Use of pi-acceptors for spectrophotometric determination of dicyclomine hydrochloride

Simple, rapid, accurate, and sensitive spectrophotometric methods are described for the determination of dicyclomine hydrochloride. The methods are based on the reaction of this drug as an n-electron donor with 2,3-dichloro-5,6-dicyano-p-benzoqunione (DDQ), p-chloranilic acid (p-CA), and chloranil (CL) as pi-acceptors to give highly colored complex species. The colored products are measured spectrophotometrically at 456, 530, and 650 nm for DDQ, p-CA, and CL, respectively. Optimization of the different experimental conditions were studied. Beer's law was obeyed in concentration ranges of 20-100, 50-250, and 80-600 microg/mL for DDQ, pCA, and CL, respectively. Colored complexes are produced in organic solvents and are stable for at least 1 h. The methods were applied to Spasmorest antispasmotic tablets and ampoules with good accuracy and precision.     

A facile synthesis of novel triazoloquinoxahnones and triazinoquinoxalinones

A series of 1-aryl-s-triazolo[4,3-a]quinoxalin-4-ones, 3 , were synthesized via the pyrolysis of the corresponding hydrazones, 6 . Thus, the cyclodehydrogenation occurred by refluxing them in an inert solvent (e.g. ethylene glycol) to give the triazoloquinoxalin-4-ones in a satisfactory yield. Using DMSO as a solvent for the above transformation afforded as a minor by-product an S-ylid. In contrast to earlier findings, annelation of a six-membered ring was successful and achieved through the pyrolysis of the pyruvate hydrazones derived of the quinoxalin-4-ones at ?230° to give the as-triazino[4,3-a]quinoxalin-5-ones, 4 . The reaction of 5 with acetylacetone afforded 3-(3′,5′-dimethylpyrazol-1-yl)-2(1H)-quinoxalinone, 10 . The structural assignments for the new compounds were based on their elemental analysis and spectroscopic data as well as an independent synthesis.     

Critical micelle concentrations for alkyltrimethylammonium bromides in water from 25 to 160°C

Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol^–1.     

Nonlinear instability of superposed magnetic fluids in the presence of an oblique magnetic field

The nonlinear evolution of interfacial waves separating two magnetic fluids subjected to an oblique magnetic field is studied in two dimensions, with the use of the method of multiple scales. It is shown that the evolution of the envelope is governed by two partial differential equations. These equations can be combined to yield two alternate Schrödinger equations with cubic nonlinearity; one of them leads to the determination of the cutoff wave number separating stable from unstable deformations while the other Schrödinger equation is used to analyze the stability of the system. The stability of the system is discussed both theoretically and computationally, and the stability diagrams are obtained. It is found in the linear theory that the oblique magnetic field has a stabilizing influence if 0 ₁ + ₂ < /2, or 3/2 < ₁ + ₂ 2 and a destabilizing influence if /2 < ₁ + ₂ < 3/2, where 0 _j , (j=1, 2) and , is the angle between the field and the horizontal axis.In the nonlinear theory, the stability analysis reveals that there exist different regions of stability and instability. It is reported that the oblique magnetic field plays a dual role in the stability criterion and the angles ₁ and ₂ play a distinctive role in this analysis besides the effect of the variation of the magnetic permeabilities.     

Radiation grafting from binary monomer mixtures. I. Vinyl ether of monoethanolamine and vinyl ether of ethyleneglycol

Gamma-radiation grafting of vinyl ether of monoethanolamine and vinyl ether of ethyleneglycol (VEEG) on polyethylene films has been studied from binary monomer mixtures. The effect of co-monomer composition and total exposure radiation dose on the grafting process is investigated. A combination of potentiometric and gravimetric techniques is applied to determine the grafting degree of each monomer in the final graft copolymer. The presence of more active monomer VEEG in the mixture was found to enhance the grafting of both monomers because the increasing of copolymerization rate which in turn increases the total grafting degree. The modification of the hydrophilic properties of the graft copolymer is studied by examining the grafted films for water- and copper (II) ions uptake.     

Enaminones in heterocyclic synthesis: Synthesis and chemical reactivity of 3‐anilino‐1‐substituted‐2‐propene‐1‐ one

The 3‐anilinoenones 3a,b were prepared from the corresponding 3‐dimemyl‐aminopropenones. The reactivity of 3a,b towards a variety of carbon and nitrogen nucleophiles as well as naphthoquinones is reported.     

Carbon‐based Nanosensors for Salicylate Determination in Pharmaceutical Preparations

Thiourea derivative‐based carbon paste electrode (TUD1‐CPE) was constructed as a potentiometric sensor for the determination of salicylate anion in pharmaceutical formulations, Aspocid® and Aspirin®. The optimized CPE contained 45.5 % graphite, 0.5 % reduced graphene oxide (rGO), 46.0 % nitrophenyl octyl ether (NPOE) plasticizer, 5.0 % TUD1 ionophore, and 3.0 % tridodecylmethyl ammonium chloride as additive. The incorporation of NPOE of high dielectric constant, and rGO in electrode caused better performance of the sensor; Nernstian response of 59.0 mV decade^?1 in the concentration range of 10^?1–10^?5 mole L^?1, a detection limit of 1×10^?5 mole L^?1 in a very short response time of 6 seconds. The prepared sensor showed high selectivity against similar anions (i. e. , benzoate, I^?, SCN^?). Selectivity was confirmed by calculating the formation constant (K_β) using sandwich membrane method, where K_β for TUD1‐salicylate is 10^0.43. Theoretical calculations at DFT‐B3LY/6‐31G** level of theory were performed to find interaction mechanism, Energies of HOMO and LUMO orbitals, non‐linear optical (NLO) properties (the electronic dipole moment (μ), first‐order hyperpolarizability (β), the hyper‐Rayleigh scattering (β_HRS) and the depolarization ratio (DR)), and other global properties; these calculations showed lower values of β and DR, higher value of β_HRS, and the shortest lengths of the four N?H bonds between TUD1 and salicylate which confirm their strong complexation and salicylate‐selectivity. Also, all the studied anion‐TUD1 exhibited relatively high NLO properties, and these results were considered as a preliminary study for investigating new types of NLO bearing materials. The sensors were applied successfully for the determination of salicylate anion in Aspocid® and Aspirin®.     

Novel Synthesis of Dihydroquinoxalinylpyridazine Derivatives

Methylquinoxaline derivative 1 undergoes bromination to give bromomethyl quinoxaline 2 , which could be transferred to cyanomethyl quinoxaline 3 . The latter compound 3 readily coupled with arene diazonium salts to give hydrazone derivatives 5a‐c . Compounds 5a,b reacted with active methylene reagents to give the target ring system, quinoxalinylpyridazine derivatives 8a‐c . Compound 1 reacted with DMFDMA to give the enamine derivative 9 , which coupled with arene diazonium salts to give the aldehydic hydrazone derivatives 10a‐c . Compound 10 reacted with active methylene compounds to give quinoxalinylpyridazine derivatives. UV characterization of some of the prepared compounds was reported.     

The use of Omega Chrome Fast Blue 2G in the microdetermination of some metals

Summary Omega Chrome Fast Blue 2G has been found to be a suitable indicator for the detection of the equivalence point of calcium, magnesium and manganese in the presence of cadmium, nickel, and aluminium, when they are masked by the addition of cyanide or triethanolamine. It is also a suitable indicator for the back titration of aluminium using calcium or magnesium as a back titrant.This dye has also been found to be a suitable reagent for the colorimetric determination of calcium, magnesium, manganese and thorium.     

Kinetics and mechanism of oxidation of a ternary complex involving dipicolinatochromium(III) and DL‐aspartic acid by N‐bromosuccinimide

The kinetics of oxidation of [Cr^III(Dpc)(Asp)(H₂O)₂] (Dpc = dipicolinic acid and Asp = DL ‐aspartic acid) by N‐bromosuccinimide (NBS) in aqueous solution have been found to obey the equation: where k₂ is the rate constant for the electron transfer process, K₁ is the equilibrium constant for deprotonation of [Cr^III(Dpc)(Asp)(H₂O)₂], K₂ and K₃ are the pre‐equilibrium formation constants of precursor complexes [Cr^III(Dpc)(Asp)(H₂O)(NBS)] and [Cr^III(Dpc)(Asp)(H₂O)(OH)(NBS)]^?. Values of k₂ = 4.85 × 10^?2 s^?1, K₁ = 1.85 × 10^?7 mol dm^?3, and K₂ = 78.2 mol^?1 dm³ have been obtained at 30°C and I = 0.1 mol dm^?3. The experimental rate law is consistent with a mechanism in which the deprotonated [Cr^III(Dpc)(Asp)(H₂O)(OH)]^? is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner‐sphere mechanism. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 394–400, 2004