In a
2-l. round-bottomed flask equipped with a
mechanical stirrer are placed
1 l. of 2 per cent sulfuric acid,
0.5 g. of vanadium pentoxide (Note
1),
110 g. (1 mole) of hydroquinone, and
60 g. (0.56 mole) of sodium chlorate. The mixture is vigorously stirred for about three hours, when the green
quinhydrone first formed is converted to yellow
quinone. The temperature of the reaction mixture rises to about 40° (Note
2). The reaction is usually complete in three and one-half to four hours. The flask is then disconnected and cooled under the tap, the mixture is filtered with suction, and the
quinone is washed once with about 100 cc. of cold water. After drying in a
desiccator over
calcium chloride, the product weighs
86–90 g. and melts at
110–112°. This material is pure enough for most purposes. Extraction of the filtrate and washings with four
100-cc. portions of benzene yields a further
12–14 g. of
quinone and brings the total amount to
99–104 g. (
92–96 per cent of the theoretical yield) (Note
3).