Current organocatalysis 

About: Current organocatalysis is an academic journal published by Bentham Science. The journal publishes majorly in the area(s): Chemistry & Catalysis. It has an ISSN identifier of 2213-3372. Over the lifetime, 47 publications have been published receiving 8 citations.

Polymer Supported Proline-Based Organocatalysts in Asymmetric Aldol Reactions: A Review

Abstract: The use of proline-based organocatalysts has acquired significant importance in organic synthesis, especially in enantioselective synthesis. Proline and its derivatives are proven to be quite effective chiral organocatalysts for a variety of transformations including the aldol reaction, which is considered as one of the important C-C bond forming reactions in organic synthesis. The use of chiral organocatalysts has several advantages over its metal-mediated analogues. Subsequently, a large number of highly efficient proline-based organocatalysts including polymer-supported chiral analogues have been identified for aldol reaction. The use of polymer-supported organocatalysts exhibited remarkable stability under the reaction conditions and offered the best results particularly in terms of its recyclability and reusability. These potential benefits along with its economic and green chemistry advantages have led to the search for many polymer-supported proline catalysts. In this review, recent developments in exploring various polymer immobilized proline-based chiral organocatalysts for asymmetric aldol reactions are described.

Agro-Waste Sourced Catalyst as an Eco-Friendly and Sustainable Approach for Knoevenagel Condensation Reaction

Abstract: Background: The present work describes an eco-friendly and sustainable approach for the Knoevenagel condensation of an aromatic aldehyde with ethyl cyanoacetate, and salicylaldehyde with Meldrum acid for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin (2-oxo-2H-1-benzopyran) derivatives, respectively. The reaction was performed under green catalytic media-Water Extract of Watermelon Fruit Peel Ash (WEWFPA), which is an eco-friendly protocol derived from the agro-waste feedstock. Various protocols have been reported for the synthesis of Knoevenagel condensation reaction using a hazardous catalyst or/and solvents found toxic to the environment, requiring longer reaction time, giving poor yield, and requiring purification of the final product. The method at hand provides several added advantages like: being a completely green method, economic, inexpensive catalyst, and the final product isolated is in pure form with good yield. Objective: The objective of the study was to develop a green methodology for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives. Results: The agro-waste based catalyst developed in the present study avoids the use of external inorganic/ organic bases and additives. Knoevenagel condensation of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives is carried out under room temperature using microwave irradiation, which is a solvent-free synthesis, requiring less time and giving better yield. Methods: We have demonstrated that WEWFPA can be employed as a green homogenous agrowaste for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives under rt stirring and microwave irradiation in a very economical way. The developed method is found to be simple and robust, non-hazardous and solvent-free to obtain the target product. Conclusion: In conclusion, we have established an efficient, simple, agro-waste based catalytic approach for the synthesis of ethylbenzylidenecyanoacetate and 3-carboxy coumarin derivatives employing WEWFPA as an efficient catalyst under rt stirring and microwave synthesis. The method is a green, economical and eco-friendly approach for the synthesis of Knoevenagel condensation products. The advantages of the present approach are that the reaction is a solvent-free synthesis, requiring no external metal catalyst, chemical base free, short reaction time and excellent yield of product. The catalyst is agro-waste derived, which is abundant in nature, thus making the present approach a greener one.

Kinetics and mechanism of reduction of hexacholoroiridate (IV) by carcinogenic nicotine as alkaloid in aqueous solutions with determination of ionization constant of nicotine

Abstract: Nicotine (NIC) is a lipid soluble alkaloid found predominately in tobacco and tobacco products including cigarettes, cigars and oral tobacco products such as snuff and chewing tobacco. Since nicotine substrate is the major constituent of tobacco smoke, it may cause negatively impacted problems to the human healthcare which keeps many users hooked. A spectrophotometric technique has been applied for investigating the kinetics of reduction of hexachloroiridiate (IV) as inert one-equivalent oxidant by carcinogenic nicotine (NIC) in aqueous perchlorate solutions. First-order in [IrCl6]2- and fractional-first-order with respect to the nicotine concentration has been revealed. Kinetic evidence for formation of 1: 1 intermediate complex between the NIC and [IrCl6]2- prior to the rate-determining step was confirmed. The ionization constants of nicotine was evaluated from the kinetic data and has been found to be 8.57x10-4 and 4.57 x 10-4 moldm-3 at ionic strength of 0.5 moldm-3 and at 30˚C and 40˚C, respectively. The activation parameters have been deduced from the kinetic results of the temperature-dependence of rate constants and a plausible reaction mechanism of the redox reaction is suggested and discussed. Nicotinic acid (Vitamin B3) was formed as oxidation product of nicotine oxidation.

Effect of Solvents in 1-Butyl-1,2,4-Triazolium Trifluoroacetate Triggered Synthesis of 2,3-Dihydroquinazolin..

Abstract: Quinazolinones are a class of heterocyclic compounds that have a wide variety of applications. They are also used in agrochemicals. There are several methodologies reported for the synthesis of 2,3-dihydroquinazolines using various catalysts. Here, by using 1-butyl-1,2,4-triazolium as cation and trifluoroacetate as anion, 2,3-dihydroquinazolin-4(1H)-one has been synthesized. For the synthesis of 2,3-dihydroquinazolin-4(1H)-one condensation of anthranilamide with the corresponding aldehyde in the presence of organocatalyst and solvent is done. Using benzaldehyde as the parent aldehyde, to validate the outcome, the benzaldehydes were selected as follows a) benzaldehyde, b) 4-methoxybenzaldehyde – electron releasing group and c) 4-nitrobenzaldehyde – electronwithdrawing group. Solvent study has been done with solvents varied from polar to apolar. Both polar protic and polar aprotic solvents are used for the reactions. The polar protic solvents used were water, methanol, ethanol, isopropanol, butanol, hexane-1-ol, and glycerol. The polar aprotic solvents used are ethyl acetate, DMF,acetonitrile, and DMSO. The moderately apolar solvents used are DCM, carbon tetrachloride, 1,4 dioxane, and chloroform. The synthesized triazolium salts are found soluble in polar aprotic, polar protic solvents and few moderately apolar solvents such as DCM, chloroform, acetonitrile, water, methanol and ethanol whereas insoluble with apolar solvents like toluene, benzene, and hexane.The yield of 2-phenyl-2,3-dihydroquinazolin-4(1H)-one was low for 1-butyl-1,2,4-triazolium trifluoroacetate based organocatalyst. But for substituted benzaldehyde, the yield was comparatively high. Comparatively, the yield for 2-(4-methoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one, where the aromatic benzaldehyde had electron-donating group, is less than 2-(4-nitrophenyl)-2,3-dihydroquinazolin-4(1H)-one, where the aromatic benzaldehyde had an electron-withdrawing group. Substituted benzaldehyde gave better yields than benzaldehyde. And nitro group which is electrowithdrawing attached to benzaldehyde enhanced the electrophilic nature at carbonyl center showed higher yields than methoxy group which is electron donating attached to benzaldehyde as it deactivates the carbonyl carbon. The polar protic solvents like water, ethanol and methanol stabilizes the ionic intermediates and gave better yield. Even the moderately apolar solvents like DCM, chloroform resulted in good yields, green solvents like water, ethanol and methanol would be a better choice as solvents. The carbon chain on the solvent has got an effect on product yield. As the carbon chain increases in solvent, the yield decreases due to the separation difficulties. The polar aprotic solvents did gave better yields but not as good as polar protic solvents.

Magnetically Recyclable Ag@Fe2O3 Core-shell Nanostructured Catalyst for One-pot Synthesis of 2-Aryl Benzimidazole and Benzothiazole

Abstract: Nanocatalysts exhibit several applications in the synthesis of many industrially important organic compounds. They manifest extremely fascinating physical and chemical properties which can be exploited in their catalytic applications. A magnetically recyclable Ag@Fe2O3 core-shell structured nanocatalyst was synthesized by a simple sol-gel technique and characterized by x-ray diffraction spectroscopy, field emission scanning electron microscope, high-resolution transmission electron microscopy, fourier transform infrared spectroscopy, vibrating sample magnetometer etc. Nanocatalyst was found to be a highly efficient heterogeneous catalyst for the synthesis of 2-aryl benzimidazoles and benzothiazoles via one-pot condensation of aromatic aldehydes and 1, 2-phenylenediamine, and 2-aminothiophenol. Ag@Fe2O3 nanocatalyst provides rapid conversion of the substrate into the desired product at room temperature within just 5-18 min in the presence of C2H5OH with good to excellent yield. The combination of Ag core with magnetic Fe2O3 shell results in improved efficiency, stability, magnetic recovery, and reusability compare to the individual nanoparticles. The synthetic protocol is featured with high yield, mild conditions, and simple work-up. Magnetic recovery of the catalyst from reaction systems and its reusability for several runs without loss of catalytic activity are additional advantages.