B.
cis-2-Phenylcyclopropanecarboxylic acid. A
1-l., three-necked flask equipped with a dropping funnel, stirrer, and a short Vigreux column (Note
7), to which is attached a partial take-off distilling head with reflux condenser, is charged with
155 g. (0.816 mole) of ethyl cis- and trans-2-phenylcyclopropanecarboxylate,
200 ml. of ethanol, 65 ml. of water, and
24.5 g. (0.612 mole) of sodium hydroxide pellets (Note
8). The mixture is heated at the reflux temperature for 5 hours during which time
200 ml. of ethanol is slowly distilled and replaced by an equal volume of water added through the dropping funnel. Heating is discontinued, 250 ml. of water and
150 ml. of benzene are added, and the mixture is stirred for 2–3 minutes. The layers are separated, and the aqueous layer is washed with two
50-ml. portions of benzene (Note
9).
The
benzene extracts are placed in the apparatus used above, and 130 ml. of water and
13 g. (0.32 mole) of sodium hydroxide pellets are added.
Benzene (200 ml.) is distilled and then the
200 ml. of ethanol obtained in the initial hydrolysis is added. The reflux-distillation process is continued for 5 hours, during which time 250 ml. of distillate is obtained. The mixture is cooled, and
65 ml. of benzene and
30 ml. of concentrated hydrochloric acid are added. The layers are separated, and the aqueous solution is washed twice with
35-ml. portions of benzene. The combined
benzene extracts are concentrated and dried by distillation of
90 ml. of benzene. The hot concentrate is decanted from a trace of salt,
70 ml. of petroleum ether is added, and the resulting solution is stored overnight at 0°. Filtration of the solid from the cold petroleum ether solution and washing with a small volume of cold
50:50 benzene–petroleum ether yields
19.5–23.8 g. (
14.6-20.7% based on the mixed ester used, or
38–46.4% based on the
cis ester, (Note
10)) of
cis-2-phenylcyclopropanecarboxylic acid, m.p.
106–109° (Note
11). An additional
2–3 g. of the
cis acid may be obtained by concentrating the mother liquors to low volume, adding
petroleum ether, and chilling the resulting solution for several days.