Organic Reactions Volume 4 - Sciencemadness Dot Org

PREPARATION OF AMINES BY REDUCTIVE ALKYLATION 181
obtained from acetaldehyde in 50% yield/ 7 but the few other aliphatic
aldehydes which have been studied have given yields of 20-30% of
the secondary amines. 18 In a few preparations of secondary amines the
primary amine obtained as a by-product from one run is added to the
next reaction mixture. By this method it is possible to obtain diethylamine
from acetaldehyde and ammonia in yields as high as 84%. 16 » 19
Acetone and methyl ethyl ketone are converted to the secondary
amines in yields of 3Q~40%, 18 ' 20 whereas diethyl ketone gives only 20% of
the secondary amine. 20 Cyclohexanone has been converted to dicyclohexylamine
in 54% yield. 11 A platinum catalyst was used with all these
ketones. In the presence of hydrogen and a nickel catalyst, acetonylacetone
and ammonia reacted to form the dimethylpyrrole (59% yield)
and the related pyrrolidine (28% yield). 1
CH3COCH2CH2COCH3+NH3 ^n H 3 C[p c H 3 and J H ^
N N
H H
Acetylacetone, by contrast, furnished acetamide in quantitative yield.
From Ammonia and Aromatic Aldehydes. The reduction of a mixture
of two moles of an aromatic aldehyde and one of ammonia provides
an excellent route to diaralkylamines. Thus, over a nickel catalyst
benzaldehyde yields 81% of the secondary amine with only 12-17% of
the primary amine. 10,21 Similar results are obtained with o-tolualdehyde
and even with o-chlorobenzaldehyde (85% of secondary amine and 4%
of primary amine). From furfural a 66% yield of difurfurylamine has
been obtained. A comparison of various preparations of dibenzylamine,
shown in Table III, p. 204, indicates the value of the method.
The aromatic aldehydes which have been converted to secondary
amines by this process are listed in Table X.
From Primary Amines and Carbonyl Compounds. As mentioned
previously, the reactions which occur in reductive alkylations of primary
amines are of the type shown on p. 182. Whether or not the reduction
will involve the addition product or the SchifPs base will depend upon
the relative rates of the reactions. Probably in most instances it is
the SchifPs base which is reduced; even though the equilibria may be
so unfavorable that the Schiff's base cannot be isolated, removal of this
17 Grigorovskii, Berkov, Gorlad, Margolina, and Levitskaya, Org. Chem. Ind.t 7, 671
(1940) [C. A., 35, 5094 (1941)].
18 Skita, Keil, and Havemann, Ber., 66, 1400 (1933).
19 Christ, Ger. pat. 671,839 [C. A., 33, 6340 (1939)].
20 Skita and Keil, Ber., 61, 1452 (1928).
21 Winans, U. S. pat. 2,217,630 [C. A., 35, 1065 (1941)].