04-13-04 18:51
No 500592
Having mild success with O2/IPA wackers, it was decided that the rxn was too tempermental (personally) and not sufficiently scalable, so the buff performic was chosen.
Following LabTop and Baalchemist write ups, all seemed well until the acid hydrolysis stage.
What follows is a brief account, for which criticism and advice is sought.
236 ml vac dist alkene (saf) converted to isoalkene by vac reflux overnight with 5.2 g KOH (all water removed by venting to atmosph for 30 mins).
then 225 ml isoalkene placed in 2L 3-neck rb, followed by 76.9g NaCOH3 and 770 ml DCM.
Prepared 384.5 g (317.8 ml) 88% formic acid and 235 g (166.3 ml) Fresh 35% H2O2. CHilled same.
Began dripping performic in at a rate that kept temp under 40 C. required approx 7 hours for this size batch.
Color converted from clear to yellow to orange juice after all performic added. Stirred for total of 24 hrs.
Two layers formed, sepped off bottom, washed aq layer with DCM, pooled extracts, vapped off DCM at atmosph to collect Monoformyl glycol as thick orange syrup --325 ml
HERE IS WHERE THE ERROR MAY HAVE OCCURRED:
Did not have vessel of sufficent size for hydrolysis as shown:
2768 g 15% H2SO4 [diluted 227.9 ml 99% H2SO4 with 2353ml H2O ( 0.1515 x 2768g =428g H2SO4 / 1.84 =227.9 ml)]
This quantity didnt fit in the 2L RB, so the reactants were divided into 2/3 and 1/3 batches (first mistake: it should have been 1/2 and 1/2 ) . The 2/3 batch 216 ml glycol was preheated to 80 C and the acid 1717 ml preheated to 80 C.
Added acid to glycol and stirred heavily for 2 hours keeping temp between 75-80 C. There was clearly too much in the flask, so stiring was not as it should have been.
The glycol stayed primarily on the bottom and was distinctively separated from the acid ( as in oil/water combo) throughout the rxn.
The layers separated immediately on stopping and sepped apart easily.
The second batch was processed with 109 ml glycol and 858 ml acid.
THe stirring was much better. THe 2 layers separated immediately as well.
Both extracts were pooled, the aq layers wsahed with DCM and the DCM vapped off, extracts pooled.
washed with 5% bicarb to neutralize ( was actually still slightly acidic when done )
Distilled the suspected raw ketone as follows:
Vac pulls 9 torr perfectly. Alkene comes over at 90 and the isolalkene at 100.
Preheated oil bath to 125C , placed ketone in 500 ml rb and then in oil bath. applied vac. It stabilized qiuckly. Raised temp steadily. When oil hit 150 C the dist temp read 50 C. Oil read 158 C the dist temp hit 119 C and a large fraction came over in 1.5 hours (78 mls).
Temp dropped sharply , so flasks were switched.
Temp rose to 124-125 C and another fractio came over (78 mls)
The first fraction was pale yellow in color, a viscous oil with a definite NOT Saf smell.
The second fraction was best described as flourscent green--a yellow color with a distinct vivd green mixed in.
It also smelled quite similar, and had a viscous nature.
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Can anyone discern what occured and why? Suspect that the hydrolysis was faulted in the first batch.
The suspected ketone seems to fit the descriptions found using the FSE, but why the 2 fractions so close together and with diff charactersitics? Is the second the ketone and the first...what?.. an incompletely hydrolized glycol?
If that is true, can the first distillation result be rehydrolysed and then distilled again to save it?
Bisulfite test will be performed on both and results posted, but any interim adivce will be greatfuuly appreciated.
The results will be applied to the wet reductive alkylation process once this issue is cleared up.
Full write ups will follow.
Thanks to all
(Hive Bee)
04-14-04 03:52
No 500712
I don't know what went wrong. But might I suggest you try a HCL rearrangement of the glycol next time.
Post 476334 (Chromic: "HCl is so good it's GOLDEN!", Chemistry Discourse)
"..when life looks like easy-street, there is danger at your door"
(Newbee)
04-15-04 02:48
No 500880
I don't know if this is the problem but off the top of my head I thought it should be about a 15% H2SO4 solution. It seemed that you used only about a 9.7% solution.
Don't know if this is enough to make a difference. Just a thought. If you're worried about not having a large enough flask you can always use empty solvent bottles (usually 4 liters) it's not like they have to take any pressure or anything and they serve the purpose just fine.
(Stranger)
04-15-04 05:52
No 500896
Thanks very much for the input.
Crap, even after 5 years of algebra, calculus and org chem, still screw up dilutions! Never had much of a mind for numbers, unfortunately. Will check again, thanks.
GREAT ref for the HCL hydrolysis! Have some handy and will try it very soon. Will follow up.
Bisulfite test will be run on both suspected ketones.
If the first test neg, does anyone have a suggestion as to the composition?
From the bottom to the top, it all still floats
(Hive Bee)
05-24-04 02:21
No 509131
Hi guys!
I have a question about the buffered performic. As you know, we stire Isosafrole, performic acid, NaHCO3 and DCM for 24 hours. My biggest flask is a 2l 3-neck rbf, that's
why my batches are limited in size.
QUESTION: Is it possible to do this without or with less DCM, i mean reacting the whole thing as usual and then, after reaction has finished 24 hours later, extract in a huge beaker
with DCM?
greetings
(Hive Bee)
05-24-04 11:58
No 509204
methlab.
Reducing the DCM by about 1/3 of that stated in labtops summary and using about 1/3 less 15% H2SO4 in the hydrolysis has no noticibale effect on yields in SWIM's experience. In fact SWIM prefers it, but make sure you have good peroxide.
That way you can use process more ketone in your flask.
The result is, a 5L flask can be used to react 1000g isosafrole in 16-24 hours to make the glycol, then the same 5L flask can be used for 2 seperate hydrolysis reactions with half portions of the glycol (and acid solutions).
This means I would expect a 2L flask would be enough for about 400g iso and give around 300g ketone.
some more tips
after stirring for 24 hours (overkill IME), let the layers settle and simply pour off the acid solution leaving the DCM and glycol in the reaction flask, THEN pour into a seperating funnel to seperate the remaing phases. DONT bother trying to wash your acid layer with clean DCM to extract organics from it, waste of time IMO.
After reacting glycol with 15% acid, do the same, that is let the layers settle in the reaction flask, the brown ketone will settle to the bottom. Then pour off the acid solution down the drain, then when most is gone THEN add to the sep funnel to remove the ketone from the small amount of acid solution.
Now you may do some math and say the numbers dont quite add up, but it works, some DCM is lost even when using ice cold condenser water and if you are really stuck let me know and i will give you exact numbers to use for your flask size.
Abacus.