Kinetic and mechanistic studies of oxidation of amine-N-polycarboxylates complexes of cobalt(II) by periodate ions in aqueous medium

The kinetics and mechanism of interaction of periodate ion with [Co^IIL(H₂O)]^2-n [L = trimethylenediaminetetraaceticacid (TMDTA)] and ethylene glycol bis(2-aminoethyl ether) N,N,N’,N’-tetraaceticacid (EGTA) have been studied spectrophotometrically by following an increase in absorbance at λ_max = 550 nm in acetate buffer medium as a function of pH, ionic strength, temperature, various concentration of periodate and [Co^IIL(H₂O)]^2-n under pseudo-first order conditions. The experimental observations have revealed that the intermediates having sufficiently high half life are produced during the course of both the reactions which finally get converted into a corresponding [Co^IIIL(H₂O)]^3-n complexes as a final reaction product. The reaction is found to obey the general rate law Rate = (k₂ [IO₄ ^?] + k₃ [IO₄ ^?]²) [Co^IIL(H₂O)]^2-n. This rate law is consistent with a four step mechanistic scheme (vide supra) where electron transfer proceeds through an inner sphere complex formation. The value of rate constant k₂ is independent of pH over the entire pH range which suggest that unprotonated form of [Co^IIL(H₂O)]^2-n is the only predominant species. The value of k₂ is invariant to ionic strength variation in both the systems. The value of k₃ is also found to be almost invariant to ionic strength in case of [Co^IITMDTA(H₂O)]^2?-[IO₄]^? system but it decreases considerably in case of [Co^IIEGTA(H₂O)]^2?-[IO₄]^? system with the corresponding decrease in ionic strength. The activation parameters have been computed and given in support of proposed mechanistic scheme.     

Transmetalation of palladium enolate and its application in palladium-catalyzed homocoupling of alkynes: a room-temperature, highly efficient route to make diynes

A novel pathway for the homocoupling reaction has been achieved using a similar protocol as the cross-coupling reaction. Ethyl bromoacetate is chosen to initiate the coupling reaction through oxidative addition to a Pd(0) species, and an PdBr(enolate) intermediate is formed. This intermediate can undergo double transmetalation with an alkynyl copper reagent, and reductive elimination produces a variety of diynes in high yields.     

Studies on polymerization of vinyl acetate using ylide as an initiator and degradative transfer agent

The polymerization of vinyl acetate initiated by β-picolinium-p-chlorophenacylide was carried out at 30, 35, and 40°C, using the conventional dilatometric technique. The initiator and the monomer exponent values were 0.80 ± 0.15 and unity, respectively. The polymerization was inhibited in the presence of hydroquinone, but was favored by nonpolar solvent and polymerization temperature. The energy of activation was 90.3 kJ mol^?1. An average value of k/k_t for the present system was found to be 0.37 × 10^?2 L mol^?1 s^?1. The results are explained in terms of radical mode of polymerization with degradative initiator transfer; the principal mode of termination, however, was biomolecular.     

Chemical chaos in novel iodate-driven oscillator-thiophenol-iodate-H2SO4 system

Chaotic oscillations in redox potential have been observed in thiophenol-KIO₃-H₂SO₄ system in batch reactors. These occur in a concentration and temperature range. Bifurcation from a stable regime to a chaotic regime occurs in a straight way in the entire concentration and temperature range. Oscillations were also studied in continuously stirred tank reactors. These oscillations are deterministic chaos. It is tentatively suggested that chaos in the system is due to a time delay caused by a large number of intermediates.     

Effect of Solvents on the Spectra of Some β-Diketones

Acetoacetanilide, benzoylacetanilide and their derivatives have been examined in ultraviolet region in a series of solvents covering a broad polarity range e. e. from chloroform (Z, 63.2) to methanol (Z .83.6). Transition energies and oscillator strengths have been calculated and transition energy (E_T) has been plotted against Z-values, a new empirical measurement of solvent polarity. A linear relationship was observed between the transition energy and Z-values for π → π* and n → π* transitions. These transitions are identified as charge transfer (c-t) transitions and with the solvents having carbonyl oxygen and sulphur atom a c-t complex formation has been suggested. Strong electron-donating substituents on phenyl group of the nitrogen atom also showed a weak to moderate n → π* transitions. These substituents have no influence on the position of the λ_max in the same solvent. Stabilization energy of the excited state of these ligands and hence the dipole moments of the excited states have been calculated in comparison with pyridinium iodide. Solvent sensitivities of these ligands have also been calculated.     

Role of liquid membrane phenomenon in the biological actions of thioridazine

Role of surface activity in the mechanism of action of thioridazine (THR) has been studied. THR has been shown to generate liquid membrane it self and also in association with the relevant membrane lipids, sphingomyelin and cholesterol in series with a supporting membrane. Transport of relevant biogenic amines e.g. dopamine, nor-adrenaline, adrenaline, serotonin, gamma amino butyric acid (GABA) and glutamic acid and ions viz. sodium, potassium, and calcium has been studied in the presence of liquid membranes generated by THR and THE in association with sphingomyelin-cholesterol. The data on modifications in the permeability of relevant biogenic amines and ions indicate that the liquid membranes generated by THR may contribute to the mechanism of action of THR.     

Anion recognition through novel C-thiophenecalix[4]resorcinarene: PVC based sensor for chromate ions

Novel ionophore, C-thiophenecalix[4]resorcinarene (I) has been synthesized and characterized by IR, NMR and C, H, N analysis. Poly(vinyl chloride) (PVC) based membranes of ionophore (I) using dibutylphthalate (DBP), dioctylphthalate (DOP), 1-chloronapthalene (CN), tris(2-ethylhexyl) phosphate (TEHP) and bis(2-ethylhexyl)sebacate (DOS) as plasticizing solvent mediators were prepared and used as Cr selective sensors. Of the various sensors prepared, the one with membrane composition 2:66:120 mg (I: PVC: DBP) exhibited the best performance. This sensor works well over a wide concentration range 5.6 × 10⁻⁶-1.0 × 10⁻¹ M (detection limit ∼ 0.30 ppm) with Nernstian compliance (29.0 mV per decade) between pH 6.5-10.0 with a fast response time of ∼13 s. The selectivity coefficient values as determined by fixed interference method (FIM) indicate excellent selectivity for Cr ions over a large number of anions. The sensor exhibits adequate shelf-life ( ∼5 months) with good reproducibility (S.D. ± 0.2 mV). The sensor has been used in the potentiometric titration of chromate with Pb(II). Determination of chromium in electroplating waste using the sensor was successfully achieved.     

A Spectrophotometric Study on Complex Formation of Tungsten (VI) with Glycine Cresol Red

Glycine cresol red (G. C. R) has been used as a complexometric indicator and a reagent for the spectrophotometric determination of inorganic ions^1-4. It forms stable coloured chelates iusolution with some metal ions under appropriate conditions. This communication give the composition and stability of tungsten G. C. R. Chelate.     

Spectrophotometric Studies on the Chelate Formation between Zirconium(IV) and Chromotrope 2R

The composition and stability of the chelate formed between Zr(IV) and chromotrope 2R has been investigated using spectrophotometric methods. The chelate is violet in color and has λmax at 530 nm. The composition, determined by different methods is 1 : 1. The chelate is stable between pH 1.0-3.0. The value of log K as determined by two different methods are 4.48±0.2 and 4.21±0.1 and the values of free energy of formation are —6.21±0.2 and —5.83±0.1 respectively at 30°C. The system obeys Beer's Law over a concentration range of 2.50 to 20.0 ppm of zirconium. The effective range of photometric determination is 3.50 to 19.05 ppm of zirconium.     

Halogen derivatives of triphenylphosphine,triphenylarsine and triphenylstibine substituted molybdenum carbonyls

Summary Halogen oxidation of several LMo(CO)s andcis-L₂Mo(CO)₄ (L = Ph₃P₁Ph₃As and Ph₃Sb) derivatives has been studied. The LMo(CO)₅ complexes react with halogens to give hexacoordinate LMo(CO)₃ X₂ (X = Cl, Br or I) derivatives which are of very rare occurrence. Similar reactions withcis-L₂Mo(CO)₄ give heptacoordinate L₂Mo(CO)₃X₂ derivatives. The complexes have been characterised by elemental analysis, i.r. and conductivity measurements.