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 twice.
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.