Negative ion mass spectra of dicarboxylic acids

The negative ion mass spectra of dicarboxylic acids show [M]^?˙ and prominent [M – H]^?ions. These ions can therefore be used to determine the molecular weight of dicarboxylic acids which do not give positive molecular ions. The [C₂H₃]^? ion is a base peak in the spectra of maleic and fumaric acids. Isomeric phthalic acids are readily differentiated.     

Mechanism of phthalic anhydride formation in the oxidation of n-pentane on a vanadium-phosphorus oxide catalyst

The reaction paths of product formation in the partial oxidation of n-pentane on vanadium-phosphorus oxide (VPO) and VPO-Bi catalysts are considered. The condensed products of n-pentane oxidation were analyzed by chromatography-mass spectrometry, and the presence of C₄ rather than C₅ unsaturated hydrocarbons was detected. It was found that the concentration of phthalic anhydride in the products increased upon the addition of C₄ olefins and butadiene to the n-pentane-air reaction mixture. With the use of a system with two in-series reactors, it was found that the addition of butadiene to a flow of n-butane oxidation products (maleic anhydride, CO, and CO₂) resulted in the formation of phthalic anhydride. The oxidation of 1-butanol was studied, and butene and butadiene were found to be the primary products of reaction; at a higher temperature, maleic anhydride and then phthalic anhydride were formed. The experimental results supported the reaction scheme according to which the activation of n-pentane occurred with the elimination of a methyl group and the formation of C₄ unsaturated hydrocarbons. The oxidation of these latter led to the formation of maleic anhydride. The Diels-Alder reaction between maleic anhydride and C₄ unsaturated hydrocarbons is the main path of phthalic anhydride formation.     

Vapor phase synthesis of phthalate esters from benzene and maleic anhydride over CrO3/magnesol and SO42-/ZrO2+

Benzene and maleic anhydride react over solid acids, viz. CrO₃/Magnesol and SO₄ ^2-/ZrO₂ catalysts to form phthalic anhydride and olefins, which in turn produce phthalate esters as end products. Based on the product distribution, a reaction pathway is proposed.     

Retrosynthetic reactions in mass spectrometry. Deacylation of ortho phthalamic acids under electron impact

Ortho Phthalamic acids under electron impact show a retrosynthetic reaction leading to both phthalic anhydride and amine complementary ions, the corresponding neutrals of which are the usual synthetic precursors of the original compounds. The single case of a primary amine derivative is examined, which shows the formation of [M? H₂O]^+˙ ions having the structure of the related N-substituted imide, by a process which parallels a well known thermal reaction. It also gives the species [C₈H₆NO₂]⁺ (of the same nominal mass as phthalic anhydride), the structure of which is still under study. Ionic structures are supported by collision induced mass analyzed ion kinetic energy spectra.     

Negative ion chemical ionization mass spectrometry—binding of molecules to bromide and iodide anions

The analytical potential of negative ion chemical ionization (NICI) mass spectrometry utilizing dibromodifluoro-methane (CF₂Br₂) and iodomethane (CH₃I)/methane (CH₄) as reagent gases is examined. The NICI mass spectrum of CF₂Br₂ contains Br^?, [HBr₂]^? and [CF₂Br₃]^? anions. Weak acids (i.e. those acids with approximately ΔH°_(acid) values between 1674 and 1464 kJ mol^?1) react with Br^? to produce minor yields of the hydrogen?bonded bromide attachment [MH + Br]^? anion or are unreactive. Strong acids (i.e. those acids with approximately ΔH°_(acid) > 1464 kJ mol^?1) produce primarily [MH + Br]^? anions with a minor yield of proton transfer [M ? H]^? anion. The NICI spectrum of CH₃I/CH₄ is dominated by I^?. Weak acids react with I^? to yield minor amounts of [MH + 1]^? or are unreactive. Strong acids produce only [MH + l]^? anions. From a consideration of the gas-phase basicity of the halide anion and the binding energy of the hydrogen-bonded halide attachment adduct, thermochemical data are used as a potential guide to rationalize or predict the ions observed in NICI mass spectra.     

Positive chemical ionization triple‐quadrupole mass spectrometry and ab initio computational studies of the multi‐pathway fragmentation of phthalates

We report the first positive chemical ionization (PCI) fragmentation mechanisms of phthalates using triple‐quadrupole mass spectrometry and ab initio computational studies using density functional theories (DFT). Methane PCI spectra showed abundant [M + H]⁺, together with [M + C₂H₅]⁺ and [M + C₃H₅]⁺. Fragmentation of [M + H]⁺, [M + C₂H₅]⁺ and [M + C₃H₅]⁺ involved characteristic ions at m/z 149, 177 and 189, assigned as protonated phthalic anhydride and an adduct of phthalic anhydride with C₂H₅⁺ and C₃H₅⁺, respectively. Fragmentation of these ions provided more structural information from the PCI spectra. A multi‐pathway fragmentation was proposed for these ions leading to the protonated phthalic anhydride. DFT methods were used to calculate relative free energies and to determine structures of intermediate ions for these pathways. The first step of the fragmentation of [M + C₂H₅]⁺ and [M + C₃H₅]⁺ is the elimination of [R? H] from an ester group. The second ester group undergoes either a McLafferty rearrangement route or a neutral loss elimination of ROH. DFT calculations (B3LYP, B3PW91 and BPW91) using 6‐311G(d,p) basis sets showed that McLafferty rearrangement of dibutyl, di(‐n‐octyl) and di(2‐ethyl‐n‐hexyl) phthalates is an energetically more favorable pathway than loss of an alcohol moiety. Prominent ions in these pathways were confirmed with deuterium labeled phthalates. Copyright © 2010 John Wiley & Sons, Ltd.     

The gas phase reaction of CF3 radicals with C6F5H in the temperature range 373–658 K

CF₃ radicals were generated by the photolysis of perfluoroacetic anhydride. In the presence of pentafluorobenzene, the CF₃ radicals react according to the following mechanism: It was found that the addition reaction (3) becomes reversible above ca. 453 K. The addition rate parameters have been revised and they satisfactorily agree with those reported previously. At temperatures higher than 593 K, only true H-abstraction occurs. The rate constant k_H for reaction (5) is given by: where θ = 2.303 RT kJmol^?1 and k_c is the rate constant for combination of CF₃ radicals. The reactions of CF₃ with benzene and pentafluorobenzene are compared.     

Effect of collision gas pressure and collision energy on reactions between oxygen and the negative molecular ion of tetrachlorodibenzo-p-dioxins in the collision cell of a triple -quadrupole mass spectrometer

Low-energy reactive collisions between the negative molecular ion of a tetrachlorodibenzo-p-dioxin (TCDD) and oxygen inside the collision cell of a triple-stage quadrupole mass spectrometer produce a substitution ion [M ? Cl + O]^?, a phenoxide ion [C₆H_4-nO₂Cl_n]^?·, [M ? HCl]^?·, and Cl^? by which 1,2,3,4-, 1,2,3,6/1,2,3,7- and 2,3,7,8-TCDD isomers can be distinguished either directly or on the basis of intensity ratios. The collision conditions have an important effect on the relative abundances. Energy- and pressure-resolved curves show that the ions formed by a collisionally activated reaction (CAR) process, i.e. [M ? Cl + O]^? and [C₆H_4-n,O₂Cl_n]^?·, are favoured by a high pressure of oxygen (3-6 mTorr) (1 Torr = 133.3 Pa) and a low collision energy (0.1-7 eV), whereas the ions formed by a collisionally activated dissociation (CAD) process, i.e. [M ? HCl]^?· and Cl^?, are favoured by high pressure and high energy. By choosing a relatively low collision energy (5 eV) and high pressure (4 mTorr), the CAR and CAD ions can be clearly detected.     

Synthesis,Crystal Structure and Magnetic Behaviour of the new Tetrameric Gadolinium Carboxylate [Gd4(OH)4(CF3COO)8(H2O)4] · 2.5 H2O

The novel tetrameric gadolinium(III) compound [Gd₄(OH)₄(CF₃COO)₈(H₂O)₄] · 2.5 H₂O was synthesized and structurally characterized by X‐ray crystallography. The Gd³⁺ ions are bridged by hydroxide ions and carboxylate groups to tetramers with Gd³⁺‐Gd³⁺ distances between 384.2(2) and 388.1(2) pm. The compound crystallizes in the monoclinic space group C2/c (Z = 4). The magnetic behaviour of [Gd₄(OH)₄(CF₃COO)₈(H₂O)₄] · 2.5 H₂O was investigated in the temperature range of 2 to 300 K. The magnetic data of this compound indicate antiferromagnetic interactions (J_ex = ?0.0197 cm^?1).     

Electron impact studies. CXX—The properties of positive ions produced by charge stripping from negative ions. The acetate and perfluoroacetate cations

The ions [CF₃CO₂]⁺ and [CH₃CO₂]⁺ give peaks of small abundance in conventional positive ion spectra. These ions can be produced by collision-induced charge stripping of the corresponding stable negative ions. Six and ten fragment ions respectively are observed in the spectra of [CF₃CO₂]⁺ and [CH₃CO₂]⁺.     

Untersuchungen zur Lewis-Acidität fluorierter Sulfonium-Ionen

On the Lewis Acidity of Fluorinated Sulfonium Ions NMR investigations show, that sulfonium salts [(CF₃)_nSF_3?n]⁺ AsF₆^? ( 1–3 , n = 0–2) add CH₃CN under formation of ψ-pentacoordinated sulfuranonium ions [(CF₃)_nSF_3?n · NCCH₃]⁺ ( 1a – 3a ,) with the donor in an axial position. In solution NSF₃ ( 4 ,) forms similar salts [(CF₃)_nSF_3?n · NSF₃]⁺ AsF₆^? ( 1b-3b ,) with weaker donor-acceptor interactions. With NSF₂NMe₂ ( 5 ,) the step of the primary addition products is passed very quickly, by fluoride-migration from 1 , and 2 , persulfuranonium ions [(CH₃)₂NSF₃NSF₂]⁺ ( 6 ,) and [(CH₃)₂NSF₃NSFCF₃]⁺ ( 7 ,), respectively, are formed, while from 3 , only decomposition products (Me₂NSF₂⁺, CF₃SSCF₃, CF₄) were obtained.     

Reactions of (Nonafluorocyclohexen-1-yl)xenon(II) Hexafluoroarsenate with Halide Anions

The products of the reaction between the electrophilic alkenylxenonium cation [1-Xe⁺–C₆F₉] and the halide anions I^?, Br^?, Cl^? and F^? depend on the hardness of the halide anion. With the soft halides I^? and Br^? Xe(II) is formally displaced by halogen as well in basic MeCN as in superacidic (AHF¹), whereas with hard fluoride and chloride no reaction takes place in AHF. In MeCN F^? initiates the formation of alkenyl radicals, which abstract hydrogen from the solvent, whereas Cl^? exhibits borderline character: RH and RCl formation. Possible reaction paths are discussed. The reactivity of the arylxenonium cation [C₆F₅Xe]⁺ in AHF toward halide ions is reported and the relative electrophilicity of the cations [C₆F₅Xe]⁺ and [1-Xe⁺–C₆F₉] is determined by the competitive reaction with Cl^?. In addition the synthesis of cyclohexene 1-CF₃–C₆F₉ from C₆F₅CF₃ and XeF₂ is performed and its electrophilicity is compared with that of the aromatic compound C₆F₅CF₃.     

EPR kinetic study of the reactions of CF3Br with H atoms and OH radicals

Reactions of CF₃Br with H atoms and OH radicals have been studied at room temperature at 1–2 torr pressures in a discharge flow reactor coupled to an EPR spectrometer. The rate constant of the reaction H + CF₃Br → CF₃ + HBr (1) was found to be k₁ = (3.27 ± 0.34) × 10^?14 cm³/molec·sec. For the reaction of OH with CF₃Br (8) an upper limit of 1 × 10^?15 cm³/molec·sec was determined for k₈. When H atoms were in excess compared to NO₂, used to produce OH radicals, a noticeable reactivity of OH was observed as a result of the reaction OH + HBr → H₂O + Br, HBr being produced from reaction (1).     

Charge-transfer complex formation and copolymerization of maleic anhydride with benzoselenophene

Under the influence of azobisisobutyronitrile, benzoselenophene and maleic anhydride slowly polymerize to form an alternating copolymer. The two comonomers form a charge-transfer complex (K^AD_c at 30° in chloroform: 0·22 l mol^?1). These properties of benzoselenophene are similar to those of benzothiophene and indole but are different from those of benzofuran. It is possible that the charge-transfer complex plays a role in the copolymerization.     

Gas-phase chemistry of electron deficient organometallic anions: the reactions of [Cr(CO)3]− ˙ and [Cr(CO)4]− ˙ with aldehydes,ketones, esters and ethers

Reactions in the gas phase of the 13- and 15-electron radical anions [Cr(CO)₃]^{? ˙} and [Cr(CO)₄]^{? ˙} with a series of 27 aldehydes, ketones, esters and ethers have been examined. Sequential alkane eliminations and metal-bonded CO ligand displacements were the principal reactions identified for the RCHO/[Cr(CO)₃]^{? ˙} systems with the latter reaction also common to the RCHO/[Cr(CO)₄]^{? ˙} systems. While [Cr(CO)₄]^{? ˙} was generally unreactive towards ketones R · R'CO, the principal products identified for [Cr(CO)₃]^{? ˙}/ketone reactions were the metal-decarbonylated species, respectively [R · R'CO · Cr(CO)_x]^{? ˙} with x = 0–3, and [R · (R' - H₂)CO · Cr(CO)₂]^{? ˙}. The reaction of [Cr(CO)₃]^{? ˙} with esters RCOOR' proceeds via metal insertion into the alkoxy C? O bond to give end products of the type [R'O · Cr · R(CO)₂]^? and [R'O? Cr(CO)₃]^? while the sole ionic products of dialkyl ether/[Cr(CO)₃]^{? ˙} reactions were identified as the alkoxytricarbonylchromium species [RO · Cr(CO)₃]^?.     

Selective vapor‐phase oxidation of o‐xylene to phthalic anhydride over Co‐Mn/H3PW12O40@TiO2 using molecular oxygen as a green oxidant

The oxidation of o‐xylene to phthalic anhydride over Co‐Mn/H₃PW₁₂O₄₀@TiO₂ was investigated. The experimental results demonstrated that the prepared catalyst effectively catalyzed the oxidation of o‐xylene to phthalic anhydride. Also, the synergistic effect between three metals plays vital roles in this reaction. From a green chemistry point of view, this method is environmentally friendly due to carrying out the oxidation in a fixed‐bed reactor under solvent‐free condition and using molecular oxygen as a green and cheap oxidizing agent. The resulting solid catalysts were characterized by FT‐IR, XRD, XPS, ICP‐OES, FESEM, TEM, EDX, DR‐UV spectroscopy, BET and thermogravimetric analysis. The oxidation of o‐xylene yields four products: o‐tolualdehyde, phthaldialdehyde, phthalide and finally phthalic anhydride as the main product. The reaction conditions for oxidation of o‐xylene were optimized by varying the temperature, weight hourly space velocity and oxygen flow rate (contact time). The optimum weight percentage of phosphotungstic acid (HPW) and Co/Mn for phthalic anhydride production were 15 wt % and 2 wt%, respectively. The best Co/Mn ratio was found to be 10/1. Oxygen flow rate was very important on the phthalic anhydride formation. The optimum conditions for oxidation of o‐xylene were T = 370 °C, WHSV = 0.5 h^?1 and oxygen flow rate = 10 mL min^?1. Under optimized conditions, a maximum of 88.2% conversion and 75.5% selectivity to phthalic anhydride was achieved with the fresh catalyst. Moreover, reusability of the catalyst was studied and catalytic activity remained unchanged after at least five cycles.     

Synthesis, Crystal Structure and Optical Properties of Europium Trifluoroacetate Complexes with 1,10-Phenanthroline and 2,2-Bipyridine

Two europium trifluoroacetate complexes, Eu(CF₃COO)₃·phen ( 1 ) and Eu(CF₃COO)₃·bpy ( 2 ) (where phen=1,10‐phenanthroline, bpy=2,2′‐bipyridine), were synthesized and characterized by elemental analysis, Fourier transform infrared spectroscopy (FT‐IR), photoluminescence (PL) spectroscopy and thermogravimetric analysis (TA). Single‐crystal X‐ray structure has been determined for the complex [Eu₂(CF₃COO)₆·(phen)₃·(H₂O)₂]·EtOH. The crystal structure of [Eu₂(CF₃COO)₆·(phen)₃·(H₂O)₂]·EtOH shows that two different coordination styles with europium ions coexist in the same crystal and have entirely different coordination geometries and numbers. This crystal can be considered as an 1:1 adduct of [Eu(CF₃COO)₃·(Phen)₂·H₂O]·EtOH (9‐coordination part) and Eu(CF₃COO)₃·phen·H₂O (8‐coordination part). The excitation spectra of the two complexes demonstrate that the energy collected by "antenna ligands" is transferred to Eu³⁺ ions efficiently. The room‐temperature PL spectra of the complexes are composed of the typical Eu³⁺ ions red emission, due to transitions between ⁵D₀→⁷F_J(J=0→4). The lifetimes of ⁵D₀ of Eu³⁺ in the complexes were examined using time‐resolved spectroscopic analysis, and the lifetime values of Eu(CF₃COO)₃·phen and Eu(CF₃COO)₃·bpy were fitting with bi‐exponential (2987 and 353 µs) and monoexponential (3191 µs) curves, respectively. In order to elucidate the energy transfer process of the europium complexes, the energy levels of the relevant electronic states had been estimated. The thermal analyses indicate that they are all quite stable to heat.     

Preparation of poly(glycidylmethacrylate‐divinylbenzene) weak acid cation exchange stationary phases with succinic anhydride,phthalic anhydride,and maleic anhydride for ion chromatography

In this work, poly(glycidylmethacrylate‐divinylbenzene) microspheres were prepared and applied for the preparation of weak acid cation exchange stationary phases. Succinic anhydride, phthalic anhydride, and maleic anhydride were selected as carboxylation reagents to prepare three weak acid cation exchangers by direct chemical derivatization reaction without solvent or catalyst. The diameters and dispersity of the microspheres were characterized by scanning electron microscopy; the amount of accessible epoxy groups and mechanical stability were also measured. The weak acid cation exchangers were characterized by Fourier transform infrared spectroscopy; the content of carboxyl groups was measured by traditional acid base titration method. The chromatographic properties were characterized and compared by separating alkali, alkaline earth metal ions and ammonium and polar amines. The separation properties enhanced in the order of succinic anhydride, phthalic anhydride, and maleic anhydride modified poly(glycidylmethacrylate‐divinylbenzene) cation exchangers.     

Protonation of CH3N3 and CF3N3 in Superacids: Isolation and Structural Characterization of Long‐Lived Methyl‐ and Trifluoromethylamino Diazonium Ions

The methylamino diazonium cations [CH₃N(H)N₂]⁺ and [CF₃N(H)N₂]⁺ were prepared as their low‐temperature stable [AsF₆]^? salts by protonation of azidomethane and azidotrifluoromethane in superacidic systems. They were characterized by NMR and Raman spectroscopy. Unequivocal proof of the protonation site was obtained by the crystal structures of both salts, confirming the formation of alkylamino diazonium ions. The Lewis adducts CH₃N₃?AsF₅ and CF₃N₃?AsF₅ were also prepared and characterized by low‐temperature NMR and Raman spectroscopy, and also by X‐ray structure determination for CH₃N₃?AsF₅. Electronic structure calculations were performed to provide additional insights. Attempted electrophilic amination of aromatics such as benzene and toluene with methyl‐ and trifluoromethylamino diazonium ions were unsuccessful.     

An Organogold(III) Difluoride with a trans Arrangement

The trans isomer of the organogold(III) difluoride complex [PPh₄][(CF₃)₂AuF₂] has been obtained in a stereoselective way and in excellent yield by reaction of [PPh₄][CF₃AuCF₃] with XeF₂ under mild conditions. The compound is both thermally stable and reactive. Thus, the fluoride ligands are stereospecifically replaced by any heavier halide or by cyanide, the cyanide affording [PPh₄][trans‐(CF₃)₂Au(CN)₂]. The organogold fluoride complexes [CF₃AuF_x]^? (x=1, 2, 3) have been experimentally detected to arise upon collision‐induced dissociation of the [trans‐(CF₃)₂AuF₂]^? anion in the gas phase. Their structures have been calculated by DFT methods. In the isomeric forms identified for the open‐shell species [CF₃AuF₂]^?, the spin density residing on the metal center is found to strongly depend on the precise stereochemistry. Based on crystallographic evidence, it is concluded that Auⁱⁱⁱ and Agⁱⁱⁱ have similar covalent radii, at least in their most common square‐planar geometry.