Loss of hydrogen cyanide from monocyanopyridines upon electron impact: Dewar pyridine structures and ring opening—Ring closure reactions revealed by 13C and 15N Labelling

Extensive ¹³C and ¹⁵N labelling has shown that the molecular ions of 2-, 3- and 4-cyanopyridine with lifetimes up to 10^?6 s eliminate hydrogen cyanide originating predominantly from the ring (?65%). Moreover, this hydrogen cyanide loss occurs after an equilibrated positional interchange of the ring carbon atoms at positions interchange of the ring carbon atoms at positions 2, 4 and 6 via Dewar pyridine structures. In molecular ions with lifetimes of 10^?6–10^?5 s skeletal rearrangements have taken place in such a way that both nitrogen atoms have become equivalent prior to the loss of hydrogen cyanide. Arguments are put forward that this equivalence of nitrogen atoms is caused by the intermediacy of ions with a 1,4-dicyanobuta-1,3-diene structure. About 60% of these intermediate ions eliminate hydrogen cyanide in a fast process. The remaining 40% of these ions undergo ring closure again to a pyridine ring in which the carbon atoms of positions 2, 4 and 6 are positionally interchanged rapidly via Dewar pyridine structures followed by ring opening again and eventual loss of hydrogen cyanide. This interpretation of the ¹³C and ¹⁵N labelling results is further corroborated by a study of the loss of hydrogen cyanide from molecular ions of 1,4-dicyanobuta-1,3-diene labelled with ¹³C in both cyano groups.     

Li-NMR study of the stoichiometry, stability and exchange kinetics of Li ion with 12-Crown-4, 15-Crown-5 and cryptands C222, C221 and C211 in 50% ionic liquid-acetonitrile mixtures

⁷Li-NMR spectroscopy was used to study the complexation of Li⁺ ion with 12C4, 15C5, C222, C221, C211 in acetonitrile (AN) and its 50% (wt/wt) mixtures with two new room temperature ionic liquids, 1-ethyl-3-methylimidazolium hexafluorophosphate (EMim PF₆) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMim BF₄) at 298 K. Excluding the cases of Li⁺-C211 in all solvents and Li⁺-C221 in AN and 50% (wt/wt) AN-EMim PF₆, in other cases, the exchange between free and 1:1 complexed Li⁺ was fast on the NMR time scale and only a single population average ⁷Li signal was observed. Formation constants of the resulting 1:1 complexes were evaluated by computer fitting of the chemical shift-mole ratio data and integration of two ⁷Li signals. All complexes in EMim PF₆ were found to be more stable than those in EMim BF₄. ⁷Li-NMR line-shape analysis was used to determine the kinetic parameters and the mechanism for the chemical exchange of Li⁺ between the free and 1:1 complex with C221 in 50% (wt/wt) AN-EMim PF₆ mixtures solution. By comparing our study with the previous one, it is derived that, increasing the percentage of ion liquid in acetonitrile, changes the mechanism and decrease the exchange rate constant of Li⁺ ion between free and complex sites.     

133Cs NMR Study of Cs+ Ion Complexes with?Aza-18-crown-6, Diaza-18-crown-6 and?Dibenzyldiaza-18-crown-6 in Binary Acetonitrile?CNitromethane Mixtures

Cesium-133 nuclear magnetic resonance spectroscopy was used as a sensitive probe to investigate the stoichiometry and stability of Cs⁺ ion complexes with aza-18-crown-6 (A18C6), diaza-18-crown-6 (DA18C6) and dibenzylediaza-18-crown-6 (DBzDA18C6) in different binary acetonitrile?Cnitromethane mixtures. In all cases, the exchange between free and complexed cesium ion was fast on the NMR time scale and only a single population average resonance was observed. The ¹³³Cs chemical shift?Cmole ratio data indicated that the cesium ion forms 1:1 cation?Cligand complexes with the investigated aza-crowns in all acetonitrile?Cnitromethane mixtures. The formation constants of the resulting complexes were evaluated from computer fitting of the chemical shift?Cmole ratio data. The stability of the resulting 1:1 complexes with Cs⁺ were found to vary in the order A18C6 > DBzDA18C6 > DA18C6. In all cases, there is the inverse relationship between the complex stability constants and the amount of acetonitrile in the mixed solvent.     

Shock tube pyrolysis of pyrrole and kinetic modeling

The kinetics of pyrolysis of pyrrole dilute in argon have been studied in a single pulse shock tube, using capillary column GC, together with GC/MS and FTIR for product identification, over the temperature range 1200–1700 K, total pressures of 7.5–13.5 atm and nominal mixture compositions of pyrrole of 5000 and 700 ppm (nominal concentrations of 5 × 10^?7 and 7 × 10^?8 mol cm^?3). Time-resolved measurements of the rate of disappearance of pyrrole behind reflected shock waves have been made by absorption spectroscopy at 230 nm, corresponding to the lowest ¹π* ← ¹π transition of pyrrole at pressures of 20 atm and mixture compositions between 1000–2000 ppm pyrrole (1.7–3.0 × 10^?7 mol cm^?3) over the temperature range of 1300 to 1700 K. At the lower end of the studied temperature range, the isomers of pyrrole, allyl cyanide and cis- and trans-crotononitrile, were the principal products, together with hydrogen cyanide and propyne/allene. At elevated temperatures, acetylene, acetonitrile, cyanoacetylene, and hydrogen became important products. The rate of overall disappearance of pyrrole, as measured by absorption spectrometry, was found to be first order in pyrrole concentration, with a rate constant k_dis(pyrrole) = 10^14.1±0.7 exp(?74.1 ± 3.0 kcal mol^?1/RT) s^?1 between 1350–1600 K and at a pressure of 20 atm. First order dependence of pyrrole decomposition and major product formation was also observed in the single pulse experiments over the range of mixture compositions studied. A 75-step reaction model is presented and shown to substantially fit the observed temperature profiles of the major product species and the reactant profile. In the model the initiation reaction is postulated to be the reversible formation of pyrrolenine, (2H-pyrrole). Pyrrolenine can undergo ring scission at the C2? N bond forming a biradical which can rearrange to form allyl cyanide and crotononitrile or undergo decomposition to form HCN and C₃H₄ or acetylene and a precursor of acetonitrile. The model predicts an overall rate of disappearance of pyrrole in agreement with the experimental measurements.     

Addition of the cyanide ion to cyclopentadienyliron complexes of arenes containing an electron-withdrawing substituent

Reactions of cyclopentadienyliron (CpFe) complexes of arenes containing an electron-withdrawing substituent with NaCN in DMF resulted in a regiospecific addition of the cyanide ion at a position ortho to the substituent, giving rise to CpFe complexes of cyanocyclohexadienyl systems. For example, the addition of the cyanide ion to η⁶-nitrobenzene-η⁵-cyclopentadienyliron hexafluorophosphate (Ia) gave the neutral complex, 1-5-η⁵-exo-6-cyano-1-nitrocyclohexadienyl-η⁵-cyclopentadienyliron (IIa). Similar cyanide additions also took place with the CpFe complexes of benzophenone and of methyl benzoate. Reactions with η⁶-anthraquinone, xanthone, thioxanthone, or thioxanthone-10,10-dioxide-η⁵-cyclopentadienyliron hexafluorophosphate (IIIa, IIIb, IIIc or IIId, respectively) resulted in the addition of the cyanide ion solely to C(1), a position ortho to the keto substituent; for example, from IIIa, the adduct was 2,3,4,4a,9a-η⁵,-exo-1-cyano-1H-anthraquinone-η⁵-cyclopentadienyliron (IVa). With the CpFe complex of fluorenone (V), however, a 3/1 mixture of products was obtained, arising from cyanide additions to C(1) and C(4a), both positions being ortho to the keto substituent in V. A possible explanation is suggested for the failure of the cyanide ion adding to C(4a) in reactions with IIIa to IIId.     

A kinetic study on the bioremediation of sodium cyanide and acetonitrile by free and immobilized cells ofPseudomonas putida

Pseudomonas putida capable of utilizing organic nitrile (acetonitrile) and inorganic cyanide (sodium cyanide) as the sole source of carbon and nitrogen was isolated from contaminated industrial sites and waste water. The bacterium possesses nitrile aminohydrolase (EC 3.5.5.1) and amidase (EC 3.5.1.4), which are involved in the transformation of cyanides and nitriles into ammonia and CO₂ through the formation of amide as an intermediate. Both of the enzymes have a high selectivity and affinity toward the⁻Cn group. The rate of degradation of aceotnitrile and sodium cyanide to ammonia and CO₂ by the calcium-alginate immobilized cells ofP. putida was studied. The rate of reaction during the biodegradation of acetonitrile and sodium cyanide, and the substrate- and product-dependent kinetics of these toxic compounds were studied using free and immobilized cells ofP. putida and modeled using a simple Michaelis-Menten equation.     

Forms of soil organic nitrogen in a Pactola soil as seen by pyrolysis/gas chromatography/atomic emission detection (Py–GC/AED)

In this study, soil organic nitrogen (SON) forms from a Pactola forest soil were investigated by using pyrolysis–cryogenic gas chromatography/atomic emission (Py–GC/AED). The samples were taken at different soil depths of 0–12 cm, 12–25 cm and 25–38 cm and separated into particle-size fractions. Each fraction was analyzed by Py–GC/AED at 300, 400 and 500 °C consecutively. The main N-structures found in pyrolysates were ammonia, acetonitrile, hydrogen cyanide, pyridine and pyrrole. Ratios of acetonitrile and hydrogen cyanide to pyridine and pyrrole decreased with soil depth. Acetonitrile and hydrogen cyanide had positive correlations with total organic N (TON) down the soil profile. A decrease of the optimal pyrolysis temperatures of soil samples with increasing soil depth was observed for acetonitrile and hydrogen cyanide. In the surface soil samples, there was no correlation found for both pyridine and pyrrole with TON. But with depth, the correlation coefficient increased and reached to 0.912 for pyridine, and 0.875 for pyrrole at the depth of 25–38 cm. The increased correlation coefficients of pyridine and pyrrole with TON in combination with the low shifts of the optimal pyrolysis temperatures of the soil samples down the soil profile for acetonitrile and hydrogen cyanide indicated clear differences in N-structures between different soil layers.     

Normal pulse polarographic quantification of cyanide and sulfide by the anodization of mercury

Normal pulse polarography is used to quantify cyanide and sulfide simultaneously by the anodic oxidation of mercury. The detection limit for cyanide is 18 μg l^-1 by the normal pulse polarographic technique. A supporting electrolyte system of 1 M Na₂CO₃ is optimal with regard to background interferences and sample loss. The electrode reaction for the oxidation of mercury in the presence of cyanide can be described by Hg + pCN^- α Hg(CN)_p^2-p + 2e^-, with p having values of 2, 3 and 4 depending on the surface concentration of cyanide. The feasibility of simultaneous cyanide and sulfide quantification is demonstrated with waste-water samples.     

Kinetics and isotope fractionation in deuterium exchange between N1-methyl-N2-phenylthiourea and S-deuterated t-butylthiol in aprotic solvents

The kinetics and isotope fractionation of deuterium in the exchange reaction between N¹-methyl-N²-phenylthiourea and S-deuterated t-butylthiol in selected aprotic solvents: methylene chloride, tetrahydrofuran, acetone, dimethyl sulphoxide and acetonitrile have been determined. The rate of the deuterium exchange in N¹H site is higher than that in N²H site and both depend visibly on the solvent. The higher the polarity of the solvent the lower the rate constant of the exchange reaction. The equilibrium isotope effect is relatively high and depends on the solvent, however, no distinct correlation could be found between the fractionation factor and electron donor or acceptor properties of the solvent.     

Proton NMR probing of stoichiometry and thermodynamic data for the complexation of Na and Li ions with 15-Crown-5 in acetonitrile-nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Li⁺ and Na⁺ ions with 15-Crown-5 (15C5) in a number of binary acetonitrile (AN)-nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 15C5 was fast on the NMR timescale and only a single population average ¹H signal was observed. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift mole ratio data. There is an inverse relationship between the complex stability and the amount of AN in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of the formation constants. In all the solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. Finally, the experimental results were compared with theoretical ones that were obtained from molecular modeling methods. Based on our results, it is most probable that Li⁺-15C5 in solvent stays in a rather nesting complex form with greater LogK_f values, but Na⁺-15C5 forms a complete perching complex form with lower LogK_f values.     

Study of complex formation between La+3, Ce+3 and Y3+ cations with some 18-membered crown ethers in methanol–water and methanol–acetonitrile binary mixtures

The complexation reactions between some rare earth metal cations (Ln; Y³⁺, La³⁺ and Ce³⁺) with 18-crown-6 (18C6), dicyclohexyl-18-crown-6 (DC18C6), benzo-18-crown-6 (B18C6) and decyl-18-crown-6 (Dec18C6), have been studied in methanol–acetonitrile (MeOH–AN) and methanol–water (MeOH–H₂O) binary mixtures using a competitive spectrophotometric method. 2-(2-thiazolylazo)-4-methyl phenol (TAC or L) was used as colorimetric complexant. It was found that the selectivity order of TAC for Ln cations is highly changed with changing the composition of the mixed solvents. Moreover, as the concentration of acetonitrile increases in MeOH–AN binary mixture, the stability of Ln–TAC complexes increases and passes through a maximum at a certain mole fraction of acetonitrile. In addition, the stability of Ln–crown ether complexes increases with increasing the concentration of methanol in MeOH–H₂O and acetonitrile in MeOH–AN binary solutions. A non linear behaviour was observed for variation of stability constants of all complexes versus the composition of the mixed solvents. The results show that 18C6 generally forms more stable complexes with La³⁺ and Ce³⁺ cations than DC18C6 in methanol and MeOH–H₂O binary mixtures, while this sequence is reversed in the methanol-acetonitrile binary mixtures which are rich with respect to acetonitrile.     

NMR STUDY OF EXCHANGE KINETICS OF THE LITHIUM ION WITH CRYPTAND C222 IN BINARY ACETONITRILE-NITROMETHANE MIXTURES

Abstract

The exchange kinetics of the lithium ion with cryptand C222 were studied in acetonitrile-nitromethane mixtures by lithium-7 NMR line-shape analysis. In all solvent mixtures used, and over the entire temperature range studied, the chemical exchange of the Li⁺ ion between the solvated and complexed sites was found to occur via a bimolecular mechanism. The activation parameters E_a, δH?, δS? and δG? for the exchange have been determined. The free energy barrier for the exchange process appears to be nearly independent of the binary mixture composition. The results confirm the preferential solvation of the lithium ion with acetonitrile in the binary mixed solvent systems used.     

Alternative mechanisms for cyanide anion exchange with acetonitrile

Mechanisms for the recently observed exchange of cyanide anion in acetonitrile have been investigated by means of semi-empirical MNDO molecular orbital calculations. A prototropic type mechanism $\text{via}$ a cyclopropane intermediate is the most likely candidate. The previously proposed concerted migration is indicated to be the least favourable reaction pathway.     

Simple determination of 90Sr in water in environmental radioactivity survey

Derivatives of dodecahydro-closo-dodecaborate(2-) anion were proposed as boron-rich compounds for boron-neutron capture therapy (BNCT) of malignant tumours. Labeling of such tumour-targeting compounds with radioisotopes would facilitate the investigation of their pharmacokinetics and help to optimize patient treatment protocols. Earlier, we reported the feasibility of labeling of closo-dodecaborate(2-) by isotopic exchange in molten acetamide. In this study, the feasibility of low-temperature isotopic exchange in the system [¹²⁵I]iodide - bis(triethylammonium) undecahydro-12-iodo-closo-dodecaborate was investigated. Our attempts to perform the exchange in solvents such as methylene chloride, acetone and acetonitrile in the presence of phase-transfer catalysts were unsuccessful. However, copper mediated exchange in aqueous media was possible. Isotopic exchange of triethylammonium undecahydro-12-iodo-closo-dodecaborate provided a 90-95% labeling yield after heating for three and half hours at 100 °C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structures of silver nitrate complexes with quinolines according to NMR data

Silver(I) nitrate complexes [AgNO₃(L)₂], where L is quinoline or 2-, 4-, and 8-methylquinoline, are synthesized and studied by the multinuclear NMR (¹H, ¹³C, ¹⁵N) method in acetonitrile. The influence of steric and electronic factors of the organic ligand on the NMR spectral parameters is revealed. The fast chemical exchange of the free and coordinated ligands is observed at room temperature. The ¹⁵N NMR spectra are most informative. The formation of a complex with 8-methylquinoline is impeded because of steric hindrances.     

A new approach to ion exchange chromatography with conductivity detection for adulterants investigation in dietary supplements

The extent of adulteration of dietary supplements has significantly increased in recent years. This situation worries health authorities and requires auxiliary analytical tools for the investigation of illegal substances purposely added. Ion exchange chromatography with conductivity detection is a consolidated analytical technique for the determination of inorganic compounds in various matrices. This technique has been applied to the pharmaceutical characterization of mainly impurities and degradation products. This work presents a new approach to ion exchange chromatography as a screening method to investigate the presence of amfepramone, femproporex, sibutramine, bisacodyl and amiloride in dietary supplements advertised for weight loss. The method was optimized and validated using a Metrosep C4 100/4.0 cation exchange column. The mobile phase consisted of 1.8 mm HNO₃ containing 2% acetonitrile (v/v), with a flow rate of 0.9 ml min^?1, and nonsuppressed conductivity detection was applied. The limits of detection and quantification varied from 1.01 to 3.62 mg L^?1 and from 1.48 to 8.72 mg L^?1, respectively. The proposed method was successful applied to 78 solid dietary supplement samples, in two of which adulterations were found. Moreover, ion exchange chromatography with conductivity detection could be easily used for quality control without prior complex sample pre‐treatment.     

An analytical method for the determination of perfluorinated compounds in whole blood using acetonitrile and solid phase extraction methods

A method for the analysis of perfluorinated compounds (perfluoroalkyl sulfonates: C4, C6, C8, C10; perfluoroalkyl sulfinates: C6, C8, C10; perfluorooctanesulfonamide, N-ethyl perfluorooctanesulfonamide, N-ethyl perfluorooctanesulfonamidoacetate, perfluorocarboxylates: C4–C14; fluorotelomer carboxylate (7:3, 8:2) in whole blood using acetonitrile and OASIS WAX^® solid phase extraction (SPE) cartridge was developed. Separation of target compounds in two HPLC columns (ion exchange JJ50-2D and C18 Betasil columns) was examined. Matrix recoveries of the developed methods ranged from 70% to 120%. Separation of possible inferences such as taurodeoxycholic acid (TDC) was accomplished using an ion exchange JJ50-2D column, and this separation was validated using whole blood of different animals.     

17O NMR Investigation of cyclic aromatic ethers

A linear relationship between the C-O-C angle and the molecular dihedral angle in a series of phenoxathi-ins and azaphenoxathiins is reported. ¹⁷O nmr spectroscopic data (natural abundance in acetonitrile at 75°C) were obtained on eight cyclic aromatic ethers 1-8 , including phenoxathiins, and two model compounds, acyclic aromatic ethers 9 and 10. The chemical shifts of the cyclic aromatic ethers were very sensitive to structural variations and were dependent upon electonic and conformational effects; however, no quantitative relationship between ¹⁷O chemical shift and geometric parameters was found.     

Synthesis of ammonium [14C]thiocyanate

Ammonium [¹⁴C]thiocyanate was prepared from potassium [¹⁴C]cyanide with a radiochemical yield of 90%. [¹⁴C]hydrocyanic acid, generated from potassium [¹⁴C]cyanide by sulphuric acid, reacts with aqueous ammonia and elemental sulphur in the presence of trace amounts of ammonium sulphide to yield ammonium [¹⁴C]thiocyanate.     

Mercury(II) cyanide complexes of thioureas and the crystal structure of [(N-methylthiourea)2 Hg(CN)2]

Mercury(II) cyanide complexes of thioureas (Tu), N-methylthiourea (MeTu), and N,N′-dimethylthiourea (DmTu)) have been prepared and characterized by IR and NMR (¹H and ¹³C) spectroscopy, and the crystal structure of one of them was determined by X-ray crystallography. An upfield shift in ¹³C NMR and downfield shifts in ¹H NMR are consistent with the sulfur coordination to mercury(II). The appearance of a band around 2200 cm^?1 in IR and a resonance around 145 ppm in ¹³C NMR indicates the binding of cyanide to mercury(II). The NMR data show that the [(Thione)₂Hg(CN)₂] complexes are stable in solution and undergo no redistribution reactions. In the crystal structure of the title complex, mercury atom is coordinated to two thione sulfur atoms of MeTu and to two cyanide carbon atoms in a distorted tetrahedral mode with the bond angles in the range of 90.2(2)°–169.3(3)°.