08-28-04 06:18
No 527946
This is going to be swims first buffered performic oxidation. He has been performing the regular performic method (due to lack of knowledge and DCM…and now feel like a looser for it).
Swim has a question which is probably quite obvious. Most methods swim has read of the buffered performic oxidation, the addition is not done with a slight reflux and the temperature is kept below 40c.
Rhodium wrote is ‘The Peracid Oxidation of Isosafrole: A Review’;
-“one hour in advance by mixing 220g (2.25 mol) 35% H2O2 and 290ml (350g, 6.45 mol) 85% HCOOH, was added dropwise to the isosafrole solution during 2h, causing the solution to evolve carbon dioxide and reflux slightly.”
Obviously Rhodium here isn’t really that concerned that the temp reached 40c. Should swim reflux or should the reaction be open?
Should the temp remain below 40c during the addition and therefore chill the performic to 0c?
I gather that HCI is now slightly proven to better a better acid than Sulfuric in the hydrolysis ?
Swims just trying to be thorough.
Thanks
(Hive Bee)
08-28-04 08:58
No 527967
The purpose of the dcm is that the solution wont ever go above 40 degrees. That way you minimize side reactions.
It will reflux.
I prepare my peracid by stirring on a cool water bater bath. 45 minutes is more then enough to let it sit. I am about to release a complete write-up and pictorial tomorrow for the buffered performic with pointers to color, etc.
And yes HCl hydrolysis is easy to do and you can get yields around 75-80% molar from iso.
(Stranger)
08-28-04 10:27
No 527976
the reaction will reflux slightly. be careful with dripping in the formic, the dripspeed should control the temperature in the flask. if dripped in too fast, everything will boil over and you will have to evacuate your lab.
(Hive Addict)
08-28-04 21:00
No 528060
I am about to release a complete write-up and pictorial tomorrow for the buffered performic
Excellent OC, ill be waiting to have a look.
-AC
Its just my opinion, but no-one listens to me anyway, and rightly so...
(Stranger)
08-28-04 22:17
No 528065
Wicked OC, can't wait for the latest proven buffered performic method.
I now know to use a condenser and allow it to slightly reflux but then should swim keep the temp (controlled with the drip rate) during the addition to approx 40c?
So no need to pre-chill other reagents (i.e to 0c) prior to the addition? Once the addition is complete temp will drop and this is not a concern...?
Thanks
(Hive Bee)
08-29-04 06:14
No 528112
No need to know what temp the solution is. The drip rate will control the reflux rate, so the faster you drip in the peracid, the harder it will reflux. Once the addition is complete, leave to stir with column on for 24 hours.
No extra heat, it will cool down not too long after the addition and will stay at room temp. So after the addition is done, leave water running in the column but dont add ice or change to cool water for nothing.
The write up Im about to release when I come back from work uses 300 grams iso in a 2L flask.
When addition complete, its quite full, but if you add the peracid over a couple of hours, its easy to control.
(Stranger)
08-29-04 20:34
No 528204
Thanks. I just wanted to iron out any uncertainty I had with this method before I started. I've learnt the hard way to many times, I need some ease at the moment...and this hopefully is going to be that. Can't wait.
I will try tomorrow. Thanks again
(arrogant bee of the day)
08-30-04 02:35
No 528235
Put the formic and H2O2 together shake for 5 secs and start addition.
No condenser necessary!
Addition can be completed in 1 hour.
Stir for 18 hours is fine. (probably less but not tested yet)
After Hcl hydrolosis, 80% by weight of iso, MDP2P.
I'm not fat, I'm just too short for my weight.
http://www.whatreallyhappened.com
(Quasiquerumodo)
08-30-04 02:53
No 528239
> After Hcl hydrolosis, 80% by weight of iso, MDP2P.
this is really not helpful if one works with non-MDP2P ketones. now i have
to compute how much molar yield that is to find out how good (or bad) that yield
really is.
ps: where do people get this silly precooling idea? this comes up every few months.
He always lied while on the earth and now he's lying in it
(Hive Bee)
08-30-04 04:32
No 528247
that I decided to keep the flask cool. My mag stirrer broke while forming the peracid. Never noticed it until i started addition, with the consequence of having the peracid boil and send formic acid everywehere. It was nasty believe me.
Since then, just to make sure, I like to prepare it cool. But the reaction is not really exothermic so you dont really need to do it. But it wont hurt.
As for peracid formation, its at its maximum about one hour after mixing the 2 solutions. This is why I say 30-45 minutes is plenty.
Placebo: I have to disagree with you here for the refuling column. I've run this numerous time and you definitely need a reflux column. If you add your peracid in one hour, its impossible it wont reflux. Unless you go at a very small scale???
I use 300 grams iso, and it takes 3 hours to add in the peracid to keep it under an acceptable reflux.
(Hive Addict)
08-30-04 19:24
No 528386
I have to disagree with you here for the refuling column. I've run this numerous time and you definitely need a reflux column. If you add your peracid in one hour, its impossible it wont reflux. Unless you go at a very small scale???
It depends on the size of the reaction. Using Placebo's advice would lead to a loss of some DCM into the atmosphere, so make sure there is good ventilation.
I use 300 grams iso, and it takes 3 hours to add in the peracid to keep it under an acceptable reflux.
By utilising a cool water bath you could probably halve that addition rate, but be warned, there will be delayed thermal activity.
http://www.geocities.com/torhavn/citizen
(arrogant bee of the day)
09-01-04 01:22
No 528811
It was after a bad experience that I decided to keep the flask cool.
...and I explained it to you in that thread. It got hot because it is starting to break down. You can do this reaction any way you like and learn the mistakes the hard way, or you can take my advice. Mixing the performic and stating addition straight away is fine and showed no loss in yeild.
As Abolt stated, without a reflux column, you will lose DCM. Who cares it is still doing it's purpose by evaporating, cooling and controlling temperature. You can run 500gm in a 3L RBF and the DCM loss is about half. Note that a water bath is used but only with room temp water as to be a heat sink but not cool/slow the reaction. The reason for all these shenanigans is the ability to use very strong overhead stirring via a drill press with paint stirrer (S.S shaft coated in teflon tape with teflon paddles) in it. The use of a room temp water bath allows for fast addition, and although there could be a delayed thermal reaction, it seems that the use of very good overhead stirring solves many problems.
Sorry about the (by weight) yeild, at least I stated it! Besides, what's worse, my laziness to convert it or yours? It was about 73% /mol!
I'm not fat, I'm just too short for my weight.
http://www.whatreallyhappened.com
(arrogant bee of the day)
09-01-04 10:22
No 528811
It was after a bad experience that I decided to keep the flask cool.
...and I explained it to you in that thread. It got hot because it is starting to break down. You can do this reaction any way you like and learn the mistakes the hard way, or you can take my advice. Mixing the performic and stating addition straight away is fine and showed no loss in yeild.
As Abolt stated, without a reflux column, you will lose DCM. Who cares it is still doing it's purpose by evaporating, cooling and controlling temperature. You can run 500gm in a 3L RBF and the DCM loss is about half. Note that a water bath is used but only with room temp water as to be a heat sink but not cool/slow the reaction. The reason for all these shenanigans is the ability to use very strong overhead stirring via a drill press with paint stirrer (S.S shaft coated in teflon tape with teflon paddles) in it. The use of a room temp water bath allows for fast addition, and although there could be a delayed thermal reaction, it seems that the use of very good overhead stirring solves many problems.
Sorry about the (by weight) yeild, at least I stated it! Besides, what's worse, my laziness to convert it or yours? It was about 73% /mol!
I'm not fat, I'm just too short for my weight.
http://www.whatreallyhappened.com