Org. Synth. 1967, 47, 69
[Acetic acid, p-dimethylaminophenyl-, ethyl ester]
Submitted by Michael G. Romanelli and Ernest I. Becker1
Checked by Roy A. Sikstrom, Douglas R. Johnson, William E. Parham, and Wayland E. Noland.
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.
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
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.
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
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.
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.
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.
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.
has been previously prepared in this laboratory by Fischer esterification of p-dimethylaminophenylacetic acid
, the acid in turn being prepared by the reductive hydrolysis of p-dimethylaminomandelonitrile
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.
TABLE I REDUCTIVE ALKYLATION OF NITRO COMPOUNDS
Chemical Abstracts Nomenclature (Collective Index Number);
palladium on charcoal
m-Nitrobenzoic acid (121-92-6)
p-NITROBENZOIC ACID (62-23-7)
p-Nitrophenylacetic acid (104-03-0)
Acetic acid, p-dimethylaminophenyl-, ethyl ester (17078-29-4)
ethyl p-nitrophenylacetate (5445-26-1)
p-dimethylaminophenylacetic acid (17078-28-3)
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