04-27-04 10:22
No 503336
Somebody recently told me that they heard someone did a solventless PTC isomerization of an allylbenzene to see whether it would work and the result was a great success.
Apparently this person had 330g of what was claimed to be 90%+ dillapiole. They put this in a 1L flask with 12g of Aliquat 336 and 20g of KOH pellets. The flask was mechanically stirred (quite hard), heated on an oil bath and held at 80-90C for 30 minutes.
A column, still head, condenser etc. were then attached to the flask in order to fractionally vacuum distill the product. Unfortunately this proved impossible as it was not possible to get the flask hot enough to drive the first fraction out the top of the insulated column. Trouble was that the PTC was making the reaction flask too foamy. Accordingly, a regular distillation was performed in order to remove dillapiole and iso-dillapiole from the PTC.
The mixture of dillapiole and isodillapiole collected weighed 300g (guess that claim on purity was more than right). After standing overnight, the distillate solidified into a white mass of crystals (isodillapiole). The crystals were slightly wet however (assumed to be dillapiole), so the product was fractionally distilled, the first ~20ml of distillate being saved for recycling. The second fraction comprised 270g of a water-white and extremely clear oil. We will see how it crystallizes.
This seems like a fantastic way to do an isomerization, as there is no need to remove the water in the KOH and the reaction is extremely quick. It seems to be cleaner than the standard isomerization procedure.
One question remains however, and that is whether the reaction is complete in half an hour or whether it takes an hour and a half (trying to get the first fractional distillation working took 1hr before giving up). Apparently the reaction smelt strongly of isodillapiole after half an hour.
