Submitted by B. B. Corson and V. N. Ipatieff.
Checked by John R. Johnson and E. A. Cleveland.
1. Procedure
In a
1-l. three-necked flask equipped with a
mechanical stirrer,
dropping funnel, and
thermometer are placed
468 g. (530 cc., 6 moles) of benzene and
92 g. (50 cc.) of concentrated sulfuric acid (sp. gr. 1.84). The mixture is cooled in an
ice bath, and
164 g. (203 cc., 2 moles) of cyclohexene (Note
1) is added with stirring over a period of one and one-half hours, while the temperature is maintained between 5° and 10°. Stirring is continued for an additional hour after all the
cyclohexene has been added.
The hydrocarbon layer is separated, cooled in ice, and washed with four
50-cc. portions of cold concentrated sulfuric acid (Note
2). The material is then washed twice with warm water (50°), twice with
3 per cent sodium hydroxide solution, and twice with pure water (Note
3). The hydrocarbon mixture is dried over anhydrous
calcium chloride (Note
4) and subjected twice to fractional distillation, using a
30-cm. Vigreux or similar column; the
cyclohexylbenzene is collected at 238–243° (Note
5) and (Note
6). The yield is
210–220 g. (
65–68 per cent of the theoretical amount).
2. Notes
In a
2-l. three-necked flask, carrying a
separatory funnel and
three-bulbed Wurtz column filled with broken glass tubing, is placed
200 g. of 85 per cent phosphoric acid. The column is attached to an
efficient condenser leading to a
receiver cooled in an ice bath, and the flask is heated in an
oil bath at 165–170°. Through the funnel
1 kg. (10 moles) of practical cyclohexanol is dropped in over a period of four to five hours. After the addition has been completed the temperature of the bath is raised gradually to 200° and maintained at 200° for one-half hour. During the whole operation the temperature at the top of the column does not rise above 90°. The upper layer of the distillate is separated (salt may be added to break up emulsions) and dried with anhydrous
magnesium sulfate; the lower aqueous layer is saved for reworking if desired; likewise the spent drying agent may be treated with water to recover admixed
cyclohexene. The crude
cyclohexene is distilled in an efficient column, and the fraction boiling at
81–83° is collected. The yield is
660–690 g. (
79–84 per cent of the theoretical amount). The residue consists largely of
cyclohexanol and may be recycled as described below.
An additional
25–30 g. of
cyclohexene may be obtained by combining the residue from the distillation of the crude
cyclohexene with the water layer from the original distillate and distilling with
25 g. of 85 per cent phosphoric acid. This distillate is added to the low-boiling fraction from the distillation of the crude
cyclohexene and separated. The upper layer is dried with anhydrous
magnesium sulfate and distilled as described above.
The
phosphoric acid may be recovered by diluting with water and filtering, then evaporating with a little
nitric acid to the proper concentration.
The same procedure when used with
86 g. (1 mole) of cyclopentanol and
15 cc. of 85 per cent phosphoric acid gave
55 g. (
81 per cent of the theoretical amount) of
cyclopentene, b.p.
44–45°. No attempt was made to recover the
cyclopentanol. (Oliver Grummitt and John R. Johnson, private communication.)
3. To avoid emulsification as much as possible it is advantageous to use warm water rather than cold, and dilute alkali rather than concentrated. The milkiness of the aqueous wash liquid represents only a very small loss of material.
4. It is well to allow suspended water to settle by standing overnight and to separate again before adding the drying agent.
5. In a typical preparation the fractions collected during the second distillation were as follows: 78–85°, 296 g.; 85–235°, 2 g.; 235–238°, 2 g.; 238–243°, 215 g.; 243–265°, 2 g.; residue above 265°, 46 g.
3. Discussion
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