278 PRACTICAL ORGANIC CHEMISTRY which is activated by (in particular) a keto, nitrile or ester (-COOR) group. Thus the addition of diethyl sodio-malonate to mesityl oxide (I) may be regarded essentially as an ionic addition to give the anion (II), which on acidification gives the ester (III) with the keto group regenerated. The Michael Reaction has clearly a wide scope in synthetic work. The compound (III) can however lose ethanoi by an internal Claisen ester condensation (p. 264) to give the cyclohexane derivative (IV), which, being the ester of a (3-keto acid, in turn readily undergoes hydrolysis and decarboxylation to give 5,5-dimethyl-cyclohexan-i,3-dione (V) or "Dimedone," a valuable reagent for the detection and estimation of formaldehyde. Required: Ethanoi, 40 ml.; sodium, 2-3 g.; ethyl malonate, 17 g.; mesityl oxide, 10-2 g.; sodium hydroxide, 10 g. The mesityl oxide (b.p. 130°) and the ethyl malonate (b.p. 199°, 95°/18 mm.) should be redistilled before use. Assemble a 250 ml. three-necked flask, fitted with a stirrer, a
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