Organic Reactions Volume 4 - Sciencemadness Dot Org

ROSENMUND REDUCTION 367
The Hydrogen. Commercial electrolytic hydrogen directly from the
cylinder is most satisfactory. When it is necessary to remove traces of
oxygen, as in the preparation of heterocyclic aldehydes, the hydrogen is
passed over a hot copper spiral 12 ' 31 ' 60,61 and dried. Drying has been
accomplished by passing the hydrogen over Dehydrite 62 or Drierite. 14
The Solvent. The solvents which have been used most frequently
are xylene and toluene. To a lesser extent benzene, tetralin, and decalin
have been employed. The use of other hydrocarbons and of ethers has
been reported. 1,63 Although aromatic hydrocarbons of commercial
grade have often been used for the Rosenmund reduction, it is preferable
to use highly purified solvents (with a known amount of regulator where
necessary) so that the preparation of a given aldehyde is reproducible.
The purification of the solvent has been generally accomplished by
distillation over sodium. Impurities containing sulfur can be destroyed
by distillation of the solvent from Raney nickel catalyst. 64 ' 65
The solvent in the Rosenmund reduction is used in amounts of three
to six times the weight of the acid chloride.
The Catalyst. As catalyst, palladium on barium sulfate is commonly
used, ordinarily with a palladium content of 5%, occasionally of 2-3%.
Generally, 1 part of the catalyst is used for 5-10 parts of acid chloride.
Other carriers, as kieselguhr, 2 - 61 charcoal, 25 ' 61 and calcium carbonate, 28
have been reported. Other metals, such as osmium, 25 platinum, 9 ' 36 ' 37
and nickel, 1 ' 86 ' 37 * 66 ' 67 have been used.
The Regulator. The poison most commonly used is the crude prepa­
ration of thioquinanthrene, called ^quinoline-sulfur^ or "quinoline~S.
Whenever the necessity of a regulator is indicated, it is advisable, for
the sake of reproducibility, to use freshly prepared a quinoline~S" 10,33
or pure thioquinanthrene % 33 (for preparation and structure, see Edinger
and associates 68 ~ 72 ) or other pure sulfur-containing compounds. 2 Of the
latter thiourea has been recommended. 9 The amount of regulator reported
varies widely. About 10 mg. of "quinoline-S" per gram of
catalyst will usually be found satisfactory. 14
60 Rojahn and Trieloff, Ann., 445, 296 (1925).
61 Rojahn and Seitz, Ann., 437, 297 (1924).
62 Mosettig and van de Kamp, J. Am. Chem. Soc, 55, 2995 (1933).
63 Zetzsehe, Enderlin, Flutsch, and Menzi, HeIv. CHm. Acta, 9, 177 (1926).
64 Mozingo, Wolf, Harris, and Folkers, J. Am. Chem. Soc, 65, 1013 (1943).
65 Adkins, Reactions of Hydrogen, University of Wisconsin Press, p. 28, 1937.
66 Schlfewienski, Z. angew. Chem., 35, 483 (1922).
67 Rosenmund, Z. angew. Chem., 35, 483 (1922).
68 Edinger, Ber., 33, 3769 (1900).
69 Edinger and Lubberger, /. prakt. Chem., [2] 54, 340 (1896).
70 Edinger, /. prakt. Chem., [2] 56, 273 (1897).
71 Edinger and Ekeley, Ber., 35, 96 (1902).
72 Edinger and Ekeley, /. prakt. Chem., [2] 66, 209 (1902).
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