Natural radionuclide-free phosphoric acid production

High-uranium phosphate rock from Itataia, Brazil, was milled for wet-process phosphoric acid production using the dihydrate method. Uranium contained in the phosphoric acid was recovered by solvent extraction. The distribution of long-lived natural radionuclides of the ²³⁸U and ²³²Th decay series involved in these operations was evaluated. ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb were found to predominate in the phosphogypsum, while ²²⁸Th, ²³⁰Th and ²³²Th in the uranium-free phosphoric acid. Thorium is removed from the phosphoric acid by solvent extraction to produce a NORM-free phosphoric acid.     

Characterization of Lippia sidoides oil extract-b-cyclodextrin complexes using combined thermoanalytical techniques

Thermoanalytical techniques, being rapid and un-expensive have been used for the investigation of the cyclodextrin inclusion complexes for three decades. The conventional thermoanalytical techniques (TG and DTA/DSC) follow the thermal properties of the uncomplexed compounds. Consequently, the inclusion complex formation as well as the liberation of the entrapped guest cannot be followed. Monitoring the products of the thermal fragmentation of parent cyclodextrin and the included molecule(s), applying TG-MS combined technique provides evidence concerning the inclusion complex formation, and besides, gives selective signal to follow the decomposition of the cyclodextrin inclusion complexes. b-cyclodextrin inclusion complexes of Thymol and Lippia sidoides Cham essential oil extract have been prepared and investigated using conventional and combined (TG-MS) thermoanalytical techniques. The evolved gas analysis proved the inclusion complex formation between the host and guests. By the evaluation of the experimental results the elaboration of the entrapped guests from the cyclodextrin cavity could be followed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Facile Preparation of (±)-12-Epiprostaglandins from 7-Oxabicyclo[2.2.1]hept-5-en-2-one via an all-cis-formyllactone related to Corey lactone

The bicyclic monoselenoacetal 7 , easily obtained from (±)-7-oxabicyclo[2.2.1]hept-5-en-2-one ( 6 ) via a radical addition-acyl migration sequence, was converted to racemic 12-epiprostaglandins 3 and 4 . The key intermediate was the all-cis-formyllactone 2b related to Corey lactone (see 12 ; Scheme 1). The presence of a (tert-butyl)-dimethylsilyl protective group for the 11-OH substituent (prostaglandin numbering) was found to be crucial in avoidingβ -elimination and epimerization during the Wittig-Horner reaction (Scheme 2). Epimerization at C(12) at the formyllactone stage (see 2b ) was also possible and gave the known precursor 1b of naturally occurring prostaglandins and analogs.     

Countercurrent chromatographic isolation of lolitrem B from endophyte-infected ryegrass (Lolium perenne L.) seed

This paper describes a new method of purification of the Lolitrem B, a tremorgenic mycotoxin produced in planta by the endophytic fungus Neotyphodium lolii. The method is based on the large-scale isolation of the toxin by countercurrent chromatography (CCC). The lolitrem B content in endophyted ryegrass seed, 11 microg/g or 11 ppm, is extracted by stirring finely ground seeds with ethanol for 3 h at room temperature. The concentrated crude extract contains about 0.6 mg/g or 600 ppm of lolitrem B. It is then submitted to CCC purification with a biphasic four-solvent liquid system. A 160-fold enrichment was obtained in one step producing a raffinate containing 10% or 100 mg/g of the toxin. Further purifications were then performed by thin layer and low pressure liquid chromatography. Twenty-eight micrograms of lolitrem B with a 96% purity grade were obtained from 8 kg of seeds (yield 32%).     

Formation et réactivité de carbanions α phosphoramides. Mise en évidence d'une nouvelle réaction d'élimination

The reactivity of (diethoxy)-N-methyl-N-benzyl phosphoramide (I) and bis(dinethylamino)-N-methyl-N-benzylphosphoramide (II) when treated with strong bases (RLi, R₂NLi) is very different: (I) gives a novel elimination, whereas (II) under the same experimental conditions gives a stable carbanion whose reactivity has been investigated.     

General access to iminosugar C-glycoside building blocks by means of cross-metathesis: a gateway to glycoconjugate mimetics

[reaction: see text] Cross-metathesis reactions of alpha-1-C-allyl-1-deoxynojirimycin derivatives 7a,b and various functionalized alkenes mediated by Grubbs's catalyst 3 are reported. The reactions showed reasonable to very good yields and excellent E/Z selectivity. This methodology allows the efficient and convergent synthesis of iminosugar C-glycosides with a great degree of structural diversity in the aglycone, opening the way to a variety of new glycoconjugate mimetics of biological interest.     

Probing electrochemical properties of pi-conjugated thienylenevinylenes/fullerene C(60) adducts by ESI/MS: evidence for dimerized cation-radicals

Oligothienylenevinylenes/C(60) dyads n-C and triads n-C(2) are studied by electrospray mass spectrometry. A clear correlation is observed between the nature of the charged species detected by mass spectrometry, i.e. protonated molecule [M + H], (+) cation radical M(+.) and dication M(++), and the oxidation potentials of the molecules. Moreover, under defined solubility conditions, mass spectrometry provides conclusive evidences for the reversible dimerization of cation-radicals of n-C(2) compounds.     

Thermogravimetric and differential scanning calorimetric investigations of manganese–glycine interactions

Thermogravimetric (t.g.) and differential scanning calorimetric (d.s.c.) data have been used to study metal–amino acid interactions in adducts of general formula MnCl₂ · ngly (gly = glycine, n = 0.7, 2.0, 4.0 and 5.0). All the prepared adducts exhibit only a one step mass loss associated with the release of glycine molecules, except for the 0.7gly adduct, which exhibits two glycine mass loss steps. From d.s.c. data, the enthalpy values associated with the glycine mass loss can be calculated: MnCl₂ · 0.7gly = 409 and 399 kJ mol^–1, MnCl₂ · 2.0gly = 216 kJ mol^–1, MnCl₂ · 4.0gly = 326 kJ mol^–1 and MnCl₂ · 5.0gly = 423 kJ mol^–1, respectively. The enthalpy associated with the ligand loss, plotted as function of the number of ligands for the n = 2.0, 4.0 and 5.0 adducts, gave a linear correlation, fitting the equation: H (ligand loss)/kJ mol^–1 = 67 × (number of ligands, n) + 76. A similar result was achieved when the enthalpy associated with the ligand loss was plotted as a function of the _a(COO^–) bands associated with the coordination through the carboxylate group, 1571, 1575 and 1577 cm^–1, respectively, for the n = 2.0, 4.0 and 5.0 adducts, giving the equation H (ligand loss) /kJ mol^–1 = 33.5 × _a(COO^–) /cm^–1 – 52418.5. This simple equation provides evidence for the enthalpy associated with the ligand loss being very closely related to the electronic density associated with the metal–amino acid bonds.     

All electron calculations of open-shell polyatomic molecules. III. Perturbation treatment of the spin polarization in vinyl and methyl radicals

A first order perturbation treatment starting with SCF-MO 'S in canonical or equivalent quasi-localized form is presented for the hyperfine coupling constants of vinyl and methyl radicals. The spin-polarisation contribution to hyperfine splittings is found to be large, negative for the proton of the radical center in both radicals and positive for the β protons of vinyl.     

Mechanisms and kinetics of polymerization of thermoplastic polyimides. II. Study of “bridged” dianhydride/aromatic amine systems

The aim of the present work was to identify and follow the main and side reactions involved in the ring dehydration of amic acid prepared from “bridged” dianhydrides whose central substituent is an electron acceptor or donor, and an aromatic diamine. Several isomeric structures may appear as a result of the opening reactivity and selectivity of anhydride groups towards the aromatic amine. Reaction mechanisms and kinetics were thus studied in solvent phase with HPLC and ¹³C-NMR and in solid molten phase by FTIR and solid ¹³C-NMR. The experimental conditions (liquid and solid) and the structure of the products (type of central substituent) affecting the mechanisms and kinetics of the reactions were noted. © 1993 John Wiley & Sons, Inc.