A colourless liquid ester with a pleasant odour, CH3COCH2COOC2H5; r.d. 1.03; m.p. <–80°C; b.p. 180.4°C. It can be prepared by reacting ethyl ethanoate (CH3COOC2H5) with sodium or sodium ethoxide. The compound shows keto-enol tautomerism and contains about 7% of the enol form, CH3C(OH):CHCOOC2H5, under normal conditions. Sometimes known as acetoacetic ester, it is used in organic synthesis.