tested this reaction for its general applicability and have found that the azines ( l a ) to (re) can be converted smoothly and quantitatively into the carbonyl compounds (2) by stirring them at room temperature with an excess of manganese dioxide in benzene or carbon tetrachloride. We have also studied the hydrazones (4.) to (4d). Whereas azines are cleaved relatively slowly (reaction time 2 h to 14 days), hydrazones afford the carbonyl compounds (2) more easily (within a few hours), and equally quantitatively, under the same conditions. In the latter case diazo-compounds (3) are formed as intermediates, which can be detected spectroscopically. 9-Fluorenone hydrazone is converted analogously into 9-fluorenone by way of 9-diazofluorene. The carbonyl compounds (2) are formed directly from the diazo compounds (3) by exchange of nitrogen for oxygen; thus diphenyldiazomethane gives benzophenone quantitatively. The fact that only acetone arises from acetone hydrazone shows that alcohols cannot be intermediates; if they were, isopropyl alcohol would be obtained since it is stable under the reaction conditions. Benzil dihydrazone gives tolane quantitatively within 30 min, but no benzil. Moreover, no benzil is obtained from benzil monohydrazone since a-diazo ketones (e.g. diazoacetophenone)and also diazoacetic esterd o not exchange their nitrogen for oxygen. This explains why diazo ketones can be isolated on oxidation of monohydrazones of a$dioxo compounds with manganese dioxide [2]. Carboxyhydrazides react with active manganese dioxide with evolution of nitrogen, giving carboxylic acids in quantitative yields.