The use of ozone as the primary digestion reagent for the cold vapor mercury procedure

Ozone was tested as an alternative digestion/oxidation system to the permanganate/peroxidisulfate currently used in the cold vapor mercury method. The results indicate that the digestion of comparable size samples to the 'Standard Method' was complete in less than 2 min. A 0.5 ml (10 ppb) sample size was completely oxidized in less than 30 s. The batch system used produced a limit of detection (LOD) for mercury(II) chloride, methylmercury chloride, and phenylmercury acetate of about 0.5 ppb.     

The use of XeF2 for preparation of azepins

Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1841–1842, October, 1994.     

Studies on potassium chlorate as a primary oxidimetric reagent

Conditions have been established for the use of potassium chlorate as a primary oxidizing agent in the direct titration of vanadium(III), tin(II) and titanium(III) with visual or potentiometric end-points.     

Understanding the process of microwave-assisted digestion combining diluted nitric acid and oxygen as auxiliary reagent

Sample preparation has a long history when thinking about the conversion of solid samples to representative solutions using concentrated acid solutions and high temperature. However, chemical sciences are evolving to cleaner procedures and surely, sample preparation must follow these steps. The advent of microwave-assisted digestion led to new devices that have allowed the development of new procedures based on diluted solutions of nitric acid and more recently the use of oxygen as a reagent. No doubts oxygen has played a major role in most dry and wet digestion procedures for digestion of organic samples, but its role was improved by using it to regenerate nitric acid and consequently decreasing the volumes of acids needed to promote efficient digestions. These aspects were clearly demonstrated by comparing the efficiency of whole milk powder digestions under different pressures of oxygen, atmospheric air or inert argon atmosphere. The pressure profiles in these conditions were also evaluated and indicate the regeneration process. The efficiency of the digestion process using oxygen was demonstrated by measuring residual carbon contents and residual acidity in digests and it was shown that both parameters were fully compatible with requirements of modern instrumental analysis without any further extensive dilution of the digestates.     

2-Mercapto-benzimidazole as an analytical reagent

Summary Palladium is quantitatively precipitated at aPH 5.0 to 10.1 by 2-mercapto-benzimidazole and the complex, Pd(C₇H₅N₂S)₂, which is found to be diamagnetic, is stable up to a temperature of 447 C. In presence of EDTA and tartrate or citrate and at aPH between 6 and 8, it is separated from alkalis, alkaline earths, Mg, Fe³⁺, Cr, Th, Zr, Ti, UO₂ ²⁺, Be, Ce³⁺, Ce⁴⁺, rare earths, Zn, Mn, Ni, Co, Pb, Bi, As, Sb³⁺, Sn⁴⁺, Tl⁺, Cu²⁺, Cd, Ir⁴⁺, Rh³⁺, Ru³⁺, Os⁴⁺, CrO₄ ^2–, MoO₄ ^2–, WO₄ ^2–, VO₃ ^–, PO₄ ^3– and AsO₄ ^3–. Pb, Ag and Hg²⁺ are kept in solution by potassium iodide while a small amount of Au³⁺ by thiosulphate. The palladium complex is either weighed after drying at 110 C or dissolved in a cyanide solution and determined volumetrically by back titrating the excess cyanide with a standard silver nitrate solution.     

2-Mercapto-benzothiazole as an analytical reagent

Summary The reagent 2-mercapto-benzothiazole quantitatively precipitates palladium at a PH 5.6 to 10.2. The red coloured compound, Pd(C₇H₄NS₂)₂, is diamagnetic and is stable up to a temperature of 388 C. Palladium is separated from alkalis, alkaline earths, Mg, Fe³⁺, Cr, Th, Zr, Ti, UO₂ ²⁺, Be, rare earths, Ce³⁺, Ce⁴⁺, Zn, Mn, Co, Ni, Pb, Bi, Sb³⁺, As³⁺, Sn⁴⁺, Tl+, Cu²⁺, Cd, Ir⁴⁺, Rh³⁺, Ru³⁺, Os⁴⁺, CrO₄ ^2–, MoO₄ ^2–, WO₄ ^2–, VO₃ ^–, PO₄ ^3– and AsO₄ ^3– at apH 6–8 in presence of EDTA and tartaric or citric acid. Besides Pb, Ag and Hg²⁺ are kept in solution with potassium iodide and Au in a limited quantity forms a soluble complex with thiosulphate. The palladium complex is either weighed after drying and determined gravimetrically or dissolved in an excess of cyanide and determined volumetrically by back titrating the latter with silver nitrate.     

Studies on the reactivity of methyl γ-tosylcrotonoate as ambident reagent in organic synthesis

The treatment of methyl(E)-4-tosyl-2-butenoate (4) with two equiv. of sodium hydride and different mono and dihalides gives mainly γ,γ- and ,- or ,γ- and ,-dialkylated products (5–7) depending on the electrophile. The corresponding monoanion dimerizes with iodine to afford stereoselectively dimethyl cis-4,5-ditosyl-2,6-cyclohexadiene-1,2-dicarboxylate (11). The tosyl group in compounds 6 and 7 is reduced and in the case of γ,γ-dimethylated 5a substituted by sodium dimethyl malonate under Pd(PPh₃)₄ catalysis. Michael addition of different nucleophiles provides the corresponding β-substituted methyl γ-tosylbutanoates 16.     

Fluorine bridging in the xenon fluoride cations and their salts: The base strengths of XeF2, XeF4 and XeF6

It is a feature of the structures of all the salts of XeF⁺, XeF₃⁺ and XeF₅⁺ that have been studied, that the cation forms one or more fluorine bridges to the anion. The length, direction and number of the fluorine bridges in these salts throw new light on the relative fluoride ion donor abilities of the xenon fluorides XeF₂, XeF₄ and XeF₆. In constrast to what has previously been supposed, it is concluded that the order of fluoride ion donor ability is XeF₂ < XeF₄ < XeF₆.     

Improvement of microwave-assisted digestion of milk powder with diluted nitric acid using oxygen as auxiliary reagent

The feasibility of using diluted HNO₃ solutions under oxygen pressure for decomposition of whole and non-fat milk powders and whey powder samples has been evaluated. Digestion efficiency was evaluated by determining the carbon content in solution (digests) and the determination of Ca, Cd, Cu, Fe, K, Mg, Mn, Mo, Na, Pb and Zn was performed by inductively coupled plasma optical emission spectrometry and Hg by chemical vapor generation coupled to inductively coupled plasma mass spectrometry. Samples (up to 500 mg) were digested using HNO₃ solutions (1 to 14 mol L^− 1) and the effect of oxygen pressure was evaluated between 2.5 and 20 bar. It was possible to perform the digestion of 500 mg of milk powder using 2 mol L^− 1 HNO₃ with oxygen pressure ranging from 7.5 to 20 bar with resultant carbon content in digests lower than 1700 mg L^− 1. Using optimized conditions, less than 0.86 mL of concentrated nitric acid (14 mol L^− 1) was enough to digest 500 mg of sample. The accuracy was evaluated by determination of metal concentrations in certified reference materials, which presented an agreement better than 95% (Student's t test, P < 0.05) for all the analytes.     

Some observations on the use of 1,4-dihydroxyanthraquinone as a fluorometric reagent for traces of lithium

A new fluorometric method for the determination of lithium based on the formation of a fluorescent species with 1,4-dihydroxyanthraquinone (Quinizarine), in acetone-water (90-10%) medium and 10⁻³M in NaOH is described. The fluorescent species has two excitation maxima at 560 and 596 nm and one emission maxima at 620 nm. It is stable at least 7 hr and the calibration graph is linear over the range 50–700 ppb Li. The method has a relative error over the average of measurements of 1.62%.     

XeF2 as a ligand in a coordination compound with the BF4- anion

The first tetrafluoroborate compound with XeF2 coordinated to a metal center, [Cd(XeF2)](BF4)2, has been synthesized. It crystallizes in monoclinic space group P21/a with a = 8.785(11) A, b = 9.079(2) A, c = 10.718(6) A, beta = 110.824(6), and Z = 4. Its crystal structure and that of Cd(BF4)2 have been solved. The latter crystallizes in orthorhombic space group Pbca. Both syntheses were performed in aHF as solvent, at room temperature, yielding colorless solids. The Raman spectra of the solids are in harmony with the crystallographic findings. [Cd(XeF2)](BF4)2 has been shown to be in equilibrium with XeF2 and Cd(BF4)2 in aHF.     

2'-hydroxychalcone as an analytical reagent for beryllium

Several o-hydroxychalcones were examined to develop specific reagents for the precipitation of beryllium in the presence of elements such as aluminium and iron, which occur in its ores. All these reagents showed specificity only in the presence of EDTA. Among them, the readily obtainable 2'-hydroxychalcone is proposed as a new specific reagent for beryllium. The chalcone complex can be dried to constant weight at 105-110 degrees and the conversion factor is 0.01978. A probable structure for the complex has been suggested. Quantitative separation of beryllium from aluminium and iron carried out by this method gave good results. This method was applied for the gravimetric determination of beryllium in beryl and the results were in good agreement with those obtained by the oxide and pyrophosphate methods.     

On the preparation of fluorine-18 labelled XeF(2) and chemical exchange between fluoride ion and XeF(2)

A recent report claims to have prepared [18F]XeF2 by exchange between a large stoichiometric excess of XeF2 and no-carrier-added 18F-, as salts of the [2,2,2-crypt-M+] (M = K or Cs) cations, in CH2Cl2 or CHCl3 solvents at room temperature. Attempts to repeat this work have proven unsuccessful and have led to a critical reinvestigation of chemical exchange between fluoride ion, in the form of anhydrous [N(CH3)4][F] and [2,2,2-crypt-K][F], and XeF2 in dry CH2Cl2 and CH3CN solvents. It was shown, by use of 19F and 1H NMR spectroscopies, that [2,2,2-crypt-K][F] rapidly reacts with CH3CN solvent to form HF2-, and with CH2Cl2 solvent to form HF2-, CH2ClF, and CH2F2 at room temperature. Moreover, XeF2 rapidly oxidizes 2,2,2-crypt in CH2Cl2 solvent at room temperature to form HF and HF2-. Thus, the exchange between XeF2 and no-carrier-added 18F- reported in the prior work arises from exchange between XeF2 and HF/HF2-, and does not involve fluoride ion. However, naked fluoride ion has been shown to undergo exchange with XeF2 under rigorously anhydrous and HF-free conditions. A two-dimensional 19F-19F EXSY NMR study demonstrated that [N(CH3)4][F] exchanges with XeF2 in CH3CN solvent, but exchange of HF2- with either XeF2 or F- is not detectable under these conditions. The exchange between XeF2 and F- is postulated to proceed by the formation of XeF3- as the exchange intermediate.