Research in pyrazolidine chemistry

An increase in the resistance of the N-N bond to hydrogenolysis on Raney nickel in alkaline media is observed not only for 1,2,4-trisubstituted 3,5-dioxopyrazolidines but also for other types of 3,5-dioxopyrazolidines that are capable of enolization. 3,5-Dioxopyrazolidines that are capable of forming betaines also do not undergo hydrogenation in neutral ethanol. The use of the potentiometric method of Sokol'skii and Druz′ made it possible to establish very slight adsorption of the enolates and betaines on the catalyst surface. The decrease in adsorbability is explained by a decrease in the effective charges on the nitrogen atom of the heteroring; this is in agreement with the results of calculations of the enolate and enol by the Pariser-Parr-Pople method. An assumption regarding the greater aromatic character of the enolate as compared with the enol is expressed on the basis of a comparison of the bond lengths.