Organic Reactions Volume 4 - Sciencemadness Dot Org

368 ORGANIC REACTIONS
General Precautions. The apparatus employed in the reduction must
be carefully dried. Catalyst and solvent too must be free from water.
When one of the lower-boiling hydrocarbon solvents is used, it is convenient
to exclude moisture completely by placing the solvent, catalyst,
and regulator in the reduction apparatus and distilling part of the
solvent. The reflux condenser jacket is left empty, and, while a slow
stream of hydrogen is passed through the stirred catalyst suspension,
the solvent is heated to boiling and some solvent allowed to distil
through the condenser. This fraction of solvent, which may be condensed
by an auxiliary condenser, carries with it any water present.
Heating is then interrupted, the circulation of water through the condenser
is started carefully, and the acid chloride is added.
The apparatus used in the Rosenmund reduction should be as nearly
all glass as possible. A Kyrides stirrer seal n made with Neoprene tubing
is convenient. When mercury-sealed stirrers are used, mercury must
not be allowed to splash into the reaction mixture. A Hershberg stirrer
made with tantalum wire u is preferable to a glass stirrer, as it is much
less likely to break during the rapid stirring which is necessary.
EXPERIMENTAL PROCEDURES
Excellent directions for the Rosenmund reduction under the usual
conditions are those of Hershberg and Cason for /3-naphthaldehyde,
published in Organic Syntheses; u these are complete, detailed, and involve
the use of the poison. Directions are given also for the preparation
of an aldehyde (2,4,6-trimethylbenzaldehyde) without the use of
the poison. 34
Preparation of the Regulator (Quinolme-Sulfur 14 ). Six grams of
freshly distilled quinoline and 1 g. of sulfur are heated under reflux for
five hours. After cooling, the mixture is diluted to 70 ml. with xylene
to permit convenient measurement of an aliquot containing the desired
amount of the regulator. This solution, which contains 0.1 g. of the
regulator per milliliter, may be diluted to larger volumes if small quantities
of the regulator are desired.
Preparation of Palladium-Barium Sulfate. 74 ' 75,76a A suspension of 1.7
g. of dry palladium chloride in 100 ml. of water containing 1 ml. of concentrated
hydrochloric acid is heated on a steam bath or is allowed to
stand (several days) until a clear, dark red solution is obtained. A
73
Wayne and Adkins, Org. Syntheses, 21, 39 (1941).
74
Schmidt, Ber.y 52, 409 (1919).
75
Mozingo, Harris, Wolf, Hoffhine, Easton, and Folkers, J. Am. Chem. Soc, 67, 2092
(1945).
75a
Mozingo, Org. Syntheses, 26, 77 (1946.)