S. Sheik Mansoor

Reusable silica-bonded S-sulfonic acid catalyst for three-component synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromenes and 2-amino-4H-pyrans in aqueous ethanol

Silica-bonded S-sulfonic acid (SBSSA)-catalyzed, facile, one-pot, three-component coupling of 5,5-dimethyl-1,3-cyclohexanedione (dimedone) or 5,5-dimethyl-1,3-cyclohexanedione, aromatic aldehydes, and malononitrile at reflux temperature is described for preparation of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene derivatives. 2-Amino-3-cyano-6-methyl-4-phenyl-4H-pyran-5-ethylcarboxylate derivatives can also be prepared in good yield under the same experimental conditions by use of ethyl acetoacetate, aldehydes, and malononitrile. The catalyst, silica-bonded S-sulfonic acid, was reused and recycled without any loss of activity or product yield.

Synthesis and in vitro microbiological evaluation of novel series of 8-hydroxy-2-(2-oxo-2 H -chromen-3-yl)-5-phenyl-3 H -chromeno [2,3- d ]pyrimidin-4(5 H )-one derivatives catalyzed by reusable silica-bonded N -propylpiperazine sulfamic acid

Abstract Silica-bonded propylpiperazine-N-sulfamic acid is employed as a recyclable catalyst for the synthesis of a series of 8-hydroxy-2-(2-oxo-2H-chromen-3-yl)-5-phenyl-3H-chromeno[2,3-d]pyrimidin-4(5H)-one derivatives by the condensation of 2-amino-3-cyano-7-hydroxy-4-phenyl-4Hchromene derivatives with coumarin-3-carboxylic acid. The heterogeneous catalyst was used for four runs. This method has the advantages of high yields, a cleaner reaction, simple methodology, short reaction times, and easy work-up. All the compounds were evaluated for their in vitro antimicrobial activity against different bacterial and fungal strains.

Studies on the Kinetics of Tetraethylammonium Bromochromate Oxidation of Some Meta- and Para-Substituted Benzyl Alcohols in Non-Aqueous Media

Abstract Tetraethylammonium bromochromate (TEABC) oxidation of 18 meta- and para-substituted benzyl alcohols (BnOH) in dimethylsulphoxide (DMSO) leads to the formation of corresponding aldehydes. The reaction is first order each in TEABC and the alcohols. The reaction is catalyzed by hydrogen ions. The hydrogen ion dependence has the form: kobs=a+b[H+]. The oxidation of αα´-dideuterio benzyl alcohol exhibited a substantial primary kinetic isotope effect (kH/kD=5.71 at 303 K). Oxidation of benzyl alcohol was studied in 17 different organic solvents. The solvent effect has been analyzed using Kamlets and Swains multi parametric equation. A correlation of data with Kamlet–Taft solvatochromic parameters (α, β, π*) suggests that the specific solute-solvent interactions play a major role in governing the reactivity. A mechanism involving a hydride ion transfer via chromate ester is proposed.

Aqua-mediated synthesis of acridinediones with reusable silica-supported sulfuric acid as an efficient catalyst

Abstract A simple approach to the synthesis of acridinediones via one-pot three-component condensation of an aromatic aldehyde, 5,5-dimethyl-1,3-cyclohexanedione (dimedone), and ammonium acetate or p-toluidine in water with use of silica-supported sulfuric acid as an efficient catalyst is described. Excellent yields, catalyst recovery and reusability, and easy work-up are attractive features of this green protocol. All the synthesized acridinediones were characterized on the basis of their melting-points, elemental analysis and spectral data.

Kinetics and Mechanism of Oxidation of Aromatic Aldehydes by Imidazolium Dichromate in Aqueous Acetic Acid Medium

The kinetics of oxidation of benzaldehyde (BA) and para-substituted benzaldehydes by imidazolium dichromate (IDC) has been studied in aqueous acetic acid medium in the presence of perchloric acid. The reaction is first order each in [IDC], [Substrate] and [H

Nano Fe 2 O 3 @SiO 2 –SO 3 H: efficient catalyst for the multi-component preparation of indeno[2′,1′:5,6]pyrido[2,3-d]pyrimidine-2,4,6(3H)-trione derivatives

Abstract A highly efficient multi-component reaction of structurally diverse aryl aldehydes, 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione and 1H-indene-1,3(2H)-dione using nano Fe2O3@SiO2–SO3H as a catalyst is described. The products are a variety of indeno[2′,1′:5,6]pyrido[2,3-d]pyrimidine-2,4,6(3H)-trione derivatives. The effect of the solvent on the product selectivity was investigated. The morphology, particle size distribution, and some properties of Fe2O3@SiO2–SO3H nanopowders have been characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray powder diffraction (XRD), N2 adsorption–desorption isotherms and thermogravimetric analysis (TGA) techniques.

Oxidation of Methionine by Tripropylammonium Fluorochromate-A Kinetic and Mechanistic Study

The kinetics of oxidation of methionine (Met) by tripropylammonium fluorochromate (TriPAFC) has been studied in the presence of chloroacetic acid in aqueous acetic acid medium. The reaction is first order with respect to methionine, TriPAFC and acid. The reaction rate has been determined at different temperatures and activation parameters calculated. With an increase in the amount of acetic acid in its aqueous mixture, the rate increases. The reaction does not induce polymerization of acrylonitrile. A suitable mechanism has been proposed.

Kinetics and the mechanism of oxidation of methoxy benzaldehydes by benzimidazolium fluorochromate in an aqueous acetic acid medium

Abstract The oxidation of benzaldehyde (BA) as well as 4-methoxy (4-MBA), 3-methoxy (3-MBA), 2-methoxy (2-MBA), 2,6-dimethoxy (2,6-DMBA), 2,4-dimethoxy (2,4-DMBA), 3,4-dimethoxy (3,4-DMBA), 2,4,6-trimethoxy (2,4,6-TMBA), 3,4,5-trimethoxy (3,4,5-TMBA) and 2,3,4-trimethoxy (2,3,4-TMBA) benzaldehydes by benzimidazolium fluorochromate (BIFC) have been studied in a 50% acetic acid–50% water medium. The oxidation leads to the formation of the corresponding carboxylic acids. The reaction is first order with respect to [BIFC], [S] and [H+]. The reaction was catalysed by H+ ions. The reaction was studied at four different temperatures, and the thermodynamic parameters were calculated. The Exner plot indicated that all of the methoxy-substituted benzaldehydes were oxidized via the same mechanism. Based on the observed kinetics, a suitable mechanism has been proposed.

Kinetics and Thermodynamics of Oxidation of Benzhydrol by Tetrabutyl Ammonium Bromochromatein the Presence of Oxalic Acid

The kinetics of oxidation of benzhydrol (BH) by tetrabutylammonium bromochromate (TBABC) was described. Product analysis confirmed the formation of benzophenone. The reaction has been studied in the presence of oxalic acid (OA). The reaction was run under pseudo-first-order conditions. The rate of reaction is first order with respect to TBABC, BH and [H+] in the presence of oxalic acid (OA). Rates of oxidation of BH were determined at different temperatures between 298 and 313 K and the activation parameters were calculated. Further, a suitable mechanism has been proposed based upon the experimental results.