Polarographisches Verhalten der C2-Halogenkohlenwasserstoffe

Summary Investigations on the polarographic and voltammetric behaviour of organic halogen compounds were carried out in order to obtain information on the redox properties and how to develop determination and detection methods. In this second report the dp-polarographic behaviour of the halogen substituted C₂-compounds has been studied in different supporting electrolytes and in various solvents. The electrode processes are discussed and the possibilities for the polarographic determination of the C₂-halogen hydrocarbons. The detection limit is 0.25 g · ml^–1 and the linear current-concentration relationship is observed up to 25 g · ml^–1. A simple and rapid method is proposed for the dp-polarographic determination of 1,2-dibromoethane in gasoline; the relative standard deviation for 20 g · ml^–1 is ±1.8%.     

Polarographic study of halogen and mercury substituted 1,3-oxazoles

A study is made of the polarographic behavior of some halogen and mercury derivatives of phenyloxazoles. By considering the mechanism of electroreduction, it is ascertained, that, the first polarographic wave corresponds to reduction of the halogen or mercury-containing substituent, and the second to reduction of the heterocyclic ring. By analysis of polarographic data it is shown that the electron density sequence for carbon atoms in the oxazole ring is C-2相似文献   

Comments on Empirical Correlations between Reduction Potential of Carbon-Halogen Bonds and NQR. Frequencies of Halogen Atoms in Organic Molecules

An empirical linear correlation exists between nuclear quadrupole resonance frequencies of halogen nuclei (³⁵Cl, ⁷⁹Br, ¹²⁷I) and the polarographic reduction potentials in series of organic halides. In terms of electronic structure this is interpreted as a significant relationship between the average p-electron population at halogen atoms and the first vacant molecular orbital of halogenated molecules. On the basis of the present correlations conclusions are drawn about some controversial mechanistic aspects of the electroreduction of the carbon-halogen bond.     

Comparative Study of Halogen‐ and Hydrogen‐Bond Interactions between Benzene Derivatives and Dimethyl Sulfoxide

The halogen bond, similar to the hydrogen bond, is an important noncovalent interaction and plays important roles in diverse chemistry‐related fields. Herein, bromine‐ and iodine‐based halogen‐bonding interactions between two benzene derivatives (C₆F₅Br and C₆F₅I) and dimethyl sulfoxide (DMSO) are investigated by using IR and NMR spectroscopy and ab initio calculations. The results are compared with those of interactions between C₆F₅Cl/C₆F₅H and DMSO. First, the interaction energy of the hydrogen bond is stronger than those of bromine‐ and chlorine‐based halogen bonds, but weaker than iodine‐based halogen bond. Second, attractive energies depend on 1/rⁿ, in which n is between three and four for both hydrogen and halogen bonds, whereas all repulsive energies are found to depend on 1/r^8.5. Third, the directionality of halogen bonds is greater than that of the hydrogen bond. The bromine‐ and iodine‐based halogen bonds are strict in this regard and the chlorine‐based halogen bond only slightly deviates from 180°. The directional order is iodine‐based halogen bond>bromine‐based halogen bond>chlorine‐based halogen bond>hydrogen bond. Fourth, upon the formation of hydrogen and halogen bonds, charge transfers from DMSO to the hydrogen‐ and halogen‐bond donors. The CH₃ group contributes positively to stabilization of the complexes.     

Theoretical study on the interactions of halogen‐bonds and pnicogen‐bonds in phosphine derivatives with Br2, BrCl,and BrF

The MP2 ab initio quantum chemistry methods were utilized to study the halogen‐bond and pnicogen‐bond system formed between PH₂X (X = Br, CH₃, OH, CN, NO₂, CF₃) and BrY (Y = Br, Cl, F). Calculated results show that all substituent can form halogen‐bond complexes while part substituent can form pnicogen‐bond complexes. Traditional, chlorine‐shared and ion‐pair halogen‐bonds complexes have been found with the different substituent X and Y. The halogen‐bonds are stronger than the related pnicogen‐bonds. For halogen‐bonds, strongly electronegative substituents which are connected to the Lewis acid can strengthen the bonds and significantly influenced the structures and properties of the compounds. In contrast, the substituents which connected to the Lewis bases can produce opposite effects. The interaction energies of halogen‐bonds are 2.56 to 32.06 kcal·mol^?1; The strongest halogen‐bond was found in the complex of PH₂OH???BrF. The interaction energies of pnicogen‐bonds are in the range 1.20 to 2.28 kcal·mol^?1; the strongest pnicogen‐bond was found in PH₂Br???Br₂ complex. The charge transfer of lp(P) ? σ*(Br? Y), lp(F) ? σ*(Br? P), and lp(Br) ? σ*(X? P) play important roles in the formation of the halogen‐bonds and pnicogen‐bonds, which lead to polarization of the monomers. The polarization caused by the halogen‐bond is more obvious than that by the pnicogen‐bond, resulting in that some halogen‐bonds having little covalent character. The symmetry adapted perturbation theory (SAPT) energy decomposition analysis showes that the halogen‐bond and pnicogen‐bond interactions are predominantly electrostatic and dispersion, respectively.     

Properties of halogen atoms for representing intermolecular electrostatic interactions related to halogen bonding and their substituent effects

The electrostatic properties of halogen atoms are studied theoretically in relation to their ability of halogen bonding, which is an attractive intermolecular interaction of a covalently bonded halogen atom with a negatively charged atom of a neighboring molecule. The electric quadrupole (of electronic origin) with a positive zz component Θ_zz of a covalently bonded halogen atom, where the z axis is taken along the covalent bond involving the halogen atom, is mainly responsible for the attractive electrostatic interaction with a negatively charged atom. This positive Θ_zz is an intrinsic property of halogen atoms with the p_x²p_y²p_z configuration of the valence electronic shell, as shown by ab initio molecular orbital calculations for isolated halogen atoms with this electronic configuration, and increases in the order of F < Cl < Br < I, in parallel with the known general sequence of the strength of halogen bonding. For halogen‐containing aromatic compounds, the substituent effects on the electrostatic properties are also studied. It is shown that the magnitude of Θ_zz and the electric field originating from it are rather insensitive to the substituent effect, whereas the electric field originating from atomic partial charges has a large substituent effect. The latter electric field tends to partially cancel the former. The extent of this partial cancellation is reduced in the order of Cl < Br < I and is also reducible by proper substitution on or within the six‐membered ring of halobenzene. Perspectives on the development of potential function parameters applicable to halogen‐bonding systems are also briefly discussed. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Polarographic maxima of the third kind. III

The polarographic maxima of the third kind in solutions of 2-oxoadamantane and of pelargic acid (C₈H₁₇COOH) were investigated. The behavior of 2-oxoadamantane is similar to that of other adamantane and camphor derivatives. The surface activity of pelargic acid is markedly enhanced in 2 M MgSO₄ solutions, however a polarographic maximum of the third kind is observed in the neighborhood of the cathodic desorption potential only. The appearance of the polarographic maxima of the third kind seems to be related to the faculty of the surfactant to form under equilibrium conditions two-dimensional condensed layers on the mercury drop surface.     

Clˉ as the halogen bond acceptor: studies on strong halogen bonds

The Clˉ anion as the halogen bond acceptor, the diiodotetrafluoroethane I(CF₂)₂I and its derivatives I(MF₂)_nI (M = C, Si, Ge, Sn) as the halogen bond donor, and the strong halogen bonds could be formed. The halogen bonds between I(MF₂)_nI and Clˉ have been designed and investigated by Moller–Plesset perturbation/aug-cc-pVDZ calculations together with the aug-cc-pVDZ-pp basis set for iodine and stannum. The halogen bonds in the I(MF₂)_nI???Clˉ complexes are strong, which are apparently related to the group IV elements, becoming stronger along the sequence of M = Si, C, Ge, Sn. Accompanied with increasing number (n) of MF₂ unit, the halogen bonds (M = Si, Ge, Sn) also become stronger. The energy decomposition analyses reveal that the exchange energy contributes most in forming these halogen-bonded interactions. In the meantime, the electrostatic energy is also a significant factor for the I???Clˉ interactions. The halogen bonds of I(MF₂)nI???Clˉ(M = C, Ge, Sn) belong to partial-covalent interactions, while they are noncovalent interactions when M = Si.     

Solvation effect of the cation of the supporting electrolyte in hexamethylphosphoramide

Polarographic reductions of sodium and potassium ions in hexamethylphosphoramide (HMPA) have been examined in various supporting electrolytes. The supporting electrolytes, which have much the same solvated radii and much the same electrocapillary curves, sometimes have a significantly different influence on the polarographic reductions of metal ions. The Li⁺ and Hex₄N⁺ ions provide a typical example. Their effective radii are seen to have much the same characteristics. However, the polarographic reduction of the sodium ion shows a difference in shape between that occurring in Li⁺ solution and that in Hex₄N⁺ solution. Another example is found in the case of Et₄N⁺, Me₄N⁺ and 5N6⁺, whose r_eff and the electrocapillary curves are much the same. However, the polarographic reductions of the sodium and potassium ions are different in these solutions. The solvation number of the solvent molecule of the supporting electrolyte cation seems to exert a great influence on these reductions. The electrocapillary curves were also examined with the tetradodecylammonium ion, tetradecylammonium ion and tetraphenylphosphonium ion used as the supporting electrolytes. The inhibition of the reduction of metal ion for these cations is evidence for their lack of solvation. The effects of the solvated asymmetrical tetraalkylammonium ions on the polarographic behaviour were also examined. When some methyl groups cooperate with the tetraalkylammonium ion, the chemical character is between that of the Et₄N⁺ ion and that of the Me₄N⁺ ion.     

Ditopic halogen bonding with bipyrimidines and activated pyrimidines

The potential of pyrimidines to serve as ditopic halogen‐bond acceptors is explored. The halogen‐bonded cocrystals formed from solutions of either 5,5′‐bipyrimidine (C₈H₆N₄) or 1,2‐bis(pyrimidin‐5‐yl)ethyne (C₁₀H₆N₄) and 2 molar equivalents of 1,3‐diiodotetrafluorobenzene (C₆F₄I₂) have a 1:1 composition. Each pyrimidine moiety acts as a single halogen‐bond acceptor and the bipyrimidines act as ditopic halogen‐bond acceptors. In contrast, the activated pyrimidines 2‐ and 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine (C₁₄H₁₃N₃) are ditopic halogen‐bond acceptors, and 1:1 halogen‐bonded cocrystals are formed from 1:1 mixtures of each of the activated pyrimidines and either 1,2‐ or 1,3‐diiodotetrafluorobenzene. A 1:1 cocrystal was also formed between 2‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene, while a 2:1 cocrystal was formed between 5‐{[4‐(dimethylamino)phenyl]ethynyl}pyrimidine and 1,4‐diiodotetrafluorobenzene.     

Determination of lead,tin, tellurium,and some doping elements in PbxSn1−xTe

A single method, based on gravimetric and polarographic analysis, has been developed to determine, in the same sample, the fundamental constituents and some doping elements in the Pb_xSn_1?xTe system. First tellurium is separated by sulfur dioxide in an acid solution (5% in HCl). This medium is suitable both for the total tellurium separation and for the subsequent tin precipitation by phenylarsonic acid. Moreover, this analytical procedure allows determination in the same sample, the concentration of some doping elements such as copper, cadmium, and zinc which are necessary to vary some physical properties of the Pb_xSn_1?xTe semiconductor system. The trace elements were determined by stripping voltammetry after tellurium, tin, and lead separation. The residual solution contains a variable amount of phenylarsonic acid which makes difficult quantitative polarographic measurements, because the electrodissolution potentials are varied and peak heights are masked. However, polarographic measurements are not altered through a wide range of phenylarsonic acid concentration if the solution is previously neutralized.     

The Polarographic Determination of Tenoxicam in the Pharmaceutical Preparations

Abstract

In this study, the polarographic behaviour and the optimum polarographic conditions for the determination of TNX using DC (direct current), DP (differential pulse), SCAP (superimposed constant amplitude pulse) and SIAP (superimposed increasing amplitude pulse) polarographic techniques are described based on the reduction of enol group of the molecule on the dropping mercury electrode. The experiments were conducted in the aqueous supporting electrolyte solution containing 0.2 M KCl and 0.2 M buffer solution. Single waves were obtained at various pH values. The limiting currents were decreased and E_1/2 values were linearly shifted to more negative potentials with an increase in the pH. The system was irreversible at both the acidic and the basic media and it was adsorptional in the acidic medium and diffusional at pH 10.8. The variation in the limiting current was found to be 0.86 μA/°C. Good relations were obtained for DC, DP, SCAP and SIAP polarographic techniques at pH 10.8. The determination of TNX in pharmaceutical preparations, namely Tilcotil® tablets, containing 20 mg of TNX were tested employing DC, DP, SCAP, SIAP polarographic techniques. The results were compared to those of HPLC and the standard deviations (SD) were found to be in the range of 0.14 and 0.22 for the techniques employed for filtered and unfiltered solutions. The polarographic techniques used for the determination of TNX seem to be accurate, rapid and practical. Therefore, the suggested method may be promising in the routine analysis.

     

Crystal structures of four δ‐keto esters and a Cambridge Structural Database analysis of cyano–halogen interactions

The revived interest in halogen bonding as a tool in pharmaceutical cocrystals and drug design has indicated that cyano–halogen interactions could play an important role. The crystal structures of four closely related δ‐keto esters, which differ only in the substitution at a single C atom (by H, OMe, Cl and Br), are compared, namely ethyl 2‐cyano‐5‐oxo‐5‐phenyl‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₂N₂O₃, (1), ethyl 2‐cyano‐5‐(4‐methoxyphenyl)‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₂₀H₂₄N₂O₄, (2), ethyl 5‐(4‐chlorophenyl)‐2‐cyano‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₁ClN₂O₃, (3), and the previously published ethyl 5‐(4‐bromophenyl)‐2‐cyano‐5‐oxo‐3‐(piperidin‐1‐yl)pent‐2‐enoate, C₁₉H₂₁BrN₂O₃, (4) [Maurya, Vasudev & Gupta (2013). RSC Adv. 3 , 12955–12962]. The molecular conformations are very similar, while there are differences in the molecular assemblies. Intermolecular C—H...O hydrogen bonds are found to be the primary interactions in the crystal packing and are present in all four structures. The halogenated derivatives have additional aromatic–aromatic interactions and cyano–halogen interactions, further stabilizing the molecular packing. A database analysis of cyano–halogen interactions using the Cambridge Structural Database [CSD; Groom & Allen (2014). Angew. Chem. Int. Ed. 53 , 662–671] revealed that about 13% of the organic molecular crystals containing both cyano and halogen groups have cyano–halogen interactions in their packing. Three geometric parameters for the C—X...N[triple‐bond]C interaction (X = F, Cl, Br or I), viz. the N...X distance and the C—X...N and C—N...X angles, were analysed. The results indicate that all the short cyano–halogen contacts in the CSD can be classified as halogen bonds, which are directional noncovalent interactions.     

A Theoretical Study of the Halogen Bond between Heteronuclear Halogen and Benzene

Halogen bonds play an important role in many fields, such as biological systems, drug design and crystal engineering. In this work, the structural characteristics of the halogen bond between heteronuclear halogen XD (ClF, BrCl, IBr, ICl, BrF and IF) and benzene were studied using density functional theory. The structures of the complexes between heteronuclear halogen and benzene have Cs symmetry. The interaction energies of the complexes between heteronuclear halogen XD (ClF, BrCl, IBr, ICl, BrF and IF) and benzene range from −27.80 to −37.18 kJ/mol, increasing with the increases in the polarity between the atoms of X and D, and are proportional to the angles of a between the Z axis and the covalent bond of heteronuclear halogen. The electron density (ρ) and corresponding Laplacian (∇²ρ) values indicate that the interaction of the heteronuclear halogen and benzene is a typical long-range weak interaction similar to a hydrogen bond. Independent gradient model analysis suggests that the van der Waals is the main interaction between the complexes of heteronuclear halogen and benzene. Symmetry-adapted perturbation theory analysis suggests that the electrostatic interaction is the dominant part in the complexes of C₆H₆⋯ClF, C₆H₆⋯ICl, C₆H₆⋯BrF and C₆H₆⋯IF, and the dispersion interaction is the main part in the complexes of C₆H₆⋯BrCl, C₆H₆⋯IBr.     

Differential-pulse polarographic determination of chromium and nickel in zircaloys using microsamples

Three methods were developed for the analysis of the alloying elements chromium and nickel in Zircaloy-2 and Zircaloy-4, alloys of zirconium used extensively in the nuclear industry as nuclear fuel sheathing. Zircaloy was dissolved in hydrofluoric acid followed by oxidation of Cr(III) to Cr(VI) by perchloric acid. The polarographic peak of CrO ₄ ^2– in alkaline medium was used to determine Cr. Nickel was determined, after HF dissolution, using the polarographic peak of the nickel-ammonia complex, Ni (NH₃) ₆ ²⁺ . In an alternative method for Ni, the sample was dissolved in HF and the polarographic peak of the nickel-fluoride complex, NiF ₄ ^2– , was used. Careful control of fluoride ion concentration and the pH eliminated the harmful effect of fluoride on the capillary behaviour of the dropping mercury electrode. The detection limits for chromium, nickel-ammonia and nickel-fluoride in Zircaloys were 0.0016, 0.0033, and 0.0041%, respectively.     

The Prominent Enhancing Effect of the Cation–π Interaction on the Halogen–Hydride Halogen Bond in M1⋅⋅⋅C6H5X⋅⋅⋅HM2

We designed M¹???C₆H₅X???HM² (M¹=Li⁺, Na⁺; X=Cl, Br; M²=Li, Na, BeH, MgH) complexes to enhance halogen–hydride halogen bonding with a cation–π interaction. The interaction strength has been estimated mainly in terms of the binding distance and the interaction energy. The results show that halogen–hydride halogen bonding is strengthened greatly by a cation–π interaction. The interaction energy in the triads is two to six times as much as that in the dyads. The largest interaction energy is ?8.31 kcal mol^?1 for the halogen bond in the Li⁺???C₆H₅Br???HNa complex. The nature of the cation, the halogen donor, and the metal hydride influence the nature of the halogen bond. The enhancement effect of Li⁺ on the halogen bond is larger than that of Na⁺. The halogen bond in the Cl donor has a greater enhancement than that in the Br one. The metal hydride imposes its effect in the order HBeH<HMgH<HNa<HLi for the Cl complex and HBeH<HMgH<HLi<HNa for the Br complex. The large cooperative energy indicates that there is a strong interplay between the halogen–hydride halogen bonding and the cation–π interaction. Natural bond orbital and energy decomposition analyses indicate that the electrostatic interaction plays a dominate role in enhancing halogen bonding by a cation–π interaction.     

Experimental Quantification of Halogen⋅⋅⋅Arene van der Waals Contacts

Crystallographic and computational studies suggest the occurrence of favourable interactions between polarizable arenes and halogen atoms. However, the systematic experimental quantification of halogen⋅⋅⋅arene interactions in solution has been hindered by the large variance in the steric demands of the halogens. Here we have synthesized molecular balances to quantify halogen⋅⋅⋅arene contacts in 17 solvents and solvent mixtures using ¹H NMR spectroscopy. Calculations indicate that favourable halogen⋅⋅⋅arene interactions arise from London dispersion in the gas phase. In contrast, comparison of our experimental measurements with partitioned SAPT0 energies indicate that dispersion is sufficiently attenuated by the solvent that the halogen⋅⋅⋅arene interaction trend was instead aligned with increasing exchange repulsion as the halogen increased in size (ΔG_X⋅⋅⋅_Ph=0 to +1.5 kJ mol⁻¹). Halogen⋅⋅⋅arene contacts were slightly less disfavoured in solvents with higher solvophobicities and lower polarizabilities, but strikingly, were always less favoured than CH₃⋅⋅⋅arene contacts (ΔG_Me⋅⋅⋅_Ph=0 to −1.4 kJ mol⁻¹).     

Phosphorus and Halogen Co‐Doped Graphene Materials and their Electrochemistry

Doping of graphene materials with heteroatoms is important as it can change their electronic and electrochemical properties. Here, graphene is co‐doped with n‐type dopants such as phosphorus and halogen (Cl, Br, I). Phosphorus and halogen are introduced through the treatment of graphene oxide with PX₃ gas (PCl₃, PBr₃, and PI₃). Graphene oxides are prepared through chlorate and permanganate routes. Detailed chemical and structural characterization demonstrates that the graphene sheets are covered homogeneously by phosphorus and halogen atoms. It is found that the amount of phosphorus and halogen introduced depends on the graphene oxide preparation method. The electrocatalytic effect of the resulting co‐doped materials is demonstrated for industrially relevant electrochemical reactions such as the hydrogen evolution and oxygen reduction reactions.     

Synthesis and properties of polyamides derived from systematically halogenated terephthalic acids with fluorine,chlorine, or bromine atoms

Aromatic polyamides were prepared from systematically halogenated terephthalic acids with hexamethylene diamine, piperazine, 4,4′-diaminodiphenylether and p-phenylene diamine by interfacial or low temperature solution polycondensation. The halogenated terephthalic acids used have mono-, di-, or tetra-substituted fluorine, chlorine, or bromine atoms on the benzene ring. The nonhalogenated terephthalic acid was also used for the comparison. The effects of halogen substitution on the benzene ring on the synthesis and some properties of polymers were examined. Reduced specific viscosity decreased in the order F > Cl > Br by halogen substitution. The incorporation of halogen substituents on the ring led to a decrease of crystallinity and fluoro-substituents hindered the crystallization more strongly. The melting point (T_m) decreased in the order F > Cl > Br by mono-substitution, and Br > Cl > F by di-and tetra-substitution. The change of T_m caused by the difference of the number of halogen substituents differed depending on the rigidity of polymer chains. The flame-retardancy estimated by thermogravimetry, self-ignition, and flash-ignition test increased with increasing halogen content of the polymers. Solubility increased remarkably by halogen substitution. The peak temperature of tan δ decreased by halogen substitution. Some discussion was made on these effects of halogen substitution.     

Superhalogens as Building Blocks of Halogen‐Free Electrolytes in Lithium‐Ion Batteries

Most electrolytes currently used in Li‐ion batteries contain halogens, which are toxic. In the search for halogen‐free electrolytes, we studied the electronic structure of the current electrolytes using first‐principles theory. The results showed that all current electrolytes are based on superhalogens, i.e., the vertical electron detachment energies of the moieties that make up the negative ions are larger than those of any halogen atom. Realizing that several superhalogens exist that do not contain a single halogen atom, we studied their potential as effective electrolytes by calculating not only the energy needed to remove a Li⁺ ion but also their affinity towards H₂O. Several halogen‐free electrolytes are identified among which Li(CB₁₁H₁₂) is shown to have the greatest potential.