Organic Reactions Volume 4 - Sciencemadness Dot Org

SYNTHESIS OF BENZOQUINONES BY OXIDATION 325
some instances. Oxidation of sulfanilic acids 148 ' 149 is only moderately
successful.
Experimental Procedures
Several detailed preparations have been described. These include
the preparation of p-benzoquinone by oxidation of hydroquinone with
sodium dichromate in sulfuric acid, 150 manganese dioxide in sulfuric
acid, 80 or sodium chlorate i$ the presence of vanadium pentoxide. 151
Toluquinone 80 is prepared by oxidation of o-toluidine with manganese
dioxide in sulfuric acid; thymoquinone 92 (2-isopropyl-5-methylquinone)
is prepared by nitrosation of thymol, reduction, and oxidation with
nitrous acid; duroquinone 100 ' 101 (tetramethylquinone) is prepared by
dinitration of durene, reduction, and oxidation with ferric chloride.
Trimethylqtxinone. 34 ' 76 A solution of 105 g. of sulfanilic acid in 500
ml. of water containing 26.5 g. of sodium carbonate is cooled to 15°,
and a solution of 37 g. of sodium nitrite in 100 ml. of water is added.
The mixture is poured immediately into 600 g. of ice and 106 ml. of concentrated
hydrochloric acid, then allowed to stand for twenty to thirty
minutes. The diazo solution is introduced slowly into a well-stirred
solution of 63 g. of pseudocumenol-6 (2,3,5-trimethylphenol) in 300 ml. of
water containing 75 g. of sodium hydroxide. An excess of alkali must
be present at this point. The mixture is allowed to stand at least two
hours (preferably overnight), during which period the ice melts and the
temperature rises to that of the room. After coupling is complete the
solution is made strongly acid with 200-250 ml. of concentrated hydrochloric
acid. Without removal of the red azo compound, 164 g. of
stannous chloride * in 200 ml. of concentrated hydrochloric acid is
added, and the mixture is heated almost to boiling until the precipitate
dissolves and the color becomes orange-brown. The mixture is transferred
to a steam-distillation flask, excess ferric sulfate (about 1400 g.
of the nonahydrate) is added, and the mixture is steam-distilled at once.
The product is removed from the distillate by ether extraction, which
must be continued until the aqueous layer is colorless, for this quinone
is fairly soluble in the large volume of water necessary for steam distillation.
The combined ether solution is dried over anhydrous sodium
sulfate, and the solvent is removed through a short packed column (to
prevent loss of quinone). The residue, which weighs 72 g. (95%), solidifies
in an ice bath and melts at 26°. Although this melting point is a
* In some preparations, reduction with sodium hydrosulfite is more satisfactory; see
ref. 33.
148 Hayduck, Ann., 172, 209 (1874).
149 Heinichen, Ann., 253, 285 (1889).
150 Vliet, Org. Syntheses, Coll. Vol. 1, 2nd ed., p. 482 (1941).
151 Underwood and Walsh, Org. Syntheses, 16, 73 (1936).