DOCSLIB.ORG

Chemical Characterisation of Benzene Oxidation Products Under High- and Low-Nox Conditions Using Chemical Ionisation Mass Spectrometry

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Chemical Characterisation of Benzene Oxidation Products Under High- and Low-Nox Conditions Using Chemical Ionisation Mass Spectrometry Atmos. Chem. Phys., 21, 3473–3490, 2021 https://doi.org/10.5194/acp-21-3473-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Chemical characterisation of benzene oxidation products under high- and low-NOx conditions using chemical ionisation mass spectrometry Michael Priestley1,6, Thomas J. Bannan1, Michael Le Breton1,d, Stephen D. Worrall1,c, Sungah Kang2, Iida Pullinen2,b, Sebastian Schmitt2, Ralf Tillmann2, Einhard Kleist7, Defeng Zhao2,g, Jürgen Wildt2,7, Olga Garmash4, Archit Mehra1,f, Asan Bacak1,e, Dudley E. Shallcross3,5, Astrid Kiendler-Scharr2, Åsa M. Hallquist8, Mikael Ehn4, Hugh Coe1, Carl J. Percival1,a, Mattias Hallquist6, Thomas F. Mentel2, and Gordon McFiggans1 1Centre for Atmospheric Science, Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK 2Institut für Energie und Klimaforschung, IEK-8, Forschungszentrum Jülich, Jülich, Germany 3School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK 4Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland 5Department of Chemistry, University of the Western Cape, Bellville, South Africa 6Department of Chemistry and Molecular Biology, University of Gothenburg, Gothenburg, Sweden 7Institut für Bio- und Geowissenschaften, IBG-2, Forschungszentrum Jülich GmbH, Jülich, Germany 8IVL Swedish Environmental Research Institute, Gothenburg, Sweden anow at: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA, USA bnow at: Department of Applied Physics, University of Eastern Finland, Kuopio, Finland cnow at: Aston Institute of Materials Research, School of Engineering and Applied Science, Aston University, Birmingham, UK dnow at: Volvo Group Trucks Technology, L3 Lundby, Gothenburg, Sweden enow at: Turkish Accelerator & Radiation Laboratory, Ankara University, Institute of Accelerator, Technologies Gölba¸sıCampus, Golbasi, Ankara, Turkey fnow at: Faculty of Science and Engineering, University of Chester, Chester, UK gnow at: Department of Atmospheric and Oceanic Sciences & Institute of Atmospheric Sciences, Fudan University, Shanghai, China Correspondence: Michael Priestley ([email protected]) Received: 4 August 2020 – Discussion started: 17 August 2020 Revised: 23 November 2020 – Accepted: 3 January 2021 – Published: 5 March 2021 Abstract. Aromatic hydrocarbons are a class of volatile or- under high- and low-NOx conditions, where a range of or- ganic compounds associated with anthropogenic activity and ganic oxidation products were detected. The nitrate scheme make up a significant fraction of urban volatile organic com- detects many oxidation products with high masses, ranging pound (VOC) emissions that contribute to the formation of from intermediate volatile organic compounds (IVOCs) to secondary organic aerosol (SOA). Benzene is one of the most extremely low volatile organic compounds (ELVOCs), in- abundant species emitted from vehicles, biomass burning and cluding C12 dimers. In comparison, very few species with industry. An iodide time-of-flight chemical ionisation mass C≥6 and O≥8 were detected with the iodide scheme, which spectrometer (ToF-CIMS) and nitrate ToF-CIMS were de- detected many more IVOCs and semi-volatile organic com- ployed at the Jülich Plant Atmosphere Chamber as part of pounds (SVOCs) but very few ELVOCs and low volatile or- a series of experiments examining benzene oxidation by OH ganic compounds (LVOCs). A total of 132 and 195 CHO Published by Copernicus Publications on behalf of the European Geosciences Union. 3474 M. Priestley et al.: Chemical characterisation of benzene oxidation products and CHON oxidation products are detected by the iodide al., 2010; Ruchirawat et al., 2005, 2007), benzene is photo- ToF-CIMS in the low- and high-NOx experiments respec- chemically active and contributes to the formation of ozone tively. Ring-breaking products make up the dominant frac- (O3) and secondary organic aerosol (SOA), both of which tion of detected signal and 21 and 26 of the products listed in act to modify the climate and contribute to poor air quality the Master Chemical Mechanism (MCM) were detected. The (Henze et al., 2008; Ng et al., 2007). SOA formation from time series of highly oxidised (O≥6) and ring-retaining oxi- benzene has previously been quantified with a focus on the dation products (C6 and double-bond equivalent D 4) equili- contribution from smaller mass, ring-breaking reaction prod- brate quickly, characterised by a square form profile, com- ucts such as epoxides (Glowacki et al., 2009) and dicarbonyl pared to MCM and ring-breaking products which increase aldehydes (e.g. O’Brien et al., 1983; Johnson et al., 2005). throughout oxidation, exhibiting sawtooth profiles. Under For example, 37 % of the glyoxal formed in the LA basin low-NOx conditions, all CHO formulae attributed to radical is estimated to derive from aromatic sources (Knote et al., termination reactions of first-generation benzene products, 2014). These smaller ring-breaking products typically make and first-generation auto-oxidation products are observed. up a larger fraction of SOA mass than the ring-retaining prod- Several N-containing species that are either first-generation ucts (Borrás and Tortajada-Genaro, 2012) and so have tradi- benzene products or first-generation auto-oxidation products tionally been the main focus for SOA quantification. Other are also observed under high-NOx conditions. Hierarchical major, toxic benzene oxidation products such as catechol, ni- cluster analysis finds four clusters, of which two describe trophenol and maleic anhydride are also known components photo-oxidation. Cluster 2 shows a negative dependency on of SOA (Borrás and Tortajada-Genaro, 2012). the NO2=NOx ratio, indicating it is sensitive to NO con- More recently the auto-oxidation mechanism has been centration and thus likely to contain NO addition products demonstrated to occur in aromatic systems (Wang et al., and alkoxy-derived termination products. This cluster has the 2017, 2020; Molteni et al., 2018; Tsiligiannis et al., 2019; highest average carbon oxidation state (OSC/ and the low- Garmash et al., 2020; Mehra et al., 2020), producing highly est average carbon number. Where nitrogen is present in a oxygenated organic molecules (HOMs, defined as contain- cluster member of cluster 2, the oxygen number is even, ing 6 or more oxygen atoms which is a product of the auto- as expected for alkoxy-derived products. In contrast, clus- oxidation mechanism) and incorporating up to 11 oxygen ter 1 shows no dependency on the NO2=NOx ratio and so is atoms (Bianchi et al., 2019). The auto-oxidation mechanism likely to contain more NO2 addition and peroxy-derived ter- of intra-molecular H shifts from the carbon backbone to the mination products. This cluster contains fewer fragmented peroxy radical centre forming peroxide groups is consistent species, as the average carbon number is higher and OSC with other VOC systems (Rissanen et al., 2014) initiated lower than cluster 2, and more species with an odd number by a variety of different oxidants (e.g. Mentel et al., 2015; of oxygen atoms. This suggests that clustering of time series Berndt et al., 2016). The inclusion of an alkyl group to a which have features pertaining to distinct chemical regimes, benzene ring facilitates HOM formation (Wang et al., 2017) for example, NO2=NOx perturbations, coupled with a priori as a consequence of the greater degrees of freedom afforded knowledge, can provide insight into identification of poten- to the molecule. Whilst benzene is not the most reactive tial functionality. of aromatic VOCs, τOH ≈ 9:5 d for benzene vs. τOH ≈ 6– 10 h for xylenes ([OH] D 2.0 × 106 molecules cm−3; Atkin- son and Arey, 2007), it is ubiquitous in the urban environ- ment and is the simplest C6 aromatic ring system to study. 1 Introduction Oxidation of benzene occurs nearly exclusively via hy- droxyl radical (OH) addition to form the cyclohexadienyl Benzene is an aromatic volatile organic compound (VOC) radical (benzene-OH adduct), which subsequently adds O2 commonly used as a vehicular fuel additive (Verma and Des to form the hydroxycyclohexadiene peroxy radical (C6H6– Tombe, 2002) and as a chemical intermediate in the man- OH–O2) (Volkamer et al., 2002) (Fig. 1). Two subsequent ufacture of a range of products, e.g. detergents (Oyoroko reaction pathways are postulated for this peroxy radical: ei- and Ogamba, 2017), lubricants (Rodriguez et al., 2018), dyes ther elimination of HO2 yields phenol, and secondary OH (Guo et al., 2018), and pesticides (Wang et al., 2014). Whilst attack must occur again, or an endocyclic di-oxygen-bridged current global estimates of benzenoid (molecules containing carbon-centred radical intermediate is formed by the addi- a benzene ring) emission to the atmosphere by vegetation are tion of the peroxy group to (typically) a β-carbon (Glowacki of a comparable order to those of anthropogenic activity (∼ 5 et al., 2009). This di-oxygen-bridged carbon-centred radical times lower; Misztal et al., 2015), and background concentra- may add another O2 and form a peroxy radical (named as tions of benzene are enhanced by increased biomass burning BZBIPERO2 in the Master Chemical Mechanism, MCM; (Archibald et al., 2015), emission of benzene to the urban at- Saunders et al., 2003). However it is not known if auto- mosphere is dominated by vehicle exhausts (Gentner et al., oxidation may continue to form a second oxygen-bridged 2012) and solvent evaporation (Hoyt and Raun, 2015). As radical, described as type II auto-oxidation (Molteni et al., well as a toxin (Snyder et al., 1975) and carcinogen (Bird et 2018; Fig. 1, BZBIPERO2-diB), or form a hydroperoxide Atmos. Chem. Phys., 21, 3473–3490, 2021 https://doi.org/10.5194/acp-21-3473-2021 M. Priestley et al.: Chemical characterisation of benzene oxidation products 3475 NO has been observed at Mace Head, Ireland, where clean low-NOx marine-influenced air can be contrasted with pol- luted NOx-containing continental air (Creasey et al., 2002). In that instance, an increase in NO concentration from 0.01 to 1 ppb reduces the HO2 V OH ratio from 200 V 1 to 10 V 1.
Load more

Recommended publications
  • Reactions of Benzene & Its Derivatives
    Organic Lecture Series ReactionsReactions ofof BenzeneBenzene && ItsIts DerivativesDerivatives Chapter 22 1 Organic Lecture Series Reactions of Benzene The most characteristic reaction of aromatic compounds is substitution at a ring carbon: Halogenation: FeCl3 H + Cl2 Cl + HCl Chlorobenzene Nitration: H2 SO4 HNO+ HNO3 2 + H2 O Nitrobenzene 2 Organic Lecture Series Reactions of Benzene Sulfonation: H 2 SO4 HSO+ SO3 3 H Benzenesulfonic acid Alkylation: AlX3 H + RX R + HX An alkylbenzene Acylation: O O AlX H + RCX 3 CR + HX An acylbenzene 3 Organic Lecture Series Carbon-Carbon Bond Formations: R RCl AlCl3 Arenes Alkylbenzenes 4 Organic Lecture Series Electrophilic Aromatic Substitution • Electrophilic aromatic substitution: a reaction in which a hydrogen atom of an aromatic ring is replaced by an electrophile H E + + + E + H • In this section: – several common types of electrophiles – how each is generated – the mechanism by which each replaces hydrogen 5 Organic Lecture Series EAS: General Mechanism • A general mechanism slow, rate + determining H Step 1: H + E+ E El e ctro - Resonance-stabilized phile cation intermediate + H fast Step 2: E + H+ E • Key question: What is the electrophile and how is it generated? 6 Organic Lecture Series + + 7 Organic Lecture Series Chlorination Step 1: formation of a chloronium ion Cl Cl + + - - Cl Cl+ Fe Cl Cl Cl Fe Cl Cl Fe Cl4 Cl Cl Chlorine Ferric chloride A molecular complex An ion pair (a Lewis (a Lewis with a positive charge containing a base) acid) on ch lorine ch loronium ion Step 2: attack of
    [Show full text]
  • Summary of Gas Cylinder and Permeation Tube Standard Reference Materials Issued by the National Bureau of Standards
    A111D3 TTbS?? o z C/J NBS SPECIAL PUBLICATION 260-108 o ^EAU U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards Standard Reference Materials: Summary of Gas Cylinder and Permeation Tube Standard Reference Materials Issued by the National Bureau of Standards QC 100 U57 R. Mavrodineanu and T. E. Gills 260-108 1987 m he National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal i s t0 strengthen and advance the nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research to assure international competitiveness and leadership of U.S. industry, science arid technology. NBS work involves development and transfer of measurements, standards and related science and technology, in support of continually improving U.S. productivity, product quality and reliability, innovation and underlying science and engineering. The Bureau's technical work is performed by the National Measurement Laboratory, the National Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Institute for Materials Science and Engineering. The National Measurement Laboratory Provides the national system of physical and chemical measurement; • Basic Standards 2 coordinates the system with measurement systems of other nations and • Radiation Research furnishes essential services leading to accurate and uniform physical and • Chemical Physics chemical measurement throughout the Nation's scientific community, • Analytical Chemistry industry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops, produces, and distributes Standard Reference Materials; provides calibration services; and manages the National Standard Reference Data System.
    [Show full text]
  • Second Tranche HTS Subheading Product Description 2710.19.30
    Second Tranche HTS Subheading Product Description 2710.19.30 Lubricating oils, w/or w/o additives, fr. petro oils and bitumin minerals (o/than crude) or preps. 70%+ by wt. fr. petro oils 2710.19.35 Lubricating greases from petro oil/bitum min/70%+ by wt. fr. petro. oils but n/o 10% by wt. of fatty acid salts animal/vegetable origin 2710.19.40 Lubricating greases from petro oil/bitum min/70%+ by wt. fr. petro. oils > 10% by wt. of fatty acid salts animal/vegetable origin 3403.19.10 Lubricating preparations containing 50% but less than 70% by weight of petroleum oils or of oils obtained from bituminous minerals 3403.19.50 Lubricating preparations containing less than 50% by weight of petroleum oils or of oils from bituminous minerals 3403.99.00 Lubricating preparations (incl. lubricant-based preparations), nesoi 3811.21.00 Additives for lubricating oils containing petroleum oils or oils obtained from bituminous minerals 3811.29.00 Additives for lubricating oils, nesoi 3901.10.10 Polyethylene having a specific gravity of less than 0.94 and having a relative viscosity of 1.44 or more, in primary forms 3901.10.50 Polyethylene having a specific gravity of less than 0.94, in primary forms, nesoi 3901.20.10 Polyethylene having a specific gravity of 0.94 or more and having a relative viscosity of 1.44 or more, in primary forms 3901.20.50 Polyethylene having a specific gravity of 0.94 or more, in primary forms, nesoi 3901.30.20 Ethylene copolymer: Vinyl acetate-vinyl chloride-ethylene terpoly w/ < 50% deriv of vinyl acetate, exc polymer aromatic/mod
    [Show full text]
  • TR-470: Pyridine (CASRN 110-86-1) in F344/N Rats, Wistar Rats, And
    NTP TECHNICAL REPORT ON THE TOXICOLOGY AND CARCINOGENESIS STUDIES OF PYRIDINE (CAS NO. 110-86-1) IN F344/N RATS, WISTAR RATS, AND B6C3F1 MICE (DRINKING WATER STUDIES) NATIONAL TOXICOLOGY PROGRAM P.O. Box 12233 Research Triangle Park, NC 27709 March 2000 NTP TR 470 NIH Publication No. 00-3960 U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Public Health Service National Institutes of Health FOREWORD The National Toxicology Program (NTP) is made up of four charter agencies of the U.S. Department of Health and Human Services (DHHS): the National Cancer Institute (NCI), National Institutes of Health; the National Institute of Environmental Health Sciences (NIEHS), National Institutes of Health; the National Center for Toxicological Research (NCTR), Food and Drug Administration; and the National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention. In July 1981, the Carcinogenesis Bioassay Testing Program, NCI, was transferred to the NIEHS. The NTP coordinates the relevant programs, staff, and resources from these Public Health Service agencies relating to basic and applied research and to biological assay development and validation. The NTP develops, evaluates, and disseminates scientific information about potentially toxic and hazardous chemicals. This knowledge is used for protecting the health of the American people and for the primary prevention of disease. The studies described in this Technical Report were performed under the direction of the NIEHS and were conducted in compliance with NTP laboratory health and safety requirements and must meet or exceed all applicable federal, state, and local health and safety regulations. Animal care and use were in accordance with the Public Health Service Policy on Humane Care and Use of Animals.
    [Show full text]
  • Heats of Formation of Certain Nickel-Pyridine Complex Salts
    HEATS OF FORFATION OF CERTAIN NICKEL-PYRIDINE COLPLEX SALTS DAVID CLAIR BUSH A THESIS submitted to OREGON STATE COLLEGE in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE June l9O [4CKNOWLEDGMENT The writer wishes to acknowledge his indebtedness and gratitude to Dr. [4. V. Logan for his help and encour- agement during this investigation. The writer also wishes to express his appreciation to Dr. E. C. Gilbert for helpful suggestions on the con- struction of the calortheter, and to Lee F. Tiller for his excellent drafting and photostating of the figures and graphs. APPROVED: In Charge of ?ajor Head of Department of Chemistry Chairrian of School Graduate Comrittee Dean of Graduate School Date thesis is presented /11 ' Typed by Norma Bush TABLE OF CONTENTS HISTORICAL BACKGROUND i INTRODUCTION 2 EXPERIMENTAL 5 Preparation of the Compounds 5 Analyses of the Compounds 7 The Calorimeter Determination of the Heat Capacity 19 Determination of the Heat of Formation 22 DISCUSSION 39 41 LITERATURE CITED 42 TABLES I Analyses of the Compounds 8 II Heat Capacity of the Calorimeter 23 III Heat of Reaction of Pyridine 26 IV Sample Run and Calculation 27 V Heat of Reaction of Nickel Cyanate 30 VI Heat of Reaction of Nickel Thiocyanate 31 VII Heat of Reaction of Hexapyridinated Nickel Cyanate 32 VIII Heat of Reaction of Tetrapyridinated Nickel Thiocyanate 33 IX Heat of Formation of the Pyridine Complexes 34 FI GURES i The Calorimeter 10 2 Sample Ijector (solids) 14 2A Sample Ejector (liquids) 15 3 Heater Circuit Wiring Diagram 17 4 heat Capacity of the Calorimeter 24 5 Heat of Reaction of Pyridine 28 6 Heat of Reaction of Hexapyridinated Nickel Cyanate 35 7 Heat of Reaction of Tetrapyridinated Nickel Thiocyanate 36 8 Heat of Reaction of Nickel Cyanate 37 9 Heat of Reaction of Nickel Thiocyanate 38 HEATS OF FOW ATION OF CERTAIN NICKEL-PYRIDINE COMPLEX SALTS HISTORICAL BACKGROUND Compounds of pyridine with inorganic salts have been prepared since 1970.
    [Show full text]
  • BENZENE AS a LARVICIDE for SCREW WORMS1 the Larval Stage
    BENZENE AS A LARVICIDE FOR SCREW WORMS1 By D. C. PARMAN Assistant Entomologist, Investigations of Insects Affecting the Health of Animals, Bureau of Entomology, United States Department of Agriculture INTRODUCTION The larval stage of CocMiomyia macellaria Fab., generally known amonff stock raisers in the Southwest as the screw worm, causes con- siderable loss to the livestock industry, estimated as high as $5,000,000 in some years. It has been apparent that the larvicides used to kill the worms are either toxic to the animal or at least in most cases detrimental to the healing of the wounds. This toxicity was at first attributed to the screw worm, but as many cases were ob- served where the animal was practically consumed by the larvae and still lived until the loss of olood or injury to some vital organ brought de^th, it was surmised that the treatments with larvicides were the cause of many deaths. During the summer of 1916 syste- matic work was begun to find a more efficient larvicide than the phenols and chloroform which were generally used. At first an attempt was made to add something to these larvicides to counteract the toxic properties. As this was not successful it was deemed best to look for a chemical that might be used with more satis- factory results. Several chemical groups were studied for possible larvicides. EXPERIMENTAL PROCEDURE All available chemicals with possible larvicidal value were selected for laboratory tests to determine whether they would kill the larvae of the screw-worm fly. The first tests were made by pouring the chemical on a number of larvae in a tube, or dusting on just enough to cover the larvae.
    [Show full text]
  • Oxidation State Slides.Key
    Oxidation States Dr. Sobers’ Lecture Slides The Oxidation State Also known as the oxidation number The oxidation state is used to determine whether an element has been oxidized or reduced. The oxidation state is not always a real, quantitative, physical constant. The oxidation state can be the charge on an atom: 2+ - MgCl2 Mg Cl Oxidation State: +2 -1 2 The Oxidation State For covalently bonded substances, it is not as simple as an ionic charge. A covalent bond is a sharing of electrons. The electrons are associated with more than one atomic nuclei. This holds the nuclei together. The electrons may not be equally shared. This creates a polar bond. The electronegativity of a covalently bonded atom is its ability to attract electrons towards itself. 3 Example: Chlorine Sodium chloride is an ionic compound. In sodium chloride, the chloride ion has a charge and an oxidation state of -1. The oxidation state of sodium is +1. 4 Example: Chlorine In a chlorine molecule, the chlorine atoms are covalently bonded. The two atoms share electrons equally and the oxidation state is 0. 5 Example: Chlorine The two atoms of a hydrogen chloride molecule are covalently bonded. The electrons are not shared equally because chlorine is more electronegative than hydrogen. There are no ions but the oxidation state of chlorine in HCl is -1 and the oxidation state of hydrogen is +1. 6 7 Assigning Oxidation States See the handout for the list of rules. Rule 1: Free Elements Free elements have an oxidation state of zero Example Oxidation State O2(g) 0 Fe(s) 0 O3(g) 0 C(graphite) 0 C(diamond) 0 9 Rule 2: Monatomic Ions The oxidation state of monatomic ions is the charge of the ion Example Oxidation State O2- -2 Fe3+ +3 Na+ +1 I- -1 V4+ +4 10 Rule 3: Fluorine in Compounds Fluorine in a compound always has an oxidation state of -1 Example Comments and Oxidation States NaF These are monatomic ions.
    [Show full text]
  • Reactions of Aromatic Compounds Just Like an Alkene, Benzene Has Clouds of  Electrons Above and Below Its Sigma Bond Framework
    Reactions of Aromatic Compounds Just like an alkene, benzene has clouds of electrons above and below its sigma bond framework. Although the electrons are in a stable aromatic system, they are still available for reaction with strong electrophiles. This generates a carbocation which is resonance stabilized (but not aromatic). This cation is called a sigma complex because the electrophile is joined to the benzene ring through a new sigma bond. The sigma complex (also called an arenium ion) is not aromatic since it contains an sp3 carbon (which disrupts the required loop of p orbitals). Ch17 Reactions of Aromatic Compounds (landscape).docx Page1 The loss of aromaticity required to form the sigma complex explains the highly endothermic nature of the first step. (That is why we require strong electrophiles for reaction). The sigma complex wishes to regain its aromaticity, and it may do so by either a reversal of the first step (i.e. regenerate the starting material) or by loss of the proton on the sp3 carbon (leading to a substitution product). When a reaction proceeds this way, it is electrophilic aromatic substitution. There are a wide variety of electrophiles that can be introduced into a benzene ring in this way, and so electrophilic aromatic substitution is a very important method for the synthesis of substituted aromatic compounds. Ch17 Reactions of Aromatic Compounds (landscape).docx Page2 Bromination of Benzene Bromination follows the same general mechanism for the electrophilic aromatic substitution (EAS). Bromine itself is not electrophilic enough to react with benzene. But the addition of a strong Lewis acid (electron pair acceptor), such as FeBr3, catalyses the reaction, and leads to the substitution product.
    [Show full text]
  • Formation of Nitrous Oxide
    1461 No. 5069 DECEMBER 24. 1966 NATURE E-+ CCI. --->- ECC1 3 + Cl- Formation of Nitrous Oxide THE mechanism of formation of nitrous oxide from am­ The tightly bound .CCI3 group will not be removable in monium nitrate is attributable to the recognized thermal the normal biochemical reaction and the enzyme molecule dissociation of ammonium salts followed in this instance will be inactivated. by nitration of ammonia and decomposition of the ensuing This process of enzyme inactivation could, in principle, nitramide. The mechanism of this latter stage has been account for the toxicity of carbon tetrachloride and studied by various workers, notably by Marlies and La similar compounds and also of many insecticides. The Merl. Further, the decomposition of methyl nitramido postulated mechanism would also explain the observation to tho oxide and methyl alcohol is on record 2. by Butlerl3 that carbon tetrachloride is reduced in vivo As the nitration process, for example, of benzene, is to chloroform. Thus a proportion of .CCls radicals may commonly accompanied by some oxidation, the possibility react with sites other than the enzyme and abstract, of its OCClllTcnce in the preparation of nitrous oxide with for example, a hydrogen atom from a hydroxyl group or formation of nitrogen peroxide is not surprising and from a sulphydryl group. The latter exchange does technically well recognized. It has also recently been the appear to be possible from energy considerations. subject of public concern. D(RS-H) = 89 kcalJmole (ref. 14), .J. KENNER D(CI3G-H) = 91·4 kcalJmole (ref. 9) 41 Burlington Road, I have found that the activation energy of the electron Withington, capture reaction in chloroform vapour Manchester 20.
    [Show full text]
  • Structure-Property Relationships of Layered Oxypnictides
    AN ABSTRACT OF THE DISSERTATION OF Sean W. Muir for the degree of Doctor of Philosophy in Chemistry presented on April 17, 2012. Title: Structure-property Relationships of Layered Oxypnictides Abstract approved:______________________________________________________ M. A. Subramanian Investigating the structure-property relationships of solid state materials can help improve many of the materials we use each day in life. It can also lead to the discovery of materials with interesting and unforeseen properties. In this work the structure property relationships of newly discovered layered oxypnictide phases are presented and discussed. There has generally been worldwide interest in layered oxypnictide materials following the discovery of superconductivity up to 55 K for iron arsenides such as LnFeAsO1-xFx (where Ln = Lanthanoid). This work presents efforts to understand the structure and physical property changes which occur to LnFeAsO materials when Fe is replaced with Rh or Ir and when As is replaced with Sb. As part of this work the solid solution between LaFeAsO and LaRhAsO was examined and superconductivity is observed for low Rh content with a maximum critical temperature of 16 K. LnRhAsO and LnIrAsO compositions are found to be metallic; however Ce based compositions display a resistivity temperature dependence which is typical of Kondo lattice materials. At low temperatures a sudden drop in resistivity occurs for both CeRhAsO and CeIrAsO compositions and this drop coincides with an antiferromagnetic transition. The Kondo scattering temperatures and magnetic transition temperatures observed for these materials can be rationalized by considering the expected difference in N(EF)J parameters between them, where N(EF) is the density of states at the Fermi level and J represents the exchange interaction between the Ce 4f1 electrons and the conduction electrons.
    [Show full text]
  • Peroxides and Peroxide- Forming Compounds
    FEATURE Peroxides and peroxide- forming compounds By Donald E. Clark Bretherick5 included a discussion of nated. However, concentrated hydro- organic peroxide5 in a chapter on gen peroxide (Ͼ30%), in contact with norganic and organic peroxides, highly reactive and unstable com- ordinary combustible materials (e.g., because of their exceptional reac- pounds and used “oxygen balance” to fabric, oil, wood, or some resins) Itivity and oxidative potential are predict the stability of individual com- poses significant fire or explosion haz- widely used in research laboratories. pounds and to assess the hazard po- ards. Peroxides of alkali metals are not This review is intended to serve as a tential of an oxidative reaction. Jack- particularly shock sensitive, but can 6 guide to the hazards and safety issues son et al. addressed the use of decompose slowly in the presence of associated with the laboratory use, peroxidizable chemicals in the re- moisture and may react violently with handling, and storage of inorganic and search laboratory and published rec- a variety of substances, including wa- organic peroxy-compounds and per- ommendations for maximum storage ter. Thus, the standard iodide test for oxide-forming compounds. time for common peroxide-forming peroxides must not be used with these The relatively weak oxygen-oxygen laboratory solvents. Several solvents, water-reactive compounds.1 linkage (bond-dissociation energy of (e.g., diethyl ether) commonly used in Inorganic peroxides are used as ox- 20 to 50 kcal moleϪ1) is the character- the laboratory can form explosive re- idizing agents for digestion of organic istic structure of organic and inor- action products through a relatively samples and in the synthesis of or- ganic peroxide molecules, and is the slow oxidation process in the pres- ganic peroxides.
    [Show full text]
  • Intramolecular Alkoxycyanation and Alkoxyacylation Reactions: New Types of Alkene Difunctionalizations for the Construction of Oxygen Heterocycles John P
    Angewandte. Highlights DOI: 10.1002/anie.201204470 Alkene Difunctionalization Intramolecular Alkoxycyanation and Alkoxyacylation Reactions: New Types of Alkene Difunctionalizations for the Construction of Oxygen Heterocycles John P. Wolfe* alkenes · catalysis · heterocycles · ketones · nitriles Saturated oxygen heterocycles, such as tetrahydrofurans and not require an exogenous carbon electrophile.[6,7] Instead, the dihydrobenzofurans, are important motifs in a myriad of carbon electrophile is covalently attached to the cyclizing biologically active compounds, including natural products and oxygen atom in the substrate, and the carboalkoxylations are pharmaceutical targets. Therefore, there has been consider- accomplished through activation of this CÀO bond by the able interest in the development of new synthetic methods for catalyst. Importantly, these two approaches lead to the the construction of these important structures.[1] Many tradi- formation of dihydrobenzofuran derivatives that bear func- tional approaches to the generation of these compounds tional groups (ketones or nitriles), which are convenient involve ring formation through intramolecular SN2 reactions handles for further elaboration of the molecule, and cannot be and related strategies. However, these approaches typically directly installed by using previously developed alkene lead to the formation of only one bond during ring closure and carboalkoxylation methods. often require somewhat complicated substrates.[1] The method of the Douglas group involves the use of Late transition metal catalyzed alkene carboalkoxylations a cationic RhI complex to catalyze the intramolecular are a subclass of alkene difunctionalization reactions[2] that alkoxyacylation of acylated 2-allylphenol derivatives have considerable utility for the construction of tetrahydro- (Scheme 2).[6] These reactions afford 2-acylmethyl dihydro- furans, dihydrobenzofurans, and related oxygen heterocycles.
    [Show full text]