Organic Syntheses, Coll. Vol. 3, p.685 (1955); Vol. 26, p.77 (1946).
A. Palladium on barium sulfate catalyst (5% Pd)
. A solution (Note 2)
of 8.2 g. of palladium chloride (0.046 mole)
in 20 ml. (0.24 mole) of concentrated hydrochloric acid
and 50 ml. of water is prepared. To a rapidly stirred, hot (80°) solution of 126.2 g. (0.4 mole) of reagent barium hydroxide octahydrate
in 1.2 l. of distilled water contained in a 4-l. beaker (Note 3)
and (Note 4)
is added all at once 120 ml. (0.36 mole) of 6 N sulfuric acid
. More 6 N sulfuric acid
is added to make the suspension just acid to litmus (Note 5)
. To this hot barium sulfate
suspension (Note 6)
are added the palladium
solution and 8 ml. (0.1 mole) of 37% formaldehyde
solution. The suspension is then made slightly alkaline to litmus with 30% sodium hydroxide
solution, constant stirring being maintained. The suspension is stirred 5 minutes longer, and then the catalyst is allowed to settle (Note 7)
. The clear supernatant liquid is decanted and replaced by water, and the catalyst is resuspended. The catalyst is washed by decantation eight to ten times. After the final decantation, the catalyst is collected on a 90-mm. medium-porosity sintered-glass funnel (Note 8)
. Most of the water is removed from the cake, but not enough to cause the cake to break or channel. The filter cake is washed with 250 ml. of water in five portions, the last being removed as completely as possible by filtration. The funnel and its contents are then placed in an oven
at 80° until the catalyst is dry. The catalyst (93–98 g.
) is powdered and stored in a tightly closed bottle (Note 9)
C. Palladium chloride on carbon (5% Pd)
. A solution of 8.2 g. (0.046 mole) of palladium chloride in 20 ml. (0.24 mole) of concentrated hydrochloric acid
and 50 ml. of water is prepared (Note 2)
. The solution is diluted with 140 ml. of water and poured over 92 g. of nitric acid-washed Darco G-60 (Note 10)
in an 8-in. evaporating dish (Note 3)
. After the palladium chloride
solution has been thoroughly mixed with the carbon
, the whole mixture is dried, first on a steam bath
and then in an oven at 100°, with occasional mixing until completely dry. The mass (98–100 g.
) is powdered and stored in a closed bottle.
The required quantity of palladium chloride
is transferred to a hydrogenation bottle and reduced with hydrogen
in the solvent to be used for the hydrogenation (Note 12)
and (Note 13)
. When no more hydrogen
is absorbed by the catalyst, it is collected (Note 14)
on a sintered-glass funnel and washed with more of the solvent to remove the hydrogen chloride
, and then returned to the reduction bottle, the last being washed in with the solvent. The material to be hydrogenated is then added and the hydrogenation is completed in the usual way.
The four procedures given for the preparation of palladium
catalysts differ in that in A the support is barium sulfate
or barium carbonate
whereas in the others the support is carbon
. In procedures A and B, alkaline formaldehyde
is the reducing agent; in C and D, hydrogen
is used. The catalysts A, B, and D are prepared and stored until required with the palladium
in the reduced form ready for use. In C,1
the palladium salt is reduced to the metal as needed, so that there is no loss of activity during storage. Catalyst A is similar to that usually recommended for Rosenmund reductions; D is essentially that developed by Hartung2
and extensively used by Cope3
and others. Catalyst D carries twice as much palladium
per unit weight as the others.
Catalysts reduced with formaldehyde
carry no adsorbed hydrogen
and are less pyrophoric. Barium carbonate
as a support may sometimes be advantageous in that the neutrality of the hydrogenation mixture may be maintained. Barium sulfate
or barium carbonate
may be a better support than carbon
, which may, in some instances, so strongly adsorb the derived product that recovery is difficult or incomplete. Palladium
may be more completely and easily recovered from a spent catalyst where carbon
rather than barium sulfate
is the support. In general, the submitter prefers a catalyst prepared according to procedure C.
Since palladium chloride
dissolves rather slowly in aqueous acid, the mixture is heated on a steam bath for about 2 hours, or until solution is complete. If the dihydrate of palladium chloride
is used the quantity should be increased to 9.9–10.0 g.
The entire preparation is carried out with all-glass or porcelain equipment in order to prevent contamination with iron
or other metals.
The catalyst may be prepared in ten times the amount given here, with a 20-l. battery jar
in place of the beaker.
A Büchner funnel may be used, but filtration through paper is very slow. The washing process may be carried out by centrifugation instead of filtration.
may be conveniently separated from the barium sulfate
by solution in aqua regia. The used catalyst is collected from the reaction mixture on a sintered-glass funnel. The organic material is removed with suitable solvents, and the solvents are replaced by water. The palladium
is dissolved in aqua regia and is washed out with dilute hydrochloric acid
, the solutions being collected for recovery of the metal. For recovery of the palladium
, the mass is ignited and the ash is extracted with aqua regia for several hours. The palladium
solution is filtered, and any residue is reignited and then treated with alkaline formaldehyde
solution to reduce any oxides of palladium
which may have been formed, and which are only slowly soluble in aqua regia. The solids are collected on a filter, and the palladium
is extracted with aqua regia.
, Darco, or other carbons may be used. The carbon
is heated on a steam bath with 10% nitric acid
for 2–3 hours, washed free of acid with water, and dried at 100–110° before use.
The solvent is conveniently that in which the hydrogenation is to be done. During the reduction of the palladium chloride
, a neutral solvent is to be preferred; any acid or alkali needed for the hydrogenation is added after reduction of the catalyst.
The presence of hydrogen chloride
during the hydrogenation of many organic compounds is desirable or without effect, so that the washing operations may be omitted in such cases. Thus, the palladium chloride
may be used in the same manner as the prereduced catalysts, i.e., simply added before reduction to the solvent and the hydrogen acceptor.
The catalyst should be kept wet with the solvent during the washing process, as it is pyrophoric.
The resulting solution is approximately equivalent to 50 ml. of the commercial palladium chloride
solution (p. 385)
suggested by Hartung and Cope.3
The checkers reduced the palladium chloride
, in three batches, in a 500-ml. bottle
. The bottle was not shaken, but the contents were rapidly stirred under a pressure of 1.1 atmospheres of hydrogen
. The reduction of each batch required about 5 hours.
catalysts have been prepared by fusion of palladium chloride
in sodium nitrate
to give palladium oxide
by reduction of palladium salts by alkaline formaldehyde6,7,8
or sodium formate
and by the reduction of palladium salts with hydrogen
The metal has been prepared in the form of palladium black
and in colloidal form in water containing a protective material,10
as well as upon supports. The supports commonly used are asbestos12 barium carbonate
,13 barium sulfate
,1,7,8,14 calcium carbonate
and strontium carbonate
The catalysts described here are prepared by modifications of the methods of Schmidt,8
Rosenmund and Langer,14
Mannich and Thiele,11
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