Organic Syntheses, CV 2, 543
o-PROPIOPHENOL AND p-PROPIOPHENOL
[Propiophenone, o- and p-hydroxy-]
Submitted by Ellis Miller and Walter H. Hartung.
Checked by W. W. Hartman and L. J. Roll.
1. Procedure
In a
2-l. three-necked, round-bottomed flask, fitted with a
reflux condenser, a
mechanical stirrer (Note
1), and a
100-cc. dropping funnel, are placed
374 g. (2.8 moles) of anhydrous aluminum chloride and
400 cc. of carbon bisulfide (Note
2). To the stirred suspension is added slowly through the dropping funnel
375 g. (2.5 moles) of phenyl propionate (Note
3). Reaction sets in almost at once with the evolution of
hydrogen chloride (Note
4), and the
carbon bisulfide begins to reflux from the heat of reaction (Note
5). When all the propionate is in (one and one-half hours is required), the mixture is further heated to gentle refluxing on a
steam bath until the evolution of
hydrogen chloride has practically ceased (about two hours). The reflux condenser is then turned downward, and the
carbon bisulfide is distilled. The steam bath is replaced by an
oil bath which is heated to 140° and maintained at 140–150° for three hours (Note
6). During this period a fresh evolution of
hydrogen chloride takes place. The mixture thickens and finally congeals to a brown resinous mass. Stirring is continued as long as possible (Note
7).
The solid is then allowed to cool, and the aluminum complex is decomposed by slowly adding first a mixture of
300 cc. of concentrated hydrochloric acid with 300 cc. of water and then 500 cc. of water (Note
8), whereupon a black oil collects at the surface. After standing overnight in the
ice box, a large portion of this layer solidifies and can be separated by filtration. This solid (
p-propiophenol) is recrystallized from
400 cc. of methyl alcohol. The yield is
129–148 g. (
34–39 per cent of the theoretical amount) of a light yellow product melting at
145–147°. A second recrystallization raises the melting point to 147–148°.
The oily filtrate combined with the concentrated mother liquors of the above recrystallization is dissolved in
500 cc. of 10 per cent sodium hydroxide and extracted with two
100-cc. portions of ether to remove non-phenolic products. The alkaline solution is acidified with
hydrochloric acid and the oily layer is separated, dried over anhydrous
magnesium sulfate, and distilled. The
o-propiophenol boils at
110–115°/6 mm. The yield is
120–132 g. (
32–35 per cent of the theoretical amount). About
40 g. of
p-propiophenol boiling at
135–150°/11 mm. is obtained. The total yield of crude
p-propiophenol is thus
169–188 g. (
45–50 per cent of the theoretical amount) (Note
9).
2. Notes
1. The
stirrer should be made of sturdy glass rod, bent preferably in the shape of a golf-club head, to provide for heavy duty when the reaction mass becomes thick.
2. When
nitrobenzene was used as a solvent the products were always tarry.
4. Because of the large volume of
hydrogen chloride evolved, it is desirable to work under a
good hood. If this is not available, the
gas-trap described on
p. 4 may be used.
5. The addition of the
phenyl propionate is regulated so as to maintain gentle refluxing.
6. The temperature of the reaction mixture is about ten degrees lower than the bath temperature, or 130–135°. The reaction temperature determines the yield ratio of the two isomers. In general, higher temperature (above 160–170°) favors the formation of the ortho isomer.
7. It is necessary to stir the thickening mass continuously to permit the escape of
hydrogen chloride formed during the heating; otherwise it may swell rapidly and choke the outlets of the flask.
8. This decomposition is strongly exothermic, and the dilute acid should be added slowly.
9. The above procedure has been found satisfactory for the preparation of a number of the homologs of
o- and p-propiophenol, such as
aceto-, butyro-, and caprophenol.
3. Discussion
This preparation is referenced from:
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