Arenediazonium Tetrachlorocuprates(II). Modified Versions of the Meerwein and Sandmeyer Reactions

Chloroarylation of unsaturated compounds with arenediazonium chlorides in the presence of CuCl₂ as catalyst involves intermediate formation of arenediazonium tetrachlorocuprates(II) [ArN₂ ⁺]₂ CuCl₄ ^2-. A procedure for preparative isolation of these intermediates was developed, and they were shown to be efficient arylating agents. Reactions of [ArN₂ ⁺]₂ CuCl₄ ^2- with unsaturated compounds gave the corresponding Meerwein products; a mechanism was proposed for these reactions. In polar solvents arenediazonium tetra- chlorocuprates(II) are converted into chloroarenes, presumably through a cyclic transition state.     

Mass spectrometry of arenediazonium salts by fast atom bombardment

Contrary to expectation, thermally labile arenediazonium salts (M) afford sizeable peaks due to ArN₂ ⁺ and (ArN₂ ⁺)M ions under fast atom bombardment; the main fragment ion is usually the highly reactive aryl cation Ar⁺, the production of which is independent of whether its ground state is singlet or triplet.     

Unimolecular (metastable) and collision-induced dissociation of ArN+2 cluster ions

Unimolecular and collision-induced dissociations of ArN⁺₂ producedby electron impact ionization (ArN⁺₂ → Ar⁺ and ArN⁺₂ → N⁺₂) were investigated quantitatively using a double-focusing sector type mass spectrometer. Information gained is relevant for the detection efficiency of clusters and for the development of appropriate theoretical fragmentation models.     

Mechanism of the benzenediazonium tetrafluoroborate thermolysis in the solid state

The thermolysis of benzenediazonium tetrafluoroborate was studied by thermogravimetry in dynamic mode. The decomposition of [ArNN]⁺BF₄⁻ in the solid state with the formation of C₆H₅F, BF₃, C₆H₆, and N₂ starts at T > 348 K. The speed of the thermolysis was estimated gravimetrically and by infrared spectroscopy, considering the change of the intensity of the absorption band at 1498 cm⁻¹, which corresponds to fluorobenzene. The maximal rate of thermolysis observes at the 366.5 K. A kinetic scheme, which includes the formation of a neutral complex [C₆H₅^δ+?BF₄^δ−], is proposed for the thermolysis of arenediazonium tetrafluoroborate. The decomposition of the complex with the formation of free-radical intermediates explains the chain character of the thermolysis.     

Reaction of diazonium salts with transition metals : V. Cationic aryldiazenido complexes of palladium

The title complex, [ArN₂Pd(PPh₃)₃]PF₆(Ar = 4-methoxyphenyl), was prepared by the reaction of ArN₂PF₆ with (PPh₃)₄Pd^o. Other ArN₂X (Ar = phenyl, 4-tolyl, 4-fluorophenyl, 2,4,6-trichlorophenyl; X = BF₄, PF₆) gave a mixture of aryldiazenido and arylpalladium complexes. The aryldiazenido complexes decompose to arylpalladium compounds at room temperature, UV irradiation facilitates this decomposition.     

Dissociation of polyatomic ions in the inductively coupled plasma

A general method for identifying the origin of a particular polyatomic ion is described. Based on a postulated dissociation reaction, measured ion signal ratios (e.g. Ar₂⁺/Ar⁺) are combined with mass bias corrections and estimates of the density of the neutral product (usually Ar, O or H atoms) to determine a gas kinetic temperature T_gas. The temperature can also be measured by the reduction in pressure when the ICP is sampled (compared to room temperature argon), or by other means. Dissociation energies and spectroscopic constants for the ions are necessary. For the particular instrument used, some of the findings of this study are: (a) ArO⁺ and ArN⁺ can be either dissociated (if the plasma potential is high) or created (if the plasma potential is low) by collisions between the sampler and skimmer; (b) the strongly-bound oxide ions O₂⁺ and MO⁺ for the rare earths are observed at levels consistent with T_gas ∼5300 K in a ‘hot’ plasma, but ClO⁺ is formed in excess; and (c) the abundances of most other polyatomic ions like H₂O⁺ and ArH⁺ correspond to higher densities than would be expected in the ICP itself.     

Electrochemical Sensor for Selective Detection of Meldonium in Urine by Voltammetry

A highly sensitive electrochemical sensor based on arenediazonium tosylates was designed to detect meldonium in urine. The effect of the concentration of ArN2⁺OTs⁻ arenediazonium tosylate modifier and various substituents was studied. Basic operating parameters for voltammetric meldonium detection were established and the procedure for urine sample preparation was developed. The following values were obtained: limit of detection (LOD) 0.005 mg ⋅ L⁻¹ (P=0.95) and limit of quantification (LOQ) 0.01 mg ⋅ L⁻¹. The relationship between the analytical signal and meldonium concentration in the solution ranging from 0.01 to 400 mg ⋅ L⁻¹ was described by a linear function. The meldonium concentration error did not exceed 18 %. The analysis time for a single urine sample was reduced to 15 minutes.     

Electrochemical monitoring of the thermal decomposition of arenediazonium ions with time in acidic MeOH/H2O mixtures: dediazotization rate constant

The rate of the spontaneous decomposition of 4-methylbenzenediazonium tetrafluoroborate, 4MBD, was determined. The effects of solvent composition (MeOH/ H₂O) on its electrochemical processes and on those of the derivatized 2-naphthol-6-sulfonate-4-toluene (6S2NPT) azo dye were investigated by Differential Pulse Polarography (DPP). This electrochemical technique shows an effective sensitivity for detecting arenediazonium ions and derivatized azo dyes. Received: 26 September 2000 / Revised: 12 December 2000 / Accepted: 13 December 2000     

The effect of pre-evaporation on ion distributions in inductively coupled plasma mass spectrometry

The connecting tube (2 or 5-mm i. d., 11-cm long) between the spray chamber and the torch was heated (to 400 °C) to investigate the effect of pre-evaporation on the distribution of ions in inductively coupled plasma mass spectrometry (ICP-MS). Axial and radial profiles of analyte ions (Al⁺, V⁺, Cr⁺, Ni⁺, Zn⁺, Mn⁺, Zn⁺, As⁺, Se⁺, Mo⁺, Cd⁺, Sb⁺, La⁺, Pb⁺) in 1% HNO₃ as well as some polyatomic ions (LaO⁺, ArO⁺, ArN⁺, CO₂⁺) were simultaneously obtained on a time-of-flight ICP-MS instrument. Upon heating the connecting tube, the optimal axial position of all elements shifted closer to the load coil. Without the heated tube, 3.5 mm was the compromise axial position for multielemental analysis, which was optimal for 6 analytes. With the heated tube, this position became 1.5 mm, which was then optimal for 9 of the 14 analytes. Furthermore, the radial profiles, which were wide with a plateau in their middle without heating, became significantly narrower and Gaussian-like with a heated tube. This narrowing, which was most important for the 5-mm tube, slightly (by a factor of two at the most) yet significantly (at the 95% confidence level) improved the sensitivity of all elements but Mn upon optimisation of the axial position for compromise multi-element analysis. Furthermore, a concurrent decrease in the standard deviation of the blank was significant at the 95% confidence level for 9 of the 14 analytes. For most of the analytes, this translated into a two-fold to up to an order of magnitude improvement in detection limit, which is commensurate with a reduction of noise resulting from the smaller droplets entering the plasma after traversing the pre-evaporation tube.     

Electrochemical determination of rate constants and product yields for the spontaneous dediazoniation of p‐nitrobenzenediazonium tetrafluoroborate in acidic aqueous solution

We have examined the kinetics and mechanisms of the dediazoniation of p‐nitrobenzenediazonium tetrafluoroborate in acidic aqueous solutions by employing differential pulse polarography (DPP) and differential pulse voltammetry (DPV) on a glassy carbon electrode combined with the use of a coupling reaction to quench unreacted p‐nitrobenzenediazonium ion. These electrochemical techniques show an effective sensitivity and selectivity for detecting arenediazonium ions and arenedediazoniation products under the appropriate experimental conditions (pH, solvent, electrolyte), which allows simultaneous monitoring of the rates of arenediazonium ion loss and product formation and determination of product yields. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 419–430, 2000     

High resolution studies of the origins of polyatomic ions in inductively coupled plasma-mass spectrometry,Part I. Identification methods and effects of neutral gas density assumptions,extraction voltage,and cone material

Common polyatomic ions (ArO⁺, NO⁺, H₂O⁺, H₃O⁺, Ar₂⁺, ArN⁺, OH⁺, ArH⁺, O₂⁺) in inductively coupled plasma-mass spectrometry (ICP-MS) are identified using high mass resolution and studied using kinetic gas temperatures (T_gas) determined from a dissociation reaction approach. Methods for making accurate mass measurements, confirming ion identifications, and correcting for mass bias are discussed. The effects of sampler and skimmer cone composition and extraction voltage on polyatomic ion formation are also explored. Neutral species densities at several locations in the extraction interface are estimated and the corresponding effects of the T_gas value are calculated. The results provide information about the origins of background ions and indicate possible locations for their formation or removal.     

Synthesis of some zerovalent complexes of iron via aryldiazenato cationic complexes

Bis (triphenylphosphine) dicarbonylaryldiazenato-iron, [Fe⁰ (ArN₂) (CO)₂ (PPh_s)₂]+(I), reacts in a solution of LiOEt under nitrogen atmosphere, with a variety of group V donor ligands, substituting the aryldiazenato ligand, ArN₂+. The effect of substitution on the stretching frequency of CO is discussed.     

Kinetics of decomposition pathways of an energetic GZT molecule

This investigation uses the Gaussian 98 program, density functional theory (DFT) B3LYP/6‐31G(d,p), and ab initio MP2/6‐31G(d,p) and HF/6‐31G(d) methods to model energetic diguanidinium 5,5′‐azotetrazolate (GZT) ionic species in order to determine their decomposition mechanisms. GZT was initially cracked into two guanidinium cations (G⁺) and a 5,5′‐azotetrazolate anion (ZT^2?). Three routes—the elimination of a hydronium ion (H⁺), the elimination of a hydrogen radical (H·), and the elimination of an amine radical (·NH₂)—are suggested for the decomposition of the G⁺ cation, and three routes—single ring opening, double ring opening and N? N bond cleavage outside the ring—are proposed for the further decomposition of the ZT^2? anion. Fourteen decomposition species were obtained on splitting both the cation and anion. This result reveals the reliability of the aforementioned decomposition mechanisms. The transition state species were also obtained using a two‐structure or three‐structure synchronous transit‐guided quasi‐Newton (STQN) between the Cartesian coordinates of related particles at specific decomposition stages in this research. The corresponding activation energies in all decomposition stages were considered to infer the most feasible pathways of GZT decomposition. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

Detection of iron species using inductively coupled plasma mass spectrometry under cold plasma temperature conditions

Under the conditions of low radio frequency (rf) power of 600 W and aerosol gas flow rate of 1.25–1.35 l/min, ⁵⁶Fe (or ⁵⁴Fe) ions can be detected from the isobaric interference of the ArO⁺ (or ArN⁺) matrix. Using this method, the detection limit of ⁵⁶Fe can reach 16 ng/l (ppt), 60 times smaller than by normal plasma conditions at 1200 W rf power. The linear dynamic range of the analyte measurement extends to 1000 ng/ml (ppb).     

The Electrochemical Behavior of α‐Ketoglutarate at the Hanging Mercury Drop Electrode in Acidic Aqueous Solution and Its Practical Application in Environmental and Biological Samples

The voltammetric behavior of α‐ketoglutarate (α‐KG) at the hanging mercury drop electrode (HMDE) has been investigated in acetate buffer solution. Under the optimum experimental conditions (pH 4.5, 0.2 M NaAc‐HAc buffer solution), a sensitive reductive wave of α‐KG was obtained by linear scan voltammetry (LSV) and the peak potential was ?1.18 V (vs. SCE), which was an irreversible adsorption wave. The kinetic parameters of the electrode process were α=0.3 and k_s=0.72 1/s. There was a linear relationship between peak current i_{p, α‐KG} and α‐KG concentration in the range of 2×10^?6–8×10^?4 M α‐KG. The detection limit was 8×10^?7 M and the relative standard deviation was 2.0% (C_α‐KG=8×10^?4 M, n=10). Applications of the reductive wave of α‐KG for practical analysis were addressed as follows: (1) It can be used for the quantitative analysis of α‐KG in biological samples and the results agree well with those obtained from the established ultraviolet spectrophotometric method. (2) Utilizing the complexing effect between α‐KG and aluminum, a linear relationship holds between the decrease of peak current of α‐KG Δi_p and the added Al concentration Cequation/tex2gif-inf-5.gif in the range of 5.0×10^?6–2.5×10^?4 M. The detection limit was 2.2×10^?6 M and the relative standard deviation was 3.1% (Cequation/tex2gif-inf-6.gif=4×10^?5 M, n=10). It was successfully applied to the detection of aluminum in water and synthetic biological samples with satisfactory results, which were consistent with those of ICP‐AES. (3) It was also applied to study the effect of Al^III on the glutamate dehydrogenase (GDH) activity in the catalytically reaction of α‐KG+NH +NADH?L ‐glutamate+NAD⁺+H₂O by differential pulse polarography (DPP) technique. By monitoring DPP reductive currents of NAD⁺ and α‐KG, an elementary important result was found that Al could greatly affect the activity of GDH. This study could be attributed to intrinsic understanding of the aluminum's toxicity in enzyme reaction processes.     

Inductively coupled plasma mass spectrometry with an enlarged sampling orifice and offset ion lens. II. Polyatomic Ion interferences and matrix effects

A new inductively coupled plasma mass spectrometer with an enlarged sampling orifice (1.31-mm dia.) and an offset ion lens yields very low levels of many troublesome polyatomic ions such as ArO⁺, ArN⁺, Ar₂ ⁺, ClO⁺, and ArCl⁺. The signals from refractory metal oxide ions are ≈ 1% of the corresponding metal ion signals, which is typical of most ICP-MS devices. Grounding the first electrode of the ion lens greatly reduces the severity of matrix effects to <- 20% loss in signal for Co⁺, Y⁺, or Cs⁺ in the presence of 10 mM Sr, Tm, or Pb. This latter lens setting causes only a modest loss (30%) in sensitivity for analyte elements compared to the best sensitivity obtainable by biasing the first lens. Alternatively, matrix effects can also be mitigated by readjusting the voltage applied to the first lens with the matrix present.     

Resolution and Trace Determination of Selected Oxyanions in Binary and Ternary Mixtures by Differential Pulse Polarography

Abstract

Resolution and trace determination of selected oxyanions in binary and ternary mixtures were studied by differential pulse polarography (DPP) at the dropping mercury electrode. The applicability of DPP for the simultaneous determination of the investigated oxyanions (TeO^{2- 4}, VO^? ₃, IO^? ₃, IO^? ₄, and BrO^? ₃) in the binary and ternary mixtures was also examined with regard to the dependence of the DP current on various parameters such as pH, pulse amplitude, scan rate and drop time. Statistical analysis is included on t h e observed concentrations for each of the oxyanions in the mixture and compared with that obtained by the calibration curves. Limits of detection and quantitat - ion have been calculated for the DPP determination of binary and ternary mixtures of these lected oxyanions.     

Shock tube study of monomethylamine thermal decomposition and NH2 high temperature absorption coefficient

CH₃NH₂ thermal decomposition is shown to provide a suitable NH₂ radical source for spectroscopic and kinetic shock tube studies. Using this precursor, the absorption coefficient of the NH₂ radical at a detection wavelength of 16739.90 cm⁻¹ has been determined. In the temperature range 1600–2000K the low‐pressure absorption coefficient is described by the polynominal equation: k_NH2=3.953×10¹⁰/T ³+7.295×10⁵/T ²−1.549×10³/T [atm⁻¹ cm⁻¹] The uncertainty of the determined absorption coefficient is estimated to be ±10%. The rate of the thermal decomposition reaction CH₃NH₂+M → CH₃+NH₂+M is determined over the temperature range 1550–1900 K and at pressures near 1.6 atm. The rate coefficient was found to be: k₁=2.51×10¹⁶ exp(−28430/T) [cm³ mol⁻¹ s⁻¹] The uncertainty of the determined rate coefficients is estimated to be ±20%. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 323–330, 1999     

Effects of Ascorbic Acid on Arenediazonium Salts Reactivity: Kinetics and Mechanism of the Reaction

We have examined the kinetics and mechanism of dediazoniation of o‐, m‐ and p‐methylbenzenediazonium (ArN) tetrafluoroborate in the presence of ascorbic acid (H₂A) at different pHs by combining spectophotometric (VIS‐UV), high performance liquid chromatography (HPLC), and polarographic measurements. Kinetic data show that, at low pH, observed rate constants increase linearly with increasing ascorbic acid concentration, but the saturation kinetics observed at higher pH suggest the formation of a transient diazo‐ether complex preceding the slow step of the reaction. Experimental evidence for the formation of such a complex was obtained from a competitive coupling reaction with the Na salt of `2‐naphthol‐6‐sulfonic acid' and by titration of ascorbic acid (H<sub>2</sub>A) with the arenediazonium ions (electrochemical measurements). HPLC Analysis of dediazoniation products indicates that, in the absence of H<sub>2</sub>A, only the heterolytic phenol derivative, ArOH, is formed quantitatively, in keeping with the predictions of the D<sub>N</sub>+A<sub>N</sub> mechanism. In the pH 2 – 4 range and in the presence of H<sub>2</sub>A, reduction products (ArH) are obtained in addition to heterolytic products (ArOH), corroborating that certain biological reducing agents like ascorbate (HA<sup>−</sup>) are capable of inducing reductive fragmentation of ArN into aryl radicals. All evidence is consistent with two competitive reaction pathways, the thermal decomposition of ArN, and a rate‐limiting decomposition of the transient diazo ether `complex', formed during the reaction of ArN with HA⁻ in a rapid pre‐equilibrium step.