Extractive fluorimetric determination of ultratraces of lead with cryptand 2.2.2 and eosin

A new speetrofluorimetric method for determination of ultratraces of lead is based on solvent extraction into chloroform of the ion-pair formed between the positively-charged cryptate of lead with cryptand 2.2.2 and the eosinate anion. The detection limit for lead is 1 ng ml , and the linear working range is from the detection limit to 250 ng ml . The relative standard deviation is 3.7% at the 100 ng ml level. The method is highly selective for the extraction and determination of lead in the presence of other cations, and has been tested for direct determination of lead contamination in soft drinks. Aggregation of the extracted ion-pair in the organic phase has been demonstrated in fundamental extraction studies.     

Ion-pair extraction and fluorimetric determination of ultratraces of strontium with cryptand 2.2.2 and eosin

A highly sensitive and selective fluorimetric determination of strontium is proposed, based on solvent extraction of the ion-pair formed between the cationic complex of Sr²⁺ with cryptand 2.2.2 and eosinate as counter ion. A linear working range from 0.7 ng/ml (limit of detection) to 500 ng/ml of strontium and a relative standard deviation of 3.5% at the 100 ng/ml level are obtained. The metal: ligand: counter ion molecular ratio in the extracted mononuclear ion-pair is 1 1 1. The equilibrium constants involved in the extraction process were calculated.     

Fluorimetric determination of ultratraces of lead by ion-pair extraction with cryptand 2.2.1 and eosin

A spectrofluorimetric study of the extraction of lead into 1,2-dichloroethane, as an ion-pair formed between the cryptand 2.2.1-lead complex and the eosinate counter-ion is described. Optimum conditions for the extraction have been established and a new spectrofluorimetric determination of ultratraces of lead is proposed (detection limit 0.8 ng/ml; relative standard deviation 2.4% at the 60 ng/ml level). The metal:ligand:counter-ion molecular ratio in the extracted mononuclear ion-pair is 1:1:1. The equilibrium constants involved in the extraction have been estimated and refined by the Letagrop-DISTR program.     

Sequential extraction-spectrofluorimetric determination of ultratraces of zinc using cryptand 2.2.1 and eosin

A highly sensitive and selective spectrofluorimetric method has been developed for the determination of ultratraces of zinc, based on solvent extraction with 1,2-dichloroethane of the ion-pair formed between eosinate anion and the positively charged cryptate of zinc with cryptand ethers. The detection limit for zinc is 1.5 ng/ml, and the linear working range up to 200 ng/ml. The relative standard deviation is 1.8% at the 100 ng/ml level. The proposed method has been tested for determination of zinc in coal and fly ash.     

Preconcentration and determination of ultratraces of lead and bismuth

The recovery and preconcentration of Pb(II) and Bi(III) by coupling ion-exchange and precomplexation with 1,2-dihydroxy-3,5-benzenedisulphonic acid and 3,3',4'-trihydroxyfuchsone-2'-sulphonic acid has been investigated. Metal recoveries at 0.1-mg l . concentrations are better than 99% in the presence of cationic, anionic and non-ionic detergents, or an organic sequestering agent such as NTA, and at high ionic strength. Experiments with radiotracers show total recovery even at 15-ng l . concentrations. In the light of the results the procedure is proposed as a simple and rapid analytical method to preconcentrate Pb(II) and Bi(III).     

Extraction-spectrophotometric determination of niobium with dibenzo-18-crown-6 and thiocyanate

A method is described for the direct spectrophotometric determination of micro-amounts of niobium by extraction into a benzene solution of dibenzo-18-crown-6 (L) from 3M hydrochloric acid containing potassium thiocyanate. The molar absorptivity of the extracted complex is 3.85 +/- 0.03 x 10(4) 1.mole(-1).cm(-1) (relative standard deviation 0.8%). Co-ordinatively unsaturated complexes of the type [NbO(SCN)(3)](2)L and NbO(SCN)(3)L are extracted, along with ion-pairs, especially when small amounts of L are used for extraction. The ion-pair complex [NbOCl(2)(SCN)(3)][(LK)(2)] seems to be the main species formed in the organic phase.     

Ion-pair extraction and fluorimetric determination of cadmium with cryptand 2.2.1 and eosin

A method is described for the direct spectrofluorimetric determination of ultratraces of cadmium by extraction into 1,2-dichloroethane of the ion-pair formed between the eosinate anion and the cationic complex of Cd²⁺ with cryptand 2.2.1. The detection limit for cadmium is 0.5 ng/ml, and the linear working range is from the detection limit to 150 ng/ml. The relative standard deviation is 1.5% at the 100 ng/ml level. The equilibrium constant has been estimated and refined by the Letagrop-DISTR program. The proposed method has been tested in the determination of cadmium in high-purity zinc. The results show good agreement with those found by the more common ICP emission photometry and anodic stripping voltammetry methods.     

Reaction of lead halides with 18-crown-6 and dicyclohexano-18-crown-6: Solvent extraction,synthesis and crystal structure of [Pb(18-crown-6)I2]

Abstract

Solvent extraction of lead halides with 18-crown-6 (18C6), dicyclohexano-18-crown-6 (DC18C6, cis-syn-cis and cis-anti-cis isomers) in chloroform was studied, and the extraction constants corrected for side reactions and ionic strength effects were obtained. The compounds of the same composition as those being extracted were also isolated in crystal form. The molecular structure of the [Pb(18C6)I₂] complex has been determined. Crystals are monoclinic, P2₁/n, a = 11.237(2), b = 10.992(2), c = 8.139(2)Å, β = 97.32(3)°, V = 997.1(7)ų, D_calc = 2.416(2)gcm^?3, Z = 2 for the composition C₁₂H₂₄O₆PbI₂. The final R-factor is 0.043 for 558 unique reflections. The lead atom is coordinated to six oxygen atoms of the crown ether and two iodine atoms forming a hexagonal bipyramidal coordination polyhedron. The 18C6 molecule and the two halogen atoms form a hydrophobic coating for the lead atom which may be assumed to be the main reason of high extraction constants of the iodine complexes. For 10-coordinate lead ion (bidentate counter ions) the cis-syn-cis isomer of DC18C6 appears to be the best extraction reagent, while for 8-coordinate lead ion (monodentate halide anion) no difference between isomers was observed.     

Reaction of H2PtCl6 with 18-crown-6 and dibenzo-18-crown-6 in 1,2-dichloroethane and acetonitrile

Compounds of the compositions [2(18-crown-6)6(H₂O)2(C₂H₄Cl₂){Pt²⁺(C₂H₄)}(Pt₂Cl₁₀)^2–], [4(18-crown-6)2(OH₃)⁺2(OH₂)2(NH₃)(Pt₂Cl₁₀)^2–], [(dibenzo-18-crown-6)6(H₂O){Pt²⁺(C₂H₄)}(Pt₂Cl₁₀)^2–], and [4(dibenzo-18-crown-6)2(OH₃)⁺2(OH₂)2(NH₃)Pt₂Cl₁₀)^2–] were prepared by reactions of H₂PtCl₆ with 18-crown-6 and dibenzo-18-crown-6.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1593–1599.Original Russian Text Copyright © 2004 by Guseva, Busygina, Khasanshin, Polovnyak, Yarkova, Yusupov.This revised version was published online in April 2005 with a corrected cover date.     

A stereoselective reduction of dibenzo-18-crown-6 ether to dicyclohexyl-18-crown-6 ether

Dibenzo-18-crown-6 ether is reduced to dicyclohexano-18-crown-6 ether under very mild conditions (room temperature and atmospheric hydrogen pressure) in the presence of rhodium salt and phase-transfer reagents. Control over the stereoselectivity of the reduction can be achieved through the proper choice of the phase-transfer agent. Moreover, at higher pressure, the stereoselectivity can be increased up to a 95/5 ratio of the syn/anti isomers of the dicyclohexano-18-crown-6 ether.     

Extractive spectrophotometric and fluorimetric determination of boron with 2,2,4-trimethyl-1,3-pentanediaol and carminic acid

Boric acid at μg/ml or ng/ml level can be extracted from 1-6M hydrochloric acid into 2,2,4-trimethyl-1,3-pentanediol solution in chloroform and thus separated from many ions which interfere in the usual spectrophotometric methods. The boron is determined directly in the organic phase without back-extraction into water, by adding a solution of carminic acid in a mixture of sulphuric and glacial acetic acids (1+2 v/v) and measuring the absorbance at 549 nm. The molar absorptivity is 2.58 × 10⁴ l.mole⁻¹.cm⁻¹ and Beer's law is valid for the 0.05–0.4 μg/ml boron range. In the fluorimetric method, 509 or 547 nm can be used as the excitation wavelength and 567 nm for emission measurement, giving a linear response in the 8–120 ng/ml boron range. Both methods have been applied to determination of boron in plants and natural waters with good precision and accuracy.     

二环己基并18冠6的制备方法

二苯并-18－冠-6;二环己基并18冠6的制备方法     

18-crown-6 ether complexes with aralkylammonium perchlorates

Thermochemical properties of crown ether complexes have been studied by simultaneous TG-DTA (thermogravimetric analysis-differential thermal analysis) coupled with a mass spectrometer, DSC (differential scanning calorimetry) and hot stage microscopy (HSM). The examined complexes contain benzylammonium- [BA], (R)-(+)-a-phenylethylammonium- [(R)-PEA], (R)-(+)- and (S)-(-)-a-(1-naphthyl)ethylammonium perchlorate [(R)-NEA and (S)-NEA] salts as guests. In the cases of BA and (R)-PEA an achiral pyridono-18-crown-6 ligand [P18C6], and in the case of (R)-NEA and (S)-NEA a chiral (R,R)-dimethylphenazino-18-crown-6 ligand [(R,R)-DMPh18C6] was used as host molecule to obtain four different crown ether complexes. In all cases, the melting points of the complexes were higher than those of both the host and the guest compounds. The decomposition of the complexes begins immediately after their melting is completed, while the BA and (R)-PEA salts and the crown ether ligands are thermally stable by 50 to 100 K above their melting points. During the decomposition of the salts and the four complexes strongly exothermic processes can be observed which are due to oxidative reactions of the perchlorate anion. Ammonium perchlorate crystals were identified among the decomposition residues of the salts. P18C6 was observed to crystallize with two molecules of water. The studied complexes of P18C6 did not contain any solvate. BA was observed to exhibit a reversible solid-solid phase transition upon heating. The heterochiral complex consisting of (S)-NEA and (R,R)-DMPh18C6 shows a solid-solid phase transition followed by two melting points. HSM observations identified three crystal modifications, two of them simultaneously co-existing. This revised version was published online in July 2006 with corrections to the Cover Date.     

The 1 : 1 complexes between benzo-18-crown-6, 18-crown-6 and aminosulfuric acid

The title compounds were prepared by treating a methanol solution of the corresponding crown ether with an aqueous solution of aminosulfuric acid.Crystals of [benzo-18-crown-6·H₂NSO₂OH] suitable for X-ray crystallography were obtained by recrystallization from methanol. The crystals are orthorhombic, space groupP2₁2₁2₁,a = 14.310(7),b = 12.516(4),c = 10.890(4) Å. Refinement led to a final conventionalR value of 0.051 for 909 reflections.Crystals of [18-crown-6·H₂NSO₂OH] suitable for X-ray crystallography were obtained by recrystallization from acetone. They are orthorhombic, space groupP2₁2₁2₁,a = 17.027(6),b = 14.866(5),c = 8.345(4) Å. The structure was solved by a heavy atom method and refined to an agreement value of 0.067.     

Extraction of rare-earth elements by alkylated dibenzo-18-crown-6 and dicyclohexano-18-crown-6 from acid solutions

The extraction of rare-earth elements (REE) by alkylated crown ethers (dibenzo-and dicyclohexano-18-crown 6; DB18C6 and DCH18C6) from acid solutions in the chloroform-water system is studied. The extraction of the REE with DCH18C6 and its alkylated derivatives in the presence of trichloroacetic acid (TCA) is far more efficient than the extraction with DB18C6 and its alkylated derivatives or when nitric or acetic acid is used instead of TCA. The distribution coefficients for the cerium metals are far higher than for the yttrium metals. The metal: crown ether ratio in the extracted complex in all cases is 1:1.     

Reaction of tetranitrodibenzo-18-crown-6 with sodium alkoxides

It is shown that the reaction of tetranitrodibenzo-18-crown-6 with sodium alkoxides in aprotic solvents at room temperature occurs with initial cleavage of the macroheterocycle and formation of an intermediate — substituted o-dinitrobenzene — whereas the reaction in protonated solvents occurs with substitution of the nitro groups. From among other derivatives of dibenzo-18-crown-6 containing azole rings linked to the benzene ring, only the furoxan-containing crown ether is cleaved under similar conditions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 37–40, January, 1989.     

Homolytic alkylation of quinaldine and quinoxaline with 18-crown-6

Homolytic alkylation of protonated quinoxaline with 18-crown-6, initiated by the system pivalic acid-iron(II) sulfate at 20–25C, gives (quinoxalin-2-yl)-18-crown-6 in 85% yield. Under analogous conditions, the reaction with quinoline affords two isomers: (quinolin-4-yl)-18-crown-6 and (quinolin-2-yl)-18-crown-6, in yields of 20 and 30% respectively.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 75–76, January, 1988.