1. Brit. Pat. 1,332,201 (1973), in Ref. Zh. Khim., 13N188P (1974).
2. Brit. Pat. 1,236,740 (1971), in Ref. Zh. Khim., 2P277P (1972).
3. U. S. Pat. 3,505,225 (1970), in Ref. Zh. Khim., 4P302P (1971).
4. U. S. Pat. 3655621 (1972), in Ref. Zh. Khim., 2P220P (1973).
5. I. V. Zarubina, T. E. Rogozhina, et al., Neftepererab. Neftekhim. (Moscow), No. 7, 15?18 (1974).