1. G.A. Olah, P.S. Iyer, G.K.S. Prakash, Synthesis (1986) 513.
2. M. Balogh, P. Laszlo, Organic Chemistry Using Clays, Springer, Berlin, 1993.
3. Catalysis by Heteropoly Acids and Multicomponent Polyoxometalates in Liquid-Phase Reactions
4. Y. Izumi, K. Urabe, M. Onaka, Zeolite, Clay, and Heteropoly Acid in Organic Reaction, Kodansha, Tokyo and VCH, Weinheim, 1992, p. 99.