Two-bulb distilling flask

Soldaini and Bert e s method. 20 c.c. of the oil and a few scraps of pumice are placed in a three-bulbed distillation flask (see p. 278) holding about 70-75 c.c., the flask being connected with a small condenser and closed with a cork traversed by a thermometer. Around the flask—which should rest on an asbestos-gauze—is placed an asbestos card sleeve, which surrounds it at a distance of about 1 cm. and reaches almost to the lowest bulb of the neck. To the free end of the condenser is fitted a graduated cylinder. The oil is then boiled at the ordinary pressure so that one drop falls into the cylinder about every two seconds. When the distillate in the cylinder amounts to one-half the amount of oil taken, i.e. 10 c.c., the cylinder is replaced by an ordinary test-tube and the flame extinguished. The few drops of subsequent distillate are returned to the residue in the distillation flask. 

Upon cooling to room temperature, a gray precipitate forms and the reaction is quenched with 220 mL of saturated, aqueous ammonium chloride. The resulting mixture is poured into a 1-L separatory funnel and extracted with 220 mL of diethyl ether. The organic fraction is washed two times with 100 mL of water, and once with 100 mL of brine, dried over magnesium sulfate, filtered, and concentrated under reduced pressure to provide 44.1 g of crude product as a pale yellow oil. Purification of this material by bulb-to-bulb distillation (140-145°C, 0.5 mm) (Note 11) into a chilled (-78°C) receiving flask yields 41.0 g (92%) of 2 as a clear, colorless oil (Note 12). 

B. 1-Benzylindole. The slurry of indole sodium is cooled to 0° (ice bath), and 2.30 ml. (2.53 g., 0.02 mole) of benzyl chloride (Note 5) is added as rapidly as possible to the stirred mixture. The mixture is then stirred for 8-15 hours (overnight), during which time the ice in the ice bath melts and the temperature of the reaction flask gradually rises to room temperature. The mixture is then diluted with 15 ml. of water and extracted with three 25-ml. portions of ether. The combined ethereal extracts are washed with two 40-ml. portions of water and dried with anhydrous magnesium sulfate. After filtration the solvent is removed at reduced pressure, and 4.4 g. of crude 1-benzylindole is obtained as a liquid. After bulb-to-bulb distillation of this material in a Kiigelrohr oven [120-130° (0.0025 mm.)], crystallization of the distillate from 15 ml. of hot ethanol affords 3.46-3.61 g. (83-87%) of 1-benzylindole. A second crop amounting to 0.17-0.26 g. (4-6%) is obtained on concentration of the mother liquors to 6 ml. The total yield of 1-benzylindole, m.p. 43-44°, is 3.72-3.78 g. (90-91%) (Notes 6 and 7). 

Distilling flasks should be chosen of such a size that the bulb is half or two-thirds full of liquid. In order to avoid bumping and superheating a few pieces of porous plate (pot) half as large as peas are dropped into the flask before each distillation. If boiling is again delayed fresh pieces of pot must be added, not to the superheated liquid, however, but after brief cooling. 

For the distillation a sausage flask or two-bulb flask (Fig. 2) is employed. 

The material may be distilled from a distillation flask of the two bulb type described in Org. Syn., Coll. Vol. 3, 133 (1955), or from a small Claisen flask. 

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