Microporous Titanosilicates as Heterogeneous Catalysts for Basic Organic Synthesis

Abstract

The products of the reactions of ethylene oxide with fatty alcohols, acids and amines are of great industrial importance. They include surfactants, plasticizers and insecticides. The reactions can be generally represented as oligomerization. Interaction between ethylene oxide and alcohols can proceed in the presence of acidic as well as basic catalysts; the main distinction being in the quantitative distribution of reaction products. In the presence of basic catalysts the rate of reaction increases with the molecular weight of the products and polyaddition reaction products have a wide distribution of molecular weights. Most of the information available comes from the well investigated uses of homogeneous bases as catalysts. Research on the use of solid catalysts in this area is comparatively recent. Heterogeneous catalysts, such as the synthetic zeolites, are better known as acid catalysts. Heterogeneous catalysts with well-defined sites able to display basic properties over a wide pH range, whilst retaining insolubilty and thermal stability, are little known. This work described herein studies the basic properties of two microporous titanosilicates, known as ETS-4 and ETS-10. Determinations of surface basicity were also carried out by following the titration method. The titanosilicates were examined as catalysts for the ethoxylation of ethylene glycol. One-parameter experiments showed that the processes observed had a first-order dependence on the concentrations of ethylene oxide and catalyst. The excess of alcohol present was assumed to lead to a first-order dependence on alcohol concentration as confirmed by studies on basic. The interaction of the proton donor agent with ethylene oxide proceeds through a tri-molecular transition state. The activated C-O bond is opened by a nucleophilic attack; a similar mechanism to an SN2 nucleophilic replacement. Titanosilicates are very effective catalysts with basic sites for organic synthesis processes.