Ethyl malonate belongs to the class of tautomeric compounds which exist in more than one structural form in equilibrium with one another. Ethyl malonate consists almost wholly of the ketonic form I. [Diagram] and contains not more than one .01 per cent of the enolic form (II.,) as determined by the bromine addition method. (Abs. A.C.S. 7, 1913. 2864-9). The dio-enolic form (III) is therefore likely to be present in minute quantity only (if at all) in the free ester. A reagent which reacts with the enolic form (II) would remove it from the equilibrium, and so cause a change of (I) into (II) and finally give rise to a derivative of the form (II). Thus by addition of one molecule of sodium ethoxide to one molecule of malonic ester in alcoholic solution, the mono sodio derivative in which one hydrogen is replaced by sodium is readily obtained. (Conrad Ber. 12, 1879. 750).