Comparison of the efficiency of two imidazole-based dicationic ionic liquids as the catalysts in the synthesis of pyran derivatives and Knoevenagel condensations

Organocatalytic Synthesis of (Hetero)arylidene Malononitriles Using a More Sustainable, Greener, and Scalable Strategy

AIM AND OBJECTIVE

The establishment of a green and sustainable Knoevenagel condensation reaction in organic chemistry is still crucial. This work aimed to provide a newly developed metal-free and halogen-free catalytic methodology for the synthesis of CS and (hetero-) arylidene malononitriles in the laboratory and industrial scale. The Knoevenagel condensation reaction of various carbonyl groups with malononitrile was investigated in ethanol, an ecofriendly medium, in the presence of seven nitrogen-based organocatalysts.

MATERIALS AND METHODS

A comparative study was conducted using two as-obtained and four commercially available nitrogen-based organocatalysts in Knoevenagel condensation reactions. The synthesis of CS gas (2-chlorobenzylidene malononitrile) using a closed catalytic system was optimized based on their efficiency and greener approach.

RESULTS

The conversion of 100% and excellent yields were obtained in a short time. The products could be crystallized directly from the reaction mixture. After separating pure products, the residue solution was employed directly in the next run without any concentration, activation, purification, or separation. Furthermore, the synthesis of 2-chlorobenzylidenemahmonitrile (CS) was carried out on a large scale using imidazole as a selected nitrogen-based catalyst, afforded crystalline products with 95 ± 2% yield in five consecutive runs.

CONCLUSION

Energy efficiency, cost saving, greener conditions, using only 5 mol% of organocatalyst, high recyclability of catalyst, prevention of waste, recycling extractant by a rotary evaporator for non-crystallized products, demonstrated the potential commercial production of CS using imidazole in ethanol as an efficient and highly recyclable catalytic system.

A water-soluble conjugated polyelectrolyte for selective and sensitive detection of carcinogenic chromium(VI)

Environmental water pollution caused by hexavalent chromium (Cr(VI)) is a threat to living beings due to its carcinogenic nature. Herein, we report the synthesis of a highly fluorescent water-soluble conjugated polyelectrolyte PPMI and its application as a fluorescence sensor to monitor traces of carcinogenic Cr(VI) ions in water. PPMI was synthesized via the oxidative polymerization method followed by post-polymer functionalization. Fluorescent PPMI exhibited a photoluminescence quantum yield of 23.87 and displayed a rapid, very selective, and sensitive turn-off fluorescence signal in response to Cr(VI), with a significantly high quenching constant of 1.32 × 106 M-1. The mechanism of sensing was found to be static quenching. The limit of detection of this highly accessible analytical method was found to be in nanomolar ranges, i.e. 0.85 nM. Additionally, sensing on solid platforms such as economical paper strips was successfully achieved, which is very challenging and highly recommended for any reliable, portable, and economical analytical method.

Importance of Hybrid Catalysts toward the Synthesis of 5H-Pyrano[2,3-d]pyrimidine-2-ones/2,4-diones (Thiones)

The pyranopyrimidine core is a key precursor for medicinal and pharmaceutical industries due to its broader synthetic applications as well as its bioavailability. Among its four possible isomers, we found that 5H-pyrano[2,3-d]pyrimidine scaffolds have a wide range of applicability, and in recent years, they have been intensively investigated, but the development of the main core is found to be more challenging due to its structural existence. In this review article, we cover all of the synthetic pathways that are employed for the development of substituted 4-aryl-octahydropyrano/hexahydrofuro[2,3-d]pyrimidin-2-one (thiones) and 5-aryl-substituted pyrano[2,3-d]pyrimidindione (2-thiones) derivatives through a one-pot multicomponent reaction using diversified hybrid catalysts such as organocatalysts, metal catalysts, ionic liquid catalysts, nanocatalysts, green solvents, catalyst-/solvent-free conditions, and miscellaneous catalysts as well as the mechanism and recyclability of the catalysts. This review mainly focuses on the application of hybrid catalysts (from 1992 to 2022) for the synthesis of 5H-pyrano[2,3-d]pyrimidine scaffolds. This review will definitely attract the world's leading researchers to utilize broader catalytic applications for the development of lead molecules.

Physico-Chemical Properties of Magnetic Dicationic Ionic Liquids with Tetrahaloferrate Anions

A series of imidazolium-based symmetrical and asymmetrical dicationic ionic liquids (DcILs) with alkyl spacers of different length and with [FeCl3 Br]- as counter ion have been synthesized. The synthesized DcILs are characterized by using FTIR and Raman spectroscopy as well as mass spectrometry, along with single-crystal XRD analysis. Physicochemical properties such as solubility, thermal stability and magnetic susceptibility are also measured. These compounds show low melting points, good solubility in water and organic solvents, thermal stability, and paramagnetism. The products of molar susceptibility and temperature (χmol ⋅T) for the synthesized DcILs have been found between 4.05 to 4.79 emu mol-1  K Oe-1 and effective magnetic moment values have also been determined to be compared to that expected from the spin-only approximation.

Recent Advances in Imidazolium-Based Dicationic Ionic Liquids as Organocatalysts: A Mini-Review

Imidazolium-based dicationic ionic liquids (DILs) are gaining considerable space in the field of organocatalysis mainly due to the opportunities in offering new possible applicable structural variations. In addition to the well-known variables which made the ionic liquids (ILs) famous as the type of cation and anion used, the nature of the molecular spacer moiety turns out a further possibility to improve some physicochemical properties, for example, solubility, acidity, electrochemical behavior, and so on. For this reason, this class of ionic liquids has been considered as possible competitors to their corresponding monocationic salts in replacing common catalysts in organic synthesis, particularly in cases in which their bidentate nature could positively affect the catalytic activity. This mini-review is intended to highlight the progress carried out in the last six years in the field of organocatalysis, including DILs as such and as hybrids with polymers, nanomaterials, and composites.

Introduction of Succinimide as A Green and Sustainable Organo-Catalyst for the Synthesis of Arylidene Malononitrile and Tetrahydrobenzo[b] pyran Derivatives

AIM AND OBJECTIVE

In this work, we tried to introduce a non-toxic and stable organic compound named succinimide as a green and efficient organo-catalyst for the promotion of the synthesis of arylidene malononitrile and tetrahydrobenzo[b]pyran derivatives. Using this method led to a clean procedure to achieve these types of bioactive compounds without a specific purification step. The rate and yield of the reactions were excellent, and also succinimide showed acceptable reusability as the catalyst.

MATERIALS AND METHODS

In a 25 mL round-bottom flask, [A: a mixture of aromatic aldehyde (1 mmol), malononitrile (1.1 mmol) and B: a mixture of aromatic aldehyde (1.0 mmol), malononitrile (1.1 mmol)] and succinimide (0.2 mmol) in H2O/ EtOH [5 mL (1:1)] was stirred at 80 °C for an appropriate time. After completion of the reaction, which was monitored by TLC [n-hexane-EtOAc (7:3)], the mixture was cooled to room temperature, and the solid product was filtered, washed several times with cold distilled water to obtain the corresponding pure product.

RESULTS

After the optimization of the conditions and amount of the catalyst, a series of aromatic aldehydes containing either-electron-donating or electron-withdrawing substituents were successfully used for both of the reactions. The reactions rates and yields under the selected conditions were excellent. The nature and electronic properties of the substituents had no obvious effect on the rate and yield of the reaction. Meanwhile, the catalyst showed acceptable reusability for these two reactions.

CONCLUSION

In this work, we have introduced Succinimide as a green and safe organo-catalyst for the efficient synthesis arylidene malononitrile and tetrahydrobenzo[b]pyran derivatives. The results showed that the catalyst had excellent efficiency in green aqueous media and also the reusability of the catalyst was good.