Kinetic and Mechanistic Insights into the Pathway Leading to Cyclic Crystalline Phosphorus Ylide Formation in the Presence of 3‐Chloropentane‐2,4‐dione: Theoretical and Stopped‐Flow Approaches

In this work, three speculative mechanisms of the reaction between triphenylphosphine and dimethyl acetylendicarboxylate in the presence of 3‐chloropentane‐2,4‐dione were energetically and thermodynamically developed using quantum mechanical calculations and were profoundly compared with stopped‐flow and UV spectrophotometry approaches. The third speculative mechanism that led to the five‐membered ring structure was experimentally and theoretically favorable. The five‐membered ring structure of product was characterized by X‐ray crystallographic data. Also, steps 1 and 2 of the third mechanism were determined as fast and rate‐determining steps, respectively. The experimental kinetic evidence of the formation and decay of intermediate in steps 1 and 2 (fast and rate‐determining steps, respectively) was compatible with theoretical data. Experimental kinetic data were recognized for overall reaction along with activation parameters for fast and rate‐determining steps of the reaction. Theoretical kinetic data (k and E_a) and activation parameters (ΔG^≠, ΔS,^≠ and ΔH^≠) were calculated for each step and overall reactions.     

Study of the vibrational characteristics of the homonuclear diatomic nuclear schrödinger equation with a numerov method using a number of empirical potential functions

Many empirical potential energy functions have been modeled to represent the potential energy function of a diatomic molecule along whole range of internuclear distance coordinate, whereby one can determine certain molecular constants. Here we employ various potential functions such as Morse, Rydberg, Varshni(II), Varshni(III), Varshni(VI), Pöschl-Teller, Hulburt-Hirschfelder, Lippincott, Frost-Musulin, Linnet, and Rosen-Morse, and the Numerov method to solve the nuclear Schrödinger equation for F2, as an example of a homonuclear diatomic molecule. Herewith, the vibrational and vibration-rotation energy levels are obtained and excellent accuracy is achieved. The potential of employing the Numerov method in engineering physics computations is emphasized.     

Trichloroisocyanuric Acid (TCCA) and N-Chlorosuccinimide (NCS) as Efficient Reagents for the Direct Oxidative Conversion of Thiols and Disulfides to Sulfonyl Chlorides

Abstract

Trichloroisocyanuric acid (TCCA) and N-chlorosuccinimide (NCS) were found to be mild and efficient reagents for the direct oxidative conversion of sulfur compounds to the corresponding arenesulfonyl chlorides in good-to-excellent yields through the oxidative chlorination. The overall process is simple and practical, and it provides convenient access to a variety of aryl or heteroarylsulfonyl chlorides. The mild reaction conditions and the broad substrate scope render this method attractive and complementary to existing syntheses of aryl or heteroarylsulfonyl chlorides.     

Quinolinium Fluorochromate: An Efficient and Convenient Reagent for Oxidative Cleavage of Thioacetals to Their Parent Carbonyl Compounds

Deprotection of thioacetals to their parent carbonyl compounds in high yields has been carried out using quinolinium fluorochromate under mild conditions.     

DFT studies on the mechanism of allylative dearomatization catalyzed by palladium

The reaction mechanism of the Pd-catalyzed benzyl/allyl coupling of benzyl chloride with allyltributylstannan, resulting in the dearomatization of the benzyl group, was studied using density functional theory calculations at the B3LYP level. The calculations indicate that the intermediate (eta(3)-benzyl)(eta(1)-allyl)Pd(PH(3)) is responsible for the formation of the kinetically favored dearomatic product. Reductive elimination of the dearomatic product from the intermediate occurs by coupling the C-3 terminus of the eta(1)-allyl ligand and the para-carbon of the eta(3)-benzyl ligand in (eta(3)-benzyl)(eta(1)-allyl)Pd(PH(3)). For comparison, various C-C coupling reaction pathways have also been examined.     

Extraction and preconcentration of salbutamol and terbutaline from aqueous samples using hollow fiber supported liquid membrane containing anionic carrier

This paper presents a new three-phase liquid-phase microextraction (LPME) strategy for extraction and preconcentration of salbutamol (SB) and terbutaline (TB) from aqueous samples, including urine. The drugs were extracted from 11 ml of aqueous sample (source phase; SP) into an organic phase with microliter volume located inside the pores of a polypropylene hollow fiber, and then back-extracted into 24 microl of a second aqueous solution as the receiving phase (RP), located in the lumen of the hollow fiber. In preliminary experiments, we tried to transport the drugs using a pH gradient between the two sides of the hollow fiber. Due to the existence of both amine and phenolic groups on the drugs, very little transport occurred and enrichment factors (EF) less than one were obtained. Further experiments were done in the presence of bis(2-ethylhexyl) monohydrogenphosphoric acid (D2EHPA) or methyltrioctylammonium chloride (Aliquat 336) in the organic phase, to extract drugs from acidic and basic matrices, respectively. Results showed that transport of drugs from alkaline solution into 1M of sodium bromide occurred when the membrane was impregnated with dihexyl ether containing 20% Aliquat 336. To optimize the EF, the effects of different parameters such as the nature of organic solvent used to impregnate the membrane, compositions and volumes of SP and RP, type and concentration of carrier, extraction time and stirring rate were investigated. Optimal results were obtained in the presence of 0.005 M of NaOH (pH 11.70) in the SP, 1M of NaBr in the RP, 20% of Aliquat 336 in dihexyl ether as membrane impregnation solvent, stirring rate of 500 rpm and extraction time of 60 min. Under these conditions, enrichment factors of 52.9 and 213.1, dynamic linear ranges of 20-5000 and 10-5000, and limits of detection of 2.5 and 0.5 ng/ml were obtained for salbutamol and terbutaline, respectively. Also determination of drugs in environmental water and urine samples in the range of nanograms per millilitre with RSDs<10% was possible using HPLC-photodiode array detection or HPLC-MS.     

Spectrophotometric study of the charge-transfer complexes of iodine with antipyrine in organic solvents

The charge-transfer complex formation of iodine with antipyrine has been studied spectrophotometrically in chloroform, dichloromethane (DCM) and 1,2-dichloroethane (DCE) solutions at 25 degrees C. The results indicate the formation of 1:1 charge-transfer complexes. The observed time dependence of the charge-transfer band and subsequent formation of I(3)(-) in solution were related to the slow transformation of the initially formed 1:1 antipyrine:I(2) outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The values of the equilibrium constant, K, are calculated for each complex and the influence of the solvent properties on the formation of EDA complexes and the rates of subsequent reaction is evaluated.