The use of redox reactions in the analysis of dyes and dye intermediates: VIII. The determination of 4,4′-dinitrostilbene-2,2′-disulfonic acid by constant potential coulometry

The number of electrons exchanged in the electrochemical reduction of 4,4′-dinitrostilbene-2, 2′-disulfonic acid on a mercury cathode in Britton-Robinson buffer solution of pH 10 and in 0.1 M tetramethylammonium bromide solution was determined. A sensitive determination of the studied compound by constant potential coulometry was developed, and its accuracy and reproducibility were found.     

The use of redox reactions in the analysis of dyes and dye production intermediates: V. A reductometric and polarographic determination of 4,4′-dinitrostilbene-2,2′-disulfonic acid

The chemical reduction of 4,4′-dinitrostilbene-2,2′-disulfonic acid with titanium(III) chloride, chromium(II) sulfate, and vanadium(II) sulfate and the polarographic reduction of 4,4′-dinitrostilbene-2,2′-disulfonic acid were studied. Conditions for analytical use of these reactions were found.     

The use of redox reactions in the analysis of dyes and dye intermediates: XIV. Direct current polarography of 4,4′-disubstituted azobenzenes in acetonitrile

The polarographic reduction of some 4,4′-disubstituted azobenzenes in an acetonitrile medium was studied. The diffusion character of the observed limiting currents was confirmed and a mechansim of polarographic reduction proposed. The possibility of analytical application is briefly discussed.     

The use of redox reactions in the analysis of dyes and dye intermediates: XIII. A titanometric determination of azo pigments

The test azo pigments (I–V) were determined reductometrically with a standard solution of trivalent titanium, in a buffered solution containing citrate ions.     

The use of redox reactions in the analysis of dyes and dye intermediates : VII. The reductometric and polarographic determination of N,N-dimethyl-4-amino-4′-hydroxyazobenzene

The chemical reduction of N,N-dimethyl-4-amino-4′-hydroxyazobenzene with titanium(III) chloride and chromium(II) sulfate was studied, as was the polarographic reduction of this substance. Optimal conditions for the analytical application of these reactions were found.     

The use of redox reactions in the analysis of dyes and dye industry intermediates: III. An indirect determination of brilliant green with ceric sulfate

The stoichiometry of the reaction of brilliant green with ceric sulfate was studied. An indirect determination of brilliant green based on its oxidation with excess ceric sulfate and the ascorbinometric or spectrophotometric determination of the diphenoquinone-(4,4′)-bis(diethylimine) produced has been developed.     

The use of redox reactions in analysis of dyes and dye intermediates: X. Polarographic and constant-potential coulometric determination of 4,4′-dihydroxyazobenzene and 4-nitro-4′-hydroxyazobenzene

Conditions have been found for a polarographic and constant-potential coulometric determination of 4.4′-dihydroxyazobenzene and 4-nitro-4′-hydroxyazobenzene in buffered media.     

The synthesis of some 4,4′-disubstituted-2,2′-biquinolines

2,2′-Biquinoline dioxide and 4,4′-dichloro-2,2′-biquinoline have been used for the preparation of the following 4,4′-disubstituted-2,2′-biquinolines: dimethoxy, diethoxy, dihydroxy, dipiperidino, dipyrrolidino, dibromo, diphenoxy, dithiophenoxy, di(p-chloro-phenoxy), di(p-bromophenoxy), di(p-fluorophenoxy), di(β-naphthoxy) and the dinitro dioxide. Molar extinction coefficients have been determined for several of the copper (I) complexes of these compounds.     

The use of redox reactions in the analysis of dyes and dye intermediates: IX. The reductometric,polarographic, and coulometric determination of 4-nitrotoluene-2-sulfonic acid

The reduction of 4-nitrotoluene-2-sulfonic acid by chemical reaction with titanium(III) chloride and by electrochemical polarography and coulometry on a mercury cathode was studied. Conditions were found for the analytical application of these reactions.     

Biselenienyl series. II. Synthesis and resolution of 2,2′-dinitro-3,3′-biselenienyl-4,4′-dicarboxylic acid

2,2′-Dinitro-3,3′-biselenienyl-4,4′-dicarboxylic acid (VI), the first recorded compound of the 3,3′-biselenienyl series, has been prepared and resolved into its optical antipodes by fractional crystallization of its brucine salt. On the basis of the quasi-racemate method of Fredga and the O.R.D. spectra, to the dextrorotatory acid is assigned the R configuration.     

The use of redox reactions in the analysis of dyes and dye intermediates : XV. Direct current polarography of some water-insoluble azo pigments in acetonitrile

The polarographic behavior of five water-insoluble azo pigments was studied in an acetonitrile medium. The diffusion character of the observed limiting currents was confirmed and a mechanism was proposed for the polarographic reduction. The possibility of an analytical application is briefly discussed.     

Phase transitions in mesophase macromolecules. VI. The transitions in poly(oxy-2,2′-dimethylazoxybenzene-4,4′-diyloxydodecanedioyl)

The transitions of poly(oxy-2,2′-dimethylazoxybenzene-4,4′-diyloxydodecanedioyl) (PDAD) have been analyzed by differential scanning calorimetry, optical microscopy, and light scattering. The mesophase glass devitrifies at 288 K [ΔC_p = 220 J/K mol]. Crystallization from the liquid mesophase can be described between 322 and 362 K by an Avrami expression with an exponent between 3 and 4. Results of light scattering and optical microscopy are in accord with a spherulitic morphology grown after athermal nucleation. Melting of the semicrystalline samples (crystallinity up to 58%) occurs at about 391 K. The heat of fusion of the completely crystalline sample is calculated to be only 13.55 kJ/mol. The mesophase to isotropic phase transition occurs at 418 K with a heat of transition of 4.1 kJ/mol. A general discussion of these transitions is given.     

The use of redox reactions in the analysis of dyes and dye intermediates: XI. A chromometric determination of some azobenzene derivatives in an acetonitrile-methanol-water mixed medium

Optimal conditions for a direct and indirect determination of 14 azobenzene derivatives with chromium(II) chloride have been found.     

On the configuration of 4,4′,6,6′-tetraphenyl-2,2′-dithiopyrylene

The title compound showed in its UV-VIS absorption spectra large red shifts of bands from solution to crystal indicating a pronounced intermolecular interaction between the dithiopyrylene π-electron systems. Dipole moment measurement in benzene solution gave a dipole moment value of 1.90 D which offers a direct evidence for the molecule in cis-configuration.     

Pseudopolymorphism in hydroxybenzophenones: the dihydrate of 2,2′,4,4′‐tetrahydroxybenzophenone

A dihydrate pseudopolymorph of bis(2,4‐dihydroxyphenyl)methanone, C₁₃H₁₀O₅·2H₂O, (I), was obtained during polymorphism screening of hydroxybenzophenone derivatives. This structure, in which the molecule sits on a twofold axis, was compared with the known anhydrous form of (I) [Schlemper (1982). Acta Cryst. B 38 , 554–559]. The role of water in the crystal assembly was established on the basis of the known monohydrate pseudopolymorph of 3,4‐dihydroxybenzophenone [Landre, Souza, Corrêa, Martins & Doriguetto (2010). Acta Cryst. C 66 , o463–o465].     

Muss spectral fragmentation pattern of 2,2′-bipyridyis. Part VI. 2,2′- thiodipyridine

The mass spectral fragmentation of 2,2′-thiodipyridine is reported. The base peak is due to the M? I ion. The principal fragmentation routes involve loss of H, CS, CHCS and HCN from the molecular ion and CS, HCN and S from the. M-I species. Rupture of the central bonds is also an important disintegration pathway.     

The use of redox reactions in the analysis of dyes and dye industry intermediates: IV. Oxidation of benzidine,o-tolidine,and o-dianisidine with chloramine T and N-bromosuccinimide

The oxidation of benzidine, o-tolidine, and o-dianisidine with chloramine T and N-bromosuccinimide was studied, the stoichiometry was established, and a mechanism was proposed. An extraction-photometric determination of these diamines was developed, based on the reaction with excess chloramine T or N-bromosuccinimide and the measurement of the absorbance of the N,N′-dihalogeno-diphenoquinonediimines formed, after their extraction into chloroform.     

Synthesis of symmetrical 2,2′,4,4′-tetrasubstituted[4,4′-bioxazole]-5,5′(4H,4′H)-diones and their reactions with some nucleophiles

Several symmetrical 2,2′,4,4′-tetrasubstituted[4,4′-bioxazole]-5,5′(4H,4′H)-diones 1a-f were obtained by dehydrodimerization of 5(4H)-oxazolones 2a-f . The configurations of four were established; one by X-ray crystallography rac- 1c , and three rac- 1a , meso- 1a and rac- 1b by ¹H nmr spectroscopy of their derivatives. Upon being heated, the bioxazolones isomerized, presumably by breakage of the 4,4′-carbon? carbon bond to form free radicals followed by their recombination. The results of a crossover experiment were consistent with a radical nature for this isomerization reaction. Treatment of three of the bioxazolones rac- 1a , meso- 1a and rac- 1c with methanol and amine nucleophiles led to ester and amide derivatives 7–11 of α,α'-dehydrodimeric amino acids.     

Synthescs and some reactions of N,N'-diamino-2,2′- and −4,4′-bipyridinium salts

The syntheses and some reaetions of N,N'-diamino-2,2′- and 4,4′-bipyridinium salts (IV, V and VI) are described. These compounds are prepared by the reaction of bipyridyls (I-III) with O-mesitylenesulfonylhydroxylamine in moderate to good yields. Compounds IV and VI were found to give the N,N'-diacyl derivatives by the reaction with acyl chlorides and to undergo 1,.3-dipolar cycloaddition reaction with an acetylenic compound to give 1:2 adducts. Photo-irradiation of N,N'-dibenzoylimino-2,2′-bipyridinium betaine (IX) isomerizes to a mono diazepine derivative (XVI).