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.     

Spectkophotometric determination of the dissociation constants of n,n'-bis(3-hydroxypropyl)dithiooxamide and n,n'-bis(2-hydroxypropyl)dithiooxamide

The dissociation constants of N,N'-bis(3-hydroxypropyl)dithiooxamide and N,N'-bis(2-hydroxypropyl)dithiooxamide were determined by a spectrophotometric method using a weighted least squares technique for the calculations. For N,N'-bis(3-hydroxypropyl) dithiooxamide a thermodynamic constant pK₁^T of 11.37 was found. At ionic strength μ = 1, pK₁ = 11.27 and pK₂ = 14.29. For N,N'-bis-(2-hydroxypropyl) dithiooxamide, these values were respectively: pK₁^T = 11.11; pK₁ = 10.99 and pK₂ = 13.75.     

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.     

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.     

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.     

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.     

The pKa values of N,N,N',N'-tetrakis-(2-hydroxypropyl)ethylenediamine

Aqueous solutions of the industrially important chelating agent N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine exhibit basic properties. The proton dissociation constants were determined to be 8.99 ± 0.04 (pK₁) and 4.30 ± 0.04 (pK₂) by potentiometric titration at 25° in 0.15M sodium chloride.     

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.     

Novel synthesis of n,n'-bis (α-isocyanato alkyl) diazenes

The conversion of aliphatic ketazines $\text{1}$ with cyanic acid into the “criss cross” cycloadducts, the triazolo-triazolediones $\text{2}$, followed by oxidative ring opening provides an efficient synthetic route to the title compounds $\text{4}$.     

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.     

(n‐Nitrophenyl)acetonitrile,with n = 2, 3 and 4

The molecular structures of the three title nitro‐substituted phenyl­aceto­nitriles, C₈H₆N₂O₂, at 123 K show that the mol­ecules are linked together very differently. In the 2‐ and 4‐nitro compounds, there are both O?H and N_cyano?H interactions, whereas the crystal lattice of the 3‐nitro compound is essentially built up by O?H interactions. The O atoms seem to prefer the aromatic H atoms, while the cyano N atoms prefer the methyl­ene H atoms. The phenyl–nitro torsion angles are ?19.83 (13), ?5.69 (12) and ?2.88 (12)°, while the phenyl–cyano­methyl torsion angles are ?62.27 (12), ?147.99 (9) and ?16.75 (14)° in the 2‐, 3‐ and 4‐NO₂‐substituted compounds, respectively.     

Synthesis of licoflavone-a and 6',6'-dimethylpyrano(2',3':7,8)flavone

Licoflavone-A assigned structure of 6-C-prenyl-7,4'-dihydroxyflavone 5 has been synthesized by condensing 5-C-prenyl-2-hydroxy-4-prenyloxyacetophenone 2 with p-prenyloxybenzaldehyde in the presence of alkali. The resulting chalcone 3 on cyclodehydrogenation with DDQ gave 6-C-prenyl-7,4'-diprenyloxyflavone 4 which on boiling with aqueous morpholine afforded the natural product. This synthesis uses, for the first time, protection of phenolic hydroxyls by O-prenylation and DDQ for conversion of chalcone to flavone. 6',6'-Dimethylpyrano (2',3':7,8)navone 8 has been synthesized by the Hlubucek reaction of 7-hydroxyflavone 6 with 2-chloro-2-methyl-3-butyne.     

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.     

Secondary interactions in n‐(chloromethyl)pyridinium chlorides (n = 2, 3, 4)

In the isomeric title compounds, viz. 2‐, 3‐ and 4‐(chloro­methyl)pyridinium chloride, C₆H₇ClN⁺·Cl^?, the secondary interactions have been established as follows. Classical N—H?Cl^? hydrogen bonds are observed in the 2‐ and 3‐isomers, whereas the 4‐isomer forms inversion‐symmetric N—H(?Cl^??)₂H—N dimers involving three‐centre hydrogen bonds. Short Cl?Cl contacts are formed in both the 2‐isomer (C—Cl?Cl^?, approximately linear at the central Cl) and the 4‐isomer (C—Cl?Cl—C, angles at Cl of ca 75°). Additionally, each compound displays contacts of the form C—H?Cl, mainly to the Cl^? anion. The net effect is to create either a layer structure (3‐isomer) or a three‐dimensional packing with easily identifiable layer substructures (2‐ and 4‐isomers).     

Crystal Structure of CH2[N(SO2F)2]2, N,N,N′,N′-tetrakis(fluorosulfuryl)methylenediamine

CH₂[N(SO₂F)₂]₂ is monoclinic, space group P2₁/c, with 8 molecules in the unit cell. The structure, which was solved by direct methods in a straightforward manner and refined to R = 0.082 for 2647 diffractometer intensities, consists of discrete molecules.     

A Facile synthesis of n,n′‐oligomethylenebis(4,5‐dihydrofuran‐3‐carboxamide)s using manganese(III)‐based radical cyclization of n,n′‐oligomethylenebis(3‐oxobutanamide)s with 1,1‐diarylethenes

The reaction of N,N′‐oligomethylenebis(3‐oxobutanamide)s with 1,1‐diarylethenes in the presence of manganese(III) acetate in acetic acid at 100° produced N N′‐oligomethylenebis(2‐methyl‐5,5‐diaryl‐4,5‐dihydrofuran‐3‐carboxamide)s. Similarly, the reaction of 3‐oxobutanamidoethyl 3‐oxobutanoate or N,N′‐(3,6‐dioxaoctamethylene)bis(3‐oxobutanamide) with 1,1‐diphenylethene gave (2‐methyl‐5,5‐diphenyl‐4,5‐dihydrofuran‐3‐amido)ethyl 2‐methyl‐5,5‐diphenyl‐4,5‐dihydrofuran‐3‐carboxylate or N,N′‐(3,6‐dioxa‐octamethylene)bis(2‐methyl‐5,5‐diphenyl‐4,5‐dihydrofuran‐3‐carboxamide) in moderate yields.     

Complex of N,N′,N′,N‴-tetrakis[2-diphenylphosphorylethyl]-1,4,7,10-tetraazacyclododecane with copper (II) perchlorate. Synthesis,structure, and conformational analysis

1,4,7,10-Tetraazacyclododecane having β-ethylphosphoryl pendant groups on the nitrogen atoms can form a complementary ligand for the Cu cation. It gives rise to a square pyramidal complex of [CuL]²⁺ compositions, the ligand entering this complex with a slight energy strain. © 1996 John Wiley & Sons, Inc.     

Theoretical study of silicon–sulfur clusters (SiS2)n− (n=1–6)

The possible geometrical structures and relative stability of silicon–sulfur clusters (SiS₂) (n=1–6) are explored by means of density functional theory (DFT) quantum chemical calculations. We also compare DFT with second‐order Møller–Plesset (MP2) and Hartree–Fock (HF) methods. The effects of polarization functions, diffuse functions, and electron correlation are included in MP2 and B3LYP quantum chemical calculations, and B3LYP is effective in larger cluster structure optimization, so we can conclude that the DFT approach is useful in establishing trends. The electronic structures and vibrational spectra of the most stable geometrical structures of (SiS₂)_n⁻ are analyzed by B3LYP. As a result, the regularity of the (SiS₂)_n⁻ cluster growing is obtained, and the calculation may predict the formation mechanism of the (SiS₂)_n⁻ cluster. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 280–290, 2001     

Quantum chemical exploration of formaldehyde clusters (H2CO)n (n = 2–4)

Global exploration of equilibrium structures and interconversion pathways on the quantum chemical potential energy surface (PES) is performed for (H₂CO)n (n = 2–4) by using the Scaled Hypersphere Search‐Anharmonic Downward Distortion Following (SHS‐ADDF) method. Density functional theoretical (DFT) calculations with empirical dispersion corrections (D3) yielded comparable results for formaldehyde dimer in comparison with recent detailed studies at CCSD(T) levels. Based on DFT‐D3 calculations, trimer and tetramer structures and their stabilities were studied. For tetramer, a highly symmetrical S₄ structure was found as the most stable form in good accordance with experimentally determined tetramer unit in the formaldehyde crystal. © 2018 Wiley Periodicals, Inc.