Uemura, Chromic and perhaps some other unknown bees studied the thermal re-arrangment of epoxides to the corresponding ketones.
This little write-up publishes some results on an epoxide re-arrangement for the anethol epoxide. The epoxide was produced in accordance with Uemura's description now also to bee found on Rhod's site (see
https://www.thevespiary.org/rhodium/Rhodium/chemistry/epoxide.html
) Two minor modifications with respect to this procedure has been performed:
1) Stirring time was only 16 hrs at a rt around 18DegC
2) Evap of the MeOH/MeCN mix has been performed under moderate vacuum (approx 200Torr) in a waterbath at 40-45DegC.
From 30 ml anethole in 300ml 1:1 mix of MeOH/MeCN with the proper 1.1 molar amount of H2O2 (30%) and 3g sodiumcarbonate (Na2CO3) stirred at rt (18DegC) for 16hrs 28,3g crude epoxide has been received. The MeOH/MeCN mix has been destilled off under reduced pressure, work-up as described. This time the crude epoxide is clear with almost no color.
Rearrangement The crude! epoxide was loaded together with some boiling stones in a 250ml flask equipped with a small Liebig condensor. The flask is heated by means of an electric mantel. At 260DegC (760Torr adjusted) the epoxide starts to boil (measured inside the liquid). Some 'spurious explosions' caused by the bumping stones or epoxide happened without getting out of control. The reflux is continued for 90min, the inside temperature stayed at 263DegC.
After cooling down a normal pressure destillation setup was performed. The flask was heated again and between 255 and 275Degc (*) 19g of a clear yellow-green oil came over. Then the temperature dropped down, a red-brown liquid remained in the destillation flask (Temp liquid > 283DegC). This is a yield of 19g ketone from 30ml olefine, approx. 57% yield which isn't really good but isn't bad either. (**).
A bisulfite test with 1ml of the received destillate worked like a super-duper-easy confirmation, no oily precipitae, after 20sec shaking pure bisulfite compound (light yellow in white gel) appeared.
Discussion This rearrangement test confirms the applicability of the thermal rearrangment reaction! The time of reflux may be reduced but Uemura wanted to make sure all epoxide got converted (Chromic noted some epoxides has been found after too short reflux time. Uemura also found some oily precipitate in the bisulfite for the 'just-only' destilled epoxide. Together with the quick asarone epoxide rearrangement test, it should bee proven, that the epoxidation-thermal rearrangemenbt route is a practical route to get the valuable ketones. Bees, if you have safrol around, please verify and post the results.
(*) Adjusted 760Torr.
(**) Say you get 70% pure epoxide from the olefine and 80% ketone from pure epoxide then you have a total yield of 56%. This would fit fine. For asarone Uemura would still prefer to purify the crude epoxide even when the new run gave only a yellow, not orange-red crude epoxide.
Carpe Diem