Organic Syntheses, CV 5, 552
Submitted by Michael G. Romanelli and Ernest I. Becker
1.
Checked by Roy A. Sikstrom, Douglas R. Johnson, William E. Parham, and Wayland E. Noland.
1. Procedure
In a
400-ml. Parr bottle are placed
41.8 g. (0.20 mole) of ethyl p-nitrophenylacetate,
40 ml. of 40% aqueous formaldehyde solution,
200 ml. of 95% ethanol, and
2.0 g. of 10% palladium on charcoal (Note
1). The bottle is then placed on a
Parr hydrogenation apparatus. The sample is evacuated and filled with
hydrogen, this process being repeated three times. The tank and bottle are then filled with
hydrogen to 55 p.s.i. The shaker is started, and the hydrogenation is allowed to proceed until the pressure drop corresponds to
1.0 mole of hydrogen (Note
2), (Note
3). The time required for hydrogenation is approximately 2.5 hours (Note
4). After venting the
hydrogen from the bottle safely (Note
1), the
ethanol solution is filtered and the catalyst washed carefully (Note
5) with
20 ml. of ethanol.
The filtrate is transferred to a flask which is placed on a
rotary evaporator. The
ethanol is then removed under reduced pressure on a
steam bath. Using
ether as a washing solvent, the residue is transferred to a small distilling flask and the ether distilled. The
ethyl p-dimethylaminophenylacetate is then distilled (Note
6), (Note
7) at reduced pressure, affording
27.7–31.8 g. (
67–77%) of colorless product, b.p.
122–124° (0.4 mm.),
n23D 1.5358.
2. Notes
1. Care must be taken in weighing out and transferring the catalyst as it can ignite mixtures of air and flammable vapors. The operation of the Parr apparatus and appropriate safety precautions in its use have been described in detail.
2
2. The hydrogenation is exothermic, and care must be taken in order to prevent the reaction from getting out of control. The submitters have not experienced this difficulty, but exothermic hydrogenations require supervision.
3. With the apparatus used, a pressure drop of 85 lb. corresponds to
1.0 mole of hydrogen. Either the particular apparatus used can be calibrated or the hydrogenation allowed to proceed until the pressure ceases to drop.
2
4. The time required for the hydrogenation will depend on several factors, such as the speed of shaking, activity and particle size of the catalyst. In the experiments run on
ethyl p-nitrophenylacetate the submitters have found that the time required varied from about 2 to 4 hours.
5. The filtration was by suction. The catalyst must not be allowed to dry out with a stream of air passing through it, as it can then readily ignite.
6. Before the actual distillation could be carried out, the flask was heated to approximately 95° and the residual
formaldehyde removed at the aspirator. Only after the
formaldehyde was removed could the pressure be reduced to that required for the distillation.
7. The checkers observed that rather rapid decomposition of the product occurs unless precautions were taken. A short path distillation using a
50-ml. distilling flask equipped with a capillary
nitrogen bubbler was employed.
3. Discussion
4. Merits of the Preparation
Besides being a convenient preparation for
ethyl p-dimethylaminophenylacetate, the procedure for reductive alkylation can be generalized.
4,5 Table I lists the results obtained by the submitters.
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