Neutron activation analysis of high-purity selenium : Determination of phosphorus,sulfur and chlorine

Chlorine was determined in selenium by irradiation of 2-g samples for 37 min at a flux of 8·10¹⁰ n/cm²/sec. Chlorine was volatilised from hot concentrated nitric acid and precipitated as silver chloride. The isotope ³⁸Cl (T_{$\text{1}\text{2}$}=37.3 min) was counted by γ-spectrometry. Sulfur and phosphorus were determined by irradiating 50-mg samples with and without cadmium shielding for 4 days at a thermal flux of 6·10¹² n/cm²/sec and a fast flux of 4·10¹¹ n/cm²/sec. The matrix activities were separated by distillation from sulfuric acid-hydrobromic acid at 200–220°. The isotope ³²P (T_{$\text{1}\text{2}$}=14.3 d) was then precipitated, together with phosphate carrier, as ammonium phosphomolybdate, and counted with a G.M. tube. Amounts of 0.4–1 p.p.m. chlorine, 65–520 p.p.b. phosphorus and 1.5–4.6 p.p.m. sulfur were found in high-purity selenium samples.     

The hydrolysis of dibromofluoromethyltriphenylphosphonium bromide

Hydrolysis of [Ph₃$\text{P}\text{+}$PCFBr₂]Br^? afforded a high yield of dibromofluoromethane and triphenylphosphine oxide. Hydrolysis in the presence of a radioactive isotope of bromine gave evidence that the mechanism of this reaction proceeds $\text{via}$ the dibromofluoromethide ion and not $\text{via}$ a bromofluorocarbene intermediate.     

The hydrolysis of bromodifluoromethyltriphenylphosphonium bromide [1]

Hydrolysis of [Ph₃$\text{P}\text{+}$CF₂Br]Br^? afforded a high yield of bromodifluoromethane and triphenylphosphine oxide. Hydrolysis in the presence of a radioactive isotope of bromine or sodium iodide gave unequivocal evidence that the mechanism for this reaction proceeds through a difluorocarbene intermediate.     

Neutron activation analysis of high-purity selenium : Part II. Determination of tellurium

Neutron activation determination of 15–25 p.p.b. of tellurium in selenium can be done by irradiating 100-mg samples for 4 days at a neutron flux of 6$\text{.}\text{?}$10¹² n. cm^-2.sec^-1. The daughter isotope of ¹³¹Te,¹³¹I is separated by distillation and extracted into carbon tetrachloride. Finally the silver iodide precipitate is measured by β,γ -coincidence counting. The standard deviation is 3–7%.     

The determination of molybdenum and tungsten in sea and surface water

A simple method for the determination of molybdenum and tungsten in sea and surface water is presented. Molybdenum and tungsten are concentrated on activated charcoal by adsorption as the ammonium pyrrolidine dithiocarbamate complex; the optimal pH for adsorption is 1.3. Mo and W are then determined by thermal neutron activation, forming ⁹⁹Mo (T_{$\text{1}\text{2}$} = 66.7 h) and ¹³⁷W (T_{$\text{1}\text{2}$} = 23.8 h), respectively. The ^99mTc daughter of ⁹⁹Mo is measured as soon as the equilibrium between ^99mTc(T_{$\text{1}\text{2}$}= 6 h) and ⁹⁹Mo is established. The detection limits are 0.05 μg Mo l^-1 and 0.05 μg W l^-1 (or 0.001 μg W l^-1 after a simple chemical separation).     

Fast neutron activation analysis of bulk coal samples for alumina,silica and ash

The fast neutron activation technique was applied to bulk samples (≈11 kg) of Australian black coal. The determination of alumina is based on the reaction ²⁷Al(n,p)-²⁷Mg by counting the 0.844-MeV peak (t_{$\text{1}\text{2}$} = 9.4 min). Silica is determined by means of the reaction ²⁸Si(n,p)²⁸Al; the 1.78-MeV peak (t_{$\text{1}\text{2}$} = 2.3 min) is counted and a correction for the interference from alumina is applied. The ash content is based on the correlation between ash and the sum of alumina and silica. The accuracies (1 SD) for the determination of alumina, silica and ash were 0.52% Al₂O₃, 0.79% SiO₂ and 1.02% ash, respectively. The ash, alumina and silica contents of the samples were in the ranges 8.8–37.5%, 1.3–10.3% and 6.4–22%, respectively.     

The behaviour of copper and thallium hexafluoromolybdates(V) in acetonitrile

Copper(I), copper(II), and thallium(III) hexafluoromolybdates(V), prepared by the oxidation of the metals in acetonitrile with molybdenum hexafluoride (A. Prescott, D.W.A.Sharp, and J.M. Winfield, $\text{J. Chem. Soc., Dalton Trans.}$, 1975, 963) have been investigated by cyclic voltametry. Half wave potentials, E_{$\text{1}\text{2}$} V vs. Ag^p+/Ag were obtained using a evacuable cell equipped with anexternal Ag^p+/Ag electrode, enabling strict anerobic conditions to be maintained. A number of reversible or quasi-reversible electron transfer processes have been observed, enabling comparison with synthetic work to be made. Results for Cu^I and Cu^II hexafluoromolybdates(V) are in accord with preparative experience. MoF₆. Mo^VI/Mo^VE_{$\text{1}\text{2}$} +1.600V, oxidises Cu metal to Cu^II in MeCN, and Cu^II is reduced by Cu^O to Cu^I , Cu^lI/Cu^IE_{$\text{1}\text{2}$} = +0.750 or +0.710V for Cu^I and Cu^II solutes respectively, Cu^I/Cu^OE$\text{1}\text{2}$ = ?0.720V not reversible. A wave at E_{$\text{1}\text{2}$} = ?0.350V is assigned to Mo^V/Mo^IV by analogy with Ag^I hexafluoromolybdate (D.W.A. Sharp, unpublished work). E_{$\text{1}\text{2}$} data for I₂ in MeCN, I₂/I₃^- = 0.280, I₃^?/I^? = -0.116V, suggest that reduction of MoF₆^? by I is not likely, in contrast to the situation in SO₂ (A.J. Edwards and R.D. Peacock, $\text{Chem. Ind.}$, 1960, 1441). Reduction of MoF₆^? by Cu^o in MeCN should be feasible, but appears to be very slow. Pure Tλ^III hexafluoromolybdate(V) is obtained from Tλ^o and MoF₆ only when the mole ratio MoF₆:Tλ>5:1. Smaller ratios produce yellow solids in which Mo:Tλ is $\text{ca}$. 2:1. Tλ^III is a stronger oxidising agent than Cu^II in MeCN, as oxidation of Cu^I by Tλ^III is rapid and quantitative. However a reversible electron transfer wave assignable to Tλ^III/Tλ^I is not observed in the expected fange +1.600 to +0.710V possibly because of solute-electrode interactions.     

An approach to the enantiocontrolled synthesis of pseudomonic acids via a novel mono—claisen rearrangement

A short, efficient approach to a key chiral intermediate for the synthesis of pseudomonic acids A and C is delineated.Pseudomonic acids A($\text{1a}$), B($\text{1b}$), and C($\text{2}$) are members of a novel of “C-glycopyranoside” antimicrobial agents which have recently attracted synthetic attetion.² Presently, we wish to report a short efficient stratedy towards the total synthesis of opticaly active pseudomonic acids. The sequence is highlighted by a novel controlled mono-Claisen rearrangement and a highly regioselective π-allylpalladium mediated displacement.Diacetyl-(L)-arabinal ($\text{3}$)³ was converted to the bis-ketenesilylacetal $\text{4}$ and warmed to 60°C according to the Ireland ester-enolate Claisen rearrangement method.⁴ Over a period of ≈5h, smooth conversion to a major rearranged product $\text{5}$ was observed by 300 MHz NMR. The identity of $\text{5}$ was confirmed by direct desilylation and methylation (KF, KHCO₃, H₂O, HMPA, CH₃I). After flash chromatography, compound $\text{7}$ was isolated in 55% overall yield from $\text{3}$. Careful inspection of the crude methylation product revealed the presence of ≈5% doubly rearranged product $\text{6}$.The rearrangement of $\text{4}$ to $\text{5}$ is a unique example of a selective mono-Claisen rearrangement in which the rate of a second similar Claisen rearrangement ($\text{5}$ → $\text{6}$) is much slower under the reaction conditions. Although the reasons for this interesting selectivity are unclear at this time,⁵ in practice, the mono-Claisen rearrangement obviates the need for selective differentiation of the two hydroxyl groups, a difficult task at best, in this case.Palladium mediated allylic acetate displacement provided an ideal method for introduction of a second chemodifferentiated side chain with allylic retention and retention of stereochemistry. Alkylation of $\text{7}$ with sodiothylmalonate using 5 mole % Pd(O)dppe₂⁶ was unusually facile (<45 min, 25°C, THF). After semi-preparative HPLC, essentially a single regio- and stereoisomer was isolated in 96% yield.⁷ Structure $\text{8}$ was confirmed by extensive ¹H-NMR decoupling, as well as an off-resonance ¹³C-NMR experiment. In particular, H₁ (δ 4.53) was coupled vicinally to H₆ and H₆′ (5 Hz, 8 Hz) and H₂ (1.5 Hz), and allylically to H₃ (2 Hz). In contrast, H₄ (δ 2.78) was coupled to H₇ (10 Hz), H_5e and H_5a (1.8 Hz, 4 Hz), H₃ (5 Hz), and H₂ (<1 Hz). In addition, H₁ and H₄ exhibited a small long range coupling constant (J = <1 Hz). The coupling constants rule out

regioisomer $\text{9}$ and are fully consistent with the indicated conformation, which minimizes 1,3-diaxial-like interactions.Finally, catalytic osmylation of $\text{8}{}^8$ gave a single cis-diol $\text{10}$ in nearly quantitative yield. Appending of suitably functionalized side chains to provide an enantiocontrolled synthesis of pseudomonic acids A($\text{1a}$) and C($\text{2}$) is in progress.^9,10     

The optical absorption and emission spectra of Cs2NaSmCl6

Optical absorption and emission spectra are reported for single crystals of the cubic elpasolite Cs₂NaSmCl₆. The variable temperature spectra obtained at high resolution are assigned using energies and relative intensities. Transitions from the ground level, ⁶H_{$\text{5}\text{2}$} to cystal fi levels of ⁶H_{$\text{7}\text{2}$-$\text{15}\text{2}$}, ⁶F_{$\text{1}\text{2}$-$\text{11}\text{2}$}, ⁴G_{$\text{5}\text{2}$-$\text{9}\text{2}$}, ⁴F_{$\text{3}\text{2}$,$\text{5}\text{2}$}, ⁴I_{$\text{9}\text{2}$}, and ⁶P_{$\text{3}\text{2}$, $\text{5}\text{2}$} are located and characterized. Intensity calculations are reported for magnetic dipole allowed transitions. The dominance of vibronic intensity in ⁶H_{$\text{5}\text{2}$}→⁶F _{$\text{1}\text{2}$-$\text{9}\text{2}$} and ⁶P_{$\text{3}\text{2}$, $\text{5}\text{2}$} transitions is accounted for qualitatively through the ligand polarization model involving quadrupole metal (Sm³⁺)-ligand (Cl^?) interaction mechanisms. The E_u″(⁶H_{$\text{5}\text{2}$})→E′(⁶H_{$\text{1}\text{2}$}) E_u′(⁶F_{$\text{1}\text{2}$}) no-phonon transition is postulated to be pure electric quadrupole allowed. The ground state magnetic moment is determined to be very small from magnetic circular dichroism (MCD) spectra.This study has led to the assignment of nearly all of the crystal field levels in the visible and IR region for Cs₂NaSmCl₆. A total of 27 such levels were identified, 17 from no-phonon transitions and the rest from vibronic transitions. The magnetic dipole intensity calculated using intermediate coupling O_h wavefunctions along with a crystal field analysis of the splitting pattern was used in the assignment of the levels. Vibronic bands were observed for all transitions and their vibrational symmetries were tentatively assigned. MCD data were used to determine the magnet moment of the ground state.     

Simultaneous determination of chromium and silicon in steel by 14-mev neutron activation analysis

Chromium and silicon are determined simultaneously in steel by 14-MeV neutron activation analysis. The activities of ⁵²V(E_γ=1.43 MeV,T_{$\text{1}\text{2}$}=3.76 min) from ⁵²Cr(n,p)⁵²V and ²⁸Al (E_γ=1.78 MeV; T_{$\text{1}\text{2}$}=2.24 min) from ²⁸Si(n,p)²⁸Al are evaluated by mixed γ-ray spectrometry. The influence of manganese and phosphorus, the main interfering elements, is negligible for most stainless steels. The count rate should be limited, to avoid ⁵²V pulse pile-up effects interfering in the ²⁸Al energy region. Precisions in the 2-10% range are reached, depending on the concentrations, for a 10-min analysis time. Results for a series of steel samples are compared with industrial analyses.     

X-ray study of Hg2Cl2Br2 and HgCl2HgBr2 reactions in solid state

The reactions (I) Hg₂Cl₂(s) + Br₂(g) and (II) HgCl₂(s) + HgBr₂(s) have been investigated by an X-ray method. Both the reactions yield two forms of the mixed halide HgClBr, designated as α-HgClBr and β-HgClBr. The cell parameters of the two are as follows:α-HgClBr: $\text{a = 6.196}\text{A}\text{?}$, $\text{b = 13.12}\text{A}\text{?}$, $\text{c = 4.37}\text{A}\text{?}$, z = 4, ? = 5.91 g/cm³. The powder pattern and cell parameters are similar to that of HgCl₂. Therefore it is probable that the chlorine atoms, in the linear halogenHghalogen molecules of HgCl₂ structure have been replaced by bromines, and since the radius of the bromine atom is larger than that of chlorine, the lattice is larger in this case.β-HgClBr: $\text{a = 6.78}\text{A}\text{?}$, $\text{b = 13.175}\text{A}\text{?}$, $\text{c = 4.17}\text{A}\text{?}$, z = 4, ? = 5.40. These parameters are the same as those reported in the literature for β-Hg(ClBr)₂, and its X-ray powder pattern is similar to HgCl₂. Therefore this phase also has linear halogenHghalogen molecules but the distribution of Cl and Br atoms is perhaps random.Heating the products (I) and (II) up to the melting point increases the amount of α phase and decreases the β phase, whereas crystallization increases the β phase. DTA study has supported the X-ray findings.     

Photodissociation of alkyl bromides

The branching ratios for the production of Br(4²P_{$\text{1}\text{2}$}) following the broadband flash photolysis of the alkyl bromides, CH₃Br and C₂H₅Br, and the perfluorinated molecules, CF₃Br, C₂F₅ Br and n-C₃F₇ Br, have been determined using time-resolved atomic absorption spectroscopy. The production of electronically excited bromine atoms is shown to be inefficient in the case of the alkyl bromides while the perfluorinated molecules yield decreasing amounts of Br(4²P_{$\text{1}\text{2}$}) as the molecular complexity increases, i.e., CF₃Br > C₂F₅Br > C₃F₅Br > C₃F₇. It is also shown that the hydrogenated bromides deactive electronically excited atoms almost two orders of magnitude faster than do the perfluorinated bromides.     

Temperature dependence of collisional deactivation of Tl(62P32)

The rate coefficients for the collisional deactivation of Tl(6²P_{$\text{3}\text{2}$}) by several gases has been determined at 300°K. This data is compared with that previously obtained at higher temperatures and the Arrhenius parameters calculated. Both the overall rate coefficients and temperature effects display trends similar to those observed for 1(5²P_{$\text{1}\text{2}$}) relaxation. The deactivation of Tl(6²P_{$\text{3}\text{2}$}) by O₂ is shown to proceed by a process involving an equilibrium with Tl(6²P_{$\text{1}\text{2}$}) and electronically excited oxygen, probably O₂(¹Δ_g).     

Synthesis and chemistry of HC(SO2F)3 and cis- and trans(HO)2TeF4

HC(SO₂F)₃ has been prepared and characterized. It turned out to be a strong acid, comparable to mineral acids. In aqueous solution the salts of the type Cs⁺C(SO₂F)₃^? are formed. The anion, as found by crystal structure analysis contains planar CS₃ configuration.Quite in contrast to these findings HC(OSO₂F)₃ is not even soluble in water.Derivatives of HC(SO₂F)₃ have been prepared so far CH₃C(SO₂F)₃ FC(SO₂F)₃ ClC(SO₂F)₃ BrC(SO₂F)₃ JC(SO₂F)₃The heavier halogen derivatives ( Cl, Br, J ) are oxidizing agents (‘positive halogen’).A mixture of $\text{cis-}$ and $\text{trans-}$ (HO)₂TeF₄ is obtained if HOTeF₅ and Te(OH)₆ are melted together. The mixture of the isomeres have been transfered into the corresponding silylesters $\text{cis}$- and $\text{trans-}$ (R₃SiO)₂TeF₄, which could be separated by fractional crystallisation and distillation.Without conformational change the pure silylesters have been reacted back to pure $\text{cis}$- (HO)₂TeF₄ and $\text{trans}$- (HO)₂TeF₄ by means of anhydrous HF. Both $\text{cis-}$ and $\text{trans}$ (HO)₂TeF₄ have been reacted with ClF to give $\text{cis}$- and $\text{trans}$- (ClO)₂TeF₄, yellow liquids. The latter react with elemental bromine to the rather unstable $\text{cis-}$ and $\text{trans-}$ (BrO)TeF₄, red liquids.Starting with $\text{cis}$-(HO)₂TeF₄ and XeF₂ a polimer Xenon compound of the formula

All materials have been characterized by melting point and vapour pressure, 19 F - nmv spectroscopy, vibrational spectroscopy, and elemental analysis.     

Fluorescence spectra of laser-excited YO molecules in a H2O2Ar flame

CW dye laser induced fluorescence emission and thermal emission spectra of YO-molecules in a 1 atm H₂O₂Ar flame of 2430 K were recorded simultaneously. Narrow band laser excitation was applied to four rotational lines in the (1, 1) Q-branch of the A²Π_{$\text{3}\text{2}$}→X²Σ⁺ transition and broadband excitation was applied to several separate Q-branches of the A²Π_{$\text{1}\text{2}$,$\text{3}\text{2}$}→X²Σ⁺ transitions. From the differences between the fluorescence emission spectra and thermal emission spectra, we conclude that collisional de-excitation of an excited vibronic level takes place by vibrational relaxation, decay to the electronic ground state and by intermultiplet transfer in order of increasing probability.     

Proton and carbon nuclear magnetic resonance study on some n- and o-acyl derivatives of monohydroxypyridines

Comparative study on the proton and carbon NMR spectra for a series of $\text{N}$- and $\text{O}$-acyl substituted monohydroxypyridines (C₅H₄NO$\text{R}$: $\text{R}$=-H, -CHO, -COCH₃, -COC(CH₃)₃, -COCF₃, -COC₆H₅, -SO₂CH₃, -SO₂C₆H₄CH₃ is reported. p]Characteristic ¹H, ¹³ NMR and IR spectral features allow simple and unambiguous distinction between the isomeric $\text{N}$- and/or $\text{O}$-acyl-derivatives of 2-, 3- and 4-hydroxypyridines, so that both forms can clearly be identified when tautomeric equilibria occur, since the tautomerism rate is slow on the NMR time scale     

Application of hydride generation for the determination of antimony and arsenic in biological material by neutron activation analysis

A rapid and sensitive procedure for the determination of antimony and arsenic in biological material is described. It is based on thermal neutron activation to ¹²²Sb (t_{$\text{1}\text{2}$} = 2.7 d) and ⁷⁶As (t_{$\text{1}\text{2}$} = 26.4 h), dry ashing with magnesium nitrate as the oxidizing agent and volatilization of the hydrides which are collected on an active carbon trap. This carbon adsorber is counted. The limit of determination is 5 ng g^-1 for both elements.     

Kinetic spectroscopy in the far vacuum ultraviolet. Part I: Detection of (2p5) 2P32,12 fluorine atoms using atomic resonance spectrometry in the wavelength range 95–98 nm

A new experimental system for atomic resonance spectrometry at λ < 105 nm in a discharge-flow system is described. The spectrum of a fluorine resonance lamp has been studied, and possible precursors for the 2p⁴ 3s excited F atoms formed are suggested. Ground state (2p⁵²P_{$\text{3}\text{2}$}) and J-excited ²P_{$\text{1}\text{2}$} F atoms have been detected for the first time in resonance absorption and fluorescence using the first resonance transitions with wavelengths between 95.2 and 97.8 nm. Preliminary measurements (using both ⁴P-²P and ²P-²P lines) of the variations with concentration of absorption intensity by ground state F ²P_{$\text{3}\text{2}$} and by J-excited F ²P_{$\text{1}\text{2}$} atoms are reported; F atom concentrations were measured using a titration method based on the rapid reaction, F + Cl₂ → FCl + Cl.     

Curve crossing in two excited states of IBr studied by photofragmentation

Curve crossing in two excited states of IBr was studied by means of photodissociation with a pulse dye laser. The ratios of the formed ground state Br(²P_{$\text{3}\text{2}$} and excited Br(²P_{$\text{1}\text{2}$}) were measured at various wavelengths. They are compared with ratios calculated with the Landau-Zener formula, using parameters given by Child. The agreement between the measurements and the calculations is very good.