thirty new 2-substituted-4-amino-5-alkyl or aryl-2,4-dihydro-1,2,4-triazol-3-ones and ten 2-substituted-5-alkyl or aryl-4-(5-nitro-2-furfurylidene)amino-2,4-dihydro-1,2,4-triazol-3-ones were synthesized and characterised by their sharp melting points, elemental analysis, ir and ¹H nmr spectra. These new derivatives of 5-nitro-2-furaldehyde were screened for their antibacterial activities. Most of the compounds showed good activity against one test organism, Staphylococcus aureus. For a few compounds, C.M.I. ranged from 4 to 8 μg/ml (higher results than nitrofurantoin).     

Formation of alkyl nitrates from the reaction of branched and cyclic alkyl peroxy radicals with NO

The yields of C₅ and C₆ alkyl nitrates from neopentane, 2-methylbutane, 2-methylpentane, 3-methylpentane, and cyclohexane have been measured in irradiated CH₃ONONO-alkane-air mixtures at 298 ± 2 K and 735-torr total pressure. Additionally, OH radical rate constants for neopentyl nitrate, 3-nitro-2-methylbutane, 2-nitro-2-methylpentane, 2-nitro-3-methylpentane, and cyclohexyl nitrate, relative to that for n-butane, have been determined at 298 ± 2 K. Using a rate constant for the reaction of OH radicals with n-butane of 2.58 × 10^?12 cm³ molecule^?1 s^?1, these OH radical rate constants are (in units of 10^?12 cm³ molecule^?1 s^?1): neopentyl nitrate, 0.87 ± 0.21; cyclohexyl nitrate, 3.35 ± 0.36; 3-nitro-2-methylbutane, 1.75 ± 0.06; 2-nitro-2-methylpentane, 1.75 ± 0.22; and 2-nitro-3-methylpentane, 3.07 ± 0.08. After accounting for consumption of the alkyl nitrates by OH radical reaction and for the yields of the individual alkyl peroxy radicals formed in the reaction of OH radicals with the alkanes studied, the alkyl nitrate yields (which reflect the fraction of the individual RO₂ radicals reacting with NO to form RONO₂) determined were: neopentyl nitrate, 0.0513 ± 0.0053; cyclohexyl nitrate, 0.160 ± 0.015; 3-nitro-2-methylbutane, 0.109 ± 0.003; 2-nitro-2methylbutane, 0.0533 ± 0.0022; 2-nitro-2-methylpentane, 0.0350 ± 0.0096; 3- + 4-nitro-2-methylpentane, 0.165 ± 0.016; and 2-nitro-3-methylpentane, 0.140 ± 0.014. These results are discussed and compared with previous literature values for the alkyl nitrates formed from primary and secondary alkyl peroxy radicals generated from a series of n-alkanes.     

Coordination compounds of copper(II) with substituted 3-{[(2-hydroxyphenyl)methylidene]amino}propane-1,2-diols

3-{[(2-Hydroxyphenyl)methylidene]amino}propane-1,2-diol, its 5-chloro-,5-bromo-, 5-nitro-, 3-methoxy derivatives, and 3-{[(2-hydroxynaphthyl-1)methylidene]amino}propane-1,2-diol react with hydrates of copper(II) chloride, bromide and nitrate in ethanol to form coordination compounds Cu(L)X·nH₂O. Template condensation reaction between 3-aminopropane-1,2-diol and 2,3-, 2,4- or 2,5-dihydroxybenzaldehyde in the presence of copper(II) nitrate trihydrate results in similar compounds Cu(L)NO₃·nH₂O. Structure of some of the condensation products was identified by X-ray analysis. Thermolysis of the substances obtained occurs through the dehydration step (70–90°C) and complete thermal decomposition (290–560°C).     

Oligonukleare Benzylthiolat‐Zinkkomplexe

Oligonuclear Benzylthiolate Zinc Complexes From solutions of zinc nitrate and sodium benzylthiolate crystallize, depending on the reaction conditions, tetraalkylammonium salts of the zinc complexes [Zn₂(SBz)₆]^2—, [Zn₄(SBz)₁₀]^2—, and [Zn₈(S)(SBz)₁₆]^2—. In each complex the zinc ions are tetrahedrally coordinated by sulfur atoms. [Zn₄(SBz)₁₀]^2— has an adamantane framework. The bridging thiolate sulfur atoms in [Zn₈(S)(SBz)₁₆]^2—, unlike those in icosahedral reference compounds, form a cuboctahedral framework.     

On the amination of 3-nitro-1,8-naphthyridines

A number of 3-nitro-2-X-1,8-naphthyridines (X = H,Cl,NH₂,OE_t) were successfully aminated into the corresponding 4-amino-3-nitro-2-X-naphthyridines, using liquid ammonia and potassium permanganate as reagents. 4-Amino-1,4-dihydro-3-nitro-2-X-1,8-naphthyridines are the actual species being oxidized by the potassium permanganate; their existence has been by ¹H nmr spectroscopy.     

Secondary Formation of Aromatic Nitroderivatives of Environmental Concern: Photonitration Processes Triggered by the Photolysis of Nitrate and Nitrite Ions in Aqueous Solution

Aromatic nitroderivatives are compounds of considerable environmental concern, because some of them are phytotoxic (especially the nitrophenols, and particularly 2,4-dinitrophenol), others are mutagenic and potentially carcinogenic (e.g., the nitroderivatives of polycyclic aromatic hydrocarbons, such as 1-nitropyrene), and all of them absorb sunlight as components of the brown carbon. The latter has the potential to affect the climatic feedback of atmospheric aerosols. Most nitroderivatives are secondarily formed in the environment and, among their possible formation processes, photonitration upon irradiation of nitrate or nitrite is an important pathway that has periodically gained considerable attention. However, photonitration triggered by nitrate and nitrite is a very complex process, because the two ionic species under irradiation produce a wide range of nitrating agents (such as ^•NO₂, HNO₂, HOONO, and H₂OONO⁺), which are affected by pH and the presence of organic compounds and, in turn, deeply affect the nitration of aromatic precursors. Moreover, aromatic substrates can highly differ in their reactivity towards the various photogenerated species, thereby providing different behaviours towards photonitration. Despite the high complexity, it is possible to rationalise the different photonitration pathways in a coherent framework. In this context, this review paper has the goal of providing the reader with a guide on what to expect from the photonitration process under different conditions, how to study it, and how to determine which pathway(s) are prevailing in the formation of the observed nitroderivatives.     

Investigations of reactions involved in flameless atomic absorption procedures : Part IV. A theoretical study of factors influencing the determination of aluminium

High-temperature equilibrium calculations are used to study potential interferences in the determination of aluminium by flameless a.a.s. The conditions for the formation of interfering aluminium compounds like AlO(g), Al₂O(g), Al₂O₃(s), AlOH(g), AlH(g), AlHO₂(g), AlS(g), AlN(g), AlN(s) and AlCl(g) have been calculated. The influence of kinetic parameters on the equilibrium calculations for the reactions involving carbon—oxygen and carbon—sulphur has been established by varying the input amount of carbon. The results indicate that even in the nanomole range the presence of elements like H, O, N, Cl and S may cause severe interferences during the atomization step (2300–2900 K)     

Synthesis of new thietanylpyrimidine and thietanylimidazole derivatives

New thietanyl-substituted derivatives of pyrimidine-2,4(1H,3H)-dione and imidazole were synthesized. The alkylation of 6-methylpyrimidine-2,4(1H,3H)-diones with 2-chloromethylthiirane in water involved the N¹ atom of the pyrimidine ring and afforded 6-methyl-1-(thietan-3-yl)-pyrimidine-2,4(1H,3H)-diones. Under analogous conditions 6-aminopyrimidine-2,4(1H,3H)-dione gave rise to 6-(thietan-3-ylamino)pyrimidine-2,4(1H,3H)-dione. Unsymmetrically substituted 2-methyl-4(5)-nitro- and 5(4)-bromo-2-methyl-4(5)-nitro-1H-imidazoles reacted with 2-chloromethylthiirane to produce mixtures of isomeric 2-methyl-4(5)-nitro-1-(thietan-3-yl)-1H-imidazoles and 5(4)-bromo-2-methyl-4(5)-nitro-1-(thietan-3-yl)-1H-imidazoles.     

Hydrogen‐bonding patterns in pyrimethaminium dinitrate

The title compound, 2,4‐diamino‐5‐(4‐chloro­phen­yl)‐6‐ethyl­pyrimidine‐1,3‐diium dinitrate, C₁₂H₁₅ClN₄²⁺·2NO₃⁻, contains two crystallographically independent pyrimethamine (PMN) mol­ecules, which differ in the relative orientations of the pyrimidine and benzene rings and of the eth­yl substitutents. In both pyrimethamine mol­ecules, all the pyrimidine N atoms are protonated, unlike most related compounds, in which only one pyrimidine N atom is protonated. The two pyrimethamine moieties are bridged by a variety of N—H⋯O(nitrate) inter­actions, including some three‐centre hydrogen bonds.     

The selection of a chemical modifier for vanadium determination in various types of natural waters by electrothermal atomic absorption spectrometry

Various modifiers (ascorbic acid, NH₄NO₃, EDTA, NH₄SCN and a mixture of Pd/Mg(NO₃)₂) are compared for the accurate determination of vanadium in natural waters by electrothermal atomic absorption spectrometry. The interferences of compounds commonly present in natural waters, such as NaCl, CaCl₂, MgCl₂ and FeCl₃ are studied. Matrix interferences were effectively eliminated by ascorbic acid or ammonium nitrate. For comparison, the standard addition method was applied without a modifier which provided satisfactory results. The accuracy of the method was confirmed by analysis of certified reference materials of waters (‘Trace Metals in Drinking Water’ and SRM 1643e ‘Trace Elements in Water’) as well as by recoveries of vanadium spiked to tap water, mineral water, synthetic riverine and synthetic sea waters. The limits of detection and characteristic masses for ascorbic acid and ammonium nitrate as the modifiers were 1.71 and 1.56?µg?L^?1 and 70 and 67?pg, respectively. Recovery was in the range of 98–105% and RSD was less than 5%.     

Autocatalytic Oxidation of Thiamine Hydrochloride (Vitamin B1) by Permanganate in Aqueous Sulfuric Acid Medium: A Kinetic and Mechanistic Study

The reaction kinetics of autocatalytic oxidation of thiamine hydrochloride (vitamin B₁) by the permanganate ion in aqueous sulfuric acid medium has been investigated spectrophotometrically under the pseudo–first‐order condition at 25°C. The observed stoichiometry is 6:5 in terms of the mole ratio of permanganate ions and thiamine hydrochloride. Formation of products was confirmed by UV–vis, IR, GC‐MS, and NMR spectral data. Usually in the permanganate oxidation–reduction reactions, one of the products, Mn²⁺ autocatalyzes the reaction, but in the present investigation the autocatalytic effect is due to the (4‐methyl–thiazol‐5‐yl) acetic acid, a product formed from the oxidation of vitamin B₁, which is a rare case. The added Mn²⁺ does not have any significant effect on the rate of reaction. The reaction is first order with respect to both permanganate and thiamine hydrochloride concentrations. An increase in the sulfuric acid concentration decreases the rate of reaction. A composite scheme and rate laws were proposed. The activation parameters with respect to the slow step and reaction constants involved in the mechanism were determined and discussed.     

2,2,4,4-Tetramethyl-2,4-disila-cyclo-butylzinkchlorid · TMEDA und verwandte Verbindungen

2,2,4,4-Tetramethyl-2,4-disila-cyclo-butylzinc Chloride · TMEDA and Related Compounds The reaction of (tmeda)lithium 2,2,4,4-tetramethyl-2,4-disila-cyclo-butanide with anhydrous zinc(II) chloride in pentane in the molar ratio of 2:1 does not yield the expected dialkylzinc derivative but the monosubstitution product 2,2,4,4-Tetramethyl-2,4-disila-cyclo-butylzinc chloride · tmeda 1 . This derivative crystallizes in the orthorhombic space group Pnma with a = 1 235.0(1); b = 1 696.8(2); c = 1 148.0(1) pm and Z = 4. The Zn? C bond lengths lie with 198,4 pm in the characteristic region for compounds containing a tetrahedrally coordinated zinc atom. The thermolysis of 1 leads under elimination of ZnCl₂ to the formation of Bis(2,2,4,4-tetramethyl-2,4-disila-cyclo-butyl)zinc · tmeda 2 . (tmeda)LiCH(SiMe₃)₂ reacts analogously with one equivalent of ZnCl₂ to Bis(trimethylsilyl)methylzinc chloride · tmeda 3 . Lithium methanide or Lithium butanide add to a Si-C bond of 1,1,3,3-tetramethyl-1,3-disila-cyclo-butane, and these acyclic lithium alkanides 4 ( a : R = Me, b : R = n-Bu) yield with zinc(II) chloride the destillable dialkyl zinc compounds Bis(2,2,4,4-tetramethyl-2,4-disilapentyl)- 5 a and Bis(2,2,4,4-tetramethyl-2,4-disila-octyl)zinc 5 b .     

5-Nitrotetrazol and 1,2,4-Oxadiazole Methylene-Bridged Energetic Compounds: Synthesis,Crystal Structures and Performances

A new structural type for melt cast materials was designed by linking nitrotetrazole ring with 1,2,4-oxadiazole through a N-CH₂-C bridge for the first time. Three N-CH₂-C linkage bridged energetic compounds, including 3-((5-nitro-2H-tetrazol-2-yl) methyl)-1,2,4-oxadiazole (NTOM), 3-((5-nitro-2H-tetrazol-2-yl)methyl)-5-(trifluoromethyl)-1,2,4 -oxadiazole (NTOF) and 3-((5-nitro-2H-tetrazol-2-yl)methyl)-5-amine-1,2,4-oxadiazole (NTOA), were designed and synthesized through a two-step reaction by using 2-(5-nitro-2H-tetrazole -2-yl)acetonitrile as the starting material. The synthesized compounds were fully characterized by NMR (¹H, ¹³C), IR spectroscopy and elemental analysis. The single crystals of NTOM, NTOF and NTOA were successfully obtained and investigated by single-crystal X-ray diffraction. The thermal stabilities of these compounds were evaluated by DSC-TG measurements, and their apparent activation energies were calculated by Kissinger and Ozawa methods. The crystal densities of the three compounds were between 1.66 g/cm³ (NTOA) and 1.87 g/cm³ (NTOF). The impact and friction sensitivities were measured by standard BAM fall-hammer techniques, and their detonation performances were computed using the EXPLO 5 (v. 6.04) program. The detonation velocities of the three compounds are between 7271 m/s (NTOF) and 7909 m/s (NTOM). The impact sensitivities are >40 J, and the friction sensitivities are >360 N. NTOM, NTOF and NTOA are thermally stable, with decomposition points > 240 °C. The melting points of NTOM and NTOF are 82.6 °C and 71.7 °C, respectively. Hence, they possess potential to be used as melt cast materials with good thermal stabilities and better detonation performances than TNT.     

Adamantylation of 3-Nitro- and 3-Ethoxycarbonyl-1,2,4-triazolo[5,1-c]-1,2,4-triazin-4-ones

Reaction of 3-nitro- and 3-ethoxycarbonyl-1,2,4-triazolo[5,1-c]-1,2,4-triazin-4-ones with 1-adamantanol (or 1-adamantyl nitrate) in concentrated sulfuric acid or with 1-bromoadamantane in sulfolane affords N-adamantyl derivatives. The adamantylation of 3-nitro-1,4-dihydro-7H-1,2,4-triazolo[5,1-c]-1,2,4-triazin-4-one yields a mixture of N⁸- and N¹-isomers that undergo interconversion in concentrated sulfuric acid along intermolecular mechanism.     

Formic acid as a reagent for alkaline permanganate : Potentiometric determination of formate

Oxidation of formate with permanganate in alkaline solutions yields a mixture of MnO₄^-2 and MnO₂. The reaction occurs slowly without an abrupt change in potential at the end-point. In 0.1N NaOH, at 80° C in the presence ofAg⁺ions or NaCl,the reaction is accelerated and yields MnO₂. The concentrations of formic acid obtained by oxidation with permanganate are comparable with those obtained by neutralization down to 2.295·10^-2N.Reduction of permanganate in the presence of Ba⁺² ions (alkalinity = 0.5 — 1.5N) or in the absence of Ba⁺ ions (alkalinity = 0.5 — 2.5N), gave accurate results for the permanganate concentration comparable with the results of the acid oxalate method.Formic acid is preferred to sodium formate on account of the greater stability of its solutions.