Kinetics and mechanism of the oxidation of a heterocyclic thioamide by silver(II)-cyclam

The kinetics of the oxidation of 4,6-dimethyl-2-mercaptopyrimidine (DMP) by Ag(cyclam)²⁺ were studied in buffer solutions from pH 5.8 to 7.2 at constant ionic strength of 0.10?M?(NaClO₄). The reaction is observed to be first-order with respect to [Ag(cyclam)²⁺] and to [DMP]. However, the reaction rate is affected by the pH of the solution owing to the acid–base equilibrium of the thiol. The mechanism postulated to account for the kinetics includes an acid–base equilibrium and oxidation of thiol (RSH) and thiolate ion (RS^?) by Ag(cyclam)²⁺ to RS^· radicals which undergo rapid dimerization to form disulfide (RSSR). From the postulated mechanism and the observed kinetics a rate expression was derived, and second-order rate constants and activation parameters were calculated. The pK _a values of the acid dissociation reaction of DMP were also determined at four temperatures using spectrophotometric methods, and thermodynamic parameters calculated from the K _a values.     

(2R,4S)-4-甲基-2-哌啶甲酸乙酯的合成

以S-(-)-α-苯乙胺为原料,经一锅法制得1-(1-苄基)-6-乙氧羰基-4-甲基-3,4-二氢哌啶(3),收率58.7%。以10%Pd/C为催化剂,3经催化氢化脱苄合成了4-甲基-2-哌啶甲酸乙酯(4),收率96%;4通过减压分馏得(2R,4S)-4,含量95%,其结构经1H NMR,IR和MS确证。     

Kinetics and Mechanism of the Autocatalytic Oxidation of Mn(II) by Bromine

The oxidation of Mn(II) by bromine is an autocatalytic reaction, which seems to be important for a detailed elucidation of chemical oscillators, based on manganese chemistry. With regard to the mechanism proposed previously, an alternative reaction mechanism is proposed, based on a micro-heterogeneous oxidation of Mn(II) ion, adsorbed on a surface of the MnO₂ colloid. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis of 4-Hydroxy- and 4-Amino-2-Methyl-3-(2-Methylindol-3-Yl)methylquinolines and Their 6- and 8-Substituted Derivatives

A method has been developed for the synthesis of substituted 4-hydroxy- and 4-amino-2-methyl-3-(2-methylindol-3-yl)methylquinolines by treating the corresponding 4-hydroxy(chloro)-2-methyl-3-(3-oxobutyl)quinolines with phenylhydrazine hydrochloride. It was found that nucleophilic substitution occurred in the case of the 4-chloroquinolines together with subsequent rearrangement to give the 4-amino derivatives. The thiosemicarbazones of the corresponding 4-hydroxy-2-methyl-3-(3-oxobutyl)quinolines were also obtained.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 554–557, April, 2005.     

Silver(I) and Silver(II) Complexes with Some Tetraazamacrocyclic Ligands in Aqueous Solutions

The reactions of silver(I) with isocyclam, scorpiand,trans-Me₂[14]anN₄, cis-Me₆[14]anN₄,(N-Me)Me₂py[14]anN₄ and py[12]anN₄ were investigated.The stability constant of the Ag(I) complex with py[12]anN₄ was determined. The aqueous solutions of the silver(II) complexes with the 14-membered ligands were obtained, and characterized by means of UV-VIS and CVA measurements. The Ag²⁺ ion does not form a five-coordinate complex with scorpiand. The formal potentials of the Ag(II)/Ag(I) system in the presence of scorpiand, trans-Me₂[14]anN₄, cis-Me₆[14]anN₄ and(N-Me)Me₂py[14]anN₄ were determined. The mechanism is also proposedfor the electroreduction of the silver(II) complexes with these compounds on a platinum electrode in aqueous solution.     

Synthesis of 2,5 -Bis(4-methyl-2-thienyl)thiophene and 2,5-Bis(4-methyl-2-thienyl)pyrrole

Syntheses of 2,5-bis(4-methyl-2-thienyl)thiophene 3 and 2,5-bis(4-methyl-2-thienyl)pyrrole 4 are described. The key step involves Stetter reaction between 4-methyl-2-thiophenecarboxaldehyde and divinyl sulfone. Cyclizaton of the resulting 1,4-bis-(4-methyl-2-thienyl)-1,4-butanedione 2 with Lawesson's reagent gives 2,5-bis(4-methyl-2-thienyl)thiophene 3, whereas condensation with ammonium acetate provides the 2,5-bis(4-methyl-2-thienyl)pyrrole 4.     

2-(5-甲基-2-苯基-4-噁唑基)乙醇的合成工艺改进

以L-天门冬氨酸为原料,经过β-甲酯化,苯甲酰化,Dak in-W est反应,环合和氢化铝锂还原等反应步骤,以36.1%的总收率得到抗糖尿病药物的重要中间体2-(5-甲基-2-苯基-4-噁唑基)乙醇.用浓硫酸取代三氯氧磷作为关环剂,简化了环合工艺和后处理操作.     

Acid-Base Properties of the Ground and Excited States of Ruthenium(II) Tris(4′-methyl-2,2′-bipyridine-4-carboxylic Acid)

The acid dissociation constant, pK_a, for the ground and excited states of ruthenium tris(4′-methyl-2,2′-bipyridine-4-carboxylic acid) complex have been measured. The ground state pK_a obtained from the pH titration curve of the complex absorption at 454 nm was 2.5. The lifetimes of the excited-state for deprotonated and protonated ruthenium complexes are 595 and 150 ns, respectively. The excited-state pK_a* is obtained from the emission titration curve at 630 nm and corrected for the excited-state lifetime to be 4.2. The increase of 1.7 pH units in the acid dissociation constant in the excited-state indicates that the ligand is much more basic in the excited-state. This result confirms the MLCT assignment for the lowest electronic transition of [Ru(mbpyCOOH)₃]²⁺.     

Kinetics of oxidation of nickel(II) aza macrocycles by peroxydisulphate in aqueous media

The kinetics of the oxidation of nickel (II) hexaaza and nickel (II) pentaaza macrocycles by the peroxydisulphate anion, S₂O₈ ²⁻, were studied in aqueous media. Effect of pH on reaction rate was also studied. The rate increases with increase of S₂O₈ ²⁻ concentration. Rates are almost independent of acid betweenpH 4 and 2, giving overall a relatively simple second-order rate law followed by oxidation within the ion pair solvent shell. Using rate =+1/2 d[Ni(L)³⁺]/dt =k[Ni(L)²⁺][S₂O₈ ²⁻], oxidation rate constants were determined.     

Reaction of 1-benzoylethylpyridinium-4-aldoxime chloride with aquapentacyanoferrate(II)

The results of a spectrophotometric investigation of the reaction of the biologically active salt 1-benzoylethylpyridinium-4-aldoxime chloride with aquapentacyanoferrate(II) ion are presented. In spite of the presence of two donor sites, only the carbonyl group of the ligand coordinates to the iron centre. Reaction kinetics are consistent with a dissociative mechanism.     

Tetraaqua-bis(3-hydroxy-4-nitrobenzoato) Co(II) and Ni(II) complexes and diaqua-bis(2-hydroxy-4-methoxybenzoato) Zn(II) complex: crystal structure and thorough metal-coordination investigation

Reactions of Co(II) and Ni(II) salts with the monosodium salt of 3-hydroxy-4-nitrobenzoic acid (3) in aqueous solution resulted in isomorphous covalent complexes 3C and 3D, of centrosymmetric geometries. In similar conditions, 2-hydroxy-4-methoxybenzoic acid (5) led to the covalent Zn(II) complex 5A, exhibiting a marked dissymmetric geometry. The present crystallographic data with structural data for a series of closely related metal complexes previously reported allow a tentative rationalization of the solid-state architecture of such complexes. The dissymmetry in 5A was interpreted on the basis of a mixed (monodentate and bidentate) metal-ligation mode and a pyramidal coordination at the metal.     

Synthesis of Derivatives of (4-Methyl-2-Quinolylthio)acetic and (4-Methyl-2-Quinolylthio)propionic Acids

An efficient synthesis has been developed for derivatives of (4-methyl-2-quinolylthio)acetic and (4-methyl-2-quinolylthio)propionic acids by the reaction of 4-methyl-2-thioxoquinoline with methyl methacrylate, the amide of methacrylic acid, acrylonitrile, ethyl bromoacetate, and ethyl acrylate. The hydrolysis of the resultant intermediates by (quinolylthio)acetic and (quinolylthio)propionic acids gave the corresponding acid products, which are also formed in the reaction of 4-methyl-2-thioxoquinoline with chloroacetic and acrylic acids. The reaction of 4-methyl-2-thioxoquinoline with allyl bromide was studied. The potassium permanganate oxidation of the resultant 2-allylthio-4-methylquinoline led to (4-methyl-2-quinolylthio)acetic acid.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 403–406, April, 2005.     

Mannich-Type Reaction for Synthesis of 3-Methyl-4-nitroimino-tetrahydro-1,3,5-oxadiazine

The reaction of N-methyl-N′-nitroguanidine with 3-methyl-4-nitroimino-tetrahydro-1,3,5-oxadiazine is a Mannich-type reaction. The reaction was catalyzed by several organic and inorganic bases at different reaction times and temperatures. Three inorganic base catalysts [potassium carbonate (K₂CO₃), sodium hydrogen carbonate (NaHCO₃), and sodium hydroxide (NaOH)] and several organic bases (methylamine, ethamine, iso-propylamine, and n-butylamine) have been studied. The results showed that both the inorganic and organic base catalysts can be used as catalysts, with the organic bases performing better. N-Methyl-N′-nitroguanidine reacts to give the title compound 2 and is catalyzed by both acids and bases. The intensity of inorganic base catalysts, reaction temperature, and reaction time had significant effects on the products.     

Color Reaction Between 4-(2-Pyridylazo)Resorcinol and Mercury (II) in the Presence of Surfactant,and Improved Spectrophotometric Determinations of Mercury(II) and Cyanide Ion with its Coloring

Abstract

The reactions among 4-(2-pyridylazo)resorcinol (PAR), mercury(II) and/or cyanide ion in the presence of water soluble surfactants alone or combination were systematically investigated at about pH 9. The spectrophotometric determinations of mercury(II) and cyanide ion were investigated by using the PAR-mercury(II)-HPC complex (3:2:2 molar ratio) in the presence of N-hexadecylpyridinium chloride (HPC) alone; calibration graphs were rectilinear in the ranges of 0 – 40 μg mercury(II) and 0 –10 μg cyanide ion in a final 10 ml with the apparent molar absorptivities of 5.9 × 10⁴ for mercury(II) and 2.5 × 10⁴ 1 mol^?1 cm^?1 for cyanide ion at 590 nm. The proposed method had advantages—rapidity, simplicity without solvent extraction, and sensitivity in comparison with reported solvent extraction methods. The interference of foreign ions decreased 1/2–l//4-fold compared with that in the presence of non-ionic surfactant alone.     

Novel 2-aminoimidazole-4-one complexes of copper(II) and cobalt(II): Synthesis,structural characterization and cytotoxicity

A series of 2-aminosubstituted (5Z)-3-phenyl-5-(pyridine-2-ylmethylene)-3,5-dihydro-4H-imidazole-4-ones (L) was prepared by the reaction of the corresponding 2-alkylthio-3,5-dihydro-4H-imidazole-4-ones with morpholine or piperidine in the presence of ytterbium(III) triflate. The resulting ligands were subsequently reacted with CuCl₂·2H₂O and CoCl₂·6H₂O to give the corresponding copper(II) and cobalt(II) complexes, respectively. Analysis revealed that the complexes were formed with an LMCl₂ (M = Cu, Co)-type composition in all cases. The structures of the three cobalt complexes prepared in this way were determined by X-ray crystallography. The results revealed that the cobalt ions in these complexes were tetrahedrally coordinated to two chloride anions and two nitrogen atoms from the pyridine and imidazole moieties of the ligand. The electrochemical properties of the ligands and their complexes were evaluated by cyclic voltammetry, and the results revealed that the first stage in the reduction of the Co(II) and Cu(II) complexes involved the reversible formation of the corresponding Co(I) and Cu(I) complexes, respectively. The cytotoxicity activities of the organic ligands and their complexes were evaluated against several cancer cell lines, including MCF-7, A549 and HEK293 cells. The copper complexes of the organic ligands bearing a phenyl or allyl moiety at their N(3) position together with a piperidine substituent at the 2-position of their imidazolone ring exhibited the greatest cytotoxicity of all of the compounds tested in the current study.     

1-Methyl-4-ferrocenylmethyl-3,5-diphenylpyrazole: A versatile ligand for palladium(II) and platinum(II)

The syntheses and characterization of two novel ferrocene derivatives containing 3,5-diphenylpyrazole units of general formula [1-R-3,5-Ph₂-(C₃N₂)-CH₂-Fc] {Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄) and R = H (2) or Me (3)} together with a study of their reactivity with palladium(II) and platinum(II) salts or complexes under different experimental conditions is described. These studies have allowed us to isolate and characterize trans-[Pd{1-Me-3,5-Ph₂-(C₃N₂)-CH₂-Fc]}₂Cl₂] (4a) and three different types of heterodimetallic complexes: cis-[M{1-Me-3,5-Ph₂-(C₃N₂)-CH₂-Fc]}Cl₂(dmso)] {M = Pd (5a) or Pt (5b)}, the cyclometallated products [M{κ²-C,N-[3-(C₆H₄)-1-Me-5-Ph-(C₃N₂)]-CH₂-Fc}Cl(L)] with L = PPh₃ and M = Pd (6a) or Pt (6b) or L = dmso and M = Pt (8b) and the trans-isomer of [Pt{1-Me-3,5-Ph₂-(C₃N₂)-CH₂-Fc]}Cl₂(dmso)] (7b). In compounds 4a, 5a, 5b and 7b, the ligand behaves as a neutral N-donor group; while in 6a, 6b and 8b it acts as a bidentate [C(sp²,phenyl),N(pyrazole)]⁻ group. A comparative study of the spectroscopic properties of the compounds, based on NMR, IR and UV-Visible experiments, is also reported.     

Complexes of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) with 4-chloro-2-methoxybenzoic acid anion

The complexes of 4-chloro-2-methoxybenzoic acid anion with Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ were obtained as polycrystalline solids with general formula M(C₈H₆ClO₃)₂·nH₂O and colours typical for M(II) ions (Mn – slightly pink, Co – pink, Ni – slightly green, Cu – turquoise and Zn – white). The results of elemental, thermal and spectral analyses suggest that compounds of Mn(II), Cu(II) and Zn(II) are tetrahydrates whereas those of Co(II) and Ni(II) are pentahydrates. The carboxylate groups in these complexes are monodentate. The hydrates of 4-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) heated in air to 1273 K are dehydrated in one step in the range of 323–411 K and form anhydrous salts which next in the range of 433–1212 K are decomposed to the following oxides: Mn₃O₄, CoO, NiO and ZnO. The final products of decomposition of Cu(II) complex are CuO and Cu. The solubility value in water at 293 K for all complexes is in the order of 10^–3 mol dm^–3. The plots of χ_M vs. temperature of 4-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II) and Cu(II) follow the Curie–Weiss law. The magnetic moment values of Mn²⁺, Co²⁺, Ni²⁺ and Cu²⁺ ions in these complexes were determined in the range of 76−303 K and they change from: 5.88–6.04 μ_B for Mn(C₈H₆ClO₃)₂·4H₂O, 3.96–4.75 μ_B for Co(C₈H₆ClO₃)₂·5H₂O, 2.32–3.02 μ_B for Ni(C₈H₆ClO₃)₂·5H₂O and 1.77–1.94 μ_B for Cu(C₈H₆ClO₃)₂·4H₂O.     

Thermal, spectral and magnetic characterization of Co(II), Ni(II) AND Cu(II) 4-chloro-2-nitrobenzoates

Physico-chemical properties of 4-chloro-2-nitrobenzoates of Co(II), Ni(II), and Cu(II) were studied. The complexes were obtained as mono- and trihydrates with a metal ion to ligand ratio of 1:2. All analysed 4-chloro-2-nitrobenzoates are polycrystalline compounds with colours depending on the central ions: pink for Co(II), green for Ni(II), and blue for Cu(II) complexes. Their thermal decomposition was studied only in the range of 293–523 K, because it was found that on heating in air above 523 K 4-chloro-2-nitrobenzoates decompose explosively. Hydrated complexes lose crystallization water molecules in one step and anhydrous compounds are formed. The final products of their decomposition are the oxides of the respective transition metals. From the results it appears that during dehydration process no transformation of nitro group to nitrite takes place. The solubilities of analysed complexes in water at 293 K are of the order of 10^–4–10^–2 mol dm^–3. The magnetic moment values of Co²⁺, Ni²⁺ and Cu²⁺ ions in 4-chloro-2-nitrobenzoates experimentally determined at 76–303 K change from 3.89 to 4.82 μ_B for Co(II) complex, from 2.25 to 2.98 μ_B for Ni(II) 4-chloro-2-nitrobenzoate, and from 0.27 to 1.44 μ_B for Cu(II) complex. 4-chloro-2-nitrobenzoates of Co(II), and Ni(II) follow the Curie–Weiss law. Complex of Cu(II) forms dimer.