Rapid and Efficient Uncatalyzed Knoevenagel Condensations from Binary Mixture of Ethanol and Water

Abstract

This paper presents a new green protocol for Knoevenagel condensations of aldehydes and compounds with an active methylene group in a binary mixture of ethanol/water (3:7, v/v). This medium favored the uncatalyzed Knoevenagel reactions and easy workup products can be obtained by precipitation in this medium and showed good isolated yields (55-100%) in short reaction times (1-60 min).

Ultrasonication‐assisted Synthesis of α, β‐Unsaturated Compounds Catalyzed by Amino‐functionalized FDU‐12 Catalyst

“…In order to highlight the solvent effect, the model reaction was also carried out without catalyst in the mixed solvent of water and ethanol. Its yield was as high as 78% after 43.0 minutes (Table , entry 9), which was enormously enhanced compared with the reaction under solvent‐free condition (Table , entry 1) . As we know that the aromatic aldehydes and the active methylene compounds are all hydrophobic, which results in the poor interrelationship between the substrates and catalyst in the presence of water.…”

Is a Catalyst Always Needed? The Case of the Knoevenagel Reaction with Malononitrile

“…[11] In 2018 another paper reported that non-catalysed reaction takes place in ethanol:water 3 : 7 at 75 °C; as examples, 2-benzylidenemalononitrile was obtained in 82 % after 4 minutes whereas 2-(4nitrobenzylidene) malononitrile in 93 % yield in 1 minute (Table 1, entries 3-4). [12] As already reported, the reaction can proceed by drying the reaction mixture or leaving it in the flask or by mixing the reactants in PEG-600 with vigorous grinding using a mortar and pestle at room temperature, until TLC showed complete disappearance of the starting materials. [15] We checked the synthesis of 2-benzylidenemalononitrile and 2-(4nitrobenzylidene) malononitrile in very mild conditions without catalyst obtaining excellent yields (Table 1, entries 5-10), con-firming what Patai reported in 1960 and observed in other papers.…”

“…The less reactive 4-methoxy derivative was obtained in 99 % yield in 1 h (entry 12) [24] whereas after the same time the non-catalysed reaction gave the product in 85 % yield in EtOH/H 2 O at 75 °C. [12] The use of other solvents can be also questionable. In many cases, reactions are carried out in solvents that display major issues based on GSK Solvent Sustainable Guide.…”

Hypervalent Iodine(III)-Catalyzed Epoxidation of β-Cyanostyrenes

“…Finally, the crude residue was purified by column chromatography using hexane as eluent and characterized as -cyanostyrene 1. [19][20][21] White solid; yield: 1.34 g (8.69 mmol, 87%); mp 81-83 C (Lit. 14 19,20,23 White solid; yield: 1.57 g (8.12 mmol, 81%); mp 161-163 C (Lit.…”

“…Naphthalenylmethylene)propanedinitrile (1k)21,26 Yellow solid; yield: 1.69 g (8.31 mmol, 83%); mp 140-142 C (Lit 26. mp 142-144 C); R f = 0.4 (EtOAc-hexane 1:49).…”