Organic Reactions, Volume 2

EXPERIMENTAL PROCEDURES 27
Preparation of 2-Allylphenol. The allyl ether is boiled in a flask under
a reflux tube, the course of the rearrangement being conveniently followed
by noting the refractive index at frequent intervals. When no has
risen to 1.55 (five to six hours) the rearrangement is substantially complete
with the minimum formation of undesirable by-products. To
separate a small amount of 2-methyldihydrobenzofuran, the product is
dissolved in twice its volume of 20% sodium hydroxide solution and
extracted twice with petroleum ether (30-60°), from which the dihydrobenzofuran
residue may be obtained by distillation. Ether should not
be used for this extraction as it removes some of the phenol from the
alkaline solution. The alkaline solution is acidified and the phenol extracted
with ether; the extract is dried over calcium chloride and distilled
under diminished pressure. A 73% yield of material boiling at
103-105.5°/19 mm., nf> 1.5445, is obtained. 2-Allylphenol is a colorless
liquid, of guaiacol-like odor, with the following properties: b.p. 220°/
760 mm., 99°/12 mm., nf>° 1.5453. 27 - *
Contrary; to the usual situation, this procedure was found more satisfactory
than the rearrangement of allyl phenyl ether by refluxing in
diethylaniline. When the ether was refluxed for six hours in three times
its volume of diethylaniline, a 61% yield of 2-allylphenol was obtained.
2-Methyldihydrobenzofuran. 2-Allylphenol is dissolved in four times
its volume of acetic acid and treated with twice its volume of 45% aqueous
hydrobromic acid. The mixture is refluxed 20 minutes, during which
an oily layer separates on top; then an excess of water is added, and the
mixture is extracted with ether. The ether solution is washed with
sodium hydroxide solution, dried, and distilled under reduced pressure.
A 51% yield of material boiling at 86.5-87.5°/19 mm., 198-199°/740
mm. 28 is obtained; n^ 1.5307. A considerable amount of tarry residue
remains after distillation.
The same procedure, with a refluxing time of one hour, gives a 73%
yield of 2,3-dimethyldihydrobenzofuran when applied to 2-(a-methylallyl)-phenol.
36
Isomerization of 2-Allylphenol to 2-Propenylphenol. 2-Allylphenol is
dissolved in three times its volume of a saturated solution of" potassium
hydroxide in methanol; part of the solvent is distilled off until the temperature
of the liquid rises to 110°, and the residue is refluxed six hours at
this temperature. The reaction product is washed free of the base, dried,
and distilled, giving a 75% yield of 2-propenylphenol boning over a
range 110-115°/15-16 mm. The compound solidifies in the receiver,
and on recrystallization from ligroin forms shining needles melting at
36.5-37° (corr.); in fused state nf, 1 1.5823, b.p. 230-231° at atmospheric
* See p. 80 of the article cited in reference 11.