Organic Reactions Volume 4 - Sciencemadness Dot Org

190 ORGANIC REACTIONS
From Schiff's Bases Derived from Aliphatic Amines. The isolation
and reduction of purely aliphatic SchifFs bases containing from five to
ten carbon atoms has been accomplished, but such bases are unstable
and their isolation is difficult. They have been prepared in yields of
50-80%, and they have given the secondary amines in yields of 40-65%
by catalytic reduction. 55 Schiff's bases derived from aldehydes having
a-methylene groups undergo condensations of the aldol type on being
heated. 66,57 - 58 Because of the occurrence of such condensations higher-
2RCH2CH=NR' -» RZNH2 + RCH2CH=CCH=NR' -4
I
R
RCH2CH2CHCH2NHR'
I
R
boiling amines may be expected as by-products from the reduction of
the Schiff's bases, particularly if vigorous conditions are used in the
preparation or isolation of the intermediates. 68
Unsaturated SchifFs bases of the type produced by the condensation
just described can be prepared also from ^-unsaturated aldehydes and
amines. Many of them have been reduced to the corresponding saturated
amines. Platinum catalyst has been used most frequently, and
the yields generally have been above 50%.
The SchifFs bases from simple aliphatic amines and benzaldehyde are
more readily prepared, and they are reduced to alkylbenzylamines in
70-100% yields by hydrogenation over nickel or platinum catalyst. A
number of amines of the general type ArCH2CH2NHAr' have been
obtained in excellent yields by hydrogenation over nickel or platinum
catalysts of the Schiff's bases prepared from substituted phenylethylamines,
including some with substituents in the side chain, and substituted
benzaldehydes (see Table X). Similar secondary amines have
been prepared from substituted benzylamines.
Schiff's bases derived from aliphatic ketones are not common intermediates.
Those derived from diisobutyl ketone and l-amino-2-propanol,
2-amino-l-propanol, 3-amino-l-propanol, and 2-amino-l-butanol
have given high yields (83-93%) of the corresponding secondary
amines by reduction over platinum catalysts. 59 ' 60,61 A few derived from
55 Campbell, Sommers, and Campbell, J. Am. Chem. Soc, 66, 82 (1944).
68 Kharasch, Richlin, and Mayo, J". Am. Chem. Soc, 62, 494 (1940).
57 Emerson, Hess, and UhIe, J. Am. Chem. Soc, 63, 872 (1941).
58 Skita and Pfeil, Ann., 485, 152 (1931).
59 Cope and Hancock, J Am. Chem. Soc, 66, 1453 (1944).
60 Hancock and Cope, J. Am. Chem. Soc, 66, 1738 (1944).
61 Hancock, Hardy, Heyl, Wright, and Cope, J. Am. Chem. Soc, 66, 1747 (1944).