An Efficient and Chemoselective Procedure for Acylal Synthesis
A novel heterogeneous efficient procedure has been developed for the chemoselective synthesis of acylals (1,1-diacetates) under solvent-free conditions. A novel catalyst prepared by the sulfuric acid catalyzed copolymerization of p-toluenesulfonic acid and paraformaldehyde displays extremely high activities for the title reactions, affording average yields over 90% within several minutes. A comparative study showed that the novel catalyst has much higher activity than other catalysts used for this purpose. Besides, the novel catalyst displays chemoselectivity for the protection of aldehydes in the presence of ketones. In addition the high acidity (4.0 mmol/g), thermal stability (200 ºC) and easy reusability make the novel catalyst one of the best choices for the process.
Preparation of Zirconium Phosphate Nanoparticles and Its Application in the Protection of Aldehydes
A novel method for the preparation of α-zirconium phosphate (ZrP) nanoparticles as an eco-friendly and recyclable heterogeneous catalyst was studied. Polyethylene glycol (PEG) was used as the organic matrix which produced a better dispersion of ZrP nanoparticles. The catalyst was characterized by several physico-chemical techniques such as ICP-OES, XRD, TPD-NH3, pyridine-FTIR, BET, FTIR, TGA, SEM and TEM. The acidic property of ZrP was studied in the protection of aldehydes with acetic anhydride (AA) in the at room temperature. The deprotection of 1,1-diacetates has also been achieved using this catalyst in water. The procedure is operationally simple, environmentally benign and only a stoichiometric amount of AA is used. The catalyst was recovered easily from the reaction mixture, regenerated, and reused at least eight times without significant loss in catalytic activity.
A New Method for Selective Protection of Two Hydroxyl Groups in Carbohydorates, Glycals in Particular
The regioselective conversion of selected carbohydrate derivatives into their allylic cyclic acetals was achieved by successive treatment with dibutyltin oxide, acrolein diacetate and catalytic amount of tetrakis(triphenylphosphine)palladium(0). Methods for the removal of the new protecting group are discussed