Organic Reactions Volume 4 - Sciencemadness Dot Org

PREPARATION OF AMINES BY REDUCTIVE ALKYLATION 197
is therefore advisable to use an alcohol solvent, a rather large quantity
of catalyst (3% of Raney nickel catalyst), fairly high pressures (perhaps
20 atm.), and a temperature such that hydrogenation proceeds rapidly.
The preparation of secondary amines by the hydrogenation of an
ethanolic solution of a primary amine and an aldehyde or ketone may
be conducted conveniently in either high- or low-pressure equipment.
At 100 to 150 atm. and 125°, 4 g. of nickel on kieselguhr or 10 g. of
Raney nickel catalyst is used for a 0.4 to 0.5 M run. 23 The reaction is
complete in one to two hours. Usually equimolar amounts of the amine
and carbonyl compound are employed, 18,23 ' 79 although a 30% excess of the
carbonyl compound may be used to ensure complete reaction of the
amine. 26 ' 59,60 ' 61 Somewhat milder conditions than those described above
are effective. Thus at 75° in a ligroin solvent, a 0.5 M run requires
three to twelve hours with 10 g. of Raney nickel catalyst. On the other
hand at 150° only 3 g. of Raney nickel catalyst and at 160° 1 g. of copper
chromite is necessary for the smooth hydrogenation of a 0.3 M run. 26
Under these conditions the reaction between an amine and a ketone
proceeds equally smoothly with or without ethanol as solvent. The use
of ethanol is recommended in alkylations with aldehydes to avoid
polymerization. 26 It is also advisable to cool the solution of the amine
during the addition of the aldehyde. With acetic acid as the solvent
extensive polymerization of the aldehyde results. 26 - 32
At pressures of 1 to 2 atm. excellent results have been obtained in
1 M runs using 0.5 g. of platinum oxide catalyst which was reduced
before the start of the alkylation. 26 Ethanol or acetic acid was used as
the solvent. Alkylation with aldehydes and aliphatic methyl ketones
proceeded smoothly without external heat. Such ketones as acetophenone,
dipropyl ketone, dibutyl ketone, and /ntnenthone required
temperatures of 50-60° in the alkylation of ethanolamine and a longer
time (twenty to thirty hours as against seven), while diisobutyl ketone
did not react. In place of the 0.5 g. of platinum oxide, 3 g. of palladinized
charcoal could serve as the catalyst, although the reaction was much
slower, requiring thirty-one hours at 60°. Successful alkylations have
also been obtained with colloidal platinum in aqueous suspension. 18
Raney nickel can also be used, but at low pressures a large amount of
catalyst is necessary. Good results have been obtained in 0.1 M runs
with 1 mole of nickel. 27 ' 32 * 36 With aromatic amines and aliphatic aldehydes,
the use of sodium acetate as a condensing agent (1 g. for a 0.1 M
run) increases the yield markedly. 32 ' 36
The best way to prepare secondary amines from SchifPs bases is to
hydrogenate them catalytically in either high- or low-pressure equip-
79 Henze and Humphreys, /. Am. Chem. Soc, 64, 2878 (1942).