Weygand/Hilgetag Preparative Organic Chemistry

Addition of hydrogen to C=C bonds and aromatic systems 23
Formation of the alloy is accompanied by evolution of much heat. Because
of the increase in temperature higher-melting alloys can often be obtained
with a greater content of active metal. In the presence of atmospheric oxygen
an aluminothermic reaction may lead to a further rise in temperature. Care
is therefore necessary! The melt can be protected against attack by atmospheric
oxygen by covering it with a layer of salt or by means of an inert
gas.
Alloys ready for use can now be obtained commercially.
After decomposition of the aluminum alloys there is still residual aluminum
in the metal, and this residue seems to be in part responsible for the activity of
the catalyst. If this residue is largely removed by continued extraction, the
catalyst becomes inactive. 157 Alloys containing more than 75% of nickel are
only partly attacked by aqueous sodium hydroxide, or are not attacked at all;
then decomposition has to be undertaken with very concentrated sodium
hydroxide solution or by adding solid sodium hydroxide to the molten mass. 158
Alloys containing between 30% and 50% of active metal are most suitable for
preparation of active metal catalysts.
The activity of Raney nickel can be increased by means of activators, for
which purpose noble metals in the form of their chlorides, chloro acids, or
salts of chloro acids are added after decomposition of the alloy or during the
washing process. 159
To increase the activity, Paul 160 added chromium, molybdenum, or cobalt
in amounts of 3-10% (calculated on the amount of nickel) during preparation
of the alloy. Hydrogenation in the presence of alkali or of organic bases is
stated to effect a still further increase in activity.
The efficiency of a Raney nickel catalyst for hydrogenation of carbonyl
groups is much diminished if the catalyst is treated with 0.1% acetic acid or
an amino acid, particularly dibasic amino acids or L-phenylalanine; but the
efficiency for hydrogenation of C=C double bonds remains unaffected. Thus
mesityl oxide was hydrogenated to isobutyl methyl ketone selectively and in
good yield; but cinnamaldehyde could not be reduced in this way. 161 For
asymmetric hydrogenation with Raney nickel modified by optically active
2-hydroxy carboxylic acids see Tatsumi et al. 162
Raney cobalt, 163 iron, 164 and copper catalysts 164 can be prepared in precisely
analogous manner. They are, however, not so versatile in their application
as Raney nickel.
157 J. Aubry, Bull. Soc. Chim. France, [v], 5, 1333 (1938).
158 Brit. Pat. 282,112 (1927) (I. G. Farbenindustrie); Chem. Abstr., 22, 3625 (1928).
159 M.Delepine and A. Horeau, Bull. Soc. Chim. France, [v], 4, 31 (1937); E. Lieber,
J. Amer. Chem. Soc, 72, 1190 (1950).
160 R. Paul, Bull Soc. Chim. France, [v], 13, 208 (1946); see also J. Ishikawa, /. Chem.
Soc. Japan, Pure Chem. Sect. [Nippon Kagaku Zasshi], 81, 1179 (1960) (cited from Chem.
Zentralbl, 1963, 19,566).
161 H. Fukawa, Y. Izumi, S. Komatsu, and S. Akabori, Bull. Chem. Soc. Japan, 35,
1703 (1962) (cited from Chem. Zentralbl, 1964, 16-0821).
162 S. Tatsumi, M. Imaida, Y. Fukuda, Y. Izumi, and S. Akabori, Bull Chem. Soc. Japan,
37, 846 (1964) (cited from Chem. Zentralbl, 1966, 19-0820).
163 U.S. Pat. 2,166,183 (1938); Chem. Abstr., 33, 8219 (1939); see also Brit. Pat. 628,407
(1949); Chem. Abstr., 44, 2675e (1950).
164 L. Faucounau, Bull. Soc. Chim. France, [v], 4, 58 (1937).