1. Swiss Patent no. 290 515, 1953; Chem. Abstr., 1955, vol. 49, p. 7606g.
2. Swiss Patent no. 296 573, 1954; Chem. Abstr., 1956, vol. 50, p. 5040a.
3. Rittersdorf, W., Rey, H., Guethlein, W., and Rieckmann, P., FRG Patent no. 2 235 152, 1974; Chem. Abstr., 1974, vol. 80, no. 142 769 d.
4. Berger, D., Fey, G., Kuhr, M., and Werner, W., EPV Patent no. 14 929, 1980; Chem. Abstr., 1981, vol. 94, no. 43 719 z.
5. Jastzebska-Glapa, M., Mlochowski, J., and Sliwa, W., J. Prakt. Chem., 1977, vol. 319, p. 883.