1. US Patent 3,274,079 (1966), to F. Passal; Chem. Abstr. 66 (1967) 16032k.
2. East German Patent 52,869 (1966), to F. Friemel; Chem. Abstr. 67 (1967) 17376h.
3. Jpn. Patent 74, 33723 (1974), to M. Jato; Chem. Abstr. 82 (1975) 91774n.
4. Jpn. Patent 75,02377 (1975), to S. Ichioka, T. Koda; Chem. Abstr. 83 (1975) 87387s.