Nano TiO2/ SiO2 as an Efficient Catalyst for Acetalization of Carbonyl Compounds under Microwave and Solvent -Free Conditions

Protection-deprotection of functional groups is a common and very essential process in multistep organic synthesis. Between different methods for protection of carbonyl compounds, acetalization plays an important role in multi-step synthesis in organic, medicinal and drug design chemistry. This reaction is extensively used in the synthesis of enantiomerically pure compounds [1]. 1,3-Dioxolane is one of the most popular protecting groups for this purpose. Although synthesis of 1,3-dioxolane is generally performed by the use of ethylene glycol in the presence of homogeneous acid catalysts such as H2SO4, p-toluenesulfonic acid (PTSA) and pyridinium salts [2–6], these homogeneous catalysts present limitations due to the use of toxic and corrosive reagents, the tedious workup procedure, and the necessity of neutralization of the strong acid media and producing undesired wastes. To overcome these problems, various heterogeneous catalysts have been employed for the synthesis of 1,3-dioxolane from carbonyl compounds and ethylene glycol. However, some of these procedures suffer from drawback such as high catalyst/substrate mole ratio and a long reaction time. Nanoparticles, especially metal oxides nanoparticles finely dispersed onto supports, have received much attention as heterogeneous catalysis due to high catalytic activity and surface area along with simplicity of the operation. In this paper we wish to report a novel and mild method for acetalization of carbonyl compound using nano particles of TiO2 supported on silica, either by microwave promotion or at room temperature under solvent free conditions. Low sensitivity towards traces of moisture and high tolerance of different functional groups make Nano TiO2/ SiO2 suitable for carrying out many organic reactions