1,1-Dihalo-2-benzycyclopropanes in reaction with nitrous acid

Interaction of 1,1-dichoro and 1,1-dibromo-2-benzylcyclopropanes with nitrous acid generated in situ was studied. It was shown that both nitration of the aromatic ring and heterocyclization of 1,1-dihalo-2-benzylcyclopropanes take place. Heterocyclization is initiated by opening of the cyclopropane ring in the reaction with nitrosyl cation. The nature of halogen atom in the cyclopropane ring affects the regioselectivity of the reactions.     

The reaction of 3-aminoisoquinoline with nitrous acid

The product of the reaction of 3-aminoisoquinoline and nitrous acid has been identified as the previously unreported 3,4-isoquinolinedione 4-oxime hydrate.     

Thermolysis under vacuum: Essential influence of the residual pressure on thermoanalytical curves and the reaction products

This paper examines the influence of residual pressures in the range from 10^–5 to 5 torr on the course of thermal analysis. With the help of examples concerning in particular the thermolysis of gibbsite, A1(OH)₃, it is shown that a) the control of residual pressure is of virtually no use unless the rate of decomposition isalso controlled (otherwise, the TG curves represent a composite phenomenon, which is practically unintelligible); b) the influence of residual pressure may be unexpectedly high both on the shape of the TG curves (and therefore on the apparent kinetic parameters) and on the nature (porosity, structure) of the products.

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Zusammenfassung Der Einfluß von Restdrücken zwischen 10^–5 und 5 torr auf thermische Zersetzungen wird geprüft. An Hand von Beispielen, insbesondere hinsichtlich der Thermolyse von Gibbsit A1(OH)₃ wird gezeigt, daß a) eine Regelung des Restdruckes nur dann von Nutzen ist, wenn auch die Zersetzungsgeschwindigkeit geregelt werden kann (ansonsten stellen die TG-Kurven ein nicht zu entzifferndes komplexes Phänomen dar) und daß b) die Wirkung des Restdruckes äußerst bedeutend sein kann, sowohl hinsichtlich der Gestalt der TG-Kurven (also der scheinbaren kinetischen Parameter), als auch der Beschaffenheit (Porosität, Struktur) des Produkts.

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Résumé On examine l'influence des pressions résiduelles comprises entre 10^–5 et 5 torrs sur le cours des décompositions thermiques. Grâce à des exemples concernant en particulier la thermolyse de la gibbsite A1(OH)₃ on montre: a) qu'un contrôle de la pression résiduelle n'est utile que si l'on peutaussi contrôler la vitesse de décomposition (sans quoi les courbes de TG représentent un phénomène composite inextricable); b) que l'effet de la pression résiduelle peut être extrêmement important, aussi bien sur la forme des courbes de TG et donc sur les paramètres cinétiques apparents) que sur la nature (porosité, structure) des produits

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10^–5 5 . , 1()₃, : ) , ( , , ), ) ( ), (, ) .

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Paper presented at the Scientific Session on Thermal Analysis held at Balatonfüred, Hungary, on 14–16 October 1976.     

S-nitrosocysteine and cystine from reaction of cysteine with nitrous acid. A kinetic investigation

The formation of the S-nitrosocysteine (CySNO) in aqueous solution starting from cysteine (CySH) and sodium nitrite is shown to strongly depend on the pH. Experiments conducted within the pH range 0.5-7.0 show that at pH below 3.5 the NO+ (or H2NO 2 +) is the main nitrosating species, while at higher pH (>3.5) the nitrosating species is most likely the N2O3. A kinetic study provided a general kinetic equation, V(CySNO) = k1[HNO2][CySH]eq [H+] + k2[HNO2]2. The first term of this equation is predominant at pH lower than 3.5, in agreement with the literature for the direct nitrosation of thiols with nitrous acid; the value for the third-order rate constant, k(1) = 7.9 x 10(2) L(2) mol(-2) min(-1), was calculated. For experiments at pH higher than 3.5, the second term becomes prevalent and the second-order rate constant k(2) = (3.3 +/- 0.1) x 10(3) L mol(-1) min(-1) was calculated. A competitive oxidation process leading to the direct formation of cystine (CySSCy) has been also found. Most likely also for this process two different mechanisms are involved, depending on the pH, and a general kinetic equation, V(CySSCy) = k3[CySH](eq)[HNO2][H+] + k3'[CySH]eq[HNO2], is proposed.     

Thermochemistry for enthalpies and reaction paths of nitrous acid isomers

Recent studies show that nitrous acid, HONO, a significant precursor of the hydroxyl radical in the atmosphere, is formed during the photolysis of nitrogen dioxide in soils. The term nitrous acid is largely used interchangeably in the atmospheric literature, and the analytical methods employed do not often distinguish between the HONO structure (nitrous acid) and HNO₂ (nitryl hydride or isonitrous acid). The objective of this study is to determine the thermochemistry of the HNO₂ isomer, which has not been determined experimentally, and to evaluate its thermal and atmospheric stability relative to HONO. The thermochemistry of these isomers is also needed for reference and internal consistency in the calculation of larger nitrite and nitryl systems. We review, evaluate, and compare the thermochemical properties of several small nitric oxide and hydrogen nitrogen oxide molecules. The enthalpies of HONO and HNO₂ are calculated using computational chemistry with the following methods of analysis for the atomization, isomerization, and work reactions using closed‐ and open‐shell reference molecules. Three high‐level composite methods G3, CBS‐QB3, and CBS‐APNO are used for the computation of enthalpy. The enthalpy of formation, ΔH^o_f(298 K), for HONO is determined as ?18.90 ± 0.05 kcal mol^?1 (?79.08 ± 0.2 kJ mol^?1) and as ?10.90 ± 0.05 kcal mol^?1 (?45.61 ± 0.2 kJ mol^?1) for nitryl hydride (HNO₂), which is significantly higher than values used in recent NO_x combustion mechanisms. H‐NO₂ is the weakest bond in isonitrous acid; but HNO₂ will isomerize to HONO with a similar barrier to the HO? NO bond energy; thus, it also serves as a source of OH in atmospheric chemistry. Kinetics of the isomerization is determined; a potential energy diagram of H/N/O₂ system is presented, and an analysis of the triplet surface is initiated. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 378–398, 2007     

Spectrophotometric determination of tryptophan by reaction with nitrous acid

The heterocyclic nucleus in tryptophan is oxidised by nitrous acid at elevated temperature to produce a phenolic intermediate which further reacts with nitrous acid to form a nitro compound that has a golden yellow colour in alkaline medium. The maximum absorbance is obtained at 400 nm with maximum molar absorptivity of 9.44 x 10(3) l.mole(-1). cm(-1). Derivatives of tryptophan such as indole-3-acetic acid, tryptamine and tryptophanamide, as well as indole, produce the same colour, but some others, e.g., 5-hydroxytryptamine and 5-hydroxyindole-3-acetic acid do not give the colour reaction. A plausible mechanism is proposed to explain this behaviour.     

N-acylaminophenylcyclopropanes in reaction with nitrous acid generated in situ

The reaction of N-acylaminophenylcyclopropanes with HNO₂ proceeds regioselectively with introduction of an N = O fragment into the three-membered ring and formation of the corresponding Δ²-isoxazolines. For ortho-substituted N-acylaminophenylcyclopropanes side processes were observed, caused by the intramolecular participation of the N-acyl group in conversions of the carbenium ions formed on opening the cyclopropane ring under the action of the nitrosating reagent, and by direct insertion of the modified ortho substituent into the three-membered ring.     

Effect of inclusion complex on nitrous acid reaction with flavonoids

The kinetic of the nitrous acid reactions with quercetin and catechin has been studied using spectrophotometric method in aqueous solution. The results show that these antioxidants participate in oxidation reactions with nitrous acid which is derived from protonation of nitrite ion in mild acidic conditions. Corresponding o-quinones as relatively stable products were detected by spectrophotometric techniques. pH dependence of the reactions has been examined and the rate constants of reactions were obtained by non-linear fitting of kinetic profiles. The effect of β-cyclodextrin on the oxidation pathway was another object of this study. It is shown that β-cyclodextrin has an inhibitory effect on the oxidation reaction. The rate constants of oxidation reactions for complexed forms and their stability constants were obtained based on changes in the reaction rates as a function of β-cyclodextrin concentration.     

Thermolysis reaction of 2-acetyl-1-oxo-five-, six-, and seven-membered ring

The rates of gas-phase thermolysis reactions of 2-acetylcyclopentanone 1,2-acetylcyclohexanone 2, N-acetylcaprolactam 3,2-acetylbutyrolactone 4,2-acetyl-2-methylbutyrolactone 5, and 3-acetyl-2-oxazolidinone 6 have been measured over a temperature range of 50 K. They undergo unimolecular first-order elimination reactions for which log A = 11.7, 11.7, 11.2, 11.4, 11.5, and 11.1 s^?1 and E_a = 193.4, 189.5, 153.2, 201.0, 206.8, and 176.1 kJ mol^?1, respectively. The effect of the ring size together with the effect of a heteroatom in the ring on the rate of thermolysis reactions for compound 1–6 is the subject of this work. © 1995 John Wiley & Sons, Inc.     

The behavior of the cyclopropyl phenyl sulfide and phenoxycyclopropane in the reaction with nitrous acid

The behavior of cyclopropyl phenyl sulfide and phenoxycyclopropane in the nitrosation reaction was studied. Cyclopropyl phenyl sulfide was found to convert quantitatively to cyclopropyl phenyl sulfoxide under the action of nitrous acid formed in situ. Under the same conditions, phenoxycyclopropane undergoes transformation to 5-phenoxyisoxasoIine (nitrophenols are formed as byproducts in this reaction).     

活性白土催化松香反应产物的GC-MS分析

把活性白土上松香催化反应产物分离为酸性物和中性物,采用气相色谱-质谱联用技术(GC-MS)分别对各部分化学组成进行定性定量分析.结果表明,活性白土上松香主要进行脱氢、脱羧及裂解反应,其产物中的酸性物共分离出2个峰,主要成分是脱氢枞酸,含量为99.61%;中性物共分离出35个峰,初步鉴定出其中33个组分,大部分为甾族类化合物和环烯烃类化合物,主要成分是5α-雄甾烷、1,4-二甲基-7-(1-甲基乙烯基)-1,2,3,5,6,7,8,8a-八氢化-1S-(1α)-蓝烃、松香酸甲酯和(-)-石竹烯,含量分别为18.75%、13.00%、12.53%和11.74%.     

Selective reaction of amino acid sulfoximines with nitrous acid; facile stereospecific conversion to amino acid sulfoxides

N-Unsubstituted sulfoximines of amino acids can he readily converted to the corresponding amino acid sulfoxides in high yields by treatment with stoichiometric quantities of nitrous acid. Under the conditions employed, reaction with L-methionine-S (or R)-sulfoximine is specific for the sulfoximine nitrogen atom, and no reaction occurs at the α-amino group. Conversion to the sulfoxide proceeds with complete retention of configuration at the sulfur atom.     

Investigation of reaction products of sulphuric acid with ilmenite

The reaction of sulphuric acid with titanium raw materials runs violently with simultaneous emission of gases. Such run of reaction creates danger of explosion. This process is very complicated from the reason of complexity of reactions and variety of compounds in reaction mixture. To determine safe conditions of reaction with high efficiency, it is necessary to investigate phase composition products of reaction. Products of reaction were investigated by using X-ray diffraction. However reaction products show high amorphy and this is the reason of difficulties to determine all phases. For this reason also was used additional method — ‘drop’ calorimeter. This method is used for determination of average specific heat of liquid or solid samples. In this case, this method was used for verification of phase composition of products of reaction. On the basis of investigation the phase composition of reaction product is following: titanyl sulfate, iron(III) sulfate, monohydrated iron(II) sulfate, magnesium sulfate and unreacted remainders of ilmenite and magnesium silicate.     

Thermolysis mechanism of chromium nitrate nonahydrate and computerized modeling of intermediate products

Thermal decomposition of chromium nitrate nonahydrate was studied by thermal analysis, differential scanning calorimetry, infrared spectroscopy, and high temperature X-ray diffraction, so that mass losses were related to the exactly coincident endothermic effects and vibrational energy levels of the evolved gases. The thermal decomposition of chromium nitrate is a complex process, which begins with the simultaneous dehydration and concurrent condensation of 4 mol of the initial monomer Cr(NO₃)₃·9H₂O. Soon after that, the resulting product Cr₄N₁₂O₃₆·31H₂O gradually loses water and azeotrope HNO₃ + H₂O, and is transformed into tetrameric oxynitrate Cr₄N₄O₁₆. At higher temperatures, the tetramer loses N₂O₃ and O₂ and a simultaneous oxidation of Cr(III) to Cr(IV) occurs. The resulting composition at this stage is chromium dioxide dimer Cr₄O₈. Finally, at 447 °C the unstable dimer loses oxygen and is transformed into 2Cr₂O₃. The models of intermediate amorphous compounds represent a reasonably good approximation to the real structures and a proper interpretation of experimental data.