Quaternary ammonium templates, effect

Chiral phase transfer catalysts have been exploited in a wide range of reactions which involve anionic intermediates. Remarkably, quaternary ammonium salts of 1 and 2 have been shown to induce asymmetry in many different synthetic reactions, and the cinchona alkaloids appear to be a charmed template for the design of effective phase transfer catalysts [14],... 

T. Dabadie, A. Ayral, C. Guizard, L. Cot, J.C. Robert and O. Poncelet, Liquid crystal templating effects on silica gels s)mthesized using quaternary ammonium surfactants. Mater. Res. Soc. Symp. Proc., 346 (1994) 849. 

In general, addition of a quaternary ammonium cation to a reaction mixture can effect changes of three types (a) a different zeolite structure is obtained (b) a zeolite crystallizes where the reaction mixture would othei wise remain amorphous indefinitely (c) the same zeolite is obtained as without quaternary, but it possesses an altered chemical composition. Unless crystallization was markedly accelerated, only (a) and (b) would represent template effects attributable to the quaternary cation, and (a) is by far the more common of the two effects. 

Experiments such as those with TMA strongly suggest template effects, but they are not of themselves conclusive. As noted earlier, crystallization products are often determined by nucleation, the first species to nucleate being the product (12), Reaction mixtures are normally inhomogeneous, an inhomogenity which could be influenced by added quaternary ammonium cations. Additional evidence for templating by TMA in these examples is provided by elemental analysis. 

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