Reaction of 2-arylazobenzimidazolium quaternary salts with amines

Different behaviors of aromatic and nonaromatic amines with respect to a change in the structure of the salt and variations in the reaction conditions were revealed in a study of the reaction of 2-arylazobenzimidazolium quaternary salts with amines. Aliphatic and secondary cyclic amines react at comparable rates via pathways involving cleavage of the azo group and replacement of the hydrogen in the para position relative to the azo group. The reaction with aromatic amines proceeds primarily via the amination pathway, and a methyl group in the meta position relative to the azo group facilitates replacement of the hydrogen atom significantly.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 817–824, June, 1982.     

Diazo compounds of the heterocyclic series. 6. Amination of methoxy-substituted 2-naphthyl- and 2-arylazobenzimidazoles

The amination of azo compounds inactivated by quaternization was carried out for the first time using 4-methoxyphenyl-, 2- and 4-methoxynaphthylazobenzimidazoles as examples. In contrast to the quaternary salts of 2-arylazobenzimidazoles, during the amination of the above bases of azo compounds, the substitution of the methoxy group rather than of the hydrogen atom was observed. The anomalous ease of substitution of the methoxy group, located in the naphthalene ring in a position adjacent to the azo bridge was attributed to the manifestation of an ortho-effect, discovered in the series of azo compounds for the first time.For Communication 5, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1209–1214, September, 1991.     

Untersuchungen der Symmetrieverhältnisse in äquatorial koordinierten 2:1-Arylazo-CoIII-Komplexen mit Hilfe der Protonenresonanz

The magnetic equivalence of ligand protons was examined with aid of NMR. spectroscopy for a large number of 1:2 Co^III-complexes of tridentated azo dyestuffs forming a representative cross section of the whole class of substances. It was established by this investigation that ligands with a moderately polarised azo group have a particular inclination to form asymmetrical complexes in which the protons of the two ligands are not magnetically equivalent. On the other hand, ligands having a non-polarised or a strongly polarised azo group tend to form symmetrical complexes. In three cases both symmetrical and asymmetrical complexes were isolated. As in previous investigations [1], up to a total of 5 complexes were again observed, which indicates at least two causes governing the symmetry conditions. The phenomena described here could be explained with an alternative coordination of the two azo nitrogen atoms. On the basis of the NMR. results, however, preference is given to an exchange of the azo with the hydrazone form.     

Reactions of 6-(Dimethylamino)fulvene with diazoazoles and arene- and azolediazonium salts

6-(Dimethylamino)fulvene reacted with 3- and 4-substituted 5-diazoazoles, as well as with 4-substituted benzene- and pyrazole-5-diazonium salts, in an aprotic solvent with high regioselectivity at an extremely high rate to give acyclic coupling products at the α-carbon atom of the cyclopenta-1,3-diene fragment. The nature of the diazo component did not affect the reaction direction, rate, or yield. Hydrolysis of the azo compounds obtained from arenediazonium salts involved elimination of the dimethylamino group with formation of aldehydes, and their reaction with pyrrolidine resulted in replacement of the dimethylamino group by pyrrolidine ring.     

Polarography as a tool in organic analysis. III

Summary Rapid indirect polarographic and visual micro-methods have been developed for the determination of azo, azo and nitro, or azo and nitroso groups in the same solution. First, the azo group is reduced with titanium(III) at p_H 1.7 and then the nitro group at p_H 5.5. The excess of reductant is determined polarographically. Mixtures containing nitroso and azo groups are analysed by indirect polarography by reducing the nitroso group first in 7N acid and then the azo group at p_H 5.

---

Zusammenfassung Indirekte polarographische und visuelle Mikromethoden zur Bestimmung von Azogruppen, Azo- und Nitrogruppen, oder Azo- und Nitrosogruppen in derselben Lösung wurden ausgearbeitet. Zuerst wird die Azogruppe bei p_H 1,7 mit Titan(III), dann die Nitrogruppe bei p_H 5,5 reduziert. Der Überschuß des Reduktionsmittels wird polarographisch bestimmt. Gemische mit Nitroso-und Azogruppen lassen sich indirekt polarographisch analysieren, indem man zuerst die Nitrogruppe in 7-n Säure und dann die Azogruppe bei p_H 5 reduziert.

     

Reduction of 4-oxo-4,6,7,8(5H)-tetrahydropyrrolo[3,2-c]azepines

1,2-Diaryl-4,6,7,8(5H)-tetrahydropyrrolo[3,2-c]azepines are obtained via the reduction of 1,2-diaryl-4-oxo-4,6,7,8(5H)-tetrahydropyrrolo[3,2-c]azepines with lithium aluminum hydride. In the case of a bromophenyl substituent reduction of the bromine atom occurs as well; similarly, in the case of a nitroaryl-substituted lactam, reduction of the amide carbonyl function is accompanied by reduction of the nitro group to an azo group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 63–65, January, 1985.     

Introducing an amine group to calix[5]arene: comparison of several methods

Abstract

Chemists often use an amine group as an intermediate in syntheses of imines, amides and ureas; however, in the case of syntheses of p-aminophenol type compounds, several problems might occur. In this article, we prepared p-aminocalix[5]arene-pentaol by reduction of both nitro and azo derivatives, and compared four methods of the amine preparation, focusing mainly on its gramme scale and time-consuming issues.     

Analogs of styryl dyes and the simplest AZO dyes from 2-dimethylaminothiophene

The condensation of 2-dimethylaminothiophene with the appropriate derivatives of quaternary benzothiazole salts has give the vinylene-homologous series of dyes with the structure (I). By coupling with benzenediazonium salts, the simplest azo dyes of structure (III) have been synthesized. The influence on the absorption spectra of the replacement of a dimethylaniline nucleus in polymethine and azo dyes by a 2-dimethylaminothiophene nucleus has been investigated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 923–925, July, 1973.     

Effect of cooperative hydrogen bonding in azo-hydrazone tautomerism of azo dyes

Azo-hydrazone tautomerism in azo dyes has been modeled by using density functional theory (DFT) at the B3LYP/6-31+G(d,p) level of theory. The most stable tautomer was determined both for model compounds and for azo dyes Acid Orange 7 and Solvent Yellow 14. The effects of the sulfonate group substitution and the replacement of the phenyl group with naphthyl on the tautomer stability and on the behavior in solvent have been discussed. Intramolecular hydrogen bond energies have been estimated for the azo and hydrazone tautomers to derive a relationship between the tautomer stability and the hydrogen bond strength. The transition structures for proton transfer displayed resonance assisted strong hydrogen bonding properties within the framework of the electrostatic-covalent hydrogen bond model (ECHBM). Evolution of the intramolecular hydrogen bond with changing structural and environmental factors during the tautomeric conversion process has been studied extensively by means of the atoms-in-molecules (AIM) analysis of the electron density. The bulk solvent effect was examined using the self-consistent reaction field model. Special solute-solvent interactions were further investigated by means of quantum mechanical calculations after defining the first-solvation shell by molecular dynamics simulations. The effect of cooperative hydrogen bonding with solvent molecules on the tautomer stability has been discussed.     

Selective detection of aqueous nitrite ions by surface-enhanced Raman scattering of 4-aminobenzenethiol on Au

In this work, we have devised a selective nitrite-ion detection method based on the surface-enhanced Raman scattering (SERS) of 4-aminobenzenethiol (4-ABT) on Au. This is possible because, firstly, SERS is a very surface-sensitive technique with monolayer detection capability, and secondly, the amine group of 4-ABT reacts readily with nitrites in acidic media, forming a diazonium group, which can subsequently form an azo bond by reacting with a variety of benzene derivatives. From the peak intensity of the diazonium group, the presence of nitrite ions above 20 μM can be identified readily. From the peak intensity of the azo moiety alone, it is even possible to detect nitrite ions at concentrations as low as 5 μM, without interference from other anions. This work clearly illustrates the usefulness of SERS in environmental science research.     

Flavylium-Based Hypoxia-Responsive Probe for Cancer Cell Imaging

A hypoxia-responsive probe based on a flavylium dye containing an azo group (AZO-Flav) was synthesized to detect hypoxic conditions via a reductase-catalyzed reaction in cancer cells. In in vitro enzymatic investigation, the azo group of AZO-Flav was reduced by a reductase in the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH) followed by fragmentation to generate a fluorescent molecule, Flav-NH₂. The response of AZO-Flav to the reductase was as fast as 2 min with a limit of detection (LOD) of 0.4 μM. Moreover, AZO-Flav displayed high enzyme specificity even in the presence of high concentrations of biological interferences, such as reducing agents and biothiols. Therefore, AZO-Flav was tested to detect hypoxic and normoxic environments in cancer cells (HepG2). Compared to the normal condition, the fluorescence intensity in hypoxic conditions increased about 10-fold after 15 min. Prolonged incubation showed a 26-fold higher fluorescent intensity after 60 min. In addition, the fluorescence signal under hypoxia can be suppressed by an electron transport process inhibitor, diphenyliodonium chloride (DPIC), suggesting that reductases take part in the azo group reduction of AZO-Flav in a hypoxic environment. Therefore, this probe showed great potential application toward in vivo hypoxia detection.     

Preparation of soluble graft polymers from allyl benzoate/2,2′‐azobis(N‐(2‐propenyl)‐2‐methylpropionamide) crosslinked polymers as insoluble polymeric azo initiators

2,2′‐Azobis(N‐(2‐propenyl)‐2‐methylpropionamide) (APMPA) having two carbon‐carbon double bonds and an azo group was copolymerized with allyl benzoate (ABz) at 60°C, providing an azo groups containing ABz/APMPA crosslinked polymer which may act as an insoluble polymeric azo initiator. The gelation in ABz/APMPA (70/30 mol/mol) copolymerization was discussed in detail in order to reveal the characteristic polymerization behavior of APMPA as a novel diallyl monomer. The effectiveness of the resulting ABz/APMPA crosslinked polymer to give a soluble graft polymer through cleavage of the azo crosslinkages at an elevated temperature was then examined by polymerizing ABz at 120°C.     

N-Bromosuccinimide assisted oxidation of 5-aminopyrazoles: formation of bis diazenylderivatives

Treatment of 5-amino-4-cyanopyrazoles with N-bromosuccinimide, in DMF at rt gave azo dyes resulting from dimerization through the amino groups and further oxidation.With bromine water the dimer was also formed but, bromination occurred on the aryl ring, either at reflux or rt. Reduction of the azo group with zinc in acetic acid originated the corresponding pyrazoles.     

Synthesis,characterization, and dyeing performance of some azo thienopyridine and thienopyrimidine dyes based on wool and nylon

A string of novel heterocyclic mono azo dyes were synthesized and their utilization in dyeing different fabrics as wool and nylon were discussed. Thienopyridine azo dyes 4 and 6 were prepared by reaction of chloro acetamidederivative 2 with diamino compounds to yield 3 and 5 , followed by reaction with NaNO₂/HCl and coupling with nucleophilic reagent. One-pot reaction of chloro acetamide 2 with ammonium thiocyanat in solvent ethanol gave the unexpected thienopyrimidine derivative 7 , which contain two active sites, the former is primary amine that was able to form diazonium salt that coupled with N,N-dimethylaniline, resorcinol, and/or self-coupling to afford the azo dyes 8-10 , and the latter is active methylene group that underwent coupling with different diazonium salts to give the azo thienopyrimidine derivative dye 11-15 . The dyeing performance of these azo dyes had been investigated in terms of their dyeing behavior and fastness properties on different fabrics. Results showed that the color strength (K/S) values, as well as, washing, rubbing, and resistance to acid, alkali and light showed high efficiency of these heterocyclic mono azo dyes to dye wool rather than nylon fibers.     

Photoinduced orientational ordering in the series of methacrylic azopolymers

Polymethacrylates with side azo fragments containing various end substituents and spacers are synthesized and characterized. Spatial ordering of azo fragments in the series of the synthesized azo polymers under the action of polarized excitation light is studied by the methods of null ellipsometry and polarization spectroscopy. Two types of anisotropy development during photoirradiation are found. In homologs with strong acceptor substituents of azo fragments, biaxial orientational structure can be observed; as the radiation dose is increased, this structure is transformed into a uniaxial structure with a negative order parameter and with an axis parallel to the polarization vector of the excitation light. In this structure, the maximum degree of orientational order is achieved in polymers with high concentrations of azo fragments. In homologs with donor substituents of azo fragments, the initial stages of irradiation likewise lead to the development of biaxial orientation; later, this orientation is transformed into an isotropic distribution. The mode of anisotropy development is controlled by the lifetime of photoisomers of azo fragments.     

Conversion of 1,3‐Dimethyl‐5‐(Arylazo)‐6‐Amino‐Uracils to 1,3‐Dimethyl‐5‐(Arylazo)‐Barbituric Acids: Spectroscopic Characterization,Photophysical Property and Determination of pKa of the Products

The study of inter‐conversion between molecules, especially biologically and pharmaceutically important molecules, is extremely important. This study reports the inter‐conversion between two azo‐derivtives: azo‐6‐aminouracils to azo‐barbituric acids. We successfully converted the 1,3‐dimethyl‐5‐(arylazo)‐6‐aminouracils ( Uazo‐1 to Uazo‐4 ) to 1,3‐dimethyl‐5‐(arylazo)‐barbituric acids ( BAazo‐1 to BAazo‐4 ) (where aryl?C₆H₅‐( 1 ); p‐MeC₆H₄‐( 2 ), p‐ClC₆H₄‐( 3 ), and p‐NO₂C₆H₄‐( 4 )) following an acid‐hydrolysis path. The products were characterized using spectroscopic tools like UV‐vis, IR, and NMR spectroscopy. UV‐vis spectra of the as‐prepared dyes reveal that in contrast to the azo‐6‐aminouracils they are hardly responsive towards solvatochromism. IR spectra exhibit three characteristic >C?O frequencies for as‐prepared azobarbituric acids instead of two for mother azo‐6‐aminouracils. ¹H NMR spectra which reflect the existence of solution species evidence the absence of >C?NH group (characteristic imido‐H at the 6‐position of hydrazone species of azo‐6‐aminouracils) and consequence presence of >C?O group at the same position in as‐prepared azobarbituric acids. They exhibit structural emissions in the range of 400–440 nm upon excitation at 360 nm. The determined acid dissociation constant (pKa) values of BAazos increase according to the following sequence: BAazo ‐ 2 > 1 > 3 > 4 .     

Effect of Substituent in Diazotized Orthanilic Acid on the Azo Coupling with 7-Acetylamino-4-hydroxynaphthalene-2-sulfonic Acid in Citrate-Phosphate Buffers

Effect of substituent in the para position with respect to the diazo group in diazotized orthanilic acid derivatives on the rate and selectivity of azo coupling with 7-acetylamino-4-hydroxynaphthalene-2-sulfonic acid was studied in citrate-phosphate buffers. The selectivity of azo coupling at the 3-position of the azo component almost does not depend on the nature of electron-donor substituent. Electron-acceptor groups considerably reduce the selectivity of formation of the 3-isomer. Previous conclusions, according to which the rate-determining stages are different depending on the site of azo coupling of diazotized orthanilic acid with 7-acetylamino-4-hydroxynaphthalene-2-sulfonic acid, were found to be also valid for some 5-substituted orthanilic acid derivatives. The rate-determining stage in the azo coupling at the 3-position can change upon introduction of strong electron-acceptor substituents capable of interacting with the diazo group. The contribution of the multicenter mechanism of deprotonation of the -complex with participation of water molecules was presumed to increase in going to the diazo components having electron-donor substituents.     

Identification and molecular characterization of a novel flavin-free NADPH preferred azoreductase encoded by <Emphasis Type="Italic">azoB</Emphasis> in <Emphasis Type="Italic">Pigmentiphaga kullae</Emphasis> K24

Background  

Microbial degradation of azo dyes is commonly initiated by the reduction of the azo bond(s) by a group of NADH or NADPH dependant azoreductases with many requiring flavin as a cofactor. In this study, we report the identification of a novel flavin-free NADPH preferred azoreductase encoded by azoB in Pigmentiphaga kullae K24.     

Strategies for continuous on-line high performance liquid chromatography coupled with diode array detection and electrospray tandem mass spectrometry for process monitoring of sulphonated azo dyes and their intermediates in anaerobic-aerobic bioreactors

On-line HPLC with diode array detection (DAD) coupled to electrospray tandem mass spectrometry (ESI-MS/MS) is presented as an integrated quality control and process integrated optimisation tool for the continuous monitoring of sulphonated azo dyes (SADs) and their intermediates in anaerobic and aerobic bioprocesses. Ion-pair RP-HPLC is found out to be more suitable for simultaneous monitoring of aromatic amines (AAs), sulphonated aromatic amines (SAAs) and sulphonated azo dyes in comparison to RP-HPLC with polar embedded phases. Monitoring of the anaerobic degradation of the diazo Reactive Black 5 displays the dependency of a two stage azo group reduction mechanism on the redox potential of the bioreactor. An autoxidation sensitive intermediate released from the anaerobic reduction is characterised by ESI-MS/MS for the first time. The functionality of the method is demonstrated by the control and evaluation of selective adaptation of bacteria to certain pollutants and the identification of unknown intermediates causing re-gaining colour released from azo dye treatment.     

MOLECULAR PROBES: PHOTOISOMERIZATION OF OPTICALLY ACTIVE AZO COMPOUNDS

Abstract— The azo group may be used as a probe to gain information about the molecular surroundings. The circular dichroism (CD) spectra of two azo steroids have been investigated in media of different viscosity and polarity. The CD spectra of the trans -compounds are only slightly affected by the environment while those of the cis -compounds are strongly dependent on the environment. Photoisomerization is analysed by absorption and ellipticity diagrams as tests for chromophoric and conformeric uniformity. Our results support an inversion mechanism of the photoisomerization of azo compounds.