In a
1-l. round-bottomed flask provided with a
reflux condenser is placed a solution of
1 g. of iodine in
500 cc. of glacial acetic acid.
One hundred grams (0.27 mole) of benzopinacol (Note
1) is added, and the flask is heated over a
wire gauze, with shaking, until the solution boils gently. It is then refluxed for five minutes during which the solid
benzopinacol disappears completely and a clear red solution is obtained (Note
2). The solution is transferred at once to a
1-l. beaker, and, upon cooling, the
benzopinacolone separates in fine threads. The product is filtered with suction, washed with two or three
60-cc. portions of cold glacial acetic acid until colorless, and dried. The filtrate is reserved for subsequent preparations. The yield of practically pure
benzopinacolone melting at
178–179° is
90–91 g. (
95–96 per cent of the theoretical amount). If a purer product is desired the material may be dissolved in
450 cc. of hot benzene, filtered, and treated with
250 cc. of hot ligroin (b.p.
90–100°). After cooling in ice the
benzopinacolone is filtered and dried. The purified product weighs
82–83 g. and melts at
179–180°.
To the
acetic acid filtrate is added another
100-g. portion of benzopinacol and the reaction is carried out in the same way. The yield of
benzopinacolone in the second and subsequent runs is
94–94.5 g. (
98–99 per cent of the theoretical amount). This procedure can be repeated in the same filtrate until
500 g. of the pinacol has been rearranged.