A 250-cc. flask, fitted with an inlet tube reaching to the bottom, a thermometer, and an exit tube for conducting away unused gas, is immersed in an ice-water bath, and to it is added 80 g. (0.69 mole) of freshly distilled indene (Note 1). While the temperature of the liquid is kept at 5–10°, dry hydrogen chloride is passed in at a moderate rate until 24–27 g. of the gas has been absorbed. The addition takes from eight to ten hours and requires little attention from the operator. The crude α-chlorohydrindene is then transferred to a 250-cc. Claisen flask and distilled at diminished pressure. After a small fore-run (5–10 g.) containing indene, α-chlorohydrindene boiling at 90–103°/15 mm. is collected; the yield is 80–90 g. (Note 2).

In a 500-cc. three-necked flask, fitted with a stirrer, thermometer, and dropping funnel, is placed 100 g. (1 mole) of chromic anhydride dissolved in 100 cc. of water, and 100 cc. of glacial acetic acid is added. The α-chlorohydrindene is then admitted through the funnel at such a rate as to keep the temperature at 35–40°, the flask being cooled externally. This addition takes about one and one-half hours; after it is complete, stirring is continued for fifteen minutes before the mixture is poured into a large beaker and diluted with 300 cc. of water. After the acid present is neutralized by the addition of solid sodium carbonate (Note 3), the α-hydrindone is expelled from the mixture by steam distillation, care being taken to avoid entrainment of froth at the beginning of the process. When about 2.5 l. of distillate has been collected, the solution again begins to froth. The operation is stopped at this point, since further distillation does not yield an appreciable quantity of product. The α-hydrindone usually solidifies, as soon as the distillate is chilled, to a mixture of colorless crystals and a yellow solid; the product is collected after thorough cooling in an ice bath. This moist solid is dissolved in 200 cc. of benzene, and the solution is subjected to distillation until free from water. After the benzene is removed by vacuum distillation on the steam bath, the α-hydrindone is distilled. It boils at 125–126°/17 mm., and the distillate is a pale yellow solid, m.p. 39–41°. The yield is 46–55 g. (50–60 per cent of the theoretical amount, based on the indene used) (Note 4) and (Note 5).