Journal of Sol-Gel Science and Technology 19, 17–22, 2000 c  2000 Kluwer Academic Publishers. Manufactured in The Netherlands. Doped Sol-Gel Materials as Heterogeneous Reagents for Organic Synthesis * LILI SARUSSI, JOCHANAN BLUM ‡ AND DAVID AVNIR †‡ Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel david@chem.ch.huji.ac.il Abstract. We advance the use of reactive doped sol-gel materials as heterogeneous reagents for organic-chemistry synthesis. Three approaches were demonstrated with SiO 2 -based materials: Direct physical entrapment of the organic reagent; in-situ generation of an inorganic reagent within the matrix; and covalent attachment of the reagent to the matrix. With the first, entrapped p-toluenesulfonic acid facilitated the 100% yield esterification of benzoic acid with 1-pentanol, and the 100% dehydration of 1-tetralol to 1,2-dihydronaphthalene; with the second approach, a sol-gel oxidant, SiO 2 /MnO 2 was used to convert benzyl alcohol to benzaldehyde and 1-tetralol to 1-tetralone; and with the third, anchored propylamine facilitated dehydrobromination reactions resulting in double-bond formation. Several other reactions with these reagents are described, and their reactivities analyzed. Keywords: Reactive materials, heterogenized reagents, oxidation, dehydration, esterification, doped sol-gel Background: Reactive doped sol-gel materials [1] have been used mainly as sensors [2], catalysts [3], electroactive [4], photoactive [5] and bioactive mate- rials [6]. Another main domain of chemical reactivity which received much less attention in this context, is the use of doped sol-gel materials as reagents for or- ganic chemistry synthesis. In this feasibility-report we extend the use of sol-gel materials for this purpose. Heterogenizing reagents for easy recovery and recy- cling is of major interest both for lab-scale syntheses and for industrial processes. Furthermore, as we have already shown [7] the sol-gel entrapment enables one to perform reactions in solvents in which the free dopant molecule is insoluble. 1. Direct Entrapment: p-Toluenesulphonic Acid for Esterification and Dehydration p-Toluenesulfonic acid (4-CH 3 C 6 H 4 SO 3 H, PTSA) is widely used in organic synthesis for various reactions ∗ Dedicated to Prof. Dr. Herbert Schumann on the occasion of his 65th birthday. † To whom all correspondence should be addressed. ‡ http://chem.ch.huji.ac.il/∼david/index.html which are facilitated by protonation. Esterifications and dehydrations of alcohols are two prominent examples for the use of this catalytic reagent. Heterogenizations of PTSA are known, and an example is its adsorption on silica surfaces [8]. Compared with adsorption, we recall that entrapment within sol-gol matrices carries the advantage for the dopant of not being prone to be washed away from the surface and of improved general protectability. Indeed, heterogenization of this reagent by anchoring it to organic polymers, suffers from cleav- age of the sulphonate residue in the course of esterifi- cation reactions [9]. PTSA was successfully entrapped in pure SiO 2 by either the “one-step”or “two-step” procedures, and in hydrophobic methylated silica, as follows. Entrapment Procedures The “one step” procedure: To a solution of 0.3 gr (1.6 · 10 −3 ) moles PTSA in 4.6 ml water, was added 7.0 ml ethanol and 7.0 ml tetraethoxysilane (TEOS). The solution was stirred at room temperature until gelation occurred (between 1 and 2 days). The wet gel was then dried at 59 ◦ C until constant weight was