The etherolysis/condensation of TiCl 4 by diisopropyl ether ( i Pr 2 O) as well as the direct condensation between TiCl 4 and Ti(O i Pr) 4 are efficient nonhydrolytic sol-gel routes to titania. A comparison of the solution chemistry of the two routes was performed by means of NMR spectroscopy. In both cases the condensation is slow at room temperature; the true precursors are titanium chloroisopropoxides in equilibrium through fast ligand-exchange reactions. The condensation takes place at 100°C after an induction period which drastically depends upon the O i Pr/Ti ratio in the reaction mixture. This behavior is related to the composition of the starting chloroisopropoxides mixture. The key species in the induction process appears to be Ti(O i Pr)Cl 3 , which catalyzes the first condensation reactions.

Titania samples prepared by different non-hydrolytic sol-gel methods, mainly based on the etherolysis and alcoholysis of titanium tetrachloride, have been found to differ in both structure and texture. Thus, the reaction of diethyl ether with TiCl, at 110 'C affords anatase, which begins to convert into rutile only around 1000 "C. The reaction of TiC1, with ethanol leads to rutile as early as 110 "C, whereas the reaction of tert-butyl alcohol at 110 "C leads to the singular formation of brookite.The development of low-temperature routes to transitionmetal oxide processable materials underlies the recent works in the field of sol-gel synthesis.' In these methods based on the hydrolysis of molecular precursors, such as metal alkoxides, the major problem is control of the reaction rates which are generally too fast. An attractive solution is to use organic additives which act as chelating ligands (carboxylic acids, pdiketones, etc.) and modify the reactivity of the precursors.2 Here we propose various non-hydrolytic sol-gel routes tested in the case of titanium, chosen as a representative transition metal.As reported previously, a novel sol-gel route is provided by the thermal condensation of metal halides with metal alkoxides:3 MX, + M(OR), -t2MO,,, + nRX (1) Alternatively, it is possible to generate the alkoxyl groups in situ by the action of alcohol4 or dialkyl ether5 on metal halides: =M-X + ROH-M-OR + HX or EM-X + R O R -t E M-OR + RX (2) Another possible variation is the direct reaction of anhydride with alkoxide precursors,6 which leads to acylation, then condensation, via the formation of an ester: M(OR),+n/2 (R'C=O),O+MO,,,+nR'COOR (3)In these non-hydrolytic reactions, the metal alkoxide, dialkyl ether, alcohol and anhydride act as oxygen donors, instead of water. The main features of these methods are: (i) low synthesis temperatures (cu. 100-150°C); (ii) a simple reaction of TiC1, [or Ti (OR),] with readily available compounds; (iii) an easily removed by-product (hydrogen halide, alkyl halide or acetate); (iv) no cosolvent required (otherwise needed to dissolve water). This paper falls into two parts. First, four typical nonhydrolytic routes to titania were compared [systems TiC1, plus Ti(OPr'),, TiCl, plus diisopropyl ether, TiC1, plus isopropyl alcohol, Ti(OPr'), plus acetic anhydride]; the structures and textures of the different samples were studied by means of Xray diffraction (XRD) and BET measurements. Secondly, the influence of the nature of the oxygen donor on the structure and crystallisation behaviour of the TiO, precursors was investigated in the etherolysis and alcoholysis methods.

Three new series comprising 24 novel cationic choline analogues and consisting of mono- or bis (N or C-5-duplicated) thiazolium salts have been synthesized. Bis-thiazolium salts showed potent antimalarial activity (much superior to monothiazoliums). Among them, bis-thiazolium salts 12 and 13 exhibited IC(50) values of 2.25 nM and 0.65 nM, respectively, against P. falciparum in vitro. These compounds also demonstrated good in vivo activity (ED(50)

A nonhydrolytic sol‐gel route based on the condensation between chlorides and oxygen donors such as ethers and alkoxides is presented. Four examples, silica, alumina, titania and binary oxides in the Al/Si system show that this is a general route. The mechanism of this condensation is completely different from the one of classical sol‐gel process, since it implies nucleophilic substitution at the carbon center instead of the metal center. As a consequence, the differences in reactivity between different metals are reduced. In addition, the structure of the precursors may be retained in the gel. Thus, the nonhydrolytic sol‐gel process is very efficient for the preparation of homogeneous bicomponent oxides. Futhermore, nonhydrated gels are formed, which allowed us to prepare amorphous aluminas with high surface areas.

Etherolysis of metal chlorides offers a versatile, simple nonhydrolytic sol-gel route to transition metal oxides. The main limitation of the process results from the insolubility of some metal chlorides in non aqueous solvents. The general tendency of this nonhydrolytic process is to delay crystallization of metal oxides.