Organic Reactions Volume 4 - Sciencemadness Dot Org

340 ORGANIC REACTIONS
an even better agent for this oxidation. The oxidation of chromans by
use of eerie sulfate in aqueous ethanol 256 may be adapted to volumetric
determination. A study has been made of the various types of quinones
obtainable by oxidation of chromans and coumarans/ 62 - 240a and of the
behavior of these compounds at the dropping mercury electrode. 256 *
The various methods of preparing a-tocopherylquinone have been critically
reviewed. 267
Ethoxy- and methoxyquinones may be prepared by oxidation of the
appropriate polyalkoxy compounds. Nitric acid in ethanol 50 ' 258 or
acetic acid 259,260 has proved useful, although there is some nitration of
OCH;
CH8O^ ^1OCH3 to] CIl3Of ^j)OCH8
"* I' Il + Nitration products
the starting material. The triethyl ether of pyrogallol is much more
resistant to oxidation and more susceptible of nitration than the trimethyl
ether, 259 The yields of the 2,6-dialkoxyquinones are, respectively,
16 and 64%. Pyrogallol trimethyl ether has been oxidized
electrolytically in 24-30% yield. 14
2,6-Dialkoxyquinones may also be obtained in 20-39% yield by
oxidation of ethers of phloroglucinol with chromic anhydride in acetic
acid. 261 Chromic anhydride or sodium dichromate in acetic acid at 100°
also has been used for the preparation of 2-methoxy~6-alkylquinones from
the appropriate l,3~dimcthoxy-5-alkylbenzenes. 262 - 265 Alkyl groups from
methyl to tetradecyl are included in the series. Unfortunately, no
yields are given.
Several 5-substituted-l,2,4-trimethoxybenzenes have been oxidized to
5-substituted~2~methoxyquinones in unspecified yields by use of nitric
acid in acetic acid at O 0 . 266 3,6-Dibromo-l,2,4-trimethoxybenzene is
256 Smith, Ruoff, and Wawzonek, J. Org. Chem., 6, 236 (1941).
ma Smith, Kolthoff, Wawzonek, and Ruoff, J. Am. Chem. Soc, 63, 1018 (1941).
267 Tishler and Wondlor, /. Am. Chem. Soc, 63, 1532 (1941).
^Graebe and Hess, Ann., 340, 232 (1905).
^Pollak and Goldstein, Monatsh., 29, 135 (1908).
260 Majima and Okazaki, Ber., 49, 1489 (1916).
261 Spath and Wesseley, Monatsh., 49, 229 (1928).
262 Fuzikawa, Ber., 68, 72 (1935).
263 Asahina, Miyasaka, and Sekizawa, Ber., 69, 1643 (1936).
264 Asano and Yamaguti, J. Pharm. Soc. Japan, 60, 105 (1940).
265 Asano and Yamaguti, /. Pharm, Soc. Japan, 60, 585 (1940).
266 Szeki, Ber., 62, 1373 (1929).