ACETO-ACETIC ESTER, C6H10O3 or CH3.CO.CH2.COOC2H5, a chemical substance discovered in 1863 by A. Geuther, who showed that the chief product of the action of sodium on ethyl acetate was a sodium compound of composition C6H9O3Na, which on treatment with acids gave a colourless, somewhat oily liquid of composition C6H10O3. E. Frankland and B. F. Duppa in 1865 examined the reaction and concluded that Geuther's sodium salt was a derivative of the ethyl ester of acetone carboxylic acid and possessed the constitution CH6CO.CHNa.COOC2H5. This view was not accepted by Geuther, who looked upon his compound C6H10O3 as being an acid. J. Wislicenus also investigated the reaction very thoroughly and accepted the Frankland-Duppa formula (Annalen, 1877, 186, p. 163; 1877, 190, p. 257).
The substance is best prepared by drying ethyl acetate over calcium chloride and treating it with sodium wire, which is best introduced in one operation; the liquid boils and is then heated on a water bath for some hours, until the sodium all dissolves. After the reaction is completed, the liquid is acidified with dilute sulphuric acid (1:5) and then shaken with salt solution, separated from the salt solution, washed, dried and fractionated. The portion boiling betbeen 175 deg. and 185 deg. C. is redistilled. The yield amounts to about 30% of that required by theory.
A. Ladenburg and J. A. Wanklyn have shown that pure ethyl acetate free from alcohol will not react with sodium to produce aceto-acetic ester. L. Claisen, whose views are now accepted, studied the reactions of sodium ethylate and showed that if sodium ethylate be used in place of sodium in the above reaction the same result is obtained. He explains the reactions
CH3.C==O + NaOC2H5 = CH3.C-OC2H5,
\ OC2H5 \OC2H5
this reaction being followed by
CH3.C-OC2H5 + CH.COOC2H5 = 2 C2 H5OH +
\OC2H5 H/ CH3.C(ONa):CH.COOC2H5;
and on acidification this last substance gives aceto-acetic ester. Aceto-acetic ester is a colourless liquid boiling at 181 deg. C.; it is slightly soluble in water, and when distilled undergoes some decomposition forming dehydracetic acid C8H8O4. It undoubtedly contains a keto-group, for it reacts with hydrocyanic acid, hydroxylamine, phenylhydrazine and ammonia; sodium bisulphite also combines with it to form a crystalline compound, hence it contains the grouping CH 3/0.CO-. J. Wislicenus found that only one hydrogen atom in the-CH2- group is directly replaceable by sodium, and that if the sodium be then replaced by an alkyl group, the second hydrogen atom in the group can be replaced in the same manner. These alkyl substitution products are important, for they lead to the synthesis of many organic compounds, on account of the fact that they can be hydrolysed in two different ways, barium hydroxide or dilute sodium hydroxide solution giving the so-called ketone hydrolysis, whilst concentrated sodium hydroxide gives the acid
CH3.CO.C(XY).CO2C2H5 -> CH3.CO.CH(XY) +
C2H5OH + CO2;
CH3.CO.C(XY).CO2C2H5 -> CH3.CO2H + C2H5OH +
(where X and Y = alkyl groups).
Both reactions occur to some extent simultaneously. Acetoacetic ester is a most important synthetic reagent, having been used in the production of pyridines (q.v.), quinolines (q.v.), pyrazolones, furfurane (q.v.), pyrrols (q.v.), uric acid (q.v.), and many complex acids and ketones.
For a discussion as to the composition, and whether
it is to be regarded as possessing the "keto', form
CH3.CO.CH2.COOC2H6 or the "enol" form CH3.C(OH):
CH.COOC2H5, see ISOMERISM, and also papers by J. Wislicenus
(Ann., 1877, 186, p. 163; 1877, 190, p. 257), A. Michael
(Journ. Prak. Chem., 1887,  37, p. 473), L. Knorr
(Ann., 1886, 238, p. 147), W. H. Perkin, senr. (Journ. of
Chem. Soc., 1892, 61, p. 800) and J. U. Nef (Ann., 1891,
266, p. 70; 1892, 270, pp. 289, 333; 1893, 276, p. 212).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)