1. Chemistry in Britain 30 (12) (1994) 970.
2. U. Curtius, L. Bottoenbruch, H. Schnell, US Patent 3 442 854 (1969), to Bayer AG.
3. H.Yamana, T. Kuni, T. Furusawa, H. Nakai, Y. Hiro, US Patent 3 888 826 (1975), to Mitsubish Gas Chemical Co.
4. D. Brunelle, US Patent 4 321 356 (1982), to General Electric Co.
5. J.B. Starr, A. Ko, US Patent 4 383 092 (1983), to General Electric Co.