1. N. V. Koshkin,Zh. Anal. Khim., 13, 308 (1958).
2. V. N. Podchainova and V. Ya. Kazakov,Zh. Anal. Khim., 15, 692 (1960).
3. N. V. Koshkin and F. B. Agrest,Khim. i. Khim. Teckhnol., 7, 731 (1964).
4. R. C. Aggarwal and R. B. S. Yadav,Ind. J. Chem., 13, 727 (1975).
5. M. J. Campbell and R. Grzeskowiak,J. Chem. Soc. A, 396 (1967).