Hydrazone Form Research Articles

Fluorescence and Absorption Spectra of Phenylazopyrazolone Dyes

Abstract The absorption and fluorescence spectra of some arylazopyrazolone dyes have been investigated. The emission is assigned to their hydrazone form. A very good linear correlation is obtained between the σ Hammett constants and the differences of the absorption maxima of the hydrazone form and the anion. Quantum chemical calculations indicate to a charge migration upon exci­tation. The electron donor substituents cause bathochromic and hypsochromic shifts in the absorption and in the fluorescence maxima resp., while the acceptor substituents shift bathochromically both maxima. All compounds studied except the p-N(CH3)2 derivative show an anomalously large Stokes shift in nonpolar solvents.

Effects of phenylbutazone and mefenamic acid on two classes of binding sites of 2-(4'-hydroxyphenylazo)benzoic acid on bovine serum albumin characterized by absorption spectra and circular dichroism spectra.

The competitive binding of phenylbutazone (PB) and mefenamic acid (MF) with 2-(4'-hydroxyphenylazo)benzoic acid (HABA) on bovine serum albumin (BSA) was studied by the investigation of the effects of these drugs on two bound forms of HABA, the azo and hydrazone forms. PB displaced preferentially the hydrazone form. MF displaced both the azo and hydrazone forms, though the azo form was preferentially displaced at the small molar ratio of MF to BSA. The binding constants of PB and MF obtained from the convenient spectrophotometry were dependent on the concentration of added drugs. These facts reflect the selective displacement of the azo and hydrazone forms. In connection with the absorption spectra of bound HABA, induced circular dichroism (CD) spectra of HABA-BSA complex were investigated. The induced CD spectra varied with the change of the molar ratio of HABA to BSA, indicating the presence of at least three different perturbed HABA molecules by BSA. The addition of PB and MF caused dramatic changes of the induced CD spectra of HABA-BSA complex. These spectral changes were discussed with the displacement of the azo and hydrazone forms.

Photooxidation von Arylazonaphtholen mit Singulett‐Sauerstoff

Photooxidation of Arylazo‐Naphtholes with Singlet OxygenThe reaction of p‐substituted 4‐arylazo‐1‐naphtholes 1 and 1‐arylazo‐2‐naptholes 5 with singlet oxygen (produced by methylene blue‐sensitized photolysis) has been studied spectroscopically in methanol as a solvent. The rate constants of dye bleaching are the same, irrespective whether the extinctions of the azo or the hydrazone forms of the tautomeric systems are measured. Both reaction series 1 and 5 afford linear Hammett plots, which is discussed in the light of the azohydrazone equilibrium of the dyes and an „ene”︁ mechanism of the reaction with singlet oxygen. It could be shown by short‐time spectroscopy that the azo‐hydrazone isomerization proceeds much faster than the attack of singlet oxygen on the hydrazone form, which explains all observed facts.

Binding of 2-(4'-hydroxyphenylazo)benzoic acid to bovine serum albumin characterized by optical spectroscopy and equilibrium dialysis.

Binding of 2-(4'-hydroxyphenylazo)benzoic acid (HABA) to bovine serum albumin (BSA) was studied by equilibrium dialysis, by the spectrophotometric method and by the absorption spectra of bound HABA. Comparison of equilibrium dialysis with the spectrophotometric method clarified the presence of a undisclosed class of binding sites, which do not cause the spectral change at about 480 nm to HABA, on BSA. Two bands observed on the absorption spectra of bound HABA were attributed to differently perturbed two HABA molecules by BSA, the azo and hydrazone forms, and these two forms correspond to HABA molecules bound to non-metachromasy sites and metachromasy sites, respectively. The concentration of each from was calculated by using estimated molar extinction coefficient.

Coupling constants nitrogen-15-nitrogen-15 and nitrogen-15-hydrogen in phenylhydrazones forming hydrogen bond

Absolute values of the coupling constants 1J(15N15N), 1J(15NH) of six phenylhydrazones forming hydrogen bond, 2J(15N15NH) of four, and 4J(15NH) of two phenylhydrazones have been determined. Three coupling constants 1J(15N15N) have been obtained from the nitrogen-15 monolabelled compounds by measuring the other nitrogen at natural abundance. The coupling constants 2J(15N15NH) have been measured with the nitrogen-15 doubly labelled compounds, because in the arrangement 15N14NH there exists a broadening of the proton signal due to nitrogen-14. Absolute values of the coupling constants 1J(15N15N) of the phenylhydrazones forming hydrogen bond to the ester group are smaller ( 10.8 Hz) than those of the phenylhydrazones having hydrogen bond to carbonyl group ( 11.1 Hz). The coupling constants 2J(15N15NH) have a value 2.4 ± 0.2 Hz. The value of 1J(15N15N) of 1-phenylazo-2-naphthalenol decreases with increasing content of hydrazone form. The values of 2J(15N15NH) of this compound are within 1.2 to 1.6 Hz.

Assignment of circular dichroism spectra of 2-(4'-hydroxyphenylazo)benzoic acid induced by bovine serum albumin to the azo form.

In the displacement study, the effects of tolbutamide on the absorption spectra and induced CD spectra of 2-(4'-hydroxyphenylazo)benzoic acid(HABA)-bovine serum albumin (BSA) complex were investigated using the samples obtained from equilibrium dialysis at pH 7.40. The binding of tolbutamide to BSA enhanced the binding of the azo form in spite of the displacement of the hydrazone form of bound HABA at the molar ratio of HABA to BSA of 0.65, causing the increase in the negative ellipticity at 445 nm, which was termed the C band. The C band could be assigned to the azo form of bound HABA.

An HMO study of the azo‐hydrazone tautomerism in diazonium coupling products of 5‐isoxazolones

AbstractThe HMO method has been used to study tautomerism in 3‐substituted 4‐arylazo‐5‐isoxazolones (2), the possible tautomeric structures being 2a‐2d. Also the common anions of these tautomers, 6, have been theoretically studied. In addition to the free molecules, HMO calculations have been carried out for structures with hydrogen bonds to protic solvents, for tautomers with intramolecular hydrogen bonds, and for dimers formed via intermolecular hydrogen bonds. In all these situations, the hydrazone form 2a has been shown to be most stable. Also the inductive effect of electron‐donating and electron‐withdrawing substituents in the arylazo moiety upon the stability of various tautomers has been investigated. The results obtained on the basis of HMO calculations are in full agreement with the experimental data of Summers and co‐workers. Several m‐ and p‐substituted 4‐arylazo‐3‐methyl‐5‐isoxazolones have been synthesized and their spectral data and melting points reported.

Synthesis and structure of complexes of acetone acylhydrazones with some transition metals

1. Coordination compounds of Co, Cu, and Ni with acetone acylhydrazones have been obtained and their structures have been studied by physicochemical methods. Acetone benzoylhydrazone and its substituted derivatives coordinate with Co(II), Ni(II), and Cu(II) ions from, their acetates in theα-hydroxyazine form, and acetone salicyloylhydrazone coordinates with Ni(II) and Co(n) in the hydrazone form and with Cu(II) in theα-hydroxyazine form. 2. The stability constants of a number of complexes of acetone acylhydrazones in methanol have been calculated on the basis of their UV-spectroscopic characteristics.

New dyes based on 3-aryl-benzo- and -naphtho-1,4-thiazines

3-Aryl-2H-1,4-benzothiazines have been converted into cyanine dyes by condensing their hydroperchlorates with aldehydes, and into azo-compounds by coupling with reactive diazonium salts. The azo-compounds were also obtained by condensing arylglyoxal hydrazonyl bromides with o-aminothiophenol; they exist predominantly in their tautomeric hydrazone forms. 2-Amino-3-mercapto-1,4-naphthoquinone condenses with ω-bromoaceto-phenones to form 3-aryl-3,4-dihydro-3-hydroxy-2H-naphtho[2,3-b]-1,4-thiazine-5,10-quinones. Attempts to dehydrate these carbinolamines gave a variety of products. Oxidation of the phenyl analogue with iodosobenzene diacetate led to acetyoxylation at C-2 by an indirect Pummerer oxidation.

Investigation of lactams

2,3,4-Trioxohexahydroazepine 4-phenylhydrazone with a 15N-labeled atom bonded to the phenyl fragment was obtained in order to establish its structure. It was established by means of the PMR spectra that this substance is a mixture of syn and anti isomers of the hydrazone form. 2,3,4-Trioxohexahydroazepine 3-phenylhydrazone was isolated when an attempt was made to indolize the 4-phenylhydrazone. Both hydrazones react with phenylhydrazine to give the same 2,3,4-trioxohexahydroazepine 3,4-bis(phenylhydrazone). Derivatives involving the carbonyl group were obtained for both hydrazones, and the conditions for their indolization were studied, as a result of which a number of azepino[4,5-b]indole derivatives were synthesized.

Resonance Raman spectroscopic studies of 2-(4′-hydroxyphenylazo)-benzoic acid and some substituted analogs—II. Binding to avidin and bovine serum albumin

Resonance Raman spectroscopic studies unequivocally indicate that the absorption band at about 500 nm, observed when 2-(4′hydroxyphenylazo)-benzoic acid (HABA) interacts with either avidin or bovine serum albumin in neutral aqueous solution, originates from the protein-bound hydrazone form of the dye. Spectroscopic comparison of the protein-bound and unbound hydrazone forms enables some of the ligand—protein interactions to be defined. Studies with HABA and some selected analogs in aqueous solution, in buffer-doped dimethyl sulfoxide ( d 6), and in the presence of α-cyclodextrin indicate that two important factors responsible for stabilising the hydrazone forms of HABA analogs are the ring substitution pattern, and intramolecular hydrogen bonding. A possible model for the HABA—protein interaction is proposed.

Resonance Raman spectroscopic studies of 2-(4′-hydroxyphenylazo)-benzoic acid and some substituted analogs—I. pH effect on spectra

The resonance Raman spectrum of 2-(4′-hydroxyphenylazo)-benzoic acid (HABA) is pH dependent; the spectral changes are related to the formation of protonated and deprotonated ionic species of the dye molecule. In addition a tautomeric equilibrium process between azo and hydrazone forms of HABA in neutral aqueous solution has been demonstrated using different excitating laser lines. In alkaline, neutral and weakly acid media HABA exists mainly in the azo form. Resonance Raman spectra between 1000 and 1700 cm −1 of six HABA analogs have been recorded at alkaline, neutral and acid pH. A comparison of these spectra allow us to assign most of the important bands, and to establish some intramolecular coupling effects.

3-Phenylazo-4-methyl-2,3-dihydro-1,5-benzodiazepin-2-ones

The corresponding azo derivatives, which exist primarily in the azo form, are formed in the reaction of 2,3-dihydro-1,5-benzodiazepin-2-ones with diazonium cations. The hydrazone form of these compounds is possible in solutions of acids.

The Degradation of Water‐soluble Azo Compounds by Dilute Sodium Hypochlorite Solution

The decolorization of azo dyes by sodium hypochlorite solution has been followed spectrophotometrically and a technique developed for determining the half‐life of the process as a convenient measure of the reaction rate. A study of a series of 2‐arylazo‐1‐naphthol‐3,6‐disulphonic acids suggests that electronic, steric and possibly other effects influence the reaction rate, and that degradation involves initial attack at a nitrogen atom of the hydrazone form, by the electrophilic chloronium ion. Sulphonic and carboxylic acid groups located ortho to the azo linkage are particularly effective in retarding the rate of degradation.The dyes 4‐(4‐sulphophenylazo)‐1‐naphthol (I) and 4‐(4‐sulphophenylazo)‐1‐(2‐chloro‐4‐amino‐s‐triazinylamino)‐naphthalene‐6‐sulphonic acid (II) were investigated in more detail to determine the effect of pH on the reaction rate, the number of molecules of sodium hypochlorite involved in the decolorization reaction the nature of the decomposition fragments. This information, together with the fact that the O‐ and N‐ methyl homologues of I were extremely resistant to degradation, enabled a mechanism to be postulated for the reaction.

Resonance Raman spectra of p‐hydroxyazobenzene and its ring deuterated derivatives in the strongly acidic solution

AbstractResonance Raman spectra of p‐hydroxyazobenzene (HAB) and its three ring deuterated derivatives have been measured in the strongly acidic solution. The observed Raman bands have been assigned by referring to the spectra of related compounds and the deuteration effect. The NN stretching band of HAB in the solution of 20% hydrochloric acid undergoes a high frequency shift by about 60 cm−1 on changing the solvent to 20% deuterochloric acid. In the strongly acidic solution HAB has been confirmed to exist as a resonance hybrid between the azo and the hydrazone forms, of which the former is predominant. A normal coordinate analysis of a simplified model, CNHNC6H4pOH, has been carried out to give a good agreement between the calculated and the observed frequencies.

Studies on benzothiazole derivatives as chelating agents. III. Acid-base equilibria and chelate formation with metal ions.

The acid dissociation constants of 2-, 4-and 7-substituted benzothiazole derivatives and the formation constants of the complexes formed by these ligands with Mg2+, Cu2+, Ni2+, Co2+, Zn2+, Mn2+ and Cd2+ were determined potentiometrically at 25°in 2/1 (v/v) dioxane/water solution. The order of the basicity of the ligands is 4-substituted > 7-substituted > 2-substituted benzothiazole derivatives. Also the basicity of the benzothiazole derivatives, substituted at the same position, is in the order : aminomethyl > azomethine > azo compounds. Except for the azonaphthol derivatives, a linear relationship exists between the basicity and the π electron density of the hydroxyl group of the ligands, which may suggest that hydrazone form is predominant in the azo-hydrazone tautomerism of the benzothiazolylazonaphthol derivatives. The stability of the metal complexes corresponds to the basicity of the ligands and the log KML values approximately follow the Mellor-Maley stability sequence. It is expected that the benzothiazolylazo derivatives would be good metallochromic indicators in chelatometric titrations with ethylenediaminetetraacetic acid as titrant.

Azo Dye Tautomeric Structures Determined by Laser-Raman Spectroscopy

Raman spectra of a number of azo dye structures have been analyzed. In azonaphthol and azopyrazol dyes, hydroxyazo to keto-hydrazone tautomerizations, [Formula: see text] were observed in aqueous basic and acidic media. Observations of azo and ring vibrations, as well as hydrazone (C=N plus C=0) bands, were made. It was noted that the azo-anions (examined at pH 12) convert to the protonated neutral hydrazone (keto) form in aqueous acid (run at pH 2). Infrared spectra were used to confirm the presence of the C=0 group in keto-tautomeric forms.

Resonance Raman spectra of some ring-deuterated derivatives of p-aminoazobenzene and p-dimethylaminoazobenzene

Resonance Raman spectra of p-H 2NC 6D 4NNC 6D 5, p-D 2NC 6D 4NNC 6D 5 and p-(CH 3) 2NC 6H 4NNC 6D 5 in neutral and acidic solutions have been recorded and isotope effects of vibrational frequencies of the azo and the hydrazone forms have been investigated. An appreciable mixing of group frequencies has been found to arise from the long range interaction between the azo group and the p-disubstituted benzene ring.

Spectres de masse d'hydrazino-2 benzo- et naphtothiazoles et d'hydrazones des méthyl-3 benzo- et naphtothiazolinones-2

Electron impact mass spectra are reported for the hydrazones of 3-methyl-2-benzothiazolinone (1), of 4-, 5-, 6-, and 7-chloro-3-methylbenzo-2-thiazolinones (2, 3, 4, and 5) and of 3-methyl-naphtho[2,1-d]-2-thiazolinone (6), as well as for 2-hydrazinobenzothiazole (7), for 4-, 5-, 6-, and 7-chloro-2-hydrazinobenzothiazoles (8, 9, 10, and 11) and for 2-hydrazinonaphtho[2,1-d]thiazole (12). The results obtained in the two series are compared. The 2-hydrazone and 3-methyl-benzo-2-thiazolinone and its derivatives all form a base peak corresponding to the molecular ion; fragmentation proceeds mainly by successive losses of·NH2, HCN, HCN, and then CS. Initial losses of N2H2, NH·, and NH3 are minor fragmentation routes.In the case of 2-hydrazinobenzothiazole and its derivatives, the base peak is still that of the molecular ion; however, the relative proportions of the various fragment ions vary with the position of sampling probe inside the apparatus. Thus it is concluded that the observed mass spectrum is that of a mixture of the possible hydrazone-hydrazine tautomers. The principal fragmentations involve the initial loss of NH3 (leading to a stabilized ion), of NH2· (probably from the hydrazone form), and of N2H2.(Journal Translation)

Acylarylnitrosamines. Part VIII. 15N-Labelling experiments and their relevance to the mechanisms of formation of benzyne from benzenediazonium acetate and of the benzenediazonium ion from hydroxyazo-compounds

Experiments using 15N-labelled N-nitrosoacetanilide and related compounds have shown that the complex reaction leading to benzyne and/or phenyl radicals does not involve the reversible extrusion of nitrogen. The contrasting observation that nitrogen exchange did occur in the formation of benzenediazonium ions by the in situ nitrosation of 15N-labelled acetanilide is attributed to the generation of unlabelled benzenediazonium ions by the reaction of phenyl radicals with the nitrosating agent. The reactions of nitrosating reagents such as p-chlorobenzoyl nitrite with 1-phenylazo-2-naphthol and related hydroxyazo-compounds to give benzenediazonium ions have been investigated, and it is suggested that nitrosation of the hydrazone from of the hydroxyazo-compound followed by rearrangement and cleavage provides the primary source of the diazonium ions but that these are again regenerated in the system from phenyl radical sand the nitrosating reagent. In accord with this, azobenzene and 4-phenylazo-1-methoxynaphthalene, which cannot exist as hydrazones do not so react, in contrast to phenylazotetrachlorocyclopentadiene, which does exist in the hydrazone form. Reactions of p-chlorobenzoyl nitrite or phentyl nitrite with 1-phenylazo-2-naphthol in benzene at 50° lead to biphenyl, via phenyl radicals, in 30 and 41% yield (82% based on azo-compound consumed).