B.
Diethyl cis-hexahydrophthalate. The reaction is carried out in a low-pressure catalytic hydrogenation apparatus.
2 In a
500-ml. Pyrex centrifuge bottle are placed
0.5 g. of Adams platinum oxide catalyst (Note
5) and
20 ml. of commercial absolute ethanol (Note
6). The bottle is connected to a
calibrated low-pressure hydrogen tank and alternately evacuated and filled with
hydrogen twice.
Hydrogen is then admitted to the system until the pressure is 1–2 atmospheres (15–30 lb.), and the bottle is shaken for 20–30 minutes to reduce the
platinum oxide. The shaker is stopped, the bottle is evacuated, and air is admitted.
Two hundred and twenty-six grams (1 mole) of diethyl cis-Δ4-tetrahydrophthalate is placed in the bottle. The
container in which the ester was weighed is rinsed with
10 ml. of absolute ethanol, which is added to the ester. The bottle is alternately evacuated and filled with
hydrogen twice.
Hydrogen is admitted to the system until the pressure is 25–30 lb. (approximately 2 atmospheres), and the bottle is shaken until the pressure drop indicates that the theoretical amount
(1 mole) of hydrogen has been taken up and the absorption ceases (3–5 hours). The bottle is evacuated and then air is admitted. The catalyst is removed by filtration through a
small Hirsch funnel. The bottle is washed with
15 ml. of alcohol, which is poured through the funnel. Most of the solvent is distilled at 25–35 mm. Distillation of the residue under reduced pressure yields
215–219 g. (
94–96%) of
diethyl cis-hexahydrophthalate, b.p.
130–132°/ 9 mm.,
nD25 1.4508–1.4510 (Note
7).