Open Access Original Research Article

A Facile Tandem Protocol for the Crossed Aldol Condensation in SiO2.OSO3H Ionic Liquid under Solventless Condition

A. Rajendran, C. Karthikeyan

Chemical Science International Journal, Page 50-57
DOI: 10.9734/ACSJ/2011/263

Objectives: Removing organic solvents in chemical synthesis is important in the drive towards benign chemical technologies. Organic solvents are high on the list of toxic compounds due to the problems in containing volatile compounds and the sheer large volume of them used in industry. Some advantages of utilizing solventless reactions are that the compounds are often sufficiently pure to avoid extensive purification using chromatography, the reactions can be rapid, and often reaching substantial completion in several minutes compared to hours in organic solvents, and the energy usage can be much lower. Among organic reactions, aldol condensations are important and excellent tools in organic synthesis, providing a good way to form carbon–carbon bonds. The main objectives of this paper are to carryout crossed - aldol condensation reactions with dicyclohexylketones with different aromatics aldehydes in the presence of silica sulphuric acid [SiO2.OSO3H] as an ionic liquid catalyst under solvent free condition to afford the corresponding α, β - unsaturated crossed - aldol products in excellent yields and to recover and reuse the catalyst for subsequent use.
Study design: Green chemical reaction using silica-sulphuric acid as a catalyst under solventless condition.
Place and Duration of Study: Department of Chemistry, Sir Theagaraya College, Chennai-21, Tamilnadu, India, between June 2009 and July 2010.
Methodology: The ionic liquid SiO2.OSO3H was prepared according to the reported procedure in an eco-friendly way by the reaction of silica gel and chlorosulphonic acid .It is interesting to note that the reaction is easy, clean and not requiring any work-up procedure. Using this ionic liquid, crossed-aldol condensation of dicyclohexyl ketones with aromatic aldehydes were carried out. After complete conversion of the ketones as indicated by the TLC, the mixture was cooled to room temperature. Dichloromethane (20 - 30 ml) was added and heated for a few minutes, the reagent was concentrated and the solid residue was recrystallized from ethanol to afford the pure product. The catalyst was recycled by washing the solid reagent remained on the filter by EtOAC (20 ml) followed by drying in an oven (50oC) for 2hr. Products were characterized by spectral analyses such as UV-Visible, FT-IR,1H NMR and 13C NMR.
Results: The reactions were completed with excellent yields (90 - 95%) within 2 - 5 hr. at the temperature range of 80-85oC. The reaction does not require any additional catalyst because the ionic liquid itself acts as a catalyst and solvent as well in these experiments, the products were isolated and the remaining catalyst was washed and reloaded with fresh substrates benzaldehyde and dicyclohexyl ketones. Under these conditions, no self-condition of the starting materials was observed. When similar reactions were carried out in sulphuric acid (conventional acid catalyst), a mixture of products was obtained in poor yields One of the greatest advantages of the reagent SiO2.OSO3H is that it is recoverable and reusable for several times without potential loss in its catalytic activity.
Conclusion: The conventional esterification reactions (without ionic liquids) suffer from many problems like poor efficiency, side reactions, consumption of huge environmentally hazardous chemicals, etc., The use of ionic liquids for these reactions eradicate the aforementioned problems encountered in the conventional procedures.

Open Access Original Research Article

MgO Enriched Coal Fly Ash as Highly Active Heterogeneous Base Catalyst for Claisen-Schmidt Condensation Reaction

Deepti Jain, Ashu Rani

Chemical Science International Journal, Page 37-49
DOI: 10.9734/ACSJ/2011/335

A novel fly ash supported solid base catalyst (MgO/fly ash) has been synthesized by using F-type fly ash and Mg(NO3)2 as precursor. The synthesized solid base possessed stable Si-O-Mg phase with sufficient hydroxyl group to catalyze liquid phase, solvent free and single step condensation of 4-methoxybenzaldehyde with 2-hydroxyacetophenone giving higher conversion (86%) of desired product (4-methoxy-2-hydroxychalcone) with 93% yield. The physio-chemical properties of MgO/fly ash catalyst were evaluated by N2 adsorption-desorption, BET surface analysis, XRD, FT-IR, SEM-EDX and AAS etc. This excellent conversion and yield shows that the catalyst has sufficient basic sites, responsible for the catalytic activity. Moreover, the catalyst was regenerated and reused up to four reaction cycles with approximately equal efficiency as in the first run, conferring that basic sites are not lixiviated in the reaction system. Furthermore, this catalyst may replace conventional environmentally hazardous homogeneous liquid bases making an ecofriendly; solvent free, atom efficient, solid base catalytic process. The application of fly ash to synthesize a solid base catalyst finds a noble way to utilize this abundant waste material.