Woronkow et al. Uc. Zap. Leningradsk. Univ. Ser. chim.Chem.Abstr., 1953 , # 12 p. 161,162, 166 Uc. Zap. Leningradsk. Univ. Ser. chim.Chem.Abstr., 1955 , p. 5272