Pressurometric titrations with xenon trioxide as oxidant

The reaction of XeO(3) with thirteen reducing agents was studied qualitatively. From these, Fe(II) and Ti(III) were chosen for direct titration with XeO(3) with pressurometric end-point detection. The precision was a few parts per thousand. Evidence was found for the production of oxygen during both titrations, and of hydrogen peroxide formation during the Ti(III) reaction. The Ti(III)/Xe reacting ratio was independent of the amount of Ti(III) from 35.5 to 87.7 micromole and was 5.93 +/- 0.03 instead of the expected 6.00. The ratio for the Fe(II) reaction varied from 5.85 to 5.95 over the Fe(II) range from 10.05 to 78.7 micromole. The stoichiometric ratio for the iodometric standardization of XeO(3) solutions was confirmed as 6.00.     

Determination of hydrogen peroxide by xenon trioxide oxidation

Aqueous xenon trioxide solution has been used as the oxidizing agent in three precise methods of analysis for hydrogen peroxide. A catalytic method, which utilizes hydrogen peroxide to initiate the reaction between t-butanol and xenon trioxide, is described for determining amounts of hydrogen peroxide as low as 0.9 microg or 36 parts per milliard (ppM). A direct spectrophotometric titration was found to have a lower limit of about 50 microg, or 20 ppM. An indirect titrimetric method was also used to determine hydrogen peroxide in amounts as low as 50 microg with a relative standard deviation of 4% which decreased to 1 % for amounts over 200 microg.     

Titrimetric determination of some organic acids by xenon trioxide oxidation

Aqueous xenon trioxide in acidic or neutral solutions oxidises carboxylic acids quantitatively to carbon dioxide and water. Micro and semimicro amounts of carboxylic acids may be determined by the iodometric titration of the excess of xenon trioxide remaining in the reaction mixture. The optimum time and temperature for the reaction depend on the structure of the acid ; dicarboxylic and hydroxy-carboxylic acids react faster than corresponding monocarboxylic acids. Oxalic and polyhydroxy acids are oxidised within 20 min at room temperature while acetic, maleic, succinic, malonic acids require 2 hr at 40 degrees . Carboxylic acids in amounts less than 100 mug are determined with a coefficient of variation of 4%, which decreases to 1 % for amounts over 250 mug.     

Kinetic studies of xenon trioxide as an oxidant-I Determination of alcohols

A kinetic study of the oxidation of some alcohols by xenon trioxide has revealed the optimum conditions for analysis of these alcohols. The rate of reaction may be increased by adding a catalyst or by increasing the pH of the solution; it may be decreased by adding an inhibitor. The initiation time of the reaction is used to determine t-butanol in amounts as low as 22 mug or 880 parts per milliard (ppM). Primary and secondary alcohols which catalyse the reaction between t-butanol and xenon trioxide may be determined in amounts as low as 2.3 mug or 92 ppM. Tertiary butanol in amounts less than 40mug is determined with a coefficient of variation of 4% while methanol, ethanol and isopropanol are determined with a coefficient of variation of 10% at the level of 25mug or more. The precision in determination of t-butanol increases with increasing concentration, while for isopropanol, ethanol and methanol it decreases.     

Explosion hazards with xenon trioxide solutions ("xenic acid/rd)

Attention is drawn to the explosion hazards associated with xenic acid (xenon trioxide solution) and hence all xenon compounds that can yield xenon trioxide by hydrolysis.     

Plutonium-244 fission xenon and primordial xenon in the Allende meteorite

The carbonaceous chondrite Allende contains (22±1)·10⁻¹² cm³STP/g of²⁴⁴Pu fission xenon and two kinds of primordial xenon: Type I and Type II. The former represents the isotopic composition of a primordial xenon, which resided in the vicinity of a supernova shortly before it exploded, while the latter represents that of the xenon, which resided in the supernova. The isotopic composition of xenon found in the pink inclusion of the Allende meteorite, corrected for the presence of very large excesses of²⁴⁴Pu fission xenon,¹²⁹Xe from the decay of¹²⁹I, and of¹²⁸Xe from the neutron-capture reactions on¹²⁷I, resembles that of Type-I primordial xenon. The isotopic composition of xenon found in the diamond inclusions of the Allende meteorite, on the other hand, represents that of Type-II primordial xenon and it resembles that of a mixture of Type-I primordial xenon whose isotopic composition is severely altered by a combined effect of (a) mass-fractionation, (b) spallation, (c) stellar-temperature neutron-capture reactions, and (d) the presence of a large excess of²⁴⁴Pu fission xenon.     

VUV spectra of the xenon fluorides

The absorption spectra of gaseous XeF₂, XeF₄, and XeF₆ have been accurately measured in the photon energy range from 6 to 35 eV with the use of the synchrotron radiation of DESY. The vibrational structure of several Rydberg transitions could be resolved. The spectra are interpreted and most of the structures could be assigned. From these data, information about the ionized species is obtained. The assignment of the first two IP's of XeF₄ is corrected.     

Autoacceleration of the free-radical chain luminescent oxidation of U(IV) with xenon trioxide in aqueous HClO<Subscript>4</Subscript>

Autoacceleration is observed in the chemiluminescent radical chain oxidation of U(IV) with xenon trioxide in aqueous perchloric acid in a Teflon (not conventional glass) reactor. The decay of chemiluminescence accompanying the reaction between U(IV) and XeO₃ in the case of excess oxidizer obeys a first-order kinetic equation only at low U(IV) concentrations of 10^?5–10^?6 mol/l. Autoacceleration takes place at comparatively high reactant concentrations, when the contribution from the heterogeneous loss of radicals on the reactor walls into chain termination is comparatively small and the role of degenerate chain branching reactions is significant. It is inferred that a critical phenomenon rare for liquid-phase radical chain processes takes place in U(IV) oxidation with xenon trioxide: a comparative small increase in the reactant concentrations causes this chemiluminescent redox process to pass from the quasi-steady-state regime to autoacceleration.     

Band fluorescence of xenon

The Xe₂ emission band at 168 nm has been observed during irradiation of xenon gas with the 147 nm resonance line. The band is attributed to Xe₂ molecules formed by reaction between ground-state and metastable (2_u) xenon atoms.     

On the behaviour of solutions of xenon in liquid cycloalkanes: Solubility of xenon in cyclopentane

The solubility of xenon in liquid cyclopentane has been studied experimentally and theoretically. Measurements of the solubility of xenon in liquid cyclopentane are reported as a function of temperature from 254.60 K to 313.66 K. The imprecision of the experimental data is less than 0.3%. The thermodynamic functions of solvation of xenon in cyclopentane, such as the standard Gibbs energy, enthalpy, entropy and heat capacity of solvation, have been calculated from the temperature dependence of Henry's law coefficients. The results provide further information about the differences between the xenon + cycloalkanes and the xenon + n-alkane interactions. In particular, interaction enthalpies between xenon and CH₂ groups in n-alkanes and cycloalkanes have been estimated and compared. Using a version of the soft-SAFT approach developed to model cyclic molecules, we were able to reproduce the experimental solubility for xenon in cyclopentane using simple Lorentz-Berthelot rules to describe the unlike interaction.     

Liquid mixtures of xenon with fluorinated species: xenon + sulfur hexafluoride

The vapor-liquid equilibrium of binary mixtures of xenon + SF6 has been measured at nine temperatures from 235.34 to 295.79 K and pressures up to 6.5 MPa. The mixture critical line is found to be continuous between the critical points of the pure components, and hence, the system can be classified as type I phase behavior in the scheme of van Konynenburg and Scott. The excess Gibbs free energies have been calculated, and the experimental results have been interpreted using the statistical associating fluid theory for potentials of variable range (SAFT-VR). Additionally, the SAFT-VR equation has been used to model other systems involving SF6 and alkanes, illustrating the predictability of the approach and further demonstrating the transferability of parameters between binary mixtures involving alkanes and xenon.     

Fluorination with xenon difluoride. Reaction with halogenated hydrocarbons

Filler and coworkers [1-5] have demonstrated the utility of xenon difluoride as a selective fluorinating agent for aromatic hydrocarbons in the liquid phase, while Mackenzie and coworker [6] have fluorinated aromatic compounds in the vapour phase. We have developed a fluorination reaction of phenyl substituted olefins resulting in high yields of vicinal difluorides [7,8] and trifluoroacetates, depending on the catalyst. In our continued interest in the use of xenon difluoride as a mild fluorinating agent for fluorination of organic compounds, we have tries to fluorinate some heterocyclic ring systems, e.g. imidazo-(1,2-b)-pyridazine, under conditions similar of those used for fluorination of phenyl substituted olefins [7,8,9] (room temperature, methylene chloride as solvent, hydrogen fluoride as catalyst). It is well known that heteroaromatic compounds are less reactive toward electrophilic substitution reactions then aromatic hydrocarbon systems. However, it has been shown that bromination of imidazo-(1,2-b) -pyridazine results in 3-bromo products [10], while in chlorination with phosphorus pentachloride [11], the entering order of chlorine atoms is at position 3 > 2, 7 > 8 > 6 (Radical reactions).     

Xenon 5d emission in pure xenon and xenon doped argon

The radiative of Xe 5d ($\text{3}\text{2}$)₁ states in photoexcited Xe and Xe doped Ar is investigated. The Xe 5d fluorescence contains new information about the deactivation of highly excited states of Xe and about the energy transfer from Ar to Xe.