1. Ullmann's Encyclopedia of Industrial Chemistry;Pollak,1998
2. A.R. Bulls, J.D. Fellmann, R.A. Periana, PCT Patent WO 9212962 (1992).
3. H. Kaneko, T. Masuda, Jpn Patent 07233135 (1995).
4. M. Kawamata, T. Takahashi, S. Fujikake, Jpn Patent 7571627 (1975).
5. D.A. Tyssee, U.S. Patent 3.945.896 (1976).