Organic Syntheses, CV 1, 462
Submitted by G. A. Hill and E. W. Flosdorf.
Checked by C. S. Marvel and A. E. Gray.
1. Procedure
In a
2-l. round-bottomed flask, fitted with a
stopper carrying a
dropping funnel and a connection to a
condenser set for distillation, are placed
750 g. of 6 N sulfuric acid (Note
1) and
250 g. of pinacol hydrate (Note
2). The mixture is then distilled until the upper layer of distillate ceases to increase in volume (Note
3). This requires about fifteen to twenty minutes. The
pinacolone layer in the distillate is separated from the water and the water is returned to the reaction flask. First,
60 cc. of concentrated sulfuric acid is added to the water, and then a second
250-g. portion of pinacol hydrate. The distillation is repeated. This process is repeated twice more until
1 kg. (4.42 moles) of pinacol hydrate has been used (Note
4).
The combined
pinacolone fraction is dried over
calcium chloride, filtered, and fractionally distilled. There is first a small low-boiling portion; then the
pinacolone comes over at
103–107°; and finally there is a higher-boiling portion which yields more
pinacolone on redistillation. The yield from a run, as described, is
287–318 g. (
65–72 per cent of the theoretical amount). This product occasionally turns slightly yellow on standing, but redistillation removes the color with almost no loss of product.
2. Notes
1.
Phosphoric acid (50 per cent) or hydrated
oxalic acid may be used to bring about this rearrangement. When these reagents are used, the reaction mixture should be boiled for three to four hours. A yield of
pinacolone corresponding to
60–65 per cent of the theoretical amount is thus obtained.
3. An oily layer always remains behind in the distilling flask.
4. Larger or smaller runs of
pinacolone may be made without materially affecting the yield.
3. Discussion
This preparation is referenced from:
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