Iranian Journal of Chemistry and Chemical Engineering
Year:2001 | Volume:20 | Issue:1|Papers Count:8

Lead is quantitatively retained on 2-(5-bromo-2-pyridylazo)-5-diethylamminophenol (5-Br-PADAP) -ammonium tetraphenylborate with microcrystalline naphthalene or by a column method in the pH range 4.0-6.0 from a large volume of aqueous solutions of various samples with preconcentration factor of 60. After filtration, the solid mass consisting of the lead complex and naphthalene was dissolved with 5 mL of dimethylformamide and the metal was determined by atomic absorption spectrometry. The calibration curve is linear in the range of 1.9-180 mug/mL in DMF with a relative standard deviation of 1.7%. The interference of a large number of anions and cations has been studied.

Efficient Knoevenagel condensation of barbituric acid with different aromatic aldehydes on basic alumina was performed in a conventional microwave oven in the absence of solvent.

A proton NMR method for the determination of solvation numbers of alkaline earth cations with hexamethyl phosphoramide (HMPA) in nitromethane (NM) as diluent is described. The method is based on monitoring the resonance frequency of HMPA protons as a function of HMPA/metal ion molar ratio at constant metal ion concentration. The average solvation number of cations, (n) over bar, at any HMPA/metal ion ratio obtained from the NMR chemical shift-molar ratio data was plotted against the molar ratios values. The solvation numbers of each alkaline earth cation was determined from the limiting value of the corresponding (n) over bar, vs. molar ratio plot.

A facile one-pot method with good yield for the synthesis of 2,4-dichloroquinoline and some related new derivatives by condensation of the appropriate primary aromatic amine with malonic acid in presence of excess phosphorus oxychloride is described.

The complexation reactions between diacetyl monooxime (Damo), imidazole (Him), histamine (Hist) and histidine (His) with Co2+, Ni2+ and Cu2+ were studied potentiometrically in aqueous solution at 25 ºC and mu = 0.5 M KNO3. The overall stability constants log b's of species were obtained by computer refinement of pH-volume data using BEST computer program. Several models were tested and, based on the lowest sigma (FIT), the best one is accepted The main species in binary complexes are MAH, MA2, MA2H, MA2H2, (in MA3 and MA(4) A = Him), and for ternary complexes are MAB, MA2B, MAB2 and MABH. The D log K-MAB and log X-MAB were calculated for MAB mixed complexes. The order found for the resulting stability constants vary as, Co2+ < Ni2+ < Cu2+.

A carbon-paste electrode modified with iron (II) phthalocyanine (FePc) was used as a sensitive potentiometric sensor for determination of 2-pyridinethiol (2PT), 2-mercaptoethanol (2ME) and sulfide ion in aqueous solutions. The modified electrode acts as an electrocatalyst for oxidation of these compounds, and lowers the overpotential for oxidation reactions by more than 400 mV, compared to the unmodified electrode. The process was dependent on the pH of the supporting electrolyte. The fast rate of electron transfer results in a near-Nernstian behavior of the modified electrode, and makes it a suitable potentiometric sensor for measurement of these compounds. Calibration studies were performed using potentiometry in oxygen or air saturated stirred solutions; linear responses were obtained over the range of about 1x10-6 to 5x10-3 M (correlation coefficients, r, of similar 0.999, n=8). The modified electrode exhibited a fast response time (< 20 s), good stability, and had an extended lifetime; the standard deviation of slopes, during a period of two months, was 1.7-2.4% (n=10). Appropriate electrochemical and analytical data are presented.

A new model for the vapor phase of a pressurized liquid called "the cluster model", which is originally introduced in this work along with an accurate equation of state for the liquid phase called the LIR is used to derive an accurate equation for the vapor pressure of liquid as a function of external pressure. The chemical potential of both phases have been found to be in good agreement with experiment. The calculated vapor pressure is compared with the Gibbs prediction. We have found that the Gibbs prediction is accurate at low external pressures and is reasonable at moderate pressures, but has a significant deviation at high external pressures. The calculated vapor pressure is used to obtain the vaporization enthalpy in terms of the external pressure. The physical interpretations for pressure dependence of both the vapor pressure and enthalpy of vaporization are also given. Compared to the temperature dependence, the pressure dependence of vapor pressure is insignificant.

A new retrofit targeting procedure, based on pinch technology has been developed. The new procedure considers existing structure of a given network and finds the most compatible configuration with the network. To achieve this aim, the procedure uses a linear programming technique that maximizes the compatibility. Good compatibility between old and new networks helps to make the best use of capital in retrofit projects. The procedure has been tested by doing two case studies, in which the results compared to other established methods, and realized significant improvement.