1,145,943. Nitroxides. SANKYO CO. Ltd. and ASAHI KASEI KOGYO K.K. 18 Sept., 1967 [19 Sept., 1966; 17 April, 1967], No. 42446/67. Heading C2C. [Also in Division C3] Piperidine - N - oxyl - spiro - hydantoins of formula where R 1 and R 2 are alkyl or may be joined to form with the carbon atom to which they are attached a 5- or 6-membered saturated homocyclic ring or a group of formula where R 3 and R 4 are alkyl, may be prepared by treating the corresponding piperidine-spirohydantoin compound with a peroxide or by reacting a piperidine-N-oxyl compound of formula with an alkali metal cyanide and ammonium carbonate. In examples (1) 1,3,8-triaza-7,7,9,9- tetramethyl - 2,4 - dioxo - spiro [4.5] decane- 8 - oxyl; and (2) cyclohexane - 1 - spiro - 2<SP>1</SP> (6<SP>1</SP>,6<SP>1</SP> - dimethylpiperidine - 11 - oxyl) - 4<SP>1</SP> spiro - 5<SP>11</SP> - hydantoin are prepared. Other nitroxides are specified.