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1.
Metals can be determined by electron spin resonance (e.s.r.) by using stable free radicals in which the molecules include complexing groups. Such reagents form complexes with metal ions which retain the properties of the free radicals producing the e.s.r. signal. The complexes formed can be separated from the excess of reagent and the metal concentrations measured from the signal intensity. This approach markedly expands the potential of e.s.r. as an analytical technique, because it is not limited to paramagnetic metals. The relatively high sensitivity of free radical determination by the e.s.r. method is an additional advantage. The properties of the spin-labelled β-diketone, 4-acetoacetyl-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl, are described. Dissociation constants are reported for the enol form (pKaT = 6.56 ± 0.02) and for the protonated (at the imidazolyl nitrogen) form (pKaT = 1.91 ± 0.02), as well as partition constants for the hexane—water (log kD(C6H14) = 0.96 ± 0.02) and chloroform—water (log KD(CHCl3) = 3.36 ± 0.04) systems. The reagent extracts Cu, Pb, Cd, Hg and Er readily; in the presence of caproic acid iron(III) is also extracted. Copper is extracted as a CuA2, complex (log KD = 2.5 ± 0.5; log Kex = -2.80 ± 0.13; log β2 = 14.3 ± 1.5). CuA2 does not give an e.s.r. signal. Iron is extracted as a mixed complex with β-diketone and caproic acid. An extraction—e.s.r. method is reported for the determination of mercury with a detection limit of 2 × 10-7 M.  相似文献   

2.
A simple and highly sensitive extraction—spectrophotometric determination of cadmium is described. The ion-associate formed between the cadmium-PAR anionic chelate and cetyldimethylbenzylammonium chloride (CDBA) is extracted with chloroform at pH 10. The absorption maximum of the extracted species occurs at 505 nm, the molar absorptivity being (9.82 ± 0.30) × 104 l mol-1 cm-1. The optimal concentration range for measurements is 0.2–1.0 μg Cd ml-1; Beer's law is obeyed. The composition of the ion-associate is estimated to be CdPAR2-2CDBA. The conditional extraction constant is log K'ex ≈ 8. The stability constant of the cadmium—PAR chelate in aqueous solution is log β2 = 17.5 ± 0.3. Extraction with N-benzoyl-N-phenylhydroxylamine is used to avoid several interferences. Moderate amounts of zinc are masked with sodium hydroxide.  相似文献   

3.
2-(5′-methyl-2′-isoxazolylazo)-4-Methoxyphenol has been synthesized and its ionization constant (pKa = 7.98 ± 0.08) spectrophotometrically determined in a 4% (vv) ethanol-water medium at μ = 0.25 M (NaClO4). The reagent originates water soluble complexes with cobalt (log β2 = 11.45 ± 0.16), copper (log β1 = 7.15 ± 0.10), and cadmium (log β1 = 3.96 ± 0.12), and can be used for the spectrophotometric determination of cobalt and copper as well as metallochromic indicator for copper.  相似文献   

4.
Pyridine-2-aldehyde-2-quinolylhydrazone (PAQH) is a selective and sensitive reagent for cobalt or nickel. The reagent reacts with only a few metals to give coloured complexes; with the exception of palladium, the cobalt chelate is the only complex relatively stable towards protons and PAQH is a very selective reagent for cobalt. In the presence of thioglycollic acid only nickel reacts with PAQH; the chelate is extracted with chloroform and its absorbance measured at 492 nm. The high molecular extinction coefficients (30·103 and 51·103) permit the determination of 0.2–2 p.p.m. of cobalt and 0.1–1 p.p.m. of nickel.  相似文献   

5.
The reactions of 4-carboxy-1,2-cyclohexanedionedioxime and nickel(II) were studied in alkaline media. Spectrophotometric studies indicate the presence of a 1:1 complex ion, NiD-. Magnetic susceptibility measurements on a series of solutions of varying ratios of vic-dioxime and nickel(II) showed that the 1:1 complex ion was diamagnetic and that two paramagnetic complexes, probably NiD24- and NiD37-, are present in solution. The stability constants for the three complexes were calculated from spectrophotometric and magnetic susceptibility data. The log K values were found to be log K1 = 28.74 ± 0.60, log K2 = 0.76 ± 0.15, and log K3 = 3.67 ± 0.73, respectively.  相似文献   

6.
The values of pK1 and pK2 for 3,5-dinitrosalicylic acid (DNSA, H2L) have been determined at 25.0°C and 0.1 M ionic strength (sodium perchlorate) as 0.25 and 7.20. respectively. The binding of nickel(II) and cobalt(II) has been investigated over the pH range 1.0–7.0 at the same temperature and ionic strength. Values of log KML for the formation of the unprotonated complexes are 4.05±01 and 3.82±01 for nickel(II) and coball(ll) respectively. Values for log KMHL are close to 11 mol-1 for both metals; it seems probable that these species are not inner-sphere complexes, and possible reasons for this are suggested. The stability constants obtained are compared with others in the literature, and the possibility of using DNSA as a metal-ion indicator is discussed briefly.  相似文献   

7.
2-(4′-methyl-2′-thiazolylazo)-4,6-dimethylphenol has been synthesized and its acid—base behaviour (pKa1=0.03 ± 0.01, pKa2=9.70±0.09) and complexation equilibria with zinc (logβ101=6.70±0.04, logβ102 = 13.70±0.02) studied in a 40% (v / v) ethanol—water medium at I=0.25 M NaClO4. A spectrophotometric method for the determination of 0.2–1.5 ppm of zinc has been developed (ε=1.83 × 104 1. mol−1 cm−1 at 590 nm) and applied to its determination in lubricating oils.  相似文献   

8.
《Polyhedron》1988,7(7):535-542
Cobalt(II) chloride complexes were investigated spectrophotometrically in hexamethylphosphoramide (HMPA) solutions. It has been established that four consecutive tetrahedral chloro complexes of cobalt(II) are formed in the Co(ClO4)2-CoCl2 and CoCl2-LiCl-HMPA solutions. The formation constants of the complexes have been calculated: log K1 = 9.0 (±0.5), log K2 = 6.5 (±0.5), log K3 = 3.05 (±0.05) and log K4 = − 1.42 (±0.03). The high stability of the dichloro-complex results in the fact that this species is the only complex of cobalt(II) existing in HMPA solutions of CoCl2.  相似文献   

9.
The thermodynamics of the complexing between hexavalent U and 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (PMBP) have been studied in 70 vol% aqueous—dioxane medium at 25 and 35±0.1°C following the Bjerrum—Calvin pH titration technique, as applied by Van Uitert and Haas. The ligand is mono-protonic. The refinement of results of formation constants has been accomplished by the method of least squares treatment after an algebraic transformation. The formation of 1:1, 1:2 and 1:3 complexes has been observed, the order of stability being log K1 > log K2 > log K3. The stability invariably increases with an increase in temperature both in aqueous as well as aqueous dioxane media. The changes in ΔG0, ΔH0 and ΔS0 at 25 and 35°C for the overall equilibrium constants have also been evaluated. Uranyl complexes of PMBP are entropy stabilized, the values of enthalpy changes being positive. Other factors which affect chelate stability are briefly discussed.  相似文献   

10.
ZFS constants (in cm?1) and decay rate constants for the lowest triplet state of pheophytins have been determined by ESR: pheophytin a: D = 341 ± 3,E = 33 ± 3, KT = 1050 s?1; pheophytin b: D = 358 ± 8, E = 46 ± 5, KT = 630 s?1; bacteriopheophytin: D = 256 ± 4, E = 54 ± 5/37 ± 5, KT ≈ 4000 s?1. In addition values for the decay rate constants and relative populating rates of the individual spin levels have been obtained; these numbers turn out to be appreciably different from those for the corresponding chlorophylls. For the series pheophytin a, b and bacteriopheophytin we find parallel behaviour with the corresponding chlorophylls. The effects of side group substitution and pyrrole ring reduction on the ZFS constant D can be understood by including configuration interaction between the excited states using the 4-orbital model. The change of the mean triplet decay constant KT upon side group substitution and pyrrole ring reduction follows an energy gap law. Substitution of the central Mg-ion by two protons, however, causes KT to increase; this is attributed to the introduction of an extra promoting mode - of the NH-group - and/or to the presence of low lying nπ* states in pheophytins.  相似文献   

11.
Cation-induced dimerization of nickel(II), platinum(II), and palladium(II) meso-tetra(benzo-15-crown-5)porphyrinates (Ni(II)TCP, Pd(II)TCP, and Pt(II)TCP) on treatment with potassium thiocyanate in a chloroform-methanol solution has been studied by electronic absorption spectroscopy. The formation of [{MTCP}2(K+)4](SCN?)4 in solution induces a hypsochromic shift of the Soret band and a bathochromic shift of the β-band with respect to their positions in the spectrum of MTCP. The equilibrium constants (K) for the 2MTCP + 4K+ = [{MTCP}2(K+)4] processes at 20°C are determined to be as follows: log K Ni(II)TCP = 27.31 ± 1.67, logK Pd(II)TCP = 27.16 ± 1.43, and logK Pt(II)TCP = 26.15 ± 1.56.  相似文献   

12.
A simple and highly sensitive extraction—spectrophotometric determination of copper (II) is described. The ion-associate formed between the copper(II)—4-(2-pyridylazo)-resorcinol (PAR) anion and tetradecyldimethylbenzylammonium chloride (TDBA) is extracted with chloroform at pH 9.7. The absorption maximum of the extracted species occurs at 510 nm, the molar absorptivity being 8.05 (± 0.07) × 104 l mol-1 cm-1. Beer's Law is obeyed in the concentration range 0.1–0.5 μg Cu ml-1. The composition of the ion-associate is estimated to be [Cu(PAR)2(TDBA)2]. The conditional extraction constant is log K'ex ≈ 8. The interference of some cations and anions is studied. The method is suitable for analysis of waters.  相似文献   

13.
The complex formation of Fe3+ with o-methyl benzamide oxime was studied spectrophotometrically in methanol solution. The stepwise process gives complexes 1∶1, 1∶2 and 1∶3. The formation constants are lgK 1 = lg β1 = 1,88 ± 0,12, lgK 2 = 3,53 ± 0,2, lgK 3 = 4,96 ± 0,2, lg β2 = 1,65 ± 0,32 and lg β3 = 1,43 ± 0,4, whereK 3 = β1 · β2 · β3. All measurements were carried out at 25°C and an ionic strength μ=1.  相似文献   

14.
The spectrophotometric study of the complexation reaction between 5,5′methylenedisalicylhydroxamic acid and V(V) shows that two complexes are formed, the 1:1 (? = 5100 liters mol?1 cm?1 at 490 nm, log Kest = 5.8 ± 0.1) and the 1:2 (L:V) (? = 6250 liters mol?1 cm?1 at 600 nm, log Kest = 6.1 ± 0.1). A spectrophotometric method is developed for the determination of vanadium (2–9 ppm) at 2 N HCl and 495 nm, which allows its determination in petroleum crude oils with a series of advantages over the ASTM D-1548-63 method.  相似文献   

15.
Abstract

The kinetics and stability constants of l-tyrosine complexation with copper(II), cobalt(II) and nickel(II) have been studied in aqueous solution at 25° and ionic strength 0.1 M. The reactions are of the type M(HL)(3-n)+ n-1 + HL- ? M(HL)(2-n)+n(kn, forward rate constant; k-n, reverse rate constant); where M=Cu, Co or Ni, HL? refers to the anionic form of the ligand in which the hydroxyl group is protonated, and n=1 or 2. The stability constants (Kn=kn/k-n) of the mono and bis complexes of Cu2+, Co2+ and Ni2+ with l-tyrosine, determined by potentiometric pH titration are: Cu2+, log K1=7.90 ± 0.02, log K2=7.27 ± 0.03; Co2+, log K1=4.05 ± 0.02, log K2=3.78 ± 0.04; Ni2+, log K1=5.14 ± 0.02, log K2=4.41 ± 0.01. Kinetic measurements were made using the temperature-jump relaxation technique. The rate constants are: Cu2+, k1=(1.1 ± 0.1) × 109 M ?1 sec?1, k-1=(14 ± 3) sec?1, k2=(3.1 ± 0.6) × 108 M ?1 sec?1, k?2=(16 ± 4) sec?1; Co2+, k1=(1.3 ± 0.2) × 106 M ?1 sec?1, k-1=(1.1 ± 0.2) × 102 sec?1, k2=(1.5 ± 0.2) × 106 M ?1 sec?1, k-2=(2.5 ± 0.6) × 102 sec?1; Ni2+, k1=(1.4 ± 0.2) × 104 M ?1 sec?1, k-1=(0.10 ± 0.02) sec?1, k2=(2.4 ± 0.3) × 104 M ?1 sec?1, k-2=(0.94 ± 0.17) sec?1. It is concluded that l-tyrosine substitution reactions are normal. The presence of the phenyl hydroxyl group in l-tyrosine has no primary detectable influence on the forward rate constant, while its influence on the reverse rate constant is partially attributed to substituent effects on the basicity of the amine terminus.  相似文献   

16.
The low-temperature heat capacities of nickel titanate (NiTiO3), cobalt titanate (CoTiO3), and cobalt carbonate (CoCO3) were measured between 2 and 300 K, and thermochemical functions were derived from the results. Our new data show previously unknown low-temperature lambda-shaped heat capacity anomalies peaking at 37 K for CoTiO3 and 26 K for NiTiO3. From our data we calculate standard molar entropies (298.15 K) for NiTiO3 of 90.9 ± 0.7 J mol-1 K-1 and for CoTiO3 of 94.4 ± 0.8 J mol-1 K-1. For CoCO3, we find only a small broad heat capacity anomaly, peaking at about 31 K. From our data, we suggest a new standard entropy (298.15 K) for CoCO3 of 88.9 ± 0.7 J mol-1 K-1.  相似文献   

17.
《Polyhedron》1988,7(6):421-424
The standard enthalpies of formation, at 298 K, of the 1-phenyl-1,3-butanedione (HBZAC) and 1,1,1-trifluoro-2,4-pentanedione (HTFAC) crystalline complexes of cobalt(II) were determined by precise solution—reaction calorimetry: ΔH0f{Co(BZAC)2,cr} = −632±6.0 kJ mol−1 ΔH0f{Co(TFAC)2,cr} = −2140±10 kJ mol−1. The average molar bond-dissociation enthalpies, <D>(CoO) were derived.  相似文献   

18.
The copolymerization of 2-naphthyl methacrylate (2-NM) with methyl methacrylate (MMA) initiated by 2,2′-azoisobutyronitrile in carbon tetrachloride, chloroform, benzene, acetone and acetonitrile was investigated. The reactivity ratios determined by the methods of Fineman-Ross and Kelen-Tüdo&#x030B;s are: in carbon tetrachloride—r2-NM = 2.46 ± 0.25, rMMA = 0.61 ± 0.06; chloroform—r2-NM = 2.71 ± 0.30, rMMA = 0.60 ± 0.06; benzene—r2-NM = 2.62 ± 0.44, rMMA = 0.63 ± 0.11; acetone—r2-NM = 4.13 ± 0.45, rMMA = 0.60 ± 0.06 and acetonitrile—r2-NM = 3.70 ± 0.30, rMMA = 0.62 ± 0.05.The dependence of the reactivity ratios on the solvent is explained on the basis of formation of complexes between the electron-donating naphthalene rings and the electron-accepting methacrylic double bonds, as indicated by NMR studies.  相似文献   

19.
Molten potassium tetrachlorogallate and potassium tetraiodogallate were studied in terms of halogenoacidity, based on X? ion-exchange. Titration of KX solution with GaX3 were achieved and characterized by the shift of cathodic voltammetric curves. Autodissociation constants Ki,X/mol2 kg?1 were determined: ?log Ki,Cl=4.25±0.05 and ?log Ki,I=2.6±0.05, as well as the solubility values of KX: 0.41±0.02 and 0.80±0.02 mol kg?1 for KCl and KI respectively.  相似文献   

20.
By using different techniques the vapor pressure of ferrocene, mono-acetyl ferrocene and 1,1′-di-acetyl ferrocene was measured. The following pressure—temperature equations were derived ferrocene log P(kPa)= 9.78 ± 0.14 ? (3805 ± 46)/T mono-acetyl ferrocene log P(kPa) = 14.83 ± 0.14 ? (5916 ± 48)/T 1,1′-di-acetyl ferrocene log P(kPa) = 8.82 ± 0.11 ? (4289 ± 44)/T By second- and third-law treatment of the vapor data the ΔH0sub,298 = 74.0 ± 2.0 kJ mole?1 for the sublimation process of ferrocene was calculated and compared with the literature data. For the sublimation enthalpy of mono- and 1,1′-di-acetyl ferrocene the values ΔH0sub,298 = 115.6 ± 2.5 kJ mole?1 and ΔH0sub,298 = 91.9 ± 2.5 kJ mole?1 were derived by second-law treatment. Thermal functions of these compounds were also estimated.  相似文献   

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