Dissociation constants of n,n'-bis(2-carboxyethyl)dithiooxamide

The dissociation constants of N,N'-bis(2-carboxyethyl)dithiooxamide have been determined by potentiometric and spectrophotometric methods. They were calculated by a modified Ricci formula and by a weighted least-squares treatment. The thermodynamic constant pK₃^T is 12.32. At ionic strength 1.00, pK₁=3.76, pK₂=4.74, pK₃=11.41 and pK₄=14.19.     

A potentiometric study of the water-soluble silver(I) complexes of n,n'-bis(2-hydroxyethyl)dithiooxamide : Part III. Determination of the different species

Silver(I) and N,N'-bis(2-hydroxyethyl)dithiooxamide (H₂X) in acidic solutions, form a series of water-soluble polynuclear complexes. These complexes can be represented by two general formulae: H_2qAg_pX_q and H_2q-1Ag_pX_q with q=1,2,3 and p=q, q-1.     

Spectrophophotometric determination of manganese with n,n,n',n'-tetrakis(2-hydraxypropyl)ethylenediamine

A new spectrophotometric method for the determination of manganese with N,N,N,N'-tetrakis-(2-hydroxypropyl) ethylenediamine has been developed. The sensitivity is 0.12 μm of Mn per cm² for log I₀/I= 0.001 and Beer's law is obeyed between 2 and 100 p.p.m. of manganese. An ionexchange separation of interfering ions was satisfactory for thc analysis of a variety of National Bureau of Standards samples with good accuracy. The standard deviation with a Mn-bronze was 1.25%.     

Spectrophotometric study of n,n'-bis(m-sulphobenzyl)dithio-oxamide as a reagent for nickel(II)

N,N'-Bis(m-sulphobenzyl) dithiooxamide forms a water-soluble intensely red chelate with nickel-(II) in buffered solutions at pH 10, A 1 Ni : 1R complex is obtained. The absorption maximum of the complex lies at 500 mμ, where the absorbance of (SB)₂DTO is negligible. The molar extinction coefficient is ca, 6962. Beer's law is obeyed over the range from 0.5 μg to 50 μg per ml.     

Spectrophotometric study of n,n'-bis (2-sulphoethyl)dithio-oxamide as a reagent for palladium

N,N'-bis(2-Sulphoethyl)dithio-oxamide forms two water-soluble yellow chelates with palladium(II), in strong hydrochloric acid solution or in buffered weak acid solution; with excess of reagent, a 1Pd:2R complex is always obtained. The absorption maximum occurs at 425 mμ in 6 M hydrochloric acid and at 382 mμ in buffered weak acid solution (pH 6.6). The colour is formed more slowly in strong acid solution, but there are fewer interferences. Relatively high concentrations of Co²⁺, Ni²⁺ and Hg²⁺can be tolerated, as well as smaller concentrations of Ir³⁺, Rh³⁺ and Cr³⁺. The molar absorption coefficients are 12,860 and 10,840 respectively in 6 M hydrochloric acid and buffered weak acid solution. The standard deviation in both cases is 0.004 absorbance units, i.e. respectively 0.033 and 0.039 μg of Pd.     

Spectrophotometric determination of the dissociation constants of n.n'-bis(2-hydroxyethyl)dithio-oxamide

The dissociation constants of N, N'-bis(2-hydroxyethyl)dithio-oxamide were determined by a spectrophotometric method. The dissociation constants were calculated by means of a weighted least squares technique. N, N'-Bis(2-hydroxyethyl)dithio-oxamide was found to be a dibasic acid with a thermodynamic dissociation constant pK1-11/04. At ionic strength μ - 0.5, pK1 - 10.71 and pK2 13.92.     

Simultaneous spectrophotometric determination of traces of cobalt,nickel and copper with n,n'-bis(3-dimethylaminopropyl)dithio-oxamide

The cobalt, nickel and copper complexes of N,N'-bis(3-dimethylaminopropyl)dithio-oxamide have been characterized in terms of color, effect of pH, rate of color formation, structure in solution, order of addition of reagents, adherence to Beer's law, and sensitivity. The reactivity of the reagent to other ions has been reported. A method for the simultaneous spectrophotometric determination of cobalt, nickel and copper has been developed. The results of the application of this procedure to synthetic samples and to several National Bureau of Standards samples are given.     

Chelating properties of n,n,n,n-tetrakis-(phosphonomethyl)-1,2-cyclohexanediamine

The octasodium salt of N,N,N',N'-tetrakis-(phosphonomethyl)-1,2-cyclohoxanediamine, Na₈-CDTMP, can be prepared in 45% yield from chloromethylphosphonic acid and 1,2-cyclohexanediamine. The titration curve resulting from the titration of the acid, CDTMP, with sodium hydroxide at 25° and μ = 0.1 was used to estimate the eight pK values for the free acid. The stability constants of metal chelatles of CDTMP were measured at 25° and μ = 0.1 potentiometrically.     

Amidines-XVIII: Tautomeric equilibria and pka values of N,N'-disubstituted amidines. Substituent effects

The influence of substitution of amidine group on tautomeric equilibria constants and basicities is discussed. Equations based on correlation analysis methods are derived enabling predictions of both, microscopic pK_a, values of individual tautomers, measured macroscopic pK_a values of the tautomeric mixture, as well as the tautomeric equilibrium constant (as pK_T). It is shown that pK_arn values of unsymmetrically N,N'-disubstituted amidines should obey a non-linear relation with σ° constants, and only for symmetrically N,N'-disubstituted amidines obey the linear Hammett equation. Tautomeric equilibrium constants of N,N'-disubstituted amidines correlate withσ° substituent constants. The methods of prediction of pK_a value of both tautomers and pK_T value are proposed.Derived relations are applied to the series of N,N'-diphenylacetamidines and benzamidines.     

Some metallofluorescent derivatives of 2,2'-diamino-diphenyl-n,n,n',n'-tetraacetic acid

The N,N,N',N'-tetraacetic acid derivatives of five 4,4'-disubstituted 2,2'-diaminodiphenyls have been prepared and their fluorescent properties examined. 2,2'-Diaminodiphenyl-4,4'-dicarboxylic acid-N,N,N',N'-tetraacetic acid exhibits intense fluorescence in aqueous solution above pH 4, and forms stable non-fluorescent l:1 complexes with copper(II) and nickel(II) ions at pH 7.5. The quenching of the fluorescence of the compound by nickel(II) may be used in the fluorimetric determination of nickel.     

Spectrophotometric or absorptiometric determination of copper with 2,2'-diaminodiethylether-n,n.n', n'-tetraacetic acid

A spectrophotometric determination of copper with 2,2'-diaminodiethylether-N,N,N',N'-tetraacetic acid is proposed. Maximum absorbance is obtained at 720 mμ at pH 2 (1–3) and 25–650 μg Cu/ml can be determined. The reaction is unaffected by temperature or time of standing, and very few ions interfere. A 1 : 1 copper-EEDTA complex is formed.     

A potentiometric study of the water-soluble silver(I) complexes of n,n'-bis(2-hydroxyethyl)dithio-oxamide (hedto) : Application of the “core+links” method

Silver(I) forms with N,N'-bis(2-hydroxyethyl)dithio-oxamide (HEDTO) water-soluble complexes in acidic medium. The composition of these complexes may be represented by the following formula: B(AB)_n in which B is the ligand and A the metal ion. There is some indication that complexes with general formula (AB)_n also are formed.     

Functionalization of highly electrophilic <Emphasis Type="Italic">N</Emphasis>-(2,2,2-trichloroethylidene)- and <Emphasis Type="Italic">N</Emphasis>-(2,2-dichloro-2-phenylethylidene) arenesulfonamides with dithiooxamide

Depending on the reactant ratio, dithiooxamide (ethanedithioamide) reacted as N-nucleophile or N,N′-binucleophile with highly electrophilic aldimines, N-(2,2,2-trichloroethylidene)- and N-(2,2-dichloro-2-phenylethylidene)arenesulfonamides, to give the corresponding mono- or bis-adducts, N-[2-polychloro-1-(arylsulfonylamino) ethyl]ethanedithioamides or N,N′-bis[2-polychloro-1-(arylsulfonylamino)ethyl]ethanedithioamides, in good yield.     

<Emphasis Type="Italic">N,N′</Emphasis>-Bis(triethoxysilylmethyl)thiocarbamide and Poly[<Emphasis Type="Italic">N,N′</Emphasis>-bis(silsesquioxanylmethyl)thiocarbamide <Emphasis Type="Italic">S,S</Emphasis>-dioxide]

Condensation of (aminomethyl)triethoxysilane with thiocarbamide in the presence of catalytic amounts of ammonium sulfate was used to synthesize N,N-bis(triethoxysilylmethyl)thiocarbamide. The latter was brought into oxidative hydrolytic polycondensation with H₂O₂ to obtain poly[N,N′-bis(silsesquioxanylmethyl)thiocarbamide S, S-dioxide] whose properties were compared with the properties of poly[N,N′-bis(silsesquioxanylpropyl)thiocarbamide S,S-dioxide]. Both polymers in highly acidic media rather strongly absorb Ag(I), while at pH 7 they reduce most absorbed Ag⁺ to the metal. Their reaction with potassium permanganate involves reduction of Mn⁷⁺ to Mn⁴⁺. The first polymer is a less effective sorbent and redox agent than the second.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 7, 2005, pp. 1154–1156.Original Russian Text Copyright © 2005 by Voronkov, Vlasova, Grigor’eva, Pozhidaev, Bol’shakova.     

3,3'-Dihydroxybenzidine-n,n,n',n'-tetraacetic acid as a metallofluorescent indicator in edta titrations

3,3'-Dihydroxybenzidine-N,N,N',N'-tetraacetic acid has been prepared and examined as a metallofluorescent indicator in compleximetric titrations. Copper(II) and lead(II) are determined by titration with EDTA in the presence of the indicator, the blue fluorescence of which is restored at the end-point. Manganese, zinc, cobalt and cadmium can also be determined if a dyestuff such as Rhodamine B is present along with the indicator.     

Synthesis,Characterization and Magnetic Properties of New Dinuclear Copper(II) Complexes with N,N′‐Disubstituted Dithiooxamides derived from α‐Amino Acids

Four new dinuclear copper(II) complexes have been synthesized and have the general formula [Cu₂(L)(H₂O)₂], where L = GLYDTO [N,N′‐bis(carboxymethyl)dithiooxamide], ALADTO [N,N′‐bis(carboxyethyl)dithiooxamide], VALDTO [N,N′‐bis(1‐carboxy‐2‐methylpropyl)dithiooxamide] and LEUDTO [N,N′‐bis(1‐carboxy‐3‐methylbutyl)dithiooxamide]. The complexes were characterized by elemental analysis as well as by IR, electronic and EPR spectroscopy. These techniques provided evidence for the presence of the CuNO₂S chromophore. Magnetic susceptibility measurements on all the complexes in the range 4–300 K show the existence of a dominant antiferromagnetic interaction with ?J values greater than 300 cm^?1. Thermal decomposition behaviour of the complexes was studied by thermogravimetry.     

Synthesis of bis(N-heterocyclic carbene) palladium complexes derived from (S,S)-1,2-bis(1-hydroxypropyl)benzene

New o-xylylene-linked bis(benzimidazolium) salts were synthesized in six-steps from C₂-symmetric chiral 1,4-diol, 1,2-bis(1-hydroxypropyl)benzene, as a starting material. The silver complex of bis(benzimidazol-2-ylidene) was obtained on treatment of bis(benzimidazolium) salt with silver oxide. The reaction of the silver bis-NHC with [PdCl₂(PhCN)₂] afforded the bis-NHC complex of palladium. The X-ray diffraction studies on Pd complexes revealed that these complexes have distorted square planar geometry around the Pd center coordinating the NHC ligand in mutually cis-position. The arene ring of o-xylylene unit hanged over the Pd center and thus these complexes showed C₁-symmetric structures. The variable temperature NMR spectroscopy revealed that these Pd complexes showed fluxional behavior between C₁- and C₂-symmetric structures in solution state.     

Preparation and structural characterization of hetero-dinuclear Schiff base copper(II)-zinc(II) complexes and their inhibition studies on Helicobacter pylori urease

A series of hetero-dinuclear Cu^II-Zn^II complexes, [CuZnCl₂L¹] (1), [CuZnCl₂L²] (2), [CuZnBr₂L³] (3), [CuZnBr₂L⁴(DMF)] (4), [CuZnCl₂L⁴] (5), [CuZnCl₂L⁵] (6), [CuZnCl₂L³] (7) and [CuZnBr₂L¹] (8), where L¹, L², L³, L⁴ and L⁵ are the deprotonated forms of N,N′-bis(3-ethoxysalicylidene)-1,3-propanediamine (H₂L¹), N,N′-bis(2-hydroxynaphthylmethylidene)-1,3-propanediamine (H₂L²), N,N′-bis(3-methoxysalicylidene)-1,3-propanediamine (H₂L³), N,N′-bis(salicylidene)-1,3-propanediamine (H₂L⁴) and N,N′-bis(salicylidene)-1,4-butanediamine (H₂L⁵), respectively, have been synthesized and characterized by physico-chemical methods and single-crystal X-ray diffraction. The complexes were tested for their urease inhibitory activity. Complexes 1 and 8 show effective urease inhibitory activity with IC₅₀ values of 2.2 and 10.7 μM. The molecular docking study of the complexes with the Helicobacter pylori urease was performed.     

Charge transfer complexes between I2 and 1,3-imidazolidine-2-thione and its n-mono- and n,n'-di-substituted derivatives

Spectrophotometric studies of iodine with 1,3-imidazolidine-2-thione and its N-mono- and N,N'-di-alkyl derivatives (alkyl = Me, Et) have been carried out in carbon tetrachloride and dichloromethane solutions. In each case, a new intense peak due to the charge transfer band of a 1:1 molecular complex was observed. The thermodynamic and spectral characteristics of these complexes have been determined. The well known “blue shift” of the visible band of I₂ is verified, but the analogous blue shift of the donor absorption is hidden by the solvents. To explain the very high differences between the stability constants of the N,N'-disubstituted derivatives and the others, an intramolecular H-bonding between NH and terminal iodine has been hypothesized. IR measurements carried out on N-ethyl-1,3-imidazolidine-2-thione seem to support this hypothesis.     

2, 2'-bis(diphenylphosphino)-1, 1'-binaphthyl(binap) : A new atropisomeric bis(triaryl)phosphine. synthesis and its use in the rh(l)-catalyzed asymmetric hydrogenation of α-(acylamino)acrylic acids

Racemic 2, 2'-bis(diphenylphosphino)-l, 1'-binaphthyl has been synthesized from 2, 2'-dihydroxy-l, l'-binaphthyl in two steps and resolved into optically pure (R)-(+) and (S) (-) enantiomers by the use of (+)-di-μ-chlorobis[(S)-N,N-dimethyl-α-phenylethylamine-2C,N]dipalladium. This new axially dissymmetric bis(triaryl)phosphine serves as an excellent ligand for Rh(l)-catalyzed asymmetric hydrogenations of α-(acylamino) acrylic acids or esters. Factors controlling the enantioselectivity and mechanistic aspects are discussed on the basis of the ³¹P-NMR measurements