References
- Raschig , F. Brit. Patent 358903 . 1931 . This patent is typical of those covering this or similar processes
- Bauer , W. and Kuhlein , K. Ger. Patent 3 002 254 . 1981 . This patent is the latest covering this conversion
- Friedlander and Zeithin Ber., 1894, 27, 196 .
- 1913 . Swarts, Bl. Acad. Belg. , : 274