Weygand/Hilgetag Preparative Organic Chemistry

316 Formation of carbon-oxygen bonds
The action of PdCl2 on olefins in aqueous solution provides a process for
the synthesis of ketones that is used both in the laboratory and in industry. 375
In accord with the equation:
R—CH=CH2 + PdCl2 + H2O > R—CO—CH3 + Pd + 2HC1
1-alkenes undergo nucleophilic attack by the reagent at the alkylated carbon
atom of the ethylenic group, so that methyl ketones are obtained, and yields
are usually in excess of 90%.
Reaction temperatures are between 20° and 70°. Within a homologous series
the rate of reaction decreases with increasing chain length: for instance, the
conversion of propene into acetone is 90% in 5 min, but of 1-decene is only
34% after 60 min; in this respect the solubility of the alkene in the aqueous
PdCl2 plays a role. 2-Alkenes also react to give methyl ketones, but more
slowly than the corresponding 1-alkenes.
Acetaldehyde is obtained from ethylene in excellent yield, and this is the
most attractive method of industrial synthesis since the metallic palladium
formed in the reaction can be regenerated by atmospheric oxygen.
b. Preparation of quinones
It is often possible to convert aromatic hydrocarbons directly into quinones.
According to a German patent 376 /?-benzoquinone is obtainable in 50-55%
yield by heating benzene with moist lead dioxide in 100% sulfuric acid at 56°
for 5 min, then pouring the mass on ice and extracting the quinone with chloroform;
this quinone can also be prepared by electrolytic oxidation of benzene,
in 65% yield. 377
Graebe and Liebermann 378 converted anthracene into anthraquinone by
oxidation with chromic acid in glacial acetic acid, although it is preferable 379
to use sodium chlorate and vanadium pentoxide as catalysts. However, anthraquinone
can also be prepared in good yield by use of potassium permanganate:
According to directions by Weygand, anthracene (2.5 g) is dissolved in warm acetic
anhydride (125 ml), treated gradually and cautiously at 80-90° with finely powdered potassium
permanganate (10 g). Oxidation is complete in 3-4 h. The mixture is cooled in ice and
filtered through a glass frit which retains the anthraquinone and potassium acetate whilst
the manganese dioxide passes in colloidal form through the filter. The material on the filter
is washed with acetic anhydride, and the sodium acetate is leached out with water. The residue
consists of anthraquinone (2.2 g, 78 %).
When melted with oxidizing agents such as nitrates, permanganates, or
chlorates, anthracene gives anthraquinone, in some cases in theoretical yield. 380
9,10-Phenanthraquinone is obtained in 80% yield by treating phenanthrene
with chromic-sulfuric acid, 381 and 2,3-dimethylnaphthalene gives 2,3-di-
375 J. Schmidt and co-workers, Angew. Chem., 71, 176 (1959); W. Hafner and co-workers,
Chem. Ber., 95, 1575 (1962).
376 Ger. Pat. 533,128; Chem. Abstr., 26, 480 (1932).
377 A. Seyewetz and G. Miodon, Bull. Soc. Chim. France, [iv], 33, 449 (1923).
378 C. Graebe and C. Liebermann, Ann. Chem. Pharm., 7, 284 (1870).
379 H. W. Underwood Jr. and W. L. Walsh, Org. Syn., Coll. Vol. 2, 554 (1943).
380 J. Sielisch, Ger. Pat. 568,784; Chem. Abstr., 27, 2698 (1933).
381 R. P. Linstead and P. Levine, /. Amer. Chem. Soc, 64, 2023 (1942).