Organic Reactions Volume 4 - Sciencemadness Dot Org

314 OEGANIC REACTIONS
quinones is not due solely to the highly substituted ring, for tetramethylo-quinone
is especially unstable. 40
The only preparations of amino-o-quinones reported are oxidations
by air in ammoniacal solution. 46 - 47>48 These compounds doubtless exist
in equilibrium with the hydroxyquinonimines.
A method generally applicable for the preparation of catechols is the
oxidation of o-hydroxybenzaldehydes with alkaline hydrogen peroxide.
This procedure 49 usually gives satisfactory yields unless the aldehydo
group is hindered by a large ortho substituent. The method is also
O2Nr^NCHO H2O2 O2Nr^NOH
k^JoH > VJOH
(70%)
moderately successful for oxidation of p-acetophenols 18 ' 49 > 60 to the corresponding
hydroquinones.
Experimental Procedure
4~o-Toluquinone. 39 ' 6x An aqueous solution of 17 g. of silver nitrate
is made slightly alkaline with sodium hydroxide. The precipitated silver
oxide 42 - 52 is washed twelve times with water, six times with acetone, and
six times with anhydrous ether, then covered with 100 ml. of anhydrous
ether. After addition of 15 g. of anhydrous sodium sulfate and a solution
of 3 g. of 4-methylcatechol 61 in 80 ml. of anhydrous ether the mixture
is shaken for three to four minutes. The precipitate is removed by
filtration from the red solution, and the filtrate is cooled in an ice-salt
mixture. One gram of dark-red prisms and blades separate; they are
collected and washed with dry ether. The filtrate and washings, on
concentration in vacuum, yield an additional gram of quinone (total
yield, 68%). 4-o-Toluquinone melts with decomposition, and the melting
point has been variously reported in the range 75-84°.
46 Kehrmaim and Prunier, HeIv. CHm. Acta, 7, 987 (1924).
47 Hoehn, BeIv. CHm. Acta, 8, 275 (1925).
48 Kehrmaim and Poehl, HeIv. CHm. Acta, 9, 485 (1926).
49 Daldn, Am. CUm. J., 42, 477 (1909).
50 Baker, J. Chem. Soc, 1941, 665.
51 Kvames, J. Am. Chem. Soc, 56, 2487 (1934).
52 Busch, Clark, Genung, Schroeder, and Evans, J. Org. Chem., 1, 2 (1936).