A.
4-Methyl-7-hydroxycoumarin (I). In a
5-l. three-necked round-bottomed flask, fitted with a
mechanical stirrer, a
thermometer reaching to the bottom, and a
dropping funnel, is placed
2 l. of concentrated sulfuric acid (sp. gr. 1.84). The flask is surrounded by an
ice bath, and when the temperature falls below 10° a solution of
220 g. (2 moles) of resorcinol in
260 g. (2 moles) of freshly distilled ethyl acetoacetate is added dropwise. The mixture is stirred, and the temperature is kept below 10° by means of ice and salt. After all the solution has been added (about 2 hours) the reaction mixture is set aside for 12–24 hours without further cooling. The reaction mixture is now poured with vigorous stirring into a mixture of 4 kg. of ice and 6 l. of water. The precipitate is collected on a filter and washed with three 50-ml. portions of cold water. The crude product is then dissolved in
3 l. of 5% aqueous sodium hydroxide solution, the solution is filtered, and the substituted
coumarin is reprecipitated from the filtrate by the slow addition of dilute (1:10)
sulfuric acid until the solution is acid to litmus. About
1.1 l. of dilute sulfuric acid is required. During the neutralization, the reaction mixture must be well stirred. The product is collected on a
Büchner funnel, washed with four 50-ml. portions of cold water, and dried. The yield of
4-methyl-7-hydroxycoumarin is
290–320 g. (
82–90%). It is sufficiently pure for use in the next step but may be purified by recrystallization from
95% ethanol using about
15 ml. of ethanol for 5 g. of product. The recrystallized material forms stout almost colorless needles melting at
185°.