Isomerization of phenylpropene was done using koh.
On another run koh and cao was used in addition.
There was no solvent used to help mix the pp with the koh or cao.
The phenylpropene was first heated to boiling, to drive off any moisture. It was said that moisture can ruin the reaction?
The addition of koh and/or koh/cao ocurred over the course of a couple minutes.
100gram phenylpropene, to 1.2 gram koh. In the other reaction Cao was said to be not crucial, and help suck up moisture, 10grams per 100gram was used
in this case.
Notes:
1. On the reaction with the koh/cao, the color stayed much lighter throughout reflux, than the koh only. koh only got dark red, almost black after
about 75% addition of koh..
2. There appears to be about 15% un reacted p.p. that hasnt been isomerized. This is shown in distillation fore-run of lower boiling point. This is
re-used.
How does this all sound?
Is KOH only a good method, or is the KOH/Cao method superior?
bbartlog - 17-11-2011 at 07:29
It sounds like you have the experimental data to answer your own question, possibly better than we could. CaO would certainly remove moisture, which I
expect could otherwise add across the double bond to form an alcohol. But yield would be a better guide than color changes - it doesn't take much by
way of condensation products to color something dark red.lancer3000 - 17-11-2011 at 19:40
Further notes:
1. Refluxing with koh only, and at atmospheric pressure, results in lots of polymerization/tar.
2. Refluxing under vacuum with koh only has less tar, although it is not known if conversion is as full.
3. Refluxing with cao and koh produced lots of residue to filter (while hot).
4. The koh method is nice, but if its true that koh and cao only need refluxing for 15min compared to 6 hours plus for koh only, this makes it much
quicker.
Sedit - 17-11-2011 at 20:12
You should really consider using an Alcohol solvent, its a base catalyses electron shift to the more stable isomerized form. The stronger the base the
faster and more complete the reaction proceeds. Since you are using CaO that will suck up any water formed and you will end up with a Potassium
alkoxide with a much higher PKA then KOH alone. lancer3000 - 17-11-2011 at 21:38
Hello Sedit.
Thanks for stopping in. I wasnt sure if I would get any help here, but greatly appreciated.
It has been noted that the koh method produces a much cleaner reaction, and less tar.
KOH only would be preferred, but I dont know when such a reaction is finished. It turns dark red/black upon 75% of addition, and stays dark. Color
is not an indicator. Odor seems to stay almost the same as well.
If isomerization occurs, this method is preferred:
1. per 100g oil, 1.2g koh added.
2. oil brought to boil before koh is added to drive off any moisture.
3. reflux under vacuum for 6 hours.
4. filtered off particles.
5. distilled iso oil.
almost time for an epoxidation. deciding on buffered or unbuffered...
Thanks!Sedit - 17-11-2011 at 23:16
Alcohol! The insitu alkoxide is where the magic is.
Make your Alkoxide before hand if you are worried that CaO is fouling things up. Use the CaO/Alcoholic KOH to push the equilibrium to the right so
that the water is removed and you are left with a Potassium Alkoxide solution after filtering out the insoluble CaOH. Its all about the strength of
the base used hence the reason NaOH will not effect isomerization. Its just not strong enough. Alkoxides are much stronger then KOH alone and to top
it off the excess alcohol will stop you from performing this neat which is one of the reasons you are having issues with tar formation.
And as far the epoxidation and what not is concerned.... lets just stick to the current chemistry at hand and not turn this into a cook book thread
please.lancer3000 - 18-11-2011 at 15:34
Your very right sedit.
When alcohol is mentioned, one would normally presume dcm, correct? Or can methanol be used as well?
When you form a alkoxide solution beforehand, is it koh and alcohol refluxed or simple mixed?
The patents I read show koh refluxed with oil. Thats it... This would surely raise conversions.
Sedit - 18-11-2011 at 15:43
DCM is not an alcohol what the hell are you talking about?
Dude, read more talk less I think I'm done here till you start to make sense.Nicodem - 18-11-2011 at 17:01
