The pyrolysis of acetaldehyde in the presence of nitric oxide

The kinetics of the acetaldehyde pyrolysis have been studied at temperatures from 450° to 525°C, at an acetaldehyde pressure of 176 torr and at 0 to 40 torr of added nitric oxide. The following products were identified and their rates of formation measured: CH₄, H₂, CO, CO₂, C₂H₄, C₂H₆, H₂O, C₃H₆, C₂H₅CHO, CH₃COCH₃, CH₃COOCH?CH₂, N₂, N₂O, HCN, CH₃NCO, and C₂H₅NCO. Acetaldehyde vapor was found to react with nitric oxide slowly in the dark at room temperature, the products being H₂O, CH₃COOCH₃, CO, CO₂, N₂, NO₂, HCN, CH₃NO₂, and CH₃ONO₂. The rates of formation of N₂ and C₂H₅NCO depend on how long the CH₃CHO-NO mixture is kept at room temperature before pyrolysis; the rates of formation of the other products depend only slightly on the mixing period. The pyrolysis of “clean” CH₃CHO–NO mixtures (i.e., the results extrapolated to zero mixing time, which are independent of products formed in the cold reaction) are interpreted as follows: (1) There are two chain carriers, CH₃ and CH₂CHO, their concentrations being interdependent and influenced by NO in different ways: the CH₃ radical is both generated and removed by reactions directly involving NO, whereas CH₂CHO is generated only indirectly from CH₃ but is also removed by direct reaction with NO. (2) An important mode of initiation by NO is its addition to the carbonyl group with the formation of which is converted into ; this splits off OH with the formation of CH₃NCO or CH₃ + OCN. (3) Important modes of termination are The steady-state equations derived from the mechanism are shown to give a good fit to the experimental rate versus [NO] curves and, in particular, explain why there is enhancement of rate by NO at higher CH₃CHO pressures and, at lower CH₃CHO pressures, inhibition at low [NO] followed by enhancement at higher [NO]. The cold reaction is explained in terms of chain-propagating and chain-branching steps resulting from the addition of several NO molecules to CH₃CHO and the CH₃CO radical. In the “unclean” reaction it is found that the rates of N₂ and C₂N₅NCO formation are increased by CH₃NO₂, CH₃ONO, and CH₃ONO₂ formed during the cold reaction. A mechanism is proposed, involving the participation of α-nitrosoethyl nitrite, CH₃CH(NO)ONO. It is suggested that there are two modes of behavior in pyrolyses in the presence of NO: (1) In the paraffins, ethers, and ketones, the effects are attributed to the addition of NO to a radical with the formation of an oxime-like compound. (2) In the aldehydes and alkenes, where there is a hydrogen atom attached to a double-bonded carbon atom, the behavior is explained in terms of addition of NO to the double bond followed by the formation of an oxime-like species.     

The pyrolysis of ethane in the presence of nitric oxide

The kinetics of the ethane pyrolysis have been studied at temperatures from 550 to 596°C and with 0 to 62% of added nitric oxide. The rates of production of various products were studied by gas chromatography; ethylene, hydrogen, methane, nitrogen, water, nitrous oxide and acetonitrile were found as primary products, with hydrogen cyanide, carbon monoxide, acetaldehyde, n-butane, 1-butene, cis- and trans-2-butene and 1,3-butadiene as secondary products. For all the primary products the orders with respect to C₂H₆and NO were determined, as were the activation energies at two different percentages of NO (15.7 and 45.5%). Nitric oxide was found to be rapidly consumed with a finite initial rate, and the rate of production of H₂O was close to that of C₂H₄ at higher nitric oxide pressures. A mechanism is proposed which gives good agreement with all of the observed results. Its main features are: (1) Initiation takes place mainly by the unimolecular dissociation of ethane; there is no evidence for or against the process NO + C₂H₆ → HNO + C₂H₅; (2) NO scavenges ethyl radicals to form acetaldoxime which decomposes, and in this way the breakdown of C₂H₅ is hastened; (3) termination takes place mainly by the unimolecular decomposition of acetaldoxime to give inactive products. Some of the relevant rate parameters are evaluated. Reactions are proposed to account for the formation of the secondary products observed.     

The recombination of iodine atoms in the presence of nitric oxide

The recombination of iodine atoms following the flash photolysis of iodine in the presence of nitric oxide is interpreted through the mechanism with k₁ = 3.5 × 10⁹ l.²/mol²·sec; k₂ ≈ 1 × 10¹¹ l./mol·sec; k₃ = 2.1 × 10⁷ l./mol·sec at 298°K; E₃ = 11 kJ/ mol; and ΔH°₁ = 76 ± 6 kJ/mol. Lower and upper limits for the equilibrium constant are also established. The absorption spectrum of INO has been extended down to 223 nm and extinction coefficients for the region of 223–310 nm and 360–460 nm have been measured.     

Reaction of arylhydrazines with nitric oxide in the presence of oxygen

Arylhydrazines were treated with nitric oxide in tetrahydrofuran in the presence of oxygen to afford dehydrazinated compounds in good yields accompanied by small amounts of arylazides.     

Nitrous oxide decomposition over Fe-ZSM-5 in the presence of nitric oxide: a comprehensive DFT study

A number of experimental studies have shown recently that ppm-level additions of nitric oxide (NO) enhance the rate of nitrous oxide (N(2)O) decomposition catalyzed by Fe-ZSM-5 at low temperatures. In the present work, the NO-assisted N(2)O decomposition over mononuclear iron sites in Fe-ZSM-5 was studied on a molecular level using density functional theory (DFT) and transition-state theory. A reaction network consisting of over 100 elementary reactions was considered. The structure and energies of potential-energy minima were determined for all stable species, as were the structures and energies of all transition states. Reactions involving changes in spin potential-energy surfaces were also taken into account. In the absence of NO and at temperatures below 690 K, most active single iron sites (Z(-)[FeO](+)) are poisoned by small concentrations of water in the gas phase; however, in the presence of NO, these poisoned sites are converted into a novel active iron center (Z(-)[FeOH](+)). These latter sites are capable of promoting the dissociation of N(2)O into a surface oxygen atom and gas-phase N(2). The surface oxygen atom is removed by reaction with NO or nitrogen dioxide (NO(2)). N(2)O dissociation is the rate-limiting step in the reaction mechanism. At higher temperatures, water desorbs from inactive iron sites and the reaction mechanism for N(2)O decomposition becomes independent of NO, reverting to the reaction mechanism previously reported by Heyden et al. [J. Phys. Chem. B 2005, 109, 1857].     

The gas-phase pyrolysis of alkyl nitrites. VII. Primary and secondary nitrites in the presence of nitric oxide

Although our pyrolytic studies of five alkyl nitrites (RONO) have shown that it is possible to determine precise, acceptable values for k₁: we have been uncertain about the mechanism for the first order production of nitroxyl from primary and secondary nitrites. Nitroxyl could arise either from the direct elimination process (5) or from the disproportionation of the alkoxyl radical concerned and nitric oxide: Thus k_exp = k₅ or k₁k₆/[k₂ + k₆]. If the route is reaction (6), E_exp should be identical to E₁, since the ratio k₆/k₂ is temperature independent. We preferred the elimination process because E_exp < E₁ and A_exp was in agreement with transition-state calculations for such elimination processes. This study was concerned with the pyrolyses of ethyl and i-propyl nitrites in the presence of nitric oxide. The results show that nitroxyl is produced via the disproportionation of the alkoxyl radical and nitric oxide, as originally suggested by Levy. This is supported by the wealth of particularly photochemical data in the literature. Our and other previous spuriously low Arrhenius parameters are attributed to heterogeneous effects.     

Discovery of nitric oxide in marine ecological system and the chemical characteristics of nitric oxide

Nitric oxide was discovered in both the lab and the alga culture pond of Daya Bay (1―300 m3) before the growth of alga reached the maximum. The results included: (1) NO was detected before the growth of alga reached the maximum in the case of red tide alga and food alga, and the concentration of NO decreased rapidly after the growth maximum; (2) the curve between NO con-centration and time indicated that the concentration of NO in the daytime was more than that at night, and the maximal concentration of NO appeared in the midday (1―3 pm); (3) the growth of alga reached the maximum in the alga culture pond of Daya Bay in about 8―10 d, and NO was discovered in 5―7 d; (4) the measured NO concentration was 10-9 mol/L, 10-9―10-8 mol/L, and 10-8 mol/L for Haeterosigma akashiwo, mixed alga in Daya Bay and Chaetoceros Curvisetus individually; (5) the relation of illumination with NO production was discussed.     

Kinetics of nitric oxide reduction by carbon monoxide in the presence of cobalt(II) complexes

Kinetic studies of nitric oxide reduction by carbon monoxide in the presence of Co(II) complexes indicate that the reaction is first order with respect to catalyst, carbon monoxide, and nitric, oxide. Co(AC₂)(OH) ₂ ^– complexes have the highest catalytic activity. A reduction mechanism is proposed.

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Co(II). , , . Co(Ac₂)(OH) ₂ ^– . .

     

A synergetic effect in nitrous acid formation by sonolysis of nitric acid in the presence of nitrous oxide

A synergetic effect is found in the sonochemical formation of HNO₂ in HNO₃ solution in the presence of an N₂O–Ar gaseous mixture. The maximum rate of HNO₂ formation is observed at an N₂O : Ar ratio of 15 : 85 (v/v). During the sonolysis of 4 M HNO₃ solutions, the rate of HNO₂ formation increases multifold due to the synergetic effect. The rate of sonochemical hydrazine decomposition in nitrate solutions also increases considerably in the presence of N₂O.     

The reaction of nitric oxide with glutathionylcobalamin

UV-vis stopped-flow results show that glutathionylcobalamin can react with nitric oxide at pH 7 to form nitrosylcob(II)alamin in a reaction second-order overall. From kinetic studies we suggest that nitric oxide attacks glutathionylcobalamin to form a caged transition state followed by formation of the nitrosylcob(II)alamin.     

Protein thiyl free radicals produced by nitric oxide and nitric oxide donors

The spin-trapping technique was used to study the radical intermediates produced by reaction of nitric oxide (^*NO) and peroxynitrite with serum albumin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Our results show that the major radical product induced by ^*NO and by peroxynitrite with serum albumin and GAPDH was a thiyl radical. The same radical can be detected in the ^*NO-transfer from S-nitroso albumin to low molecular weight thiols. Moreover, ^*NO or peroxynitrite treatment of GAPDH was able to induce NAD-dependent covalent modification of the enzyme in erythrocyte ghosts.     

The kinetics of Ogawa band chemiluminescence in the nitric oxide afterglow

Nitric oxide Ogawa band chemiluminescences emanating from NO(b⁴Σ⁻) υ′ = 4, 3 and 2, associated with combining N(⁴S) and O(³P) atoms in a discharge flow system, have been detected photoelectrically. In N₂ carrier the intensities (Iυ′) followed relationships Iυ′ = kυ′ [N][O] with kυ′ independent of [N₂] in the range (4 - 15) X 10⁻⁵ mol/dm³ at both 195 K and 298 K. The temperature coefficients of kυ′, expressed as T^-nv′, were n₃ = 1.8±0.4, n₂ = 1.5±0.8 and n₃ - n₄ = 0.62±0.20. Addition of Ar (⩽76%) had no effect upon kυ′ but distinct quenching of k₃ and k₂ occurred when N₂ was partly replaced with CO₂, N₂O and H₂O (⩽46%). On the simplest basis CO₂ was about twice, N₂O about four times and H₂O about six times as effective as N₂ in removing NO(b⁴Σ−) υ′ = 2, 3. Only with H₂O was any quenching detected for k₄ and that ∼3 times less than for k₃.The results for υ′ = 4 were interpreted in terms of the lowest rotational level being within 5 to 10 kJ/mol of the first dissociation limit of NO, so that preassociation/predissociation operates in the mechanism.Absolute intensity measurements gave 1/photons dm⁻³ s⁻¹ = 1.4 X 10³ ([N][O]/mol²/dm⁶) for the bands observed between 700 and 1000 nm. A lower radiative lifetime limit of 6 X 10⁻⁶ s is deduced for υ′ = 3 on the basis of a mechanism where depopulation is dominated by collisional removal and quenching in mixed carriers.     

Fluorination of derivatives of tri- and pentavalent phosphorus acids by perfluoropropylene oxide

Perfluoropropylene (I) efficiently fluorinates esters and ester anhydrides of P^III ana P^V acids to give acid fluoride derivatives of pentavalent phosphorus acids. Phosphites are initially oxidized to the corresponding phosphoryl compounds with subsequent substitution of the oxygen by two fluorine atoms by means of excess oxide (I).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2848–2851, December, 1990.     

The role of tetrahydrobiopterin in catalysis by nitric oxide synthase

Electronic structure calculations show that the cofactor H4B can be a key factor in a proton transfer relay in nitric oxide synthase, and that 4-amino-H4B cannot fulfill this role.     

The kinetics of the15N/14N isotopic exchange between nitric oxide and nitric acid

The rate of the¹⁵N/¹⁴N isotopic exchange between NO−HNO₃ at high nitric acid concentration (2–10M) have been measured. The experimental data were obtained by contacting nitric oxide at atmospheric pressure with nitric acid solution labelled with¹⁵N, in a glass contactor.     

Nitrogen isotope exchange between nitric oxide and nitric acid

The rate of nitrogen isotope exchange between NO and HNO₃ has been measured as a function of nitric acid concentration of 1.5–4M·1^–1. The exchange rate law is shown to beR=k[HNO₃]²[N₂O₃] and the measured activation energy isE=67.78kJ ·M^–1 (16.2 kcal·M^–1). It is concluded that N₂O₃ participates in¹⁵N/¹⁴N exchange between NO and HNO₃ at nitric acid concentrations higher than 1.5M·1^–1.