Organic Reactions Volume 4 - Sciencemadness Dot Org

318 OEGANIC REACTIONS
CH3 Na2o2o7> H3Cj r „ (5o%)
H2SO4
HgC
Na2207
-» No qumone
H2SO4
When a p-dialkylbenzene is nitrated as the first step in a quinone
synthesis the mixture of nitro compounds need not be separated, for
the mixture of amines obtained by reduction can be oxidized to give a
single quinone. This procedure followed by dichromate oxidation
furnishes 5-nonyltoluquinone in 17% yield and 5-hendecyltoluquinone
in 22% yield. 77
Manganese dioxide is a very useful and convenient reagent for oxidation
of simple amines as well as other types of compounds, and it is
sometimes preferred even where other methods give somewhat better
yields. When a mixture of the amine, manganese dioxide, and dilute
sulfuric acid is steam-distilled the quinone usually separates (or is
extractable) from the distillate in the pure state. This method has been
used for preparing 2-bromo-5~chloroquinone from 2-chloro~5-bromoaniline,
78 ' 79 and it is stated that the results are much better than those
of dichromate oxidation. Manganese dioxide is preferred for oxidation
of o-toluidine to toluquinone (48% yield), and detailed directions for
this preparation have been reported. 80 When 2,4,5-trimethylaniline is
oxidized with manganese dioxide the 4-methyl group is eliminated and
p-xyloquinone is formed in 35% yield. 81
Oxidation of Aminophenols and Diamines. Alkyl- and aryl-quinones
usually are prepared from amines or phenols having favorable substituents
in the para positions, and various methods for introducing these
substituents have been developed. Perhaps the most successful is the
coupling procedure perfected 82 in the naphthalene series and extensively
employed 76,83> 84,85 in the benzene series. This method has been de-
77 Hasan and Stedman, J. Chem. Soc, 1931, 2112.
78 Nef, Am. Chem. J.f 13, 422 (1891).
79 Clark, Am. Chem. J., 14, 553 (1892).
80 Fieser, Experiments in Organic Chemistry, 2nd ed., Boston, Heath, 1941, p. 228.
81 Heymann and Koenigs, Ber., 20, 2395 (1887).
82 Fieser, Org. Syntheses, 17, 9, 68 (1937).
83 Smith, Hoehn, and Whitney, J. Am. Chem. SoC1 62, 1863 (1940).
84 Smith and Opie, J. Org. Chem., 6, 427 (1941).
85 Smith and Austin, J. Am. Chem. Soc., 64, 528 (1942).