Syntheses and crystal structures of two self-assembled dizinc(II) helicates with novel hydrazone linked polypyridyl ligands

The rationally designed polydentate ligands, L ¹ and L ² , based on the pyridinyl moiety and the hydrazone fragment have been synthesized to coordinate zinc(II) ions. We utilize pyridine as a rigid core connecting two bipyridines as ligand building blocks with a hydrozone linker for the L ¹ . The L ² has a reversed design in which a bipyridine was used as a hinging-available building block of the ligand core, connecting two pyridazine arms with a hydrazone linker. Two novel helical dizinc(II) complexes were obtained by the reaction of L ¹ and L ² with zinc(II) perchlorate in acetonitrile. The structures of both helicates were confirmed by X-ray diffractometry. Single-stranded helicate Zn ₂ L ¹ contains two zinc ions bridged by an oxygen atom. Except for the L ² ligand, no other bridging species were found between the two zinc ions in the double-stranded helicate Zn ₂ L ₂ ² . The self-assembling process of helicate Zn ₂ L ¹ in solution state was studied by UV–Vis spectrometric titration experiments. The stepwise formation constants imply a slightly positive cooperative behavior for the formation of helicates.     

Preparation,molecular and crystal structures of 3-(1-amino-2,2,2-trifluoroethylidene)-1,1,4,5,6,7-hexafluoroindan-2-one, 2-amino-1,1,4,5,6,7-hexafluoro-3-trifluoroacetylindene,and their complexes with dioxane and pyridine

3-(1-Amino-2,2,2-trifluoroethylidene)-1,1,4,5,6,7-hexafluoroindan-2-one (2) is synthesized by the interaction between 3-(1-amino-2,2,2-trifluoroethylidene)-2-imino-1,1,4,5,6,7-hexafluoroindan (1) and isopropylnitrite, and 2-amino-1,1,4,5,6,7-hexafluoro-3-trifluoroacetylindene (3) is prepared by hydrolysis. Single crystals are grown, and the molecular and crystal structure of enaminoketones obtained, the complex of compound 2 with 1,4-dioxane, and the complex of compound 3 with pyridine is studied. DFT calculations have been performed to find the complex formation energies of compounds 2 and 3 with dioxane and pyridine in the gas phase.     

Molecular modeling and cyclization reactions of 2-(4-oxothiazolidine-2-ylidene) acetonitrile

Diazotization of 2-(4-oxothiazolidine-2-ylidene) acetonitrile 1 with aryl diazonium chloride derivatives afforded 4-thiazolidinones 2a, b, whereas 3a, b derivatives produced through reaction of arylcarbonohydrazonoyl dicyanide with thioglycolic acid. Cyclization of 2a with aromatic aldehydes and malononitrile gave the expected substituted thiazolo [3,2-a] pyridines 4a, b. The reaction of 1 with anthraldehyde (1:1 molar ratio) gave the expected 4,5-dihydro-4-oxothiazole derivatives 5 which condensed with other mole p-chlorobenzaldehyde and gave the corresponding bisarylidine derivative 6. Thiazolo [3,2-a] pyridine enaminonitrile derivative 7 produced through addition of malononitrile to bisarylidine 6. Also, compound 7 reacted with other mole of malononitrile and furnished thiazolo [3,2-a] pyridine 12, furthermore, compound 7 refluxed with phenyl hydrazine, thiourea, and formic acid, to form the corresponding thiazolo [3,2-a] pyridines 13, 15 and 17, respectively. Also, compound 1 reacted with phNCS in presence of KOH and afforded 19. The molecular modeling of the synthesized compounds has been drawn and their molecular parameters were calculated. Also, valuable information is obtained from calculation of the molecular parameters including electronegativity, net dipole moment of the compounds, total energy, electronic energy, binding energy, electrophilicity index, HOMO and LUMO energy.     

Synthesis and structures of Cu<Superscript>I,II</Superscript> complexes with a 2,2´-bipyridine derivative bearing a (+)-3-carene moiety

The complex salt {[CuL₂][Cu₄I₆]?MeCN}_n (1) and the compound [Cu₄L₃I₄]?3 MeCN (2) (L is a chiral ligand bearing a natural monoterpene (+)-3-carene moiety) were synthesized. The crystal structures of compounds 1 and 2 were determined by X-ray diffraction. The structure of compound 1 consists of complex cations [CuL₂]²⁺ (N₃O₂ polyhedron is a trigonal bipyramid) and Cu^I coordination polymers (CuI₄ polyhedron is a tetrahedron) as anions. The experimental magnetic moment μ_eff at 300 K is 1.90 μ_B, which is consistent with the X-ray diffraction data and the assumption that compound 1 is mixed-valence. The structure of compound 2 comprises a tetranuclear Cu^I complex, in which three Cu atoms are coordinated by two N atoms of the ligand L and two I atoms, and the fourth Cu atom is coordinated by four I atoms (coordination polyhedra are distorted tetrahedra). Compounds L and 2 were found to influence the viability of human laryngeal carcinoma cells (Hep2). The IC₅₀ value for complex 2 (13.0±1.7 μM) is substantially smaller than IC₅₀ for compound L (30.5±0.5 μM).     

Reaction of amides of 2,3-dibromopropionic and 2-bromoacrylic acids with pyridine and triphenylphosphine

By refluxing pyridine with 2,3-dibromopropionic acid amide in acetonitrile, amide of 3-bromo-2-pyridiniumbromidopropionic acid I was synthesized. The latter is inert toward the second molecule of pyridine under the used conditions. Compound I was found to react with triphenylphosphine to form a mixture of 3-triphenylphosphoniumbromidopropionitrile II and 1-triphenylphosphoniumbromido-2-pyridiniumbromidoethane III. Schemes of reactions were suggested involving attack of phosphine on the carbonyl group as the first stage. The reaction of α-bromoacrylic acid amide with triphenylphosphine was shown to yield also compound II. Evidently, this reaction proceeds through intermediate formation of enolphosphonium salt.     

Cyclization of pyrazolones: novel synthesis of pyrano,pyrido, pyrimido and spiropyrazole derivatives

Depending on the reaction conditions, two alternative cyclizations are possible for [3?+?3] cyclocondensation of pyrazolone derivative 1a and ethyl cyanoacetate of type pyrano [2,3-c] pyrazol-6(1H)-one 2 and pyrano [2,3-c] pyrazol-4(1H)-one 3. Keeping of enaminic system 3 and benzylidene malononitrile in the presence of catalytic amount of trimethylamine resulted in pyridine cyclization affording pyrazolopyranopyridine derivative 4, not 5. The pyrazolone derivative 6a was obtained as a result of the acid-mediated addition reaction between compound 1a, urea and/or ammonium thiocyanate. In addition, the bispyrazolone of type 6b was obtained from the condensation reaction of urea and pyrazolone derivative. The spiro compound 7 was obtained from the double-addition reaction of pyrazolone to cinnamoyl isothiocyanate. A one-pot three-component condensation of a 3-hydroxybenzaldehyde, pyrazolone 1a, urea and/or thiourea under Biginelli conditions resulted in tetrahydropyrazolo pyrimidine derivatives 8a and 8b, respectively. The acid-mediated reaction of benzaldehyde and pyrazolone derivative 1a in the presence of Ac₂O yielded styrylpyrazole derivative 9. The polyfunctionalized product 9 reacted with hydrazine to furnish pyrazolotriazoloe of type 10. Treatment of styrylpyrazole derivative 9 with aniline furnished the aniline derivative 11 and none of the expected polyheterocyclic derivative 12 was obtained. Compound 9 undergoes pyridine cyclization to produce 13 under the effect of urea. N-phenyl pyrazolone converted into pyrano-dipyrazolone derivative 14. Pyran of type 14 underwent a ring transformation upon treatment with urea and/or thiourea to give the same dipyrazolo pyrimidine derivative 15. The newly synthesized compounds were characterized by FT-IR, ¹H-NMR, ¹³C-NMR, ESI/LC-MS and elemental analysis.     

BODIPY-derived ratiometric fluorescent sensors: pH-regulated aggregation-induced emission and imaging application in cellular acidification triggered by crystalline silica exposure

Modification of classic fluorophore to possess the emission transitions between aggregation-induced emission (AIE) and intrinsic emission offers reliable approach to the design of ratiometric fluorescent sensors. In this study, a proton acceptor benzimidazole was integrated with BODIPY to form three compounds, BBI-1/2/3, which demonstrated the AIE (~595 nm, I_agg) in neutral aqueous medium and intrinsic BODIPY emission (~510 nm, I_int) in acidic medium. All the three showed the ratiometric pH sensing behavior in a dual excitation/dual emission mode, yet BBI-3 displayed still the dual emission ratiometric pH sensing ability. The pH-dependent emission ratio I_int/I_agg of the three were fully reversible, and no interference was observed from normal abundant chemical species in live cells. Their different pK_a (BBI-1, pK_a 4.4; BBI-2, pK_a 2.7; BBI-3, pKa 3.6) suggested that the substituents on benzimidazole moiety were essential to govern their functioning pH range. The ratiometric imaging of BBI-1 in A549 cells provided an effective intracellular pH (pHi) calibration formula corresponding to emission ratio of I_int/I_agg. Ratiometric pH_i imaging in A549 cells upon small particle exposure confirmed the particle-induced cellular acidification with this formula. Both particle size and the chemical nature of the particle contribute to the observed acidification effect. The synchronization of lysosome disruption to cellular acidification in A549 cells upon crystalline silica exposure was directly observed for the first time with BBI-1, showing the potential application of BBI-1 in the study of silicosis and other related diseases. This study demonstrated that endowing fluorophore with AIE/intrinsic emission transition could be a promising strategy for ratiometric sensor design.     

Copper(II) Complexes with Chiral Ligands Containing Fragments of Monoterpenoids and Amino Acid Esters

Complexes [CuL¹Cl₂] (I), [CuL²Cl₂] · EtOH (II), and Cu₂L³Cl₄ (III) containing esters of the N-derivatives of optically active amino acids based on (+)-3-carene (L¹, L²) and (?)-α-pinene (L³) are synthesized. The crystal and molecular structures of compounds I and II are determined by X-ray diffraction analyses (CIF files CCDC nos. 1560071 (I), 1560072 (II)). The crystal structure of compound I consists of mononuclear complex molecules. In the structure of compound II, the unit cell contains two crystallographically independent molecules of mononuclear complex [CuL²Cl₂] and two EtOH molecules. Ligands L¹ and L² perform the tridentate-chelating function by the N atoms of the NH and NOH groups and by the O atom of the C=O group. In compounds I and II, the coordination polyhedra Cl₂N₂O of the Cu atoms are trigonal bipyramid. According to the data of IR and electronic spectroscopy, binuclear complex III has similar coordination polyhedra. The experimental values of μ_eff for compounds I, II, and III at 300 K are 1.93, 1.88, and 2.71 μB. For complex III, the μ_eff(T) dependence in a range of 2–300 K indicates a weak ferromagnetic exchange interaction.     

Cobalt(II) complexes with pentadentate Schiff bases 2,6-diacetylpyridine hydrazones: Syntheses and structures

Seven new cobalt(II) complexes based on the Schiff bases, 2,6-diacetylpyridine bis(isonicotinoylhydrazone) (H₂L¹) and 2,6-diacetylpyridine bis(nicotinoylhydrazone) (H₂L²), are synthesized and studied by X-ray diffraction analysis: [Co(H₂L¹)(NCS)₂] · 2.25H₂O (I), [Co(H₂L²)(NCS)₂] · CH₃OH (II), [Co(H₂L²)(NCS)(H₂O)]NCS (III), [Co(H₄L¹)(NCS)₂](NO₃)₂ · 2H₂O (IV), [Co(H₄L¹)(NCS)₂][Co(NCS)₄] · 0.75H₂O (V), [Co(H₄L²)(NCS)₂][Co(NCS)₄] · 1.75H₂O (VI), and [Co(H₂L²)(NCS)(CH₃OH)]₂[Co(NCS)₄] · 2CH₃OH (VII) (CIF files CCDC 941186 (I), 1457906 (Ia), 1457905 (II), 941187 (III), 1457907 (IV), 1457908 (V), 1457909 (VI), and 941188 (VII)). The organic ligands in the complexes act as pentadentate neutral H₂L or doubly protonated (H₄L)²⁺ coordinated through the same set of donor atoms N₃O₂. In all compounds I–VII, the coordination polyhedron of the Co²⁺ ion in a complex with the Schiff bases has a shape of a pentagonal bipyramid. The hydrazones are arranged in the equatorial plane of the bipyramid. Its axial vertices are occupied by the nitrogen atoms of the NCS￣ anions in compounds I, II, and IV–VI and by the nitrogen atoms of NCS￣ and oxygen of the water molecule in compound III or methanol in compound VII. The NO ₃ ^- anions or [Co(NCS)₄]^2￣ complex anions obtained by the reactions are involved along with the NCS￣ anions in the formation of compounds IV–VII.     

Biomimetic oxidation of catechol employing complexes formed in situ with heterocyclic ligands and different copper(II) salts

In the present work, catecholase activity is presented. The complexes were prepared by condensation of the organic ligand pyrazolyl L ₁ –L ₄ and copper(II) ion in situ. The pyrazolyl compounds L ₁ –L ₄ used in this study are: L ₁ is (3,5-dimethyl-pyrazol-1-ylmethyl)-(4-methyl-pyridin-2-yl)-pyrazol-1-ylmethyl-amine; L ₂ is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-pyrazol-1-ylmethyl-amino]-phenyl}-ethanone; L ₃ is 1-{4-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-phenyl}-ethanone, and L ₄ is 2-[(3,5-dimethyl-pyrazol-1-ylmethyl)-[1,2,4]triazol-1-ylmethyl-amino]-6-methyl-pyrimidin-4-ol, and copper ions salts Cu(II) are (Cu(CH₃COO)₂, CuCl₂, Cu(NO₃)₂ and CuSO₄). In order to determine factors influencing the catecholase activity of these complexes, the effect of ligand nature, ligand concentration, nature of solvent and nature of counter anion has been studied. The best activity of catechol oxidation is given by the combination formed by one equivalent of ligand L ₂ and one equivalent of Cu(CH₃COO)₂ in methanol solvent which is equal to 9.09 µmol L^?1 min^?1. The Michaelis–Menten model is applied for the best combination, to obtain the kinetic parameters, and we proposed the mechanism for oxidation reaction of catecholase.     

Synthesis,crystal structures,and properties of copper(II) dicarboxylate complexes with [bis(2-pyridylcarbonyl)amido]

Four new complexes, [Cu₂(Bpca)₂(L¹)(H₂O)₂] · 3H₂O (I), [Cu₂(Bpca)₂(L²)(H₂O)₂] (II), [Cu₂(Bpca)₂(L³)] · 2H₂O (III), [Cu₂(Bpca)₂(L¹)(H₂O)] · 2H₂O (IV) (Bpca = bis(2-pyridylcarbonyl)amido, H₂L¹ = glutaric acid, H₂L² = adipic acid, H₂L³ = suberic acid, H₂L⁴ = azelaic acid) have been synthesized and characterized by single-crystal X-ray diffraction methods (CIF files CCDC nos. 1432836 (I), 1432835 (II), 817411 (III), and 817412 (IV)), elemental analyses, IR spectra. Structural analyses reveal that compounds I, II, and IV have similar structures [Cu(Bpca)]⁺ units bridged by dicarboxylate forming dinuclear units, whereas the dinuclear of compound III are edge-shared through two carboxylate oxygen atoms of different suberate anions. Hydrogen bonds are response for the supramolecular assembly of compounds I to IV. The temperature-dependent magnetic property of III was also investigated in the temperature range of 2 to 300 K, and the magnetic behaviour suggests weak antiferromagnetic coupling exchange.     

Terpyridine functionalized α-cyanostilbene derivative as excellent fluorescence and naked eyes Fe<Superscript>2+</Superscript> probe in aqueous environment

A novel carbazole derivative (L) functionalized by terpyridine was designed and synthesized. Its structure was fully characterized by FT-IR, HR-MS, ¹H NMR spectra. L formed J-aggregates and possessed aggregation-induced emission enhancement property in aqueous environment. In addition, compound L showed specific response to Fe²⁺ in UV–vis spectra at 557 nm in EtOH–H₂O mixed solvent, owing to metal-to-ligand-charge-transfer (MLCT). The emission quenched much more sharply than other metal ions when adding Fe²⁺. The interaction between compound L and Fe²⁺ was analyzed by UV–vis and fluorescence spectrum titration. The limit of detection was calculated to be 1.63 μM. The stoichiometric of L and Fe²⁺ was 2:1 confirmed by Job’s plots. Competition experiment indicated that other metal ions caused little interference. In this way, L could be a fluorescent and “naked eyes” probe for Fe²⁺ detection. This dual mode Fe²⁺ sensor can be considered to have potential value in practical applications.     

Single crystal x-ray diffraction study of dioxane,pyrazine, and pyridine complexes of 3-(1-amino-2,2,2-trifluoroethylidene)-2-imino-1,1,4,5,6,7-hexafluoroindan

Single crystals of complexes of 3-(1-amino-2,2,2-trifluoroethylidene)-2-imino-1,1,4,5,6,7-hexafluoroindan (1) with 1,4-dioxane, pyrazine, and pyridine have been synthesized. Their structure was investigated by X-ray analysis. In crystals of the dioxane complex, compound 1 is present together with its tautomer — 2-amino-3-(1-imino-2,2,2-trifluoroethyl)-1,1,4,5,6,7-hexafluoroindene (1a), and these compounds are in an equilibrium ratio of ～60:40. Gas-phase quantum chemical calculations have been performed to examine the possibility of a tautomeric equilibrium of enaminoimine 1 in the corresponding complexes.     

Transition metal complexes of a hydrazone derived from hydralazine hydrochloride and 3,5-di-tert-butylsalicylaldehyde

Mononuclear Co(III), Ni(II) and Cu(II) coordination compounds of (E)-1-(3,5-di-tert-butyl-2-hydroxybenzylidene)-2-(phthalazin-1-yl)hydrazine (LH) were prepared and characterized by physicochemical and spectroscopic methods. The metal-to-ligand ratio was found to be 1:2 in [Co(L)₂]Cl·2H₂O (1) and [Ni(L)₂]·2H₂O (2), while it is 1:1 in [Cu(L)Cl]·2CH₃OH (3). The X-ray crystal structures of LH and complex 1 is are reported. LH shows monobasic behavior, coordinating through NNO donor atoms. The complexes were investigated for their antimicrobial properties. Complexes 1 and 3 show excellent antibacterial and antifungal activities, respectively.     

Synthesis and antimicrobial activity of fused isatin and diazepine derivatives derived from 2-acetyl benzofuran

Acetyl benzofurans 1a, 1b reacted with isatins 2a–2f in the presence of pyridine to give corresponding 3-[2-(1-benzofuran-2-yl)-2-oxoethyl]-3-hydroxy-1,3-dihydro-2H-indol-2-one derivatives 3a–3l. Dehydration of the latter in acidic media led to the corresponding α,β-unsaturated ketones 4a–4l. The structures of newly synthesized compounds 3a–3l and 4a–4l were established on the basis of analytical and spectral data. The synthesized compounds were screened for their antibacterial and antifungal activities. Compounds 5d, 5f, and 5h displayed excellent antimicrobial activity. The synthesized compounds were studied for docking on the enzyme, Glucosamine-6-phosphate Synthase.     

Neutral and cationic (pyrazolylmethyl)pyridine palladium(II) complexes: kinetics and chemoselectivity studies in hydrogenation of alkenes and alkynes

Reactions of (3,5-dimethylpyrazolylmethyl)pyridine (L1) and (3,5-diphenylpyrazolylmethyl)pyridine (L2) with either [PdCl₂(NCMe)₂] or [PdClMe(COD)] afforded the respective neutral palladium complexes, [PdCl₂(L1)] (1), [PdCl₂(L2)] (2) and [PdClMe(L1)] (3). Treatment of complex 1 with equimolar amounts of PPh₃ or PPh₃/NaBAr₄ produced the corresponding cationic complexes [Pd(L1)ClPPh₃]Cl (4) and [Pd(L1)ClPPh₃]BAr₄ (5), respectively. Complexes 1–5 formed active catalysts in hydrogenation of alkenes and alkynes. Isomerization reactions were predominant in the hydrogenation reactions of terminal alkenes, while hydrogenation of alkynes involved a two-step process via alkene intermediates prior to the formation of the respective alkenes. The lack of induction periods in the hydrogenation reactions in addition to pseudo-first-order kinetics with respect to the substrates established the homogeneous nature of the active species.     

Synthesis,antibacterial activity,and fluorescence properties of a novel series from [2,4-dioxochromen-3(4<Emphasis Type="Italic">H</Emphasis>)methyl]amino acid

A new solvent-free method for synthesis of starting compounds 2,4-dioxochromen-3(4H)methyl amino acetic acid derivatives 1a–e via a green approach is reported. Also, the behavior of compound 1a towards various nitrogen nucleophiles such as primary amines, hydrazine hydrate, and hydroxylamine hydrochloride to give corresponding compounds 2–4 was studied. Furthermore, chlorination of compound 1a using a mixture of PCl₅/POCl₃ to yield acid chloride derivative 5 and the reaction of the latter compound 5 with various amino acids to obtain dipeptide compounds 6a–e are described. Moreover, cyclization of compound 1a in alkaline medium to afford dihydrochromeno[3,4-c]pyrrole-1-carboxylic acid 7 and cyclization of 6b in acidic medium, namely Ac₂O, to yield piperazine derivative 8 are reported. Also, reaction of compound 1a with maleic anhydride in dioxane to afford Diels–Alder adduct 9, which posteriorly reacted with hydrazine hydrate to give 10, was investigated. Most of the newly synthesized compounds were screened against Gram-positive and Gram-negative bacteria, with compound 5 exhibiting the maximum inhibition zone towards all four types of bacteria. In addition, the absorption and fluorescence emission of some of the substituted coumarins were studied in dioxane, revealing that the substituents altered both the absorption and fluorescence emission maxima.     

Facile synthesis of some condensed 1,3-thiazines and thiazoles under conventional conditions: antitumor activity

1,3-Thiazine 3 was obtained from cinnamoyl thiourea derivative 2 as the kinetic control product. Refluxing of 2 with sodium ethoxide afforded pyrimidine derivative 4. Moreover, stirring of 2 with bromine/acetic acid gave thiazole 5 that was condensed with o-phenylene diamine forming benzimidazole 6. Heating of arylthiourea 8 with maleic anhydride or phenacyl chloride afforded thiazole derivatives 9 and 10, respectively. Condensation of compound 10 with o-phenylene diamine gave benzimidazole 11. Reaction of p-amino benzoic acid with chloro acetyl isothiocyanate, acetylacetone and ethylacetoacetate produced imidazole 14, enaminone 15 and crotonate 16 derivatives, respectively. Stirring a mixture of benzoyl isothiocyanate with 15 and/or 16 resulted in pyridine-2-thione 17. The yields of the prepared compounds were 41–93%. The experimental section is simple and easy. The detailed synthesis, spectroscopic data, IC₅₀ and antitumor activity of the synthesized compounds were reported. The cytotoxicity of the newly synthesized products showed that compound 4 is the most active compound towards the cancer cell line at which its reactivity is higher than that of the standard doxorubicin (anticancer reference drug).     

Thermodynamics of interactions between lead(II) and cadmium(II) ions and azulene-based complexing polymer films

In order to understand the essential processes/interactions between the metal ions and modified electrodes which are based on complexing polymeric films, access to thermodynamic characteristics is compulsory. The paper enlarges the information concerning the sorption of metal ions within complexing polymer films, particularly based on azulene, which can be involved in metal detection sensors. Interactions between lead(II) or cadmium(II) ions and complexing polymer films have been studied using chemical preconcentration–anodic stripping method. The films have been obtained by controlled potential electrolysis in millimolar solutions of 4-azulen-1-yl-2,6-bis(2-thienyl)pyridine (L) in acetonitrile. PolyL films affinities towards these metal ions have been quantified at different temperatures by means of sorption isotherms. Parameters for sorption of lead(II) and cadmium(II) ions within polyL films have been calculated for Freundlich, Langmuir and Redlich–Peterson isotherms. The best fit was obtained when using Langmuir isotherm. The results evidence that lead ions are better sorbed than cadmium within polyL film. Thermodynamic parameters for the chemical sorption of lead(II) and cadmium(II) ions within polyL films have been calculated.     

Amine electrosynthesis from 1-ethyl-4-nitro-3-cyanopyrazole

Polarography and preparative electrolysis are used to show that the electrochemical behavior of 1-ethyl-4-nitro-3-cyanopyrazole (1) in acidic aqueous-alcoholic solutions resembles the behavior of nitrobenzene. By varying the parameters of the electroreduction (ER) of compound 1, one can obtain either 1-ethyl-4-amino-3-cyanopyrazole (2) or 1-ethyl-4-amino-3-cyano-5-chloropyrazole (3). Compound 2 is formed during the ER of compound 1 in the presence of a mediator (titanium(III)) at temperatures below 10°C. Compound 3 is produced by the direct reduction of compound 1 on a lead electrode (30% ethanol, 10% HCl). The yield of amine chlorohydrates 2 and 3 is 56 and 92%, respectively. The mediated ER of compound 1 at catholite temperatures higher than 10°C yields a mixture of compounds 2 and 3; the proportion of the latter increases with temperature to become the major product at 60°C. Compound 3 is formed due to the rearrangement of the hydroxylamine derivative produced by the ER of compound 1, followed by the substitution of chlorine for the hydroxy group.