Abstract: Aqueous solutions of disodium a-diazobenzylphosphonate can be prepared by the action of alkali on the dicyanoethyl ester of a-diazobenzylphosphonic acid. The salt is somewhat unstable at room temperature even at neutrality; the decomposition is general acid catalyzed. The properties of the dianion are compared with those of the corresponding mono-and dicyanoethyl esters and of other diazo compounds that can serve as reagents ...