Iranian Journal of Catalysis
Volume:4 Issue: 3, Summer 2014

A simple highly versatile and efficient sonochemical synthesis of 1,2,4,5-tetrasubstituted and 2,4,5-trisubstituted imidazoles is achieved by condensation of 1,2-dicarbonyl compound, aldehyde, ammonium acetate and primary amine using antimony trichloride immobilized on silica gel (SiO2-OSbCl2) as a catalyst in ethanol at moderate temperature. Operational simplicity, practicability and applicability to various substrates make this method an interesting alternative to previously applied procedures. From the environmental standpoint, this eco-friendly green catalyst is stable, highly active, easy to prepare and handle.

Reaction between aromatic aldehydes and 3–methyl-1-phenyl-2-pyrazoline-5-one catalyzed by nano-SiO2/HClO4 in water under reflux provided a simple and efficient route for the synthesis of 4-((5-hydroxy-3-methyl-1-phenyl-1H-pyrazol-4-yl)(aryl)methyl)-3-methyl-1-phenyl-1H-pyrazol-5-ol derivatives in high yields.

The thermodynamic of the known and very effective catalytic system, hydrogen peroxide (H2O2) and methyltrioxorhenium (MTO) is studied in different solvents using UV-Visible spectroscopic method. The thermodynamic parameters (ΔG, ΔH and ΔS) for two equilibrium reactions, MTO + H2O2 ⇌ A + H2O and A + H2O2 ⇌ B.H2O (A, [MeRe(O)2(O2)]; B.H2O, [MeRe(OH2)(O)(O2)2]), are determined. The obtained free energies of the reactions depend on dielectric constants of solvent, which are explained by Onsager’s reaction field theory.

Effects of water on the catalytic performances of MoVTeNbO catalyst in the oxidation of propane to acrylic acid have been investigated at different reaction temperatures and different steam contents. Obtained results show that both catalytic performances and catalyst structure are very sensitive to the presence of water vapor in the reaction feed. Presence of water induces some structural modifications: improvement the crystallinity, decreasing production of non-selective sites and enhanced presence of the orthorhombic (M1) phase leading to better acrylic acid selectivity. Moreover, the number as well as strength of the acid sites detected after reaction in water-present condition is lower than those of the used one in dry condition.

An efficient and simple procedure for the synthesis of 1,8-dioxo-octahydroxanthenes from the aromatic aldehydes and 5,5-dimethylcyclohexane-1,3-dione (dimedone) in the presence of boric acid [BO3H3 or B(OH)3] as an inexpensive and reusable catalyst is described. The salient features of this methodology are: the elimination of corrosive liquid acids, high yields, simple methodology, short reaction times, easy work-up and green heterogeneous catalyst.

Silica-bonded n-propyldiethylenetriamine sulfamic acid (SBPDSA) was found as an efficient solid acid for the synthesis of coumarins. Coumarin derivatives were obtained via the Pechmann condensation reaction of phenols and β-keto-esters at 80 oC under solvent-free conditions. Also, biscoumarins were obtained via the condensation of aldehydes and 4-hydroxycoumarin in water at reflux conditions. The heterogeneous solid acid showed much the same efficiency when used in consecutive reaction runs.

The Brønsted acidic ionic liquid ([BMIm]HSO4) catalyzed three-component synthesis of 2H-indazolo[2,1-b]phthalazine-trione derivatives at room temperature. The integrity of the ionic liquid remains reasonably unchanged when it is separated from the reaction mixture by water extraction, as it can be recycled several times without any loss of activity in each of the title syntheses. The products and ionic liquid could be conveniently separated from the reaction mixture, indicating that the whole process was performed as a green chemical transformation. The salient features of this one pot protocol are short reaction times, cleaner reaction profiles and simple workup.

Suzuki cross-coupling reaction of different aryl halides with arylboronic acids was successfully carried out in methanol using ortho-palladated complex of 2-methoxyphenethylamine. All substrates afforded the corresponding products in good to high yields in the presence of low amounts of this complex as efficient and active catalyst. Application of microwave irradiation improved the yields of the reactions and reduced the reaction times some extent in comparison with traditional heating conditions.

A simple and mild procedure for the conversion of anilines into aryl isocyanates is described using the 3-hydroxypropylammonium acetate (HPAA) ionic liquid as a novel and efficient media has been explored in the synthesis of aryl isocyanates from the reaction of substituted urea with sodium nitrite in a water immiscible solvent. This ionic liquid can be easily recovered and reused for many times without noticeable loss of activity.

2,4-dinitrophenylhydrazanomethylphenol (DNPHMP) was immobilized onto silicate rice husk ash to form a heterogeneous catalyst denoted as RHDNPH. The elemental and EDX analysis of RHDNPH showed the nitrogen is incorporated into silica. The RHDNPH had 154.6 m2g-1 as a specific surface area. The FT-IR clearly showed the appearance of –NH and C=N absorption band at the expected range. The TGA curve shows that the RHDNPH was stable at the temperature of less than 200 °C. Hydrolysis experiments of cellulose were conducted in liquid face reaction at 140 °C, and 150 mg of catalyst mass in 11 h. The maximum hydrolysis of cellulose was 84 % with 100 % selectivity of glucose over the catalyst. The catalyst was simple in its preparation, stable during the cellulose hydrolysis in addition to repeatedly without a significant loss of its catalytic activity.

In this paper, we used quantum chemical approach to shed light on the catalytic mechanism of γ-carbonic anhydrase (γ-CA) to convert carbon dioxide to bicarbonate ion. Density functional theory (DFT) using B3LYP and UB3LYP functional and three split-valance including 6-31G*, 6-311G** and 6-311++G** basis sets were used to calculate the details of electronic structure and electronic energy of active and inactive forms of γ-CA enzyme active center, and complex between γ-CA and carbon dioxide. The catalytic mechanism involved the nucleophilic attack of cobalt bound hydroxide ion to CO2. In the following, the five coordinate cobalt complex as a transition state is formed and then the produced bicarbonate is displaced by a water molecule and give cobalt bound hydroxide for the next turn of catalysis. The activation energy barrier for this mechanism is about 7.9 kcal/mol.

A variety of alcohols readily add to 3,4-dihydro-2H-pyran under solvent free conditions in the presence of catalytic amount of acidic ionic liquid [Et3N(CH2)4SO3H][OTs] to afford the corresponding tetrahydropyranyl ethers in good to excellent yields at room temperature. The use of this procedure allows easy separation of the desired products from ionic liquid and recycling the ionic liquid. Some of the major advantages of this procedure are nonaqueous work-up, very good yields, catalytic amount of catalyst and reusability of ionic liquid.