Analytical application of triethylenetetraaminehexa- acetic acid: Part 2. Polarographic Investigation of the reactions of TTHA at the dropping mercury electrode

TTHA gives an anodic d.c. wave and s.w. peak corresponding to oxidation of mercury at the d.m.e. surface with formation of a Hg(II)—TTHA complex. Similar processes are known for other ligands, e.g. EDTA and DCTA, but the greater stability of the Hg(II)—TTHA complex gives a significant improvement in the shapes of the anodic wave and s.w. peak. An increase in pH shifts the E_{$\text{1}\text{2}$} and E_p values towards more negative values because the conditional stability constant of the Hg(II)—TTHA complex is increased. Although the half–wave potentials of the reduction wave of Hg(II)—TTHA and of the anodic wave of TTHA, are the same, other criteria for the reversibility of polarographic reactions suggest that the anodic TTHA process at the d.m.e. is not completely reversible. The temperature coefficient of the wave and s.w. peak as well as the dependence of the wave height on the square root of the mercury head prove that the process is diffusion–controlled. Supporting electrolytes are given for which the d.c. wave and the s.w. peak of TTHA are well-shaped, with linear dependence between the wave or peak height and the concentration of TTHA in the ranges 5 × 10^-5–5 × 10^-4 M (d.c.) and 1 0^-5–1 × 10^-4 M (s.w.).     

Voltammetry and controlled-potential coulometry with boron carbide electrodes

With the boron carbide electrode, E_{p$\text{p}\text{2}$} values were determined for the reduction of the following ions: Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II), Ru(IV), Sb(V), and U(VI). The linear dependence of peak current on concentration is demonstrated for the U(VI) → U(IV) and Fe(III) → Fe(II) reductions at the boron carbide electrode. The suitability of the electrode for the controlled-potential coulometric ti trations of Fe(II) → Fe(III), Fe(III) → Fe(II), and U(VI) → U(IV) was studied; the results were inconclusive because of the small surface area that could be used conveniently and the possibility of oxygen leaks in the cell.     

Polarographic determination of iron(II) and iron(III) complexes with edta

The iron(II) and iron(III) complexes with EDTA can be determined separately and in mixtures in acetate-buffered medium at pH 4.0. The E_{$\text{1}\text{2}$}values are in the range ?0.105 to ?0.112 V vs. SCE. Linear calibration plots are obtained over the range 0–1.0 mM for each oxidation state. A sample-handling procedure for avoiding oxidation of iron(II) species is described. It is shown that the acetate buffer system does not affect the stability of the iron-EDTA complexes.     

The polarographic reduction of some dinitroaniline herbicides

Polarography of 2,6-dinitroaniline herbicides in aqueous ethanol revealed a marked pH dependence of the reduction potentials. The study included the herbicides trifluralin (I), benefin (II), isopropalin (III), dinitramine (IV), nitralin (V), and oryzalin (VI), for which E_{$\text{1}\text{2}$} values (mV vs. SCE) for the first polarographic wave, at pH 1.5, 5.1, 7.4, and 9.2, respectively, were (I) ?190, ?430, ?540, ?640; (II) ?190, ?430, ?540, ?640; (III) ?170, ?360, ?560, ?650; (IV) ?230, ?510, ?720, ?810; (V) ?160, ?330, ?540, ?650; (VI) ?160, ?370, ?540, ?680.     

Substitution in barium-fluoride apatite: The crystal structures of Ba10(PO4)6F2, Ba6La2Na2(PO4)6F2 and Ba4Nd3Na3(PO4)6F2

The crystal structures of the apatites Ba₁₀(PO₄)₆F₂(I), Ba₆La₂Na₂(PO₄)₆F₂(II) and Ba₄Nd₃Na₃(PO₄)₆F₂ (III) have been determined by single-crystal X-ray diffraction. All three compounds crystallize in a hexagonal apatite-like structure. The unit cells and space groups are: I, a = 10.153(2), c = 7.733(1)Å, $\text{P6}{}_3\text{m}\text{; a = 9.9392(4), c = 7.4419(5)}$Å, $\text{P}\text{6}$; III, a = 9.786(2), c = 7.281(1)Å, $\text{P}\text{3}$. The structures were refined by normal full-matrix crystallographic least squares techniques. The final values of the refinement indicators R_w and R are: I, R_w = 0.026, R = 0.027, 613 observed reflections; II, R_w = 0.081, R = 0.074, 579 observed reflections; III, R_w = 0.062, R = 0.044, 1262 observed reflections.In I, the Ba(1) atoms located in columns on threefold axes, are coordinated to nine oxygen atoms; the Ba(2) sites form triangles about the F site and are coordinated to six oxygen atoms and one fluoride ion. The fluoride ions are statistically displaced ～0.25 Å from the Ba(2) triangles. This displacement of the F ions is analogous to the displacement of OH ion in Ca₁₀(PO₄)₆(OH)₂.The structures of II and III contain disordered cations. In II there is disorder between La and Na in the column cation sites as well as triangle sites. In III, Nd and Na ions are ordered in the column sites, but there is disorder among Ba and the remaining Nd and Na ions in the triangle sites to give an average site population of $\text{2}\text{3}\text{Ba}\text{,}\text{1}\text{6}\text{Nd}\text{,}\text{1}\text{6}\text{Na}$. The coordination of the rare earth ions and Na ions in the ordered column sites are nine and six oxygens, respectively, in accord with the greater charge of the rare earth ions as compared with Na. The F ions in both II and III suffer from considerable disorder in position, and their locations are not precisely known.     

Palladium-catalyzed asymmetric cyclization of methyl (E)-oxo-9-phenoxy-7-nonenoate and its analogs

Asymmetric cyclizations of methyl (E)-3-oxo-9-phenoxy-7-nonenoate ($\text{1}$) or methyl (E)-3-oxo-9-(methoxycarbonyl)oxy-7-nonenoate ($\text{4}$) without added base were carried out in the presence of a catalytic amount of palladium(II) acetate and chiral diphosphine as ligands. Allylic carbonate $\text{4}$ reacted by use of Pd(OAC)₂-(S)-(R)-BPPFA at room temperature to give (R)-3-vinylcyclohexanone ($\text{3}$), after decarboxylation, in up to 48% e. e.     

Determination of stability constants by semi-integral analysis of voltammograms obtained with a computerized electrochemical system

A versatile computerized electrochemical system is used for the determination of stability constants of lead(II) propanoate and 2-hydroxypropanoate complexes by semi-integral linear sweep voltammetry. Semi-integral voltammograms are analogous in characteristics to d.c. polarograms, and the half-wave potentials (E_{$\text{1}\text{2}$}) and limiting currents (i₁) for a depolarizer can be obtained by nonlinear least-squares fitting of semi-integrally transformed voltammograms. An advantage of the proposed method is that E_{$\text{1}\text{2}$} and i₁ values are obtained from a single mercury drop (hanging or dropping mercury electrode); working time is reduced while accuracy and precision are maintained. The computer-controlled system provides automated reagent addition, signal generation, response measurement and sampling, data evaluation, etc. The results agree well with those obtained by the usual d.c. polarographie method.     

Extraction-polarographic determination of cobalt(II) and nickel(II) as 2,2′-bipyridine complexes in acetonitrile

The tris(2,2′-bipyridine)cobalt(II) complex gives a reversible d.c. wave with E$\text{1}\text{2}$ = ?1.02 V vs. SCE and a sharp differential pulse peak at E_p = ?1.03 V in a salted-out acetonitrile phase. A simple selective method is described for the determination of cobalt(II); down to 0.25 μg of cobalt(II) can be determined in presence of large amounts of Ni, Zn, Cd, Pb, and Cu; iron(III) can be masked with sodium fluoride. The method is applicable to the determination of >0.0l% cobalt in nickel salts and >5 × 10^?5% cobalt in iron salts. Nickel(II) can also be extracted from aqueous solution and determined by differential pulse polarography, even in presence of a 20-fold amount of cobalt(II) by masking with EDTA; >0.01% of nickel in cobalt salts can be determined reproducibly.     

Stéréosélectiveté de la condensation aldolique. Réaction du benzaldéhyde et d'énolates carbéniates magnésiens α-chlorés

Alkyl chloracetates III (R′ = H) and phenylchloracetates III (R′ = Ph) condense with PhCHO in the presence of (i-Pr)₂NMgBr giving alkyl-2-chloro-3-hydroxy-3-phenyl propionates (RS, RS) (I) and (RS, SR) (II) in equal ratio ($\text{1}\text{1}$) for III (R′ = H) and in the ratio $\text{65}\text{35}$ for III (R′ = Ph) irrespective of the group R. When the same reaction is performed with alkyl chloropropionates III (R′ = CH₃) the isomer ratio is dependent upon the group R. These results are interpreted by considering a planar (R′ = H or Ph) or pyramidal (R′ = CH₃) geometry of the intermediate enolate-carbeniate.     

Crystallographic studies on cation substitutions in the system (Na,K) (V,P)O3

Three compounds in the system (Na,K) (V,P)O₃ were synthesized and their structures were refined by full matrix least squares method in the space group $\text{C2}\text{c}$. Their compositions were shown by site population analysis to be Na(V_0.66P_0.34)O₃ (I), (Na_0.88K_0.12)VO₃ (II), and (Na_0.5K_0.5)VO₃ (III). All are related to the structure of α-NaVO₃ which in turn is related to the clinopyroxene structure characterized by infinite chains of SiO₄ tetrahedra sharing vertices and two inequivalent metal cation sites M1 and M2. Both sites feature sixfold coordination in compounds I and II, while the Na and K are ordered into M1 and M2 sites, respectively in III, with the latter showing eightfold coordination. The pentavalent cations are randomly distributed in tetrahedral sites in I, and in II the K was found to occupy the M2 sites only. Changes in the α-NaVO₃ structure upon cation substitution are discussed in terms of rotation and displacement of the tetrahedral chains. Parameters for measuring these chain movements are proposed and found to exhibit an almost linear relationship with the ratio $\text{〈X?0〉}\text{〈M2?0〉}$ in cases where the M1 site is exclusively occupied by Na.     

Etude polarographique du rhodium(III) en milieu thiocyanate. Application au dosage microanalytique de composes organometalliques: Polarographie study of rhodium(III) in thiocyanate media. Application to the microanalysis of organometallic compounds.

Polarographie study of rhodium(III) in thiocyanate media. Application to the microanalysis of organometallic compounds.Reduction of rhodium(III) at the dropping mercury electrode is performed in thiocyanate media by classical a.c. and pulse polarography, and linear sweep voltammetry. The reduction (E$\text{1}\text{2}$ = —0.5 V vs. SCE) is shown to be a 3e irreversible transfer. Coulometric investigation confirms this result and rhodium gives a dark grey deposit at the mercury surface. This explains the i—t curves even in the presence of gelatin as maximum suppressor and the anomalous slope of log [i/(i_d - i)] at potentials more cathodic than the E$\text{1}\text{2}$ value. A.c. and differential pulse polarography are suitable for analysis down to the 0.1-ppm level. Palladium and platinum do not interfere although there is enhancement of the base line, but ruthenium affects the end of the polarogram, probably because of catalytic hydrogen evolution. Applications to organometallic compounds and industrial catalytic bimetallic grids show good agreement with the predicted compositions.     

Bis(dimethylmetall(III)glyoximato)metallate(II) (metall(III) = Al,Ga, In,metall(II) = Ni,Pd, Pt,Cu)

When the trimethyl derivatives of aluminium, gallium and indium react with glyoximato metallates, (R₂C₂N₂(O)OH)₂Met^II (R = H, CH₃; Met^II = Ni, Pd, Pt, Cu), in a $\text{2}\text{1}$ molar ratio, 2 mol of methane are evolved and monomeric bis(dimethylmetal(III)glyoximato)metallates(II) (metal(III) = Al, Ga, In) are formed in high yields. The vibrational and NMR spectra of the new complexes were measured and were partly resolved. The X-ray structure determinations of two of these compounds show non-planar structures of approximate C_2h and C₂ symmetry, respectively, with weak metal(III)?metal(II) π-interactions.     

The study of redox reactions of bisarenechromium complexes by the rotating disk and the rotating ring disk electrode techniques: III. Cathodic reduction of chromium(0) π-complexes and the corresponding arenes in dimethyl sulfoxide solutions

The rotating disk (RDE) and the rotating ring-disk (RRDE) electrode techniques have been employed to study the cathodic behavior of eight bisarenechromium complexes and seven corresponding arenes in DMSO solutions. In the first electrochemical step of the process reversible addition of one electron results in anion-radicals, whose formation has been demonstrated for certain arenes and chromium π-complexes by oxidation of these particles on the ring electrode.Substituents on different ligands of bisarenechromium complexes were found to exert pronounced mutual influences. The role of the chromium atom in transfer of electronic effects from one ligand to another is discussed.It was found that a linear correlation exists between the variations in the free energy of the equilibrium “initial compound

anion-radical” (due to coordination of free arene with chromium which is displayed as a shift of the cathodic process half-wave potential ΔE_{$\text{1}\text{2}$}^CL) and the half-wave potential of the oxidation of the corresponding Cr⁰ π-complex to a cation E_{$\text{1}\text{2}$}^X ΔE_{$\text{1}\text{2}$}^CL = a + αE_{$\text{1}\text{2}$}^X At E_{$\text{1}\text{2}$}^X < ?0.3 V, complex formation slows down the cathodic process and at E_{$\text{1}\text{2}$}^X > ?0.3 V the process is facilitated.     

Synthesis of “capped porphyrins”

The synthesis of “capped porphyrins” ($\text{10}$), ($\text{18}$), and ($\text{28}$), and their (chloro)iron(III), iron(II), cobalt (II), and zinc(II) complexes is reported. These complexes serve as models for the active site of the oxygen binding haemoproteins. In addition to reversible binding of dioxygen by each of the iron (II) porphyrin complexes, the 1-methyl-imidazole-(“C₃-capped porphyrin”) iron (II) complex ($\text{23}$) reacts reversibly with carbon monoxide, in solution at 25°C.     

Numerical evaluation of complex stability constants from polarographic data for quasi-reversible processes

Stability constants of copper(II) butyrate complexes were determined by polarography. Numerical treatment of polarographic data for quasi-reversible electrode processes was developed and yielded good estimates of reversible E_{$\text{1}\text{2}$} values. An improved three-electrode polarographic apparatus was constructed based on operational amplifiers.     

Zum einfluss des leitelektrolyten auf die polarographi- sche reduktion des methylbromids

The irreversible polarographic reduction of methyl bromide was studied in aqueous solution in the presence of various base electrolytes.E_{$\text{1}\text{2}$} values became more positive with increasing charge density and surface activity of the cations. Mixed electrolytes with alkali metal salts and tetraalkylammonium salts or cationic surfactants suppressed this increase inE_{$\text{1}\text{2}$} values. With such mixed electrolytes containing highly active surfactants of sufficient charge density, a normal polarographic determination of methyl bromide is possible. The final diffusion rate of the active component has also a considerable effect on E_{$\text{1}\text{2}$} values so that the E_{$\text{1}\text{2}$} values of such systems cannot be characterized by the solution composition alone.     

Short synthesis of 6-oxoprostaglandin E1 and 6-oxoprostaglandin F1α

6-Oxoprostaglandin E₁ methyl ester was synthesized in a single pot from ($\text{R}$)-4-$\text{t}$-butyldimethylsiloxy-2-cyclopentenone by organocopper conjugate addition with an ω side-chain unit, trapping of the resulting enolate with 6-methoxycarbonyl-2-nitrohex-1-ene, and treatment with aqueous titanium(III) trichloride. Hydrolysis of the methyl ester was accomplished by porcine liver esterase. 6-Oxoprostaglandin F_1α, was obtained from 6-nitroprostaglandin E₁ methyl ester in four steps.     

Polyèdre de coordination de l'etain(II) dans SnC2O4: Relations structurales entre SnC2O4, Na2C2O4 et Na2Sn(C2O4)2

The crystal structure of SnC₂O₄ has been determined by X-ray single-crystal techniques and refined to R = 0,018 for 1139 reflections. The cell is monoclinic, space group $\text{C2}\text{c}$ with Z = 4 formula units, the parameters being a = 10,375(3)Å. b = 5,504(2)Å, c = 8,234(3)Å, β = 125,11(2)°. The oxalato groups, located on symmetry centers, are chelated to two Sn atoms through one oxygen on each carbon atom, giving rise to an infinite string (SnC₂O₄)_n. The Sn(II) atom is one-side bonded to four oxygen atoms with two SnO bonds of 2,232(2) Å and two of 2,393(2) Å. The tin atom is in a distorted trigonal bipyramid SnO₄E, the lone pair E occupying one of the apices of the equatorial trigonal base of the polyhedron. Crystal structure comparison with disodium bisoxalatostannate(II), Na₂Sn(C₂O₄)₂, permits one to deduce SnC₂O₄ by crystallographic shear operation $\text{1}\text{8}\text{[34}\text{2}\text{](001)}$ of $\text{c}\text{2}$ periodicity. Na₂Sn(C₂O₄)₂ can be described as an intergrowth of SnC₂O₄ and Na₂C₂O₄ structures and consldered as the first member of a new series Na₂Sn_1+n(C₂O₄)_2+n with n integer ? 0.     

Excited-state electron-transfer quenching by a series of water photoreduction mediators

Rate constants k_q for the quenching of the excited state of Ru(bipy)₃²⁺ by a series of viologen salts having different redox potential E_{$\text{1}\text{2}$} have been determined in deaerated aqueous solutions at pH = 5 by laser flash photolysis. The k_q values are found to decrease with increasing —E_{$\text{1}\text{2}$} and to correlate with the reaction free-energy change ΔG. Such a correlation is shown to be consistent with the Rehm—Weller model for electron-transfer reactions.     

Metallextraktion mit N-thiobenzoyl-N-phenylhydroxylamin: Extraction of metal ions with N-thiobenzoyl-N-phenylhydroxylamine

The extraction parameters pH_{$\text{1}\text{2}$} and K_ex for Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb with N-thiobenzoyl-N-phenylhydroxylamine are reported. N-Thiobenzoyl-N-phenylhydroxylamine extracts metals from more strongly acidic solutions than does N-benzoyl-N-phenylhydroxylamine. Iron(III) is extracted as a 1:2 chelate with the extracant, whereas iron(II) forms the expected tris chelate by oxidation. The other bivalent ions are extracted as their bis chelates.