Org. Synth. 1939, 19, 36
Submitted by B. B. Corson and V. N. Ipatieff.
Checked by John R. Johnson and E. A. Cleveland.
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).
For the preparation of moderate amounts of cyclohexene
the dehydration of cyclohexanol
with 85 per cent phosphoric acid
, according to the procedure of Dehn and Jackson, J. Am. Chem. Soc. 55
, 4285 (1933), is very convenient. Furthermore, very little carbonization occurs, in contrast with the sulfuric acid
method described in Org. Syn. Coll. Vol. I, 1941, 183
, where there is much carbonization and the product is contaminated with sulfur dioxide
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.)
The purpose of the sulfuric acid
is to convert dicyclohexyl sulfate
to cyclohexyl hydrogen sulfate
, which is removed by the subsequent washing operations.
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.
It is well to allow suspended water to settle by standing overnight and to separate again before adding the drying agent.
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.
The distillation residue becomes semi-solid on cooling owing to the separation of 1,4-dicyclohexylbenzene
. The latter may be recovered by filtering with suction, washing with methyl alcohol
, and crystallizing from acetone (using 4 cc. of acetone per gram of the crude solid)
. The yield of purified dicyclohexylbenzene
, m.p. 100–101°
, is 15–24 g.
has been prepared by the hydrogenation of biphenyl1
and of cyclohexenylbenzene
by the reaction of cyclohexyl chloride3 or bromide4
in the presence of aluminum chloride
; and from benzene
in the presence of aluminum chloride
,5 sulfuric acid
or boron halides.7
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
calcium chloride (10043-52-4)
sulfuric acid (7664-93-9)
methyl alcohol (67-56-1)
sodium hydroxide (1310-73-2)
nitric acid (7697-37-2)
sulfur dioxide (7446-09-5)
aluminum chloride (3495-54-3)
phosphoric acid (7664-38-2)
cyclohexyl chloride (542-18-7)
magnesium sulfate (7487-88-9)
Cyclohexane, phenyl- (827-52-1)
cyclohexyl hydrogen sulfate
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