R e c e i v e d on M a y 2 3 , 1973 1
The preparation of 2,2,6,6-tetradeuteriocyclohexanone is reported using a 10 % DCI-D PO exchange solution, generated from PC15 and D20. Another p r ~c e d u r e ~~u s : ~ a K CO -0 0 exchange solution,which results in a significant amount of base-catalyzed aldol condensation. An alternate acidcatalyzed procedure for the preparation of 2,2,6,6-tetradeuteriocyclohexanone is reported here, utilizing a k-toluenesulfonic acid-cJ-DCI exchange solution, generated from p -toluenesulfonyl chloride (TsCI) and D20. TsCI is less hygroscopic than PC15, and can lead to an exchange medium of greater isotopic (deuterium) purity. Thus, 1 gram of cyclohexanone i s treated twice for 24 hr periods with 1 gram of TsCI and 20 ml of D20 at reflux under an inert atmosphere. Short-path distillation of the concentrated pentane extract affords 2,2,6,6-tetradeuteriocyclohexanone, which shows 96%-$ and 4% -c13 by mass spectral analysis. Since TsCI does not hydrolize very quickly in water at 25" and p-toluenesulfonic acid is very water-soluble, the TsCI can be washed before use with D20. This will lead to an exchange medium of even greater isotopic purity. The use of TsCI to generate acid-catalyzed exchange solutions should prove to be generally useful because of its advantages over other reagents.