formula [(CH3)2N]2Se. The solid is thermolabile, being converted with loss of oxygen into the liquid [(CH3)2N]2Se. We have also prepared the solid [(CH3)2N]2SeO from SeOCI2 and dimethylamine [5].[(CH3)2N]zSeO and [(CH&NH212Se205 (1) are always formed together in a 1 : 1 molar ratio. Thus, the following equation can be written for the aminolysis of selenium dioxide:It therefore appears that not every Se-0-Se bridge in the selenium dioxide undergoes aminolysis. Terminal anionic groups apparently increase the stability of adjacent Se-0-Se bridges towards solvolysis. This interpretation is supported by the fact that the diselenites (NH4)2Se205 and K2Se205 are resistant to liquid dimethylamine at room temperature and even to liquid ammonia. Received, October 23rd, 1964 [Z 8491675 IE] German version: Angew. Chem. 76. 992 (1964) [ I ] Investigations of Selenium-Oxygen Compounds, Part 29. ~ The reaction of 2-chloropyridine N-oxide with KNH2 in liq. ammonia leads mainly to undefined products plus 5 % 2aminopyridine N-oxide and 1 % 3-aminopyridine N-oxide; the latter two products are suggestive of the intermediate occurrence of 3,4-dehydropyridine N-oxide ( I ) . In contrast, 3chloropyridine N-oxide yields only the 3-amino compound [l]. We heated 3-chloropyridine N-oxide for 8 days with piperidine in anhydrous benzene at 100 "C and obtained ca. 80 % of the starting material, non-identified products, and 3piperidinopyridine N-oxide (82 % [2] ; picrate has m. p. 189 "C), plus 4 % [2] 4-piperidinopyridine N-oxide (m.p. of picrate 153-154OC), but could not detect the 2-piperidino isomer. Analogously, when 3-bromoquinoline N-oxide was heated with piperidine at 115 "C for three days, 22 % [2] 4piperidinoquinoline N-oxide [3] (m. p. of picrate 132-1 33 "C) was isolated in addition to a small amount of starting material, non-identified products, and 3-piperidinoquinoline N-oxide (20 % [2]; m.p. of picrate 165--166'C), but again no 2-piperidino isomer was found.The formation of the 4-piperidino compounds indicates an elimination/addition mechanism for the substitution proceeding via the heterocyclic N-oxides (2) and (3) t41.In contrast to the 3-halogeno compounds, 2-and 4-chloropyridine N-oxides and 4-chloroquinoline N-oxide appear to react completely according to the normal addition/elimina-tion mechanism [5] when heated in piperidine t o about 100 'C, for only the "non-rearranged" substitution products, viz. 2-piperidinopyridine N-oxide (m.p. 124.5-125.5 "C), 4-piperidinopyridine N-oxide, and 4-piperidinoquinoline N-oxide are formed in almost quantitative yield. Received, October 26th, 1964 [ Z 852/678 I€] German version: Angew. Chem. 76, 993 (1964) [I] R . 1. Martens and H .