Use Of HClO4 Research Articles

Accessing simply-substituted 4-hydroxytetrahydroisoquinolines via Pomeranz–Fritsch–Bobbitt reaction with non-activated and moderately-activated systems

Background: 1,2,3,4-Tetrahydroisoquinolines (THIQs) are common motifs in alkaloids and in medicinal chemistry. Synthetic access to THIQs via the Pomeranz–Fritsch–Bobbit (PFB) methodology using mineral acids for deactivated, electron-poor aromatic systems, is scarcely represented in the literature. Here, the factors controlling the regiochemical outcome of cyclization are evaluated.Results: A double reductive alkylation was telescoped into a one-pot reaction delivering good to excellent yields of desired aminoacetals for cyclization. Cyclization of activated systems proceeded smoothly under standard PFB conditions, but for non-activated systems the use of HClO4 alone was effective. When cyclization was possible in both para- and ortho-positions to the substituent, 7-substituted derivatives were formed with significant amounts of 5-substituted byproduct. The formation of the 4-hydroxy-THIQs vs the 4-methoxy-THIQ products could be controlled through modification of the reaction concentration. In addition, while a highly-activated system exclusively cyclized to the indole, this seems generally highly disfavored. When competition between 6- and 7-ring formation was investigated in non-activated systems, 5,7,8,13-tetrahydro-6,13-methanodibenzo[c,f]azonine was exclusively obtained. Furthermore, selective ring closure in the para-position could be achieved under standard PFB conditions, while a double ring closure could be obtained utilizing HClO4.Conclusion: Reactivity differences in aminoacetal precursors can be employed to control cyclization using the PFB methodology. It is now possible to select confidently the right conditions for the synthesis of N-aryl-4-hydroxy-1,2,3,4-tetrahydroisoquinolines.

On the sequential separation and quantification of 237Np, 241Am, thorium, plutonium, and uranium isotopes in environmental and urine samples

The implementation of the one-pass-through separation technique using two stacked chromatography columns of TEVA – TRU resins for the separation of 237Np, 241Am, thorium, plutonium and uranium from environmental and urine samples was investigated. The sequential separation technique proved to be successful and gave similar results to those obtained when using individual separations. The analysis time was considerably improved. The amount of chemical waste was also reduced by 50% and the use of HClO4 was avoided. The technique of ICP-MS was also investigated as a complementary technique to alpha-spectrometry.

Characterization of Geological Certified Reference Materials by Inductively Coupled Plasma-Mass Spectrometry

A rapid, safe, and efficient microwave-assisted acid digestion method is reported to determine thirty-six elements in three international geological reference materials and two in-house reference materials using high resolution inductively coupled plasma mass spectrometry. This method was also employed to determine the radiogenic isotopic composition of Sr and Nd in two geological reference materials by multicollector inductively coupled plasma mass spectrometry. In order to ascertain the most suitable preparation method, four microwave-assisted digestion procedures were compared. The presence of insoluble fluorides on the recoveries of Ba, Rb, Sr and rare earth elements was resolved through sequential evaporation at 80 degrees Celsius followed by microwave digestion. Digestion methods without using HClO4 or H3BO3 and using only H3BO3 were unsuitable due to lower recoveries and higher procedural blanks, respectively. Digestion methods that involved the use of HCl-HNO3-HF and HCl-HNO3-HF-HClO4 were most suitable, resulting in better recoveries of the elements. However, the HCl-HNO3-HF method was preferred compared to HCl-HNO3-HF-HClO4 because the former avoids the use of HClO4 and thus was used in measurements of the radiogenic isotopes of Sr and Nd. The optimized method was used to verify the reference values for the isotopic compositions of Sr and Nd in geological standard reference materials.

Enhancement of electron transfer kinetics on a polyaniline-modified electrode in the presence of anionic dopants

The electrocatalytic redox behavior of 1,4-naphthoquinone (NQ) has been studied on a polyaniline-modified platinum electrode (PANI) using cyclic voltammetry and rotating disc electrode (RDE) as diagnostic techniques. The modified electrode was prepared by electropolymerization of aniline in different acidic solutions. The PANI showed electrocatalytic activity toward the redox behavior of NQ. This process includes the participation of PANI to the redox reaction of NQ via the surface catalysis phenomena. The cyclic voltammograms of NQ in HCl on the PANI-Cl-modified electrode showed an overlapped oxidation peak, the peak potential of which did not change with increasing scan rate. The influence of other anions including \( ClO^{ - }_{4} \) and \( SO^{{2 - }}_{4} \) as dopant was also studied and compared with Cl−. The use of HClO4 as a supporting electrolyte resulted in well-separated redox peaks. The RDE voltammogram was used to obtain a quantitative assessment of reaction rate at the PANI-modified electrode. It was found that PANI acts as an electrocatalyst for NQ reduction with decreasing ΔEp and increasing k°.

A Method for Determination of Selenium in Organic Tissues Using Microwave Digestion and Liquid Chromatography

An existing laboratory procedure for selenium analysis using open-vessel wet digestion and liquid chromatographic fluorescence determination was modified for use with microwave digestion. The proposed microwave digestion method eliminated the hazards associated with the use of HClO4 while maintaining excellent recoveries of selenium. A 2-step HNO3/H2O2 digestion procedure was developed. Digested samples were derivatized with 2,3-diaminonaphthalene, and the resultant piazselenol complex was measured fluorometrically using a liquid chromatograph. Measured values were in agreement with 9 different certified reference materials. The detection limit for this method was 0.54 ng Se/g tissue (3 sigma), and the calibration curve remained linear (r2 = 0.9968) up to 2 microg Se/g.

Classical wet ashing versus microwave-assisted attacks for the determination of chromium in plants

Microwave-assisted pre-treatments for the determination of Cr in plants are compared with classical wet-ashing procedures using open attacks in sand-baths. Four certified plant reference materials were analysed: pine needles (NIST SRM 1575), rye grass (BCR CRM 281), beech leaves (BCR CRM 100) and an aquatic plant (Trapa natans) (BCR CRM 596). The use of acidic procedures with HClO4 or H2SO4 yielded different Cr results for these materials when classical wet-ashing procedures were used, as the use of HClO4 caused losses of volatile chromium compounds. The shorter time of analysis required (60 min) in open-focused microwave-assisted attack allows the use of HClO4 for obtaining results very close to the certified values for CRM plant materials. This type of microwave digestion also led to good reproducibility values with relative standard deviations between 5 and 10%.

Characterisation of a cationic triniobium aqua ion cluster and related studies

A green air-sensitive niobium cation has been characterised in acidic aqueous solutions following Dowex cation-exchange column chromatography of hydrolysed solutions of [NbCl3(dme)](dme = 1,2-dimethoxyethane) in aqueous HCl. Redox titrations and oxygen-17 NMR studies on the green ion suggest the presence of the incomplete cuboidal structure [Nb3(µ3-Cl)(µ-O)3(OH2)9]4+(NbIII,IV,IV). Air-free solutions in HCl, CF3SO3H and p-MeC6H4SO3H are stable for weeks frozen at –18 °C but the use of HClO4 results in fairly rapid oxidation to colourless NbV. Water-exchange kinetic studies (use of 17O NMR) have identified two distinct types of water ligand consistent with the incomplete cuboidal triangular structure. Those water ligands trans to the capping (Cl) atom (one per Nb)(k298= 8.3 × 10–3 s–1) are significantly more inert than those trans to the bridging oxo groups (two per Nb)(k298= 352 s–1). The reaction products obtained by treatment of the green ion with aqueous methanolic NCS–, [NbIII,IV,IV3(µ3-S)(µ-O)3(NCS)9]6–(S2– deriving from NCS–), and with aqueous ethanolic hydridotris(pyrazol-1-yl)borate, HB(pz)3–, [Nb3(µ3-BO4){µ-(O,OH)}3{HB(pz)3}3][the BO45– ligand deriving from the hydrolysis of HB(pz)3–], suggest the ready formation of a range of triangular Nb3 cluster cores with different complexing ligands.

Electrochemical studies of polyaniline and its application

The weight change of polyaniline (PAn) positive electrode in LiClO 4/propylene carbonate (PC) electrolyte during charge/discharge process was observed in situ by an electrogravimetric technique. The weight of PAn in the electrolyte increased linearly upon charge and decreased linearly upon discharge. The result suggests that the charge/discharge reaction of PAn in the non-aqueous electrolyte proceeds with doping/undoping of anion species. The anion species is supposed to be ClO4- anion solvated with 3–4 propylene carbonate molecules. The solubility of the doped anion to the solvent affects the rechargeability of PAn. Therefore, the use of HClO4 or HBF4 aqueous electrolyte is preferable for the synthesis of PAn. PAn in the non-aqueous medium is very stable even in the higher oxidized state and shows the highest discharge capacity (150 Ah/kg) of the other conducting polymers.

Digestion of plant tissue for analysis by ICP emission spectroscopy

Abstract A method of digesting plant tissue samples for multi‐element analysis by inductively‐coupled plasma (ICP) emission spectroscopy was developed which does not require the use of HclO4. A substitute oxidant, H2O2, eliminated the hazards associated with hot, concentrated HClO4. Optimal conditions for pre‐digestion and digestion were investigated. The procedure adopted consists of a pre‐digestion in concentrated HNO3 from room temperature to 60°C in 30 min followed by digestion at 90°C for 90 min with the addition of 30% H2O2 Analysis of NBS standard tissue samples by the proposed method gave results in good agreement with analysis following digestion in HNO3,‐HClO4 and with certified values, except for Fe.

Variations of activity coefficients in concentrated electrolyte solutions at constant lonic strength

Measurements of different types on various (trace) electrolytes in HClO4−Na(Li)ClO4 solutions at several (constant) values of the ionic strength have been used to determine the variation of their activity coefficients with changing amount of perchloric acid in the solution. These variations (with respect to the hydrogen ion) differ considerably among different cations and anions. The results for the alkali metal ions and the anions are interpreted in the light of the recent work of Pitzer on short-range ionic interactions. The results for the cations with outerd-electrons and the alkaline earth metal ions are interpreted in terms of ion-solvent interactions. It is concluded that the use of HClO4−NaClO4 solutions of high ionic strength (rather than the use of HClO4−LiClO4 solutions) is advisable in studies where the variation in activity coefficients must be accounted for. Finally, it is shown that the usual interpretation of the influence of the salt medium in studies of complex equilibria and reaction kinetics is sometimes questionable.

The use of HClO4 in the determination of reductant soluble iron phosphate in soil

An improved method for the determination of reductant soluble iron-phosphate in the Chang and Jackson's inorganic phosphate fractionation procedure is described.