Heterocyclic Hydrazones Research Articles

Fused polyaza‐heterocycles and 1,3,4‐thiadiazoles via a tricyano synthon

Abstractmagnified imageTreatment of 2‐cyano‐3‐phenyl‐2‐pentenedinitrile with some heterocyclic diazonium salts afforded the corresponding heterocyclic hydrazones. Some of the latter hydrazones were converted into fused polyaza‐heterocycles upon boiling in pyridine. Reaction of 2‐cyano‐3‐phenyl‐2‐pentenedinitrile with phenylisothiocyanate gave a tricyano‐thiole derivative which on treatment with hydrazonoyl chlorides and 1‐(benzothiazol‐2‐yl)‐2‐bromoethanone furnished 1,3,4‐thiadiazole and thiazole derivatives, respectively.

Synthesis, Characterization and Biological Activity Evaluation of Novel Pd(II) and Pt(II) Complexes with Heterocyclic Hydrazone Ligands

New complexes of Pt(II) with condensation derivatives of ethyl hydrazinoacetate and either 2-acetylpyridine or 2-quinolinecarboxaldehyde, and of Pd(II) with the condensation derivative of ethyl hydrazinoacetate and 2-quinolinecarboxaldehyde were synthesized and characterized by elemental analysis, IR, 1H- and 13C-NMR spectroscopy, and molar conductivity measurements. The complexes have a square planar geometry, ligands binding as bidentates in the neutral form, and the remaining two coordination sites being occupied by chloride ions. Biological activity of new complexes, and of previously synthesized Pd(II), Cd(II), Co(III) and Zn(II) complexes with this ligand type was evaluated by the brine shrimp test. All the complexes showed a moderate activity.

Polystyrene sulfonic acid catalyzed greener synthesis of hydrazones in aqueous medium using microwaves

An environmentally benign aqueous protocol for the synthesis of cyclic, bi-cyclic, and heterocyclic hydrazones using polystyrene sulfonic acid (PSSA) as a catalyst has been developed; the simple reaction proceeds efficiently in water in the absence of any organic solvent under microwave irradiation and involves basic filtration as the product isolation step.

New Heterocyclic Hydrazones in the Search for Antitubercular Agents: Synthesis and In Vitro Evaluations

Sixteen pyrrole containing hydrazones were synthesized from isoniazid (INH) or from 1H-1- pyrrolylcarbohydrazides. Nine products exhibited 92-100% inhibitory activity against Mycobacterium tuberculosis H37Rv at 6.25 μg/mL (Microplate Alamar Blue Assay). Two leads showed MICs 0.78 and > 0.1 μg/mL, SIs > 12.82 and > 100.

A convenient new synthesis of fused 1,2,4-triazoles: the oxidation of heterocyclic hydrazones using copper dichloride

A series of 1,2,4-triazoles have been prepared by oxidative intramolecular cyclization of heterocyclic hydrazones with copper dichloride. General applicability of this simple transformation was confirmed by the synthesis of moderate to high yields of 1,2,4-triazolo[4,3- a]pyridines, 1,2,4-triazolo[4,3- a]pyrimidines, 1,2,4-triazolo[4,3- b]pyridazines, 1,2,4-triazolo[4,3- a]phthalazines, and 1,2,4-triazolo[4,3- a]quinoxalines. A 1,2,4-triazolo[4,3- e]purine-6,8( 7H)-dione was obtained in a lower yield.

Solid-state synthesis of heterocyclic hydrazones using microwaves under catalyst-free conditionsPresented, in part, at the 5th Electronic Conference on Synthetic Organic Chemistry, (ECSOC-5), 1–30 September 2001, E0014, http://www.mdpi.org/ecsoc-5.htm

The reactions of neat 5- or 8-oxobenzopyran-2-ones, 1–3, with a variety of aromatic and heteroaromatic hydrazines, 4, are accelerated upon irradiation in a household microwave oven in the absence of any catalyst, solid support or solvent. The approach provides an attractive and environmentally friendly pathway to several synthetically useful heterocyclic hydrazones.

ChemInform Abstract: Catalyst‐Free Reactions under Solvent‐Free Conditions: Microwave‐Assisted Synthesis of Heterocyclic Hydrazones Below the Melting Points of Neat Reactants.

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Catalyst-free reactions under solvent-free conditions: microwave-assisted synthesis of heterocyclic hydrazones below the melting points of neat reactants.

The reaction of neat 5- or 8-oxobenzopyran-2(1H)-ones, 1-3, with a variety of aromatic and heteroaromatic hydrazines, 4, is remarkably accelerated upon irradiation in a household microwave oven in the absence of any catalyst, solid support or solvent thus providing an environmentally friendly route to several heterocyclic hydrazones.

A New Spectrophotometric Method with Di-2-Pyridyl Ketone Benzoylhydrazone for Determination of Nickel(II)

Nitrogen-containing heterocyclic hydrazones have been used as analytical reagents, mainly to metallic ion spectrophotometric determinations in natural water samples. Using the reagent di-2-pyridil ketone benzoilhydrazone (DPKBH) we have developed a spectrophotometric method for the determination of Ni(II) in samples of several sources. DPKBH was used in excess in order to coordinate Ni(II) and the highest sensitivity was obtained in 50% v/v ethanol solutions when ammonium acetate buffer was added to maintain pH≅6. Analysis for Ni(II) in natural water is frequently performed by EAAS following preconcentration involving solvent extraction. While these methods are sensitive, they also require relatively expensive instrumentation and are generally time-consuming. In contrast, the advantages of the proposed method are the use of simple instrumentation and the possibility of its application in the field. The method is fast, shows high sensitivity, good precision and several samples can be prepared and measured until 10 hours later . The best order for the addition of reagents, stability of the complex, effect of the reagents excess and foreign ions besides composition of the complex are here reported. A linear behavior was observed between absorbance and nickel concentration. The favorable range is 8.50×10−7 to 1.72×10−5 mol.L−1. The correlation coefficient is 0.997. The intercept of the linear curve is 3.55×10−3 and the slope is 4.00×104cm−1.moI−1.L. The standard error of the intercept and slope is 3.73×10−3 and 4.48×10−4, respectively.

Theoretical Studies of Flow Injection Analysis and Application for Monitoring Water Quality at Power Plants with Newly Developed Fl Analyzer/A Study on Applications of Heterocyclic Hydrazones in Analytical Chemistry

Theoretical Studies of Flow Injection Analysis and Application for Monitoring Water Quality at Power Plants with Newly Developed Fl Analyzer/A Study on Applications of Heterocyclic Hydrazones in Analytical Chemistry

Kinetic studies of complexation reactions of water-soluble hydrazones with nickel(II) and palladium(II) ions

The kinetics of complexation reactions of five water-soluble heterocyclic hydrazones with nickel(II) and palladium(II) ions have been investigated by stopped-flow spectrophotometry. Rates of complexations with nickel(II) and palladium(II) in the absence of chloride ion were found to be proportional to the first order of the ligand and metal ion concentrations and to the inverse first order of the hydrogen ion concentration except for the complexation of α-(2-benzimidazolyl)-α-(5-nitro-2-pyridyl)hydrazono-3-toluenesulfonic acid with palladium(II). Rates of complexation with palladium(II) in the presence of chloride ion were best described by a two-term expression, both terms being first order in the palladium ion and ligand concentrations and inverse first order in the hydrogen ion concentration. The first term has zero dependence of the chloride ion concentration, whereas the second is first order with respect to the chloride ion concentration. The rate constant for each complexation reaction was determined. The complexation of the hydrazones with nickel(II) was estimated to go according to an Eigen mechanism and that with palladium (II) according to the associative mechanism.

Complexation Behavior of Heterocyclic Hydrazones. II. Effects of Steric Factors on Formation Constants for Nickel(II) Complexes with Heterocyclic Hydrazones

Abstract The equilibria of nickel(II) ion with thirteen nitrogen-heterocyclic hydrazones (neutral form: HL) with and without blocking group(s) have been investigated spectrophotometrically in 28% aqueous dioxane solution at 25 °C and an ionic strength of 0.2 (KCl). For a series of 2-pyridinecarbaldehyde 5-substituted-2-pyridylhydrazones, the following linear free energy relationships (LFER) were derived between the overall formation constants, β1, β1′, and β2, of Ni(HL)2+, NiL+, and Ni(HL)22+ complexes, respectively, and the dissociation constants, Ka1 and Ka2, of H3L2+ and H2L+, respectively: log β1 = 0.95 (pKa1 + pKa2)/2 + 4.60, 1/2 log β2 = 0.95 × (pKa1 + pKa2)/2 + 4.82, and log β1′ = 1.40 (pKa1 + pKa2)/2 + 9.73. The steric effects of the 6-methyl group in pyridine and the quinolyl ring in place of pyridyl group on the complex formation were evaluated on the basis of LFER. The complex stabilization effect of the pyridyl group substituted for formyl hydrogen was also evaluated for Ni(HL)22+, Ni(HL)2+, and NiL+ complexes. These results together with LFER were discussed in conjunction with the thermodynamic parameters for the formation of Ni(HL)2+ complex and the ligand field parameters, Dq, for Ni(HL)2+ and Ni(HL)22+ complexes.

THE CRYSTAL STRUCTURE OF DIBROMO (PHENYL-2-PYRIDYL DIMETHYLHYDRAZONE)PALLADIUM(II)

Abstract Nitrogen-containing heterocyclic compounds play an important role in several biological processes. Furthermore, their biological activity seems often to depend upon interaction with a metal ion. Interest in the study of hydrazones and their metal complexes has been growing because of their physiological activity, coordination capability and application in analytical chemistry.1,2 Many hydrazones and their metallic derivatives show very interesting biological activity, e.g., as antitumour or anticonvulsant agents, and behave as cytotoxic compounds toward tumour cells.3 During the past few years, in addition to platinum compounds, coordination compounds of palladium(II) and (IV) seem to be promising in cancer chemotherapy.4 Due to the biological activity of heterocyclic hydrazones and in continuing our systematic investigations of the platinum group metals with hydrazones and generally with heterocyclic nitrogen donor ligands,5–10 we report here the crystal structure of dibromo(phenyl-2-pyridyldime...

Extraction Equilibria of Nickel(II) with Several Heterocyclic Substituted-Hydrazones

The extraction of nickel(II) with seven N, N, N-tridentate heterocyclic hydrazones, a neutral form of which is abbreviated as HL, using chloroform or benzene as an extraction solvent has been studied, the extraction equilibria being analyzed on the basis of the data for the proton dissociation of H3L2+, the formation of Ni(HL)2+ and Ni(HL)22+ complexes and the proton dissociation of Ni(HL)22+ complexes in aqueous solution. Nickel(II) is extracted as NiL2, although it forms such complexing ions as Ni(HL)2+ or Ni(HL)22+ in the aqueous phase. The distribution constants of HL and NiL2 (the abbreviations of which are Kd and Kdm, respectively) have been determined under the same condition as in aqueous solution. The logarithmic plots of Kdm vs. Kd displayed two straight lines with slopes of 1.9; one is for hydrazones bearing one pyridyl or one quinolyl ring in the aldehyde moiety and the other for hydrazones bearing another pyridyl ring introduced to the aldehyde moiety. This is attributed to an intramolecular hydrogen bond between the imino hydrogen and the nitrogen of pyridine of the latter hydrazones.

Synthetic and Antimicrobial Studies of some Heterocyclic Hydrazones and their Bivalent Metal Complexes

Synthetic and Antimicrobial Studies of some Heterocyclic Hydrazones and their Bivalent Metal Complexes

Spectrophotometric Study of the Formation and Protolytic Equilibria for Iron(II) Complexes of Di-2-pyridylmethanone 2-Pyridyl-hydrazone and Di-2-pyridylmethanone 2-Quinolylhydrazone

The stoichiometrics, stability constants and deprotonation constants of the complexes formed between iron(II) and either of two heterocyclic hydrazones, di-2-pyridylmethanone 2-pyridylhydrazone (DPPH) or di-2-pyridylmethanone 2-quinolylhydrazone (DPQH), have been determined spectrophotometrically at 25° C and μ=0.2. Iron(II) reacts with DPPH and DPQH in acidic media to form a dipositively charged bis complex, Fe(HL)22+, which undergoes successive deprotonation to monocationic (Fe(HL)L*) and neutral bis (FeL2) complexes, along with a decrease in the solution acidity. The acid-strengthening effect of coordinated metal on the imino group of the ligand is briefly discussed. There was no evidence for the formation of mono complexes. The logarithmic stability constants of the neutral complexes, FeL2, were 36.8 and 33.0 for the DPPH and DPQH complexes, respectively.

Kinetic Study of Solvent Extraction of Nickel(II) from Aqueous Solution by some Heterocyclic Substituted-Hydrazones

Solvent extraxction of nickel(II) complexes with five heterocyclic hydrazones(containing pyridine- or/and quinoline-nitrogen atoms as the coordinating sites) into chloroform or benzene has been studied kinetically at 25°C and μ=01 by means of a spectrophotometric method. The kinetics of extraction of nickel(II) ion is first order in each of the aqueous nickel(II) concentration and the hydrazone concentration in the organic phase. The observed second-order rate constant, kobs'-pH profiles suggest three rate-determining steps to be considered in the aqueous phase: Ni2++ H2L+→, Ni2++HL→and Ni(OH)++HL→ The rate constant for the formation of 1:1 complex with 2-pyridylmethanone 2-pyridylhydrazone (PAPH) was consistent with those for bipyridine and terpyridine. Replacement of pyridyl group by quinolyl group affects the distribution constant(Kd) of the ligand between the two phases rather than the rate constants for rate-determining steps, and consequently the difference in kobs is chiefly governed by Kd. The influence of the structure of ligands on the rate constants is also discussed.

15N NMR Spectroscope of Pyrazolines-2 and Their Salts

Abstract 15N NMR Spectroscopy is one of the most powerful tools to study the structure of organic molecules.1–3 δ2 -pyrazolines 1 are heterocyclic hydrazones, which as a result of their cyclic structure, are stable in acidic media. Thus, their protonation has been studied by 1H and 13C NMR spectroscopies.4,5 Pyrazolines are protonated and quaternarized at N1 2 and 3. It is possible to obtain the isomeric quaternary salts 4 by C-protonation of δ3 -pyrazolines.6

Stereoisomerization in heterocyclic hydrazones derived from 2-acylpyridines and their oxidative cyclization with mercury(II) acetate and lead tetra-acetate to fused 1,2,4-triazoles and 1,2,3-triazolium systems

Hydrazones prepared by coupling 2-acylpyridines with arylhydrazines were isolated predominantly as E-isomers when the acyl substituent R was small (H or Me). When R was a phenyl group significant yields of Z-isomers, containing an intramolecular hydrogen bond, were also isolated. Oxidation reactions of these hydrazones were not influenced by the E- or Z-geometry of the substrate contrary to earlier reports. A common metallo intermediate with a Z-structure was encountered in the oxidations of the E- and Z-pyridine 2-carbaldehyde 2-pyridylhydrazone with mercuric acetate. In oxidations of a series of hydrazones with lead tetra-acetate the product controlling factor was the nature of the methine substituent R. For ketone derivatives (R ≠ H) oxidation to fused 1,2,3-triazolium systems occurred via a 5-exo-tet cyclization with E- and Z-hydrazone substrates. For aldehyde systems (R = H) the oxidation involved dehydrogenation to a nitrilimine and gave products by solvent addition or a 5-endo-dig cyclization to fused 1,2,4-triazolo systems.

Detection of a metallo-intermediate and geometrical isomerizations in an oxidative cyclisation of a heterocyclic hydrazone with mercury (II) acetate

Oxidative cyclisation of the E-isomer of 2-pyridylcarbaldehyde 2-pyridylhydrazone with mercury (II) acetate involved an amino-N-mercurio intermediate with a Z-structure and an E→Z→E series of isomerizations.