Organic Syntheses, Coll. Vol. 3, p.794 (1955); Vol. 23, p.90 (1943).
The hydrogenation is carried out in a low-pressure catalytic hydrogenation apparatus. Raney nickel
catalyst (p. 181)
is washed with ether
three times on a Büchner funnel
, then 8 g. of it is transferred under ether
to the hydrogenation bottle. The bottle is fitted with a rubber stopper
bearing a small dropping funnel
and a glass tube that leads to one arm of a three-way stopcock
. The other arms of the stopcock are connected respectively to a water pump
and a source of inert gas (Note 1)
in such a way that the ether
can be pumped off and the bottle can then be filled with the inert gas. When this has been done, 50.5 g. (0.6 mole) of dihydropyran (p. 276)
is introduced through the dropping funnel.
The bottle is connected to the hydrogenation apparatus and alternately evacuated and filled with hydrogen
is then admitted to the system until the pressure gauge reads 40 lb. The shaker is started, and the pressure drops to the theoretical value for absorption of 0.6 mole in 15–20 minutes; beyond this point shaking causes no further absorption of hydrogen (Note 2)
. The bottle is removed and the nickel
catalyst is allowed to settle. The tetrahydropyran
is decanted, but enough is left in the bottle to cover the catalyst (Note 3)
. The product boils at 85–86°
, but it need not be distilled for many purposes. The yield is practically quantitative.
is a convenient inert gas, but natural gas containing no oxygen
, or sulfur
compounds, is equally suitable; the checkers used hydrogen
As the catalyst becomes older, it loses its activity somewhat and a longer time is required for the pressure to drop to the theoretical value.
The same catalyst may be used many times. For the next run the dihydropyran
is merely poured into the bottle containing the catalyst which is wet with the product of the previous run.
This preparation is referenced from:
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