Silica sulfuric acid as an efficient and reusable reagent for crossed-aldol condensation of ketones with aromatic aldehydes under solvent-free conditions

Abstract

pode ser reutilizado diversas vezes sem perda do rendimento da reação.Aromatic aldehydes undergo crossed-aldol condensation with ketones in the presence of silica sulfuric acid under solvent-free conditions to afford the corresponding α, β-unsaturated aldol products in excellent yields. The reagent is reusable for several times without any decrease in the yield of the reactions.

Solvent Free Synthesis of α, á-Bis(substituted-benzylidene)cycloalkanones Using Covalently Anchored Sulfonic Acid on Silica Gel (SiO<sub>2</sub>-R-SO<sub>3</sub>H) as an Efficient and Reusable Heterogeneous Catalyst

“…Silica sulfonic acid, nanoporous silica-based sulfonic acid and polymer supported sulfonic acid type catalysts are also employed for such condensations. Reaction times are reported to be in 3 -12 hour range [24][25][26]. In the present work, we have used covalently anchored sulfonic acid on silica gel (Catalyst 1, Scheme 1), which its applications have been reported in a few number of organic transformations [6,8,27,28] under solvent-free conditions to prepare α, ά-bis(substitutedbenzylidene) cycloalkanones (Scheme 2) in excellent yields, short reaction times and clean work up procedures.…”

Preheated Fly-Ash Catalyzed Aldol Condensation: Efficient Synthesis of Chalcones and Antimicrobial Activities of Some 3-Thienyl Chalcones

“…Scientists and specially chemists have used microwave irradiation technique for solid phase green synthesis 8,9 . Numerous green catalysts such as fly-ash: sulphuric acid 1 , silica-sulphuric acid 10,11 anhydrous zinc chloride 12 , ground chemistry catalysts-grinding the reactants with sodium hydroxide 13 , aqueous alkali in lower temperature 14 , solid sulphonic acid from bamboo 15 , barium hydroxide 16 anhydrous sodium bicarbonate 17 , microwave assisted synthesis 18 , Fly-ash:water 2,19 , triphenylphosphite 20 , alkali earth metals 21 , KF/Al 2 O 3 22 and sulfated titania 23 and silicotungstic acid 24 have been reported for the synthesis of many number of organic compounds. Chalcones possess various multipronged activities such as antimicrobial 25 , antidepressants 26 , antiplasmodial 27 , anti-aids 28 and insect antifeedant activities 3,29 .…”

KF-Melamine Formaldehyde Resin (KF-MFR) as a Versatile and Efficient Heterogeneous Reagent for Aldol Condensation of Aldehydes and Ketones under Microwave Irradiation

“…Chalcones can be traditionally prepared by classical ClaisenSchmidt condensation in the presence of many organic and inorganic bases, 4 using conventional heating, microwave and/or ultrasonic irradiation techniques. 5 Aldol condensation can be catalyzed by various heterogeneous Lewis acids as supports including Mg(HSO 4 ) 2 , 6 silica sulfuric acid, 7 CsOH-SiO 2 , 8 Mg/Al mixed oxides, 9 FeCl 3 •6H 2 O, 10 KF-Al 2 O 3 11 and polymer supported sulphonic acid. 12 Although many of these reagents and supports are seems to be useful for aldol condensations, however, many of these entries are suffered from many disadvantageous such as non-reusability, low thermal and chemical resistance, toxicity, harsh reaction condition, tedious work-up procedure, prolonged reaction times, poor yields and low selectivity.…”