Type Of Halogen Research Articles

Electrical relaxation of superionic conducting glasses AgX-AgPO3 (X=I, Br, Cl)

The complex impedance of superionic conducting glasses (AgX)0.3-(AgPO3)0.7 (X = I, Br, Cl) was measured in the frequency range 5 Hz–500 kHz and temperatures between 299 K and 348 K. The frequency dependence of Σ′ (the real part of complex conductivity) shows two regions: low and high frequencies. The first is attributed to the electrode-electrolyte polarization, while the second is attributed to the bulk conduction. The replacement of AgCl by AgBr or Agl at the same molar fraction is found to improve the bulk conductivity of the studied glasses. The electrical conductivity spectra exhibit one relaxation peak associated with dielectric loss which arises from the thermally activated jumps of Ag+ ions. The dependence of the relaxation time upon the halogen type is discussed in terms of the structural aspects, where the silver halides tend to form microdomains. The special characteristic of fast ionic conduction depending upon halide type is emphasized.

Silicone Surfactants for Pentane Blown Rigid Foam

Auxiliary blowing agents are utilized in most polyurethane applications. However, the impact of these blowing agents on final foam properties is most critical in the rigid foam area. In most rigid applications the blowing agent serves a dual role in both generating the foam volume, and, in addition, the residual gas remaining within the cells functions to reduce the rate of heat transfer and improve the insulation properties of the foam. Traditionally CFCs have been used as the preferred blowing agent within the polyurethane industry due to their excellent volatility, low flammability, and thermal characteristics. Within the last few years the use of many grades of CFCs have come under restriction due to their implication in depleting atmospheric ozone levels, and these products will ultimately be banned according to the Montreal Protocol. Other types of halogen containing replacements such as HCFCs and HFAs are being examined as potential replacements for the CFCs. However, the future viability of these types of materials is in question, as their toxicological, environmental and economic impact are still under examination. One of the most viable alternatives to replace CFCs as a blowing agent in rigid foam formulations is n-pentane or one of the isomers of pentane. These materials are considered to be excellent replacement candidates due to their availability, low pricing, and most importantly, zero ozone depleting potential(ODP). The use of pentane in rigid continuous laminate boardstock foam has already been initiated, with commercial utilization anticipated in other rigid applications within the next 12 to 18 months. Pentane is the most non polar of the auxiliary blowing agents used in polyurethane foam applications. As a result of the chemical and physical characteristics of pentane, the solubility and compatibility with the polyurethane raw materials and developing foam mixture are completely different compared to all other blowing technologies. This low solubility of pentane in the final polyurethane foam matrix results in very low diffusion rates of pentane. Therefore, initially obtained thermal insulation values are maintained with minimal drift. Due to the inflammable nature of pentane, new processing and handling procedures are required in addition to modifications to the foam formulations. Considering the potential flammability and explosion hazards, minimizing pentane emissions during production is an absolute requirement to safely utilize this new technology. The current and proposed environmental legislations on organic emissions is another reason to ensure minimal levels of VOCs when using pentane as a blowing agent in the production of rigid foams. One of the primary applications for panels produced by the continuous lamination process is in the construction industry, where the flammability rating is one of the most important properties of these materials. The use of an inflammable liquid as a blowing agent, where most of the residual material is retained within the foam cells, requires further formulation modifications to maintain the flame retardancy characteristic of the foams. System modifications, such as incorporating flame retardant additives and water as a co-blowing agent, further increases the polarity of the resultant polyol preblend. The increased polarity of this preblend accompanied by the very low polarity of the pentane puts further limitations on the total system solubility. To improve the solubilization/compatibilization of pentane into these systems, new surfactant technology is required. The primary role of a silicone surfactant in a rigid polyurethane system is to emulsify the incompatible reactants of the preblend and phases that occur during the reaction. In order to achieve similar processing performance and final foam physical properties with these modified formulations containing pentane, new specially designed silicone surfactant molecules are required. In order to investigate the silicone surfactant structure/foam performance relationship, a design study was initiated in a variety of formulations. In addition to the standard performance evaluations, special techniques were developed and effected to understand the solubility, emulsification and compatibility characteristics of pentane during the production and aging of the foam. This paper will discuss the influence of different silicone surfactants on the emulsification and stabilization of pentane in polyol premixes, reaction mixtures and during foam formation. The influence of the silicone surfactants on the physical properties of the final foam will also be discussed.

Beam‐induced dehalogenation in LSIMS: Effect of halogen type and matrix chemistry

AbstractThe LSIMS beam‐induced dehalogenation of several 4‐halo‐phenylalanine methyl esters (I, Br, Cl, F) was investigated and compared to that of atrazine using 12 different matrix compounds including diethyl phthalate for which the empirical electron affinity was known. The extent of dehalogenation, induced by a one‐electron reduction process, is in agreement with the leaving group ability of the corresponding halogens (I >Br >Cl >F) and the dehalogenation inhibiting efficiency of the matrices. The latter is rationalized in terms of electron scavenging capacity and matrix structural features relating to that capacity. The extent of dehalogenation observed for 4‐I‐phenylalanine methyl ester is similar to that of atrazine, a chlorinated compound, which indicates that the halogen effect is not overwhelming in determining the extent of dehalogenation. The bracketing of matrix reduction potential was attempted based on the propensity of the matrices to induce M+· formation from analytes of known oxidation potentials. The ability of matrices to induce M+· formation parallels their dehalogenation and reduction inhibiting efficiencies. The last observation underlines the importance of matrix redox properties in effecting or inhibiting beam‐induced processes, be they reductive or oxidative.

A Raman investigation of lead haloborate glasses

Glasses of the (65−x)PbO⋅xPbX2⋅35B2O3 system (where X=F, Cl, Br, and I) have been made and investigated by Raman measurements. Three low frequency bands with high Raman intensities have been observed at about 40, 105, and 135 cm−1, respectively. It is found that the intensities of the depolarized low frequency Raman contour peaked at 40 cm−1 are exceptionally high and strongly dependent on the halogen type and content. We attribute this nonsymmetric low-frequency Raman contour to the collective modes of the BO3–PbO4 bridged local structures and propose a model to interpret the experimental data. Our results suggest that the liberation of these local structures is related to the lead as well as the halogen. Cl, Br, and I enter the glass as nonbridging anions and weaken the cohesion of the glass network in the increased order of Cl, Br, and I.

Thermooxidative decomposition and combustion of halogen?Tin-containing synthetic fibres

The possibility of decreasing the combustibility of PCA and PETP fibres by treatment with acetone solutions of PVC containing tin oxides or salts was investigated. It was found that the PVC—ZnSn(OH)6 system is the most efficient fire-retardant system for PETP. The oxygen index of PETP after treatment with this system was 27.1%. It was shown that in contrast to other types of halogen—metal-containing fire retardants whose effect is basically manifested in the gas phase, the synergistic system containing PVC and tin-containing compounds changes the direction of the reactions in the condensed phase of combustion. The capacity of the polymer (PCA, PETP) for carbonization increases in the presence of PVC and tin-containing compounds as a result of the formation of thermostable structures characterized by a high concentration of halogen, and the temperature of the onset of oxidation decreases.

Oxidation of halogenated propanes with Methylosinus trichosporium (OB3b)

Halogenated propanes (1-chloropropane, 1-bromopropane, 2-chloropropane, and 2-bromopropane) were oxidized with Methylosinus trichosporium (OB3b). 1-Propanol, 1-halogenated-2-propanol, and 1-halogenated-3-propanol were produced from 1-halogenated propane, and 2-halogenated-1-propanol and acetone were produced from 2-halogenated propane, showing that all the carbon atoms of the halogenated propanes were attacked by activated oxygen. The optical purity of halohydrin obtained from halogenated propane with M. trichosporium was independent of halogen type.

Cerebral monitoring during carotid surgery

Carotid artery surgery is undertaken either after resolution of a transient ischaemic attack or to prevent a stroke in an asymptomatic patient. In both cases the patient's neurological status is normal at the time of surgery which obviously cannot improve patients but can make them worse. To reduce the risk of operative morbidity, several cerebral protection techniques have been devised, but none of these is 100% efficient and monitoring is needed to detect any deleterious effects of clamping. We sent a questionnaire 1 to 119 French vascular surgeons asking them to identify the technique they routinely used for internal carotid surgery (ICA). Of these, 19.3% never used a shunt and 2.5% used one routinely. The vast majority (78.2%), however, shunted selectively depending on the results of cerebral monitoring which is used to determine when shunting is necessary and if it is effective. The adequacy of the cerebral circulation can be monitored either by haemodynamic measurement of cerebral blood flow or by recording brain activity which is directly related to cerebral blood flow. Haemodynamic monitoring of cerebral blood flow can be achieved by measuring carotid stump pressure (CSP), evoked cortical potential or the electroencephalogram (EEG). CSP is a controversial method, the accepted threshold for shunting ranging from 25 mmHg 2 to 70 mmHg 3 with 50 mmHg as the most widely used value. It should be pointed out that baseline CSP is always established just before clamping the artery and that a decrease in blood pressure during the operation can lead to a decrease in CSP, sometimes to dangerously low levels. To be reliable the threshold must be correlated with the profile of serial pulse recordings. If the profile is flat, brain protection cannot be assumed to be adequate even if CSP is above the threshold. Despite these problems CSP remains the most popular monitoring technique. Transcranial Doppler (TCD) is a more recent technique, monitoring velocity in the middle cerebral artery (MCA) and other branches of the circle of Willis. 4 In our preoperative tests this method demonstrated a positive correlation between the efficiency of the circle of Willis and CSP in 98% of cases. We also used TCD peroperatively to check MCA velocities during carotid artery clamping. They varied from a normal value of 40 cm to a lower threshold of 2025 cm. Usually after surgery or clamping of the artery velocities rose to as high as 45 cm. s Cerebral autoregulation sometimes offsets reduced blood flow and a spontaneous increase in MCA velocity was observed during clamping, which was due to regional vasoactive reactions. While TCD represents an improvement in peroperative monitoring, 6 it is not infallible. Measurement of cerebral blood flow (CBF) using Xe 1337 requires complex facilities but can be used to compare flow in the cerebral hemispheres and checks residual flow on the clamped side. At 25 ml/100 g/min a slowdown in the EEG is observed and at 15ml/ 100 g/min it becomes flat. These values are affected by the type of halogen used for anaesthesia (range 1230 ml/100 g/min). Morawetz 8 concluded that CBF and EEG were less informative than clinical neurological status. A reliable gauge of the effectiveness of the arterial circulation may be obtained in several ways. Conventional EEG monitoring which was used in the early days of carotid artery surgery has now been replaced by computer assisted EEG. Localised disturbances may occur such as diminished alpha and beta waves with the appearance of delta waves. These changes can result from brain ischaemia and also from excessive anaesthesia. Sundt 9 never observed a patient awakening with new EEG changes that were not already detected during anaesthesia. He reported signs of cerebral ischaemia with a normal

Electronic structure and models of receptor of monooxygenase inductors from a number of polychlorinated polycyclic compounds. 3. Mndo calculations of chlorine and fluorine derivatives of dibenzo-p-dioxins

MNDO calculations for dibenzo-para-dioxin (DD) and its chlorine- and fluorine-substituted derivatives have shown that the geometric structure of the molecules and the Π-donor properties are very little dependent on the type of halogen (chlorine or fluorine) or on the position of the halogen in the molecule. The chlorine and fluorine derivatives of the DD do exhibit substantial differences in the charges on the C atoms directly connected to the halogens. The higher atomic charges on the C atoms connected to F atoms suggests that the fluorine-containing DDs will be capable of metabolism to mercapturic acids.

Irreversible inhibition of rat hepatic glutathione S-transferase isoenzymes by a series of structurally related quinones

The effect of several structurally related 1,4-benzoquinones (BQ) and 1,4-naphthoquinones (NQ) on the activity of rat hepatic glutathione S-transferases (GST) was studied. For the 1,4-benzoquinones, the extent of inhibition increased with an increasing number of halogen substituents. Neither the type of halogen nor the position of chlorine-atoms was of major importance. Similarly, 2,3-dichloro-NQ demonstrated a considerably higher inhibitory activity than 5-hydroxy-NQ. 2-Methyl derivatives of NQ did not inhibit GST activity at all. The irreversible nature of the inhibition was shown both by the time-course of the inhibition as well as by the fact that removal of the inhibitor by ultrafiltration did not restore the enzymatic activity. Incubation of quinones and enzyme in the presence of the competitive inhibitor S-hexylglutathione, slowed the inhibition considerably, indicating an involvement of the active site. Isoenzyme 3-3 was found to be most sensitive towards the whole series of inhibitors, whereas the activity of isoenzyme 2-2 was least affected in all cases. The inhibition by quinones is probably mainly due to covalent modification of a specific cysteine residue in or near the active site. The differential sensitivities of individual isoenzymes indicates that this residue is more accessible and/or easier modified in isoenzyme 3-3 than in any of the other isoenzymes tested. The findings suggest that quinones form a class of compounds from which a selective in vivo inhibitor of the GST might be developed.

Halogenations of Aromatic Compounds with Halide Anions in the Presence of Nitrobenzenesulfonyl Peroxides. A Novel Method for the Formation of Positive Halogens

Abstract A novel type of positive halogens, sulfonyl hypochlorite or sulfonyl hypobromite was formed in the reactions of halide anions with nitrobenzenesulfonyl peroxides; these hypohalites could be used as effective reagents for halogenation of aromatic rings.

The direct mutagenic activity of α,ω-dihalogenoalkanes in Salmonella typhimurium: Strong correlation between chemical properties and mutagenic activity

A series of 18 α,ω-dihalogenoalkanes ( h(CH 2)n h with n = 1−6 and h = Cl, Br, I ) was tested for direct mutagenic activity in Salmonella strains TA1530, TA1535 and TA100 using spot-test procedures. The results indicate that the mutagenic behaviour of these compounds is strongly dependent upon the carbon chain length as well as the type of halogen involved. This behaviour correlates with the leaving group ability and the degree of neighbouring group participation in nucleophilic displacement reactions of the different halogen atoms.

ChemInform Abstract: NUCLEAR MAGNETIC RESONANCE STUDIES OF PYRAMIDAL INVERSION IN COMPLEXES OF TRICARBONYLRHENIUM(I) HALIDES WITH ALIPHATIC AND AROMATIC MIXED THIO‐SELENO ETHERS

AbstractDie Titelkomplexe (Ia)‐(Ic) wurden aus ReX(CO)3(THF) oder [ReX(CO)4]2 und einem Überschuß des Liganden unter Rückfluß in CHCl3 in 2‐12 h dargestellt (keine Ausb.‐Angaben) und 1H‐NMR‐spektroskopisch bei variablen Temp. untersucht.

Electron density and bond polarization effects in reactions of energetic carbon-11 leading to acetylene

Evidence is presented indicating that reactions of energetic carbon-11 are effected by the presence and type of halogen in gas-phase methyl halides. Correlations of acetylene-/sup 11/C yields with /sup 1/H and /sup 19/F NMR chemical shifts of the substrates indicate that electron density and bond polarization factors influence the mechanism(s) leading to hot products such as (/sup 11/)C/sub 2/H/sub 2/. (/sup 11/)C/sub 2/H/sub 2/ was formed primarily by an intramolecular mechanism in methyl chloride.

Thermal properties of halogen-containing organic antipyrenes for polymers

Thermal properties were studied of many compounds inhibiting the combustion of polymers-compounds with chloro- and bromo-substituted aromatic and cycloaliphatic fragments in the molecule. The ability of antipyrenes to undergo distillation and decomposition with the liberation of gaseous halogen-containing products during isothermal and dynamic heating in argon was determined both in the free state and in radation-modified binary and ternary (with addition of Sb 2O 3) mixtures with PE. It was found that the type of halogen and the chemical structure of antipyrene have a marked effect on the temperature range, type and rate of liberation of halogen in the form of hydrogen halide and antimony trihalide, which basically determines the fire-resistance of polymer materials containing these antipyrenes.

Nuclear magnetic resonance studies of pyramidal inversion in complexes of tricarbonylrhenium(I) halides with aliphatic and aromatic mixed thio–seleno ethers

Mixed-chalcogen ligand complexes of type fac-[ReX(CO)3(MeSZSeMe)](X = Cl, Br, or l; Z= CH2CH2 or o-C6H4) have been prepared and their temperature-dependent 1H n.m.r. spectra studied. Pyramidal S and/or Se inversions were observed in all cases and quantitatively assessed for the complex fac-[ReBr(CO)3{o-MeS(C6H4)SeMe}] and the dithio-analogues fac-[ReX(CO)3{o-MeS(C6H4)SMe}](X = Cl, Br, or l). The effects of π conjugation and halogen type on the barrier energies are discussed.

The participation effect of halogen atoms in stereospecific Friedel–Crafts alkylations

The Friedel–Crafts alkylation of benzene with optically active 1,2-, 1,3-, 1,4-, and 1,5-dihalogenoalkanes gave the corresponding primary phenylalkyl halides with a stereospecificity which depended primarily on the type of terminal halogen or the variation in carbon chain length.

Picosecond fluorescence studies of xanthene dyes

Subnanosecond lifetime measurements using picosecond pulses from a mode locked Nd3+/glass laser together with conventional absorption and fluorescence yield methods have been used to study the photophysics of fluorescein and three of its halogenated derivatives (eosin, erythrosin, and rose bengal) in aqueous and simple alcoholic solvents. For each of the dye molecules absorption and fluorescence maxima move towards higher energy (blue shift) as the solvent changes from i-PrOH to HlO. Fluorescence lifetimes and quantum yields are found to decrease markedly with this solvent change and also with in- creased halogenation (heavy-atom effect) of the fluorescein parent. Published triplet yield data confirm that the variations observed in the nonradiative part of the decay rate can be attributed almost wholly to variations in the rate of SI-TI intersys- tem crossing. A simple and reasonable explanation of the observed effects can be found if for these particular solvent-solute combinations stabilization energies lie in the order AE(TI) < AE(S1) < AE(S0). This idea is consistent with both the increased SI-S0 spectral blue shifts and the enhanced intersystem crossing rate, arising from a smaller SI-TI energy gap, when these dye molecules are placed in a more aqueous solvent environment. The studies are relevant to the use of these dyes as fluorescent probes in biologically important molecules. I. Introduction The fluorescence properties of the xanthene dyes have both theoretical and practical interest. The advent of the dye laser' has sparked off renewed interest in the correlation between molecular structure and fluorescence properties, while the use of fluorescent dye probes in structural studies of molecules of biological significance has become an area of considerable a~tivity.~,~ The usefulness of a fluorescent probe relies on variations in the dye's fluorescent properties with alterations in its environment, solvent polarity being an example. Despite a considerable amount of work, no detailed theory explaining the often very dramatic effects of environment and structure on fluorescence has emerged. For example, the effect of solvent and macromolecular environment on the fluorescence lifetime and quantum yield of perhaps the most widely used fluorescent probe, ANS- ( 1 -anilinonaphthalene-8-sulfonate), not well understood although various mechanisms for the fluorescence quenching in polar solvents have been pr~posed.~-~ Until a better understanding of the environmental factors affecting the fluorescence of dye molecules has been achieved, detailed conclusions based on fluorescent probe studies must be treated with caution. Fluorescein and its halogenated derivatives provide an ex- cellent model series for studies of this kind, for not only do the degree and type of halogenation greatly alter the fluorescence yield, but the photophysical properties of these dyes are also very dependent on the nature of the solvent. We have studied absorption and emission spectra, fluorescence lifetimes, and fluorescence yields of eosin, erythrosin, and rose bengal (Figure 1 j in a series of alcohols and in aqueous solution. The data provide a clear picture of the changes in nonradiative decay rate that occur in these molecules as a result of changes in the solvent environment. 11. Experimental Section (a) Chemicals. Eosin (BDH) was purified by recrystallization from acidic solution and rose bengal (BDH) was purified by chromatog- raphy on an alumina-talc column. The erythrosin sample (BDH) was used as supplied. Spectroscopic grade (Merck) methanol, ethanol, 2-propano1, and triply distilled water were used as solvents. All the aqueous solutions were buffered to pH 9.2. Dye concentrations of

Copolymerization of Isobutene and Isoprene at “High” Temperature with Syncatalyst Systems Based on Aluminum Organic Compounds

Abstract New catalyst systems based on alkylaluminum derivatives and halogen or interhalogen compounds were found highly efficient in the synthesis of high-molecular-weight IIR at temperatures above − 50°C. The reaction mechanism was studied in detail for the system Et2AlCl + Cl2. The reactions occurring between chlorine, isobutene, Et2AlCl, and the solvent (CH3Cl) were elucidated and studied under various experimental conditions (e.g. presence or absence of light, simultaneous presence of the copolymerization system components, temperature, type of halogen, use of model compound of isobutene). It was concluded that halogenium ions, i.e. Cl+, Br+, or I+, are the initiating species. Kinetic and conductometric investigations showed that scarcely dissociated ion pairs, e.g. Cl+[Et2AlCl2]−, were formed in the absence of monomer; but in the presence of isobutene, a noticeable increase of the electrical conductivity and rapid polymerization occurred. The maximum polymerization rate was first order with respect to the concentrations of monomer, Cl2, and Et2AlCl. In the homopolymerization of isobutene, transfer to monomer and termination reactions were negligible. The MW of IIR was found to be mainly dependent on the concentrations of the catalyst components, on isoprene concentration, and on temperature. The reactivity ratio of isobutene with isoprene was found to be r1=2.5±0.5 at −35°C, while the activation energies relative to MW were −5.8 ± 0.4, kcal/mol for polyisobutene, and −5.7 ± 0.7 and − 4.3 ± 0.5 kcal/mol for IIR containing, respectively, 1.3 and 1.9 mol% of isoprene. The evaluation of some physicochemical and technological properties of typical IIR produced with the system Et2AlCl + Cl2, indicated that isoprene is randomly distributed along the chains and that the MWD is monomodal, while the glass transition temperature, tensile properties, mechanical-dynamic spectra, and kinetics of vulcanization are very similar to those of commercial IIR. Very preliminary data, referring to several classes of new catalyst systems yielding IIR having good properties, were also obtained. The syncatalyst systems here described can work in a homogeneous phase consisting of an aliphatic hydrocarbon besides methyl chloride, still giving IIR with high MW. Therefore, a completely homogeneous process can be envisioned for the synthesis of IIR at −50°C thus avoiding a great part of the fouling problems of the slurry process. The economic advantage of using “high” temperatures of polymerization is briefly discussed in terms of energy savings.

Thermogravimetry and differential scanning calorimetry of some poly-p-xylylenes containing halogen atoms

Poly-p-xylylene and three halogen-containing poly-p-xylylenes prepared by the Gorham method from purified dimers were characterized by thermogravimetry and differential scanning calorimetry to determine their relative thermal stabilities in nitrogen and air. As judged by these techniques, thermal stability in nitrogen is not greatly changed by halogenation of the cyclic dimer from which polymer is made. However, thermal oxidative stability depends on the type and degree of halogenation. Aliphatic fluorine atoms greatly improved upon the thermal oxidative stability of poly-p-xylylene. To a lesser but significant degree, two aromatic chlorine atoms, poly(dichloro-p-xylylene), also improved upon the thermal oxidative stability of poly-p-xylylene or poly-(chloro-p-xylylene). Oxidative degradation caused a rapid exothermic weight loss near 300°C for poly(dichloro-p-xylylene) and near 250°C for poly-p-xylylene and poly(chloro-p-xylylene) when films were heated at 10°C/min. Poly(dichloro-p-xylylene) maintained a constant weight during an induction period before it started to lose weight when it was heated isothermally at temperatures below 300°C. However, poly-p-xylylene and poly(chloro-p-xylylene) gained weight during oxidation before they lost weight when heated isothermally below 250°C.

The occurrence of the H 3+ ion in the mass spectra of organic compounds

The H 3 + ion is shown to be a normal component of low yield in the fragmentation pattern of organic compounds (except C 2H 2). The pattern of H 3 + is tabulated for the 780 eV mass spectrum of each of 33 compounds of various types. Specific studies of the energetics of formation of H 3 + from CH 4, C 2H 6 and CH 3Cl, and of D 3 + from CD 4 were conducted. The H 3 + ion is shown to be derived from two sources, a low initial kinetic energy component which arises from fragmentation of the singly charged molecular ion and a high initial kinetic energy component whose appearance potential and kinetic energy release are consistent with fragmentation of the doubly charged molecular ion. Systematic variations of H 3 + pattern factors with carbon number are shown for the n-alkanes and 1-alkenes and with halogen type for the series of methyl halides.