Negative- and positive-ion chemical ionization mass spectra of aromatic amines: Surface-assisted reactions involving oxygen

The O₂–N₂ and O₂–Ar negative-ion chemical ionization mass spectra of aromatic amines show a series of unusual ions dominated by an addition appearing at [M + 14]^?˙. Other ions are observed at [M – 12]^?˙, [M + 5]^?˙, [M + 12]^?˙, [M + 28]^?˙ and [M + 30]^?˙. Ion formation was studied using a quadrupole instrument equipped with a conventional chemical ionization source and a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. These studies, which included the examination of ion chromatograms, measurement of positive-ion chemical ionization mass spectra, variation of ion source temperature and pressure and experiments with ¹⁸O₂, indicate that the [M + 14]^?˙ ion is formed by the electron-capture ionization of analytes altered by surfaceassisted reactions involving oxygen. This conversion is also observed under low-pressure conditions following source pretreatment with O₂. Experiments with [¹⁵N]aniline, [2,3,4,5,6-²H₅] aniline and [¹³C₆]aniline show that the [M + 14]^?˙ ion corresponds to [M + O ? 2H]^?˙, resulting from conversion of the amino group to a nitroso group. Additional ions in the spectra of aromatic amines also result from surface-assisted oxidation reactions, including oxidation of the amino group to a nitro group, oxidation and cleavage of the aromatic ring and, at higher analyte concentrations, intermolecular oxidation reactions.     

煤热解过程中含氮气相产物转化规律的实验研究

为了研究煤在热解过程中含氮气相产物的生成规律,在滴管炉反应系统中对四种原煤以及两种脱除矿物质煤样分别在500℃、700℃、900℃和1100℃进行了实验研究。结果表明,随着温度的升高,作为NO前驱物的HCN和NH3的收率随之增加,N2的收率也增加。煤种对含氮气相产物的生成规律也有着较大的影响,煤化程度比较低的煤在热解过程中,燃料氮向气相含氮产物的转化率较高;煤化程度比较高的煤转化率则偏低,大部分的氮缩聚在多环芳香结构中,成为焦炭氮。煤中的矿物质对燃料氮向N2的转化起到了促进作用,而对燃料氮向HCN和NH3的转化起到了抑制作用。     

Electric discharge-induced oxidation of hydrogen cyanide

The AC high-voltage discharge-induced decomposition chemistry of trace levels of hydrogen cyanide in helium has been studied. In the absence of oxygen only low levels of molecular nitrogen were evolved. With oxygen added, the principal products were CO, CO₂, and N₂. No significant concentrations of NO or N₂O were observed. The response of a commercial NO_x analyzer to HCN and C₂N₂, in the NO_x mode, was determined to be linear through three decades in concentration. The oxidation chemistry of HCN and C₂N₂ in the stainless steel converter of the analyzer was studied as a function of the amount of added oxygen.NRL/NRC Postdoctoral Fellow (1983–1985).     

The effect of encapsulated Zn-POM on the catalytic activity of MIL-101 in the oxidation of alkenes with hydrogen peroxide

Zinc monosubstituted Keggin heteropolyanion [PZnMo₂W₉O₃₉]^5? was electrostatically bound to nanocages of MIL-101 polymer matrix. The Zn-POM@MIL-101 catalyst was characterized by XRD, N₂ adsorption, atomic absorption (AAS), and FT-IR spectroscopic methods. The catalytic activity of the new composite material, Zn-POM@MIL-101, was assessed in the oxidation of alkenes using aqueous hydrogen peroxide as oxidant. Zn-POM@MIL-101/H₂O₂ catalytic system demonstrated good catalytic activity in the oxidation reactions. Zn-POM@MIL-101 was reusable for three catalytic cycles. While the MIL-101 matrix is an active catalyst in these oxidation reactions, the presence of Zn-POM significantly changed the selectivity and reaction times.     

Palladium-catalyzed aziridination of alkenes using N,N-dichloro-p-toluenesulfonamide as nitrogen source

N,N-Dichloro-p-toluenesulfonamide (TsNCl₂) was found to be an efficient nitrogen source for the aziridination of unfunctionalized alkenes using palladium catalysts. Among the palladium salts, palladium acetate was the most effective catalyst for this reaction. A variety of alkenes were reacted at room temperature with TsNCl₂ to form the desired aziridines in moderate to good yields. This method can complement our previous protocol which is limited to the use of electron-deficient α,β-unsaturated alkenes.     

Rapid ‘on-column’ preparation of hydrogen [11C]cyanide from [11C]methyl iodide via [11C]formaldehyde

Hydrogen [¹¹C]cyanide ([¹¹C]HCN) is a versatile ¹¹C-labelling agent for the production of ¹¹C-labelled compounds used for positron emission tomography (PET). However, the traditional method for [¹¹C]HCN production requires a dedicated infrastructure, limiting accessibility to [¹¹C]HCN. Herein, we report a simple and efficient [¹¹C]HCN production method that can be easily implemented in ¹¹C production facilities. The immediate production of [¹¹C]HCN was achieved by passing gaseous [¹¹C]methyl iodide ([¹¹C]CH₃I) through a small two-layered reaction column. The first layer contained an N-oxide and a sulfoxide for conversion of [¹¹C]CH₃I to [¹¹C]formaldehyde ([¹¹C]CH₂O). The [¹¹C]CH₂O produced was subsequently converted to [¹¹C]HCN in a second layer containing hydroxylamine-O-sulfonic acid. The yield of [¹¹C]HCN produced by the current method was comparable to that of [¹¹C]HCN produced by the traditional method. The use of oxymatrine and diphenyl sulfoxide for [¹¹C]CH₂O production prevented deterioration of the molar activity of [¹¹C]HCN. Using this method, compounds labelled with [¹¹C]HCN are now made easily accessible for PET synthesis applications using readily available labware, without the need for the ‘traditional’ dedicated cyanide synthesis infrastructure.

In a reaction column, gaseous [¹¹C]methyl iodide was converted to [¹¹C]formaldehyde in a first layer containing N-oxide and then transformed into hydrogen [¹¹C]cyanide in a second layer containing hydroxylamine-O-sulfonic acid within 2 minutes.     

Theoretical investigation for the reaction of N<Subscript>2</Subscript>O with CO catalyzed by Pt-Graphene

To find an efficient catalyst to catalytic conversion of hazardous gases maybe the important way for solving environmental problems. We performed the first-principles density functional theory (DFT) to investigate the CO oxidation by using N₂O as an oxidizing agent over an Pt-Graphene catalyst. The results indicated that CO oxidation by N₂O on Pt-Graphene may occur via two pathways: (1) Adsorption of N₂O followed by CO and (2) Adsorption of CO followed by N₂O. Although the CO was more likely to adsorb on the Pt-Graphene than N₂O, but when the Pt site was first covered by the CO, the higher barrier energy (20.28 kcal/mol) would limit the reaction to react. However, the N₂O molecule was first decomposed on the Pt-site yielding the N₂ and O-Pt-Graphene, which was an active species for the CO oxidation. Thus, control of the adsorbing molecules over Pt-Graphene might be a key factor for the activity of the catalyst, and this may open new avenues in searching for oxidation of CO at an economical cost.     

The Behaviors of Metal Acetylides with Dinitrogen Tetroxide

Lithium phenylacetylide ( 1a ) and N₂O₄ ( 2 ) at −78° yield diphenylbutadiyne ( 6a ) by oxidative coupling, phenylacetylene ( 7a ) by oxidation and then solvent H‐abstraction, and benzoyl cyanide ( 8 ) by dimerizative‐rearrangement of nitroso(phenyl)acetylene ( 23 ). Nitro(phenyl)acetylene ( 3 , R=Ph) is not obtained. Benzonitrile ( 9 ), a further product, possibly results from hydrolytic decomposition of nitroso(phenyl)ketene ( 27 ) generated from phenylacetylenyl nitrite ( 26 ). Phenylacetylene ( 7a ) and 2 give, along with (E)‐ and (Z)‐1,2‐dinitrostyrenes ( 34 and 35 , resp.), 3‐benzoyl‐5‐phenylisoxazole ( 10 ), presumably as formed by cycloaddition of benzoyl nitrile oxide ( 40 ) to 7a . Further, 2 reacts with other lithium acetylides ( 1b – 1e ), and with sodium, magnesium, zinc, copper, and copper lithium phenylacetylides, 1f – 1l , to yield diacetylenes 6a – 6c and monoacetylenes 7a – 7c . Conversions of metallo acetylide aggregates to diacetylenes are proposed to involve generation and addition reactions of metallo acetylide radical cationic intermediates in cage, further oxidation, and total loss of metal ion. Loss of metal ions from metallo acetylide radical cations and H‐abstraction by non‐caged acetylenyl radicals will give terminal acetylenes. The principal reactions (75–100%) of heavy metal acetylides phenyl(trimethylstannyl)acetylene ( 44 ) and bis(phenylacetylenyl)mercury ( 47 ) with 2 are directed nitrosative additions (NO⁺) and loss of metal ions to give nitroso(phenyl)ketene ( 27 ), which converts to benzoyl cyanide ( 8 ).     

‘Reductive ozonolysis’ via a new fragmentation of carbonyl oxides

This account describes the development of methodologies for ‘reductive’ ozonolysis, the direct ozonolytic conversion of alkenes into carbonyl groups without the intermediacy of 1,2,4-trioxolanes (ozonides). Ozonolysis of alkenes in the presence of DMSO produces a mixture of aldehyde and ozonide. The combination of DMSO and Et₃N results in improved yields of carbonyls but still leaves unacceptable levels of residual ozonides; similar results are obtained using secondary or tertiary amines in the absence of DMSO. The influence of amines is believed to result from conversion to the corresponding N-oxides; ozonolysis in the presence of amine N-oxides efficiently suppresses ozonide formation, generating high yields of aldehydes. The reactions with amine oxides are hypothesized to involve an unprecedented trapping of carbonyl oxides to generate a zwitterionic adduct, which fragments to produce the desired carbonyl group, an amine, and ¹O₂.     

Laser photodissociation of s-tetrazine: Product vibrational excitation

The photosensitive and thermally unstable molecule s-tetrazine decomposes to yield one nitrogen molecule and two HCN molecules. Following pulsed irradiation of tetrazine vapor at 492.3 nm, we have observed time resolved infrared fluorescence from HCN(001). In a similar experiment, small quantities of CO₂ were added to the sample cell, and we observed infrared fluorescence from CO₂ (001) populated by VV energy transfer. From fluorescence intensity measurements, we have been able to estimate the amount of excitation in certain product vibrations. We conclude that ≈ 1% of the HCN is produced in the (001) state, and the “equivalent” of ≈ 0.1 quantum of N₂ vibrational excitation is excited. This latter figure may include some excitation of HCN (ν₁), but the measured energy transfer rate coefficients are consistent with N₂ excitation. The small amount of HCN(ν₃) and N₂ vibrational excitation is surprising, as the photodissociation is exothermic by more than 100kcal/mole.     

Importance of hydrophobicity in the liquid phase oxidation catalyzed by titanosilicates

In the oxidation of alkanes, Ti-beta catalysts synthesized by the dry gel conversion method show higher turnover number and H₂O₂ selectivity than the conventionally synthesized ones, which is ascribed to higher hydrophobicity of the former. Trimethylsilylation of mesoporous materials is effective in enhancing the activity through increasing hydrophobicity. It has been revealed that the hydrophobicity of the catalysts whether microporous or mesoporous is a crucial factor in their activity in the liquid-phase oxidation of hydrophobic reactants such as alkanes and simple alkenes using aqueous H₂O₂ solutions as oxidant.     

Selective oxidation of alkenes using [bmim]5[PW11ZnO39]·3H2O hybrid catalyst

The catalytic activity of [bmim]₅[PW₁₁ZnO₃₉]·3H₂O as a hybrid catalyst was studied in the oxidation of various alkenes in acetonitrile, using hydrogen peroxide as oxygen source. The effect of reaction parameters such as type of solvent and oxidant, amount of catalyst and oxidant, and temperature was also investigated. From our results, [bmim]₅[PW₁₁ZnO₃₉]·3H₂O hybrid catalyst gave higher yields and selectivity in the oxidation of alkenes and was reused four times without loss of its catalytic activity.     

Sodium borohydride-iodine mediated reduction of γ-lactam carboxylic acids followed by DDQ mediated oxidative aromatisation: a simple approach towards N-aryl-formylpyrroles and 1,3-diaryl-formylpyrroles

A simple methodology for the conversion of substituted N-aryl-γ-lactam 2/3-carboxylic acids to substituted N-aryl-2/3-formyl-pyrroles has been developed. Several N-aryl-γ-lactam 2/3-carboxylic acids were reduced to substituted (N-aryl-pyrroliden-2/3-yl)-methanols in good yields by using the NaBH₄-I₂ system. Aromatisation and in situ oxidation of these alcohols using DDQ produced N-aryl-2/3-formyl-pyrroles, which act as key starting material and intermediates in the synthesis of several bioactive compounds.     

The Effect of Vibrational Excitation of Molecules on Plasmachemical Reactions Involving Methane and Nitrogen

An experimental study of plasmachemical reaction involving CH₄ and N₂ molecules in rf discharge was studied in order to know the effect of vibrational excitation of N₂ molecules. When the relative nitrogen concentration was greater than 0.8, the main product of CH₄ decomposition was HCN, and the rate of methane decomposition at this condition was faster than that one in pure methane. These results could be confirmed through the mass spectroscopic method. The reason for these results is the vibrational energy of N₂ excited by rf discharge. The chain reaction mechanisms of producing HCN by vibrational excitation of N₂ were examined closely through numerical simulation. The rate-controlling step was the dissociation reaction of excited nitrogen molecule to the atomic nitrogen, so the process of HCN synthesis was limited by the value of reaction constant, k^N.     

Tuning the Electron Localization of Gold Enables the Control of Nitrogen‐to‐Ammonia Fixation

The (photo)electrochemical N₂ reduction reaction (NRR) provides a favorable avenue for the production of NH₃ using renewable energy in mild operating conditions. Understanding and building an efficient catalyst with high NH₃ selectivity represents an area of intense interest for the early stages of development for NRR. Herein, we introduce a CoO_x layer to tune the local electronic structure of Au nanoparticles with positive valence sites for boosting conversion of N₂ to NH₃. The catalysts, possessing high average oxidation states (ca. 40 %), achieve a high NH₃ yield rate of 15.1 μg cm^?2 h^?1 and a good faradic efficiency of 19 % at ?0.5 V versus reversible hydrogen electrode. Experimental results and simulations reveal that the ability to tune the oxidation state of Au enables the control of N₂ adsorption and the concomitant energy barrier of NRR. Altering the Au oxidation state provides a unique strategy for control of NRR in the production of valuable NH₃.     

Conversion of ammonia to dinitrogen in wastewater by Nitrosomonas europaea

Because Nitrosomonas europaea contains ammonia-oxidizing enzyme, nitrite reductase, and nitrous oxide reductase, the conversion of ammonia to dinitrogen was tried with different reaction conditions. In aerobic reaction conditions, ammonium was converted to nitrite (NO ₂ ⁻ ), while under oxygen-limiting or oxygen-free conditions, NO ₂ ⁻ -N formed from ammonia oxidation by N. europaea was reduced to N₂O and dinitrogen with 22% conversion. During denitrification, optimal pH for the production of N₂O and dinitrogen was found to be 7.0–8.0. Dinitrogen was not produced in acidic pH<7.0. A low partial oxygen pressure as well as oxygen-free conditions are favorable for high production of dinitrogen.     

Homogeneous [RuIII(Me3tacn)Cl3]‐Catalyzed Alkene cis‐Dihydroxylation with Aqueous Hydrogen Peroxide

A simple and green method that uses [Ru(Me₃tacn)Cl₃] ( 1 ; Me₃tacn=N,N′,N′′‐trimethyl‐1,4,7‐triazacyclononane) as catalyst, aqueous H₂O₂ as the terminal oxidant, and Al₂O₃ and NaCl as additives is effective in the cis‐dihydroxylation of alkenes in aqueous tert‐butanol. Unfunctionalized alkenes, including cycloalkenes, aliphatic alkenes, and styrenes (14 examples) were selectively oxidized to their corresponding cis‐diols in good to excellent yield (70–96 %) based on substrate conversions of up to 100 %. The preparation of cis‐1,2‐cycloheptanediol (119 g, 91 % yield) and cis‐1,2‐cyclooctanediol (128 g, 92 % yield) from cycloheptene and cyclooctene, respectively, on the 1‐mol scale can be achieved by scaling up the reaction without modification. Results from Hammett correlation studies on the competitive oxidation of para‐substituted styrenes (ρ=?0.97, R=0.988) and the detection of the cycloadduct [(Me₃tacn)ClRuHO₂(C₈H₁₄)]⁺ by ESI‐MS for the 1 ‐catalyzed oxidation of cyclooctene to cis‐1,2‐cyclooctanediol are similar to those of the stoichiometric oxidation of alkenes by cis‐[(Me₃tacn)(CF₃CO₂)Ru^VIO₂]⁺ through [3+2] cycloaddition (W.‐P. Yip, W.‐Y. Yu, N. Zhu, C.‐M. Che, J. Am. Chem. Soc. 2005 , 127, 14239).     

Enzymatic and catalytic reduction of dinitrogen to ammonia: Density functional theory characterization of alternative molybdenum active sites

We used density functional calculations to model dinitrogen reduction by a FeMo cofactor containing a central nitrogen atom and by a Mo‐based catalyst. Plausible intermediates, reaction pathways, and relative energetics in the enzymatic and catalytic reduction of N₂ to ammonia at a single Mo center are explored. Calculations indicate that the binding of N₂ to the Mo atom and the subsequent multiple proton–electron transfer to dinitrogen and its protonated species involved in the conversion of N₂ are feasible energetically. In the reduction of N₂ the Mo atom experiences a cycled oxidation state from Mo(IV) to Mo(VI) by nitrogenase and from Mo(III) to Mo(VI) by the molybdenum catalyst, respectively, tuning the gradual reduction of N₂. Such a wide range of oxidation states exhibited by the Mo center is crucial for the gradual reduction process via successive proton–electron transfer. Present results suggest that the Mo atom in the N‐centered FeMo cofactor is a likely alternative active site for dinitrogen binding and reduction under mild conditions once there is an empty site available at the Mo site. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Not Limited to Iron: A Cobalt Heme–NO Model Facilitates N–N Coupling with External NO in the Presence of a Lewis Acid to Generate N2O

Some bacterial heme proteins catalyze the coupling of two NO molecules to generate N₂O. We previously reported that a heme Fe–NO model engages in this N?N bond‐forming reaction with NO. We now demonstrate that (OEP)Co^II(NO) similarly reacts with 1 equiv of NO in the presence of the Lewis acids BX₃ (X=F, C₆F₅) to generate N₂O. DFT calculations support retention of the Co^II oxidation state for the experimentally observed adduct (OEP)Co^II(NO?BF₃), the presumed hyponitrite intermediate (P^.+)Co^II(ONNO?BF₃), and the porphyrin π‐radical cation by‐product of this reaction, and that the π‐radical cation formation likely occurs at the hyponitrite stage. In contrast, the Fe analogue undergoes a ferrous‐to‐ferric oxidation state conversion during this reaction. Our work shows that cobalt hemes are chemically competent to engage in the NO‐to‐N₂O conversion reaction.     

Copper‐Catalyzed Oxyboration of Unactivated Alkenes

The first regiodivergent oxyboration of unactivated terminal alkenes is reported, using copper alkoxide as a catalyst, bis(pinacolato)diboron [(Bpin)₂] as a boron source, and (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) as an oxygen source. The reaction is compatible with various functional groups. Two regioisomers are selectively produced by selecting the appropriate ligands on copper. The products may be used as a linchpin precursor for various other functionalizations, and net processes such as carbooxygenation, aminooxygenation, and dioxygenation of alkenes can be achieved after C?B bond transformations. Mechanistic studies indicate that the reaction involves the following steps: 1) Transmetalation between CuOtBu and (Bpin)₂ to generate a borylcopper species; 2) regiodivergent borylcupration of alkenes; 3) oxidation of the thus‐generated C?Cu bond to give an alkyl radical; 4) trapping of the resulting alkyl radical by TEMPO.