alking - 10-2-2017 at 09:20
Yes, another thread on this. I'm sure this has been answered before but I'm unfortunately unable to find it.
So the den alcohol in question is klean strip green formula. It's roughly 90% ethanol, less than 5% MeOH, up to 5% acetic acid, ethyl acetate, and
methyl isobutyl ketone, and the remaining compounds are undisclosed denaturants. I don't care about removing the methanol, but I would like to remove
the rest.
So far I have attempted to hyrdrolize any ethyl acetate with NaOH, which will salt out any acetic acid as well. Then I distill. Will anything still
remain? I'm not sure, but I can't quite get to that step yet bc the hydrolysis is taming longer than expected and something else appears to be
polymerizing in the process as a black oil that reeks of crude oil forms over time and I'm wondering what this may be as well as how long I could
expect it to take.
So far I refluxed ~950ml of the alcohol in 100g of NaOH for about 2 hours, then distilled. It still had some acetate smell, or at least some kind of
off smell, so I took a sample and left it in some NaOH overnight to see if there was any change. In the morning the solution was orange so clearly
there is still some of this polymerized crap forming. So from there I put it all back in a flask with another 100g of NaOH, and a bit of water in case
there was not enough present to hydrolyze all of the EtOAc too, and it has been refluxing for ~12 hours now. The solution is again black. Now it may
be done, maybe not, but the only way I can think to test it is by distilling some and seeing if I get a color change again. So I'm wondering if there
is an easier test I could run or if anyone has direct experience doing this to tell me how long I should expect the process to take?
DraconicAcid - 10-2-2017 at 09:27
Anything that has polymerized will probably be left behind when distilling. I'd just stop refluxing and start collecting.
Amos - 10-2-2017 at 09:46
I imagine this will be of use to you: https://www.youtube.com/watch?v=rq7a5_tvBPM
Praxichys - 10-2-2017 at 10:05
Yep, distill that off and test it. If you have a column, you should try to fractionally distill what you have now, stopping when the temp gets much
past 80°C.
The polymerization is probably occurring because you have a MIBK impurity undergoing aldol condensations. The orange color is from partial
polymerization and the black crap is just further polymerization after that.
You definitely don't need that much NaOH. Even though the commercial stuff can be something like 17% water, you still only need about 40g/L to
neutralize 5% acetic acid, then perhaps 10g extra for the EtOAc, which I'm assuming is <1%.
If you distilled to dryness the first time or didn't carefully watch the head temp, that would explain the MIBK content. It's also possible that local
overheating could have charred some of the sodium acetate left in the flask, giving off some acetyl byproducts. Regular ethanol will not go
yellow/brown when subjected to NaOH overnight, and polymerization of whatever is in there is increasing its MW and thus BP, making itself easier to
remove. Distill, test, repeat.
[Edited on 10-2-2017 by Praxichys]
PHILOU Zrealone - 10-2-2017 at 12:17
With NaOH, you hydrolyse the ethyl acetate to ethanol and acetate anion that will remain into the flask as NaOAc.
You at the same time favourize condensation crotonisation of the methyl-isobutyl-keton (the orange product is the multimerization (polymerization)
product...polymers have higher boiling points and will remain into the flask.
So remaining into the flask...exces NaOH, NaOAc, polymer of crotonisation-condensation of MIBK...passing into the distillation flask ethanol and
methanol.
Eventually if you heat too strongly and dry some methane from Na acetate thermolysis in strongly lye media...
alking - 10-2-2017 at 12:42
Okay, thanks guys. So I guess I can't improve on what I'm doing then, except perhaps using a bit less lye. I was mostly posting this to find out if
anyone knows how long this should take? I figured 2 hours would be enough, but apparently not. It's a pain to have to switch out condensers and rig it
up for distillation just to check the progress, but I guess that's the easiest way to check. It's been refluxing for ~16 hours or more now so I really
hope it's done at this point.
Based on the amount of work involved so far I should have just purchased some lab grade denatured ethanol for ~2x the price. If I scaled this up to
3-5 liters and didn't have to monitor the progress it might be worth it, but not to get ~800ml of ethanol. Oh well, everything is a learning
experience.
PHILOU Zrealone - 10-2-2017 at 13:09
You don't have to reflux it if you have time...just add NaOH solution (thus water) in slight excès for neutralization of acetic acid, for hydrolysis
of Ethyl acetate and crotonization-condens- of MIBK.
Estimate that you have 10% acetic acid.
Then leave it without care and attention for days, weeks or monthes...and then distil...much more energy sparing.
alking - 10-2-2017 at 14:02
True, but half the reason I went this route is simply because I didn't want to wait for some lab grade to be shipped to me. In retrospect I wish I had
just done that though. So I'm distilling it now and the first fraction is coming over at 77.0-77.2 so there must be some ethyl acetate left even after
refluxing for more than 16 hours. I wouldn't have thought it would take so long.
On the plus side I must be getting a good separation though so maybe I can just fractionate it out. I left the reflux condenser on, a 300mm coil
condenser, to use as a fractionating column, then stacked a bead packed 300mm liebig on that, and then a partially packed chromatography reservoir on
that.
My intention was to speed up the distillation by having a longer and thus more efficient column. I was only expecting this to serve to fraction out
the EtOH/MeOH from the water though, I didn't think it would be efficient enough to separate the EtOAc, but I am pleasantly surprised at just how well
this works. When only using the reflux or the liebig, packed, as a column it would take me literally all day just to distill 40% vodka to ~85%, but
damn, I'm now distilling at 5x the rate and getting a damn good separation unless the still head temperature is just a coincidence.
alking - 11-2-2017 at 07:57
So it was just a coincidence unsurprisingly, I knew that column didn't work that well. Anyway I tested the product and it still turns yellow in some
lye. I am confused why this would possibly take so long to hydrolyze, and there must be a significant amount in here or something. I'm not boiling the
flask dry, is it somehow possible some of the polymerized product is... what's the opposite of polymerization? Cracking? Maybe I'm just not being
patient enough, but I've read letting it sit in bicarbonate for a week at room temperature should do it so how could refluxing for 24+ hours in a
strong lye solution not?
PirateDocBrown - 11-2-2017 at 12:10
Two hours hydrolysis ought to be more than enough.
I'd go ahead and just do a total strip distill at first, leaving just a bit of sludge behind from the original material. See how good what you get is,
before deciding on further processing.
Your anomalous results are having me question the purity of your starting conditions. Try some of that product from a different source? Perhaps a
different source of NaOH?
The way I would normally go would be column distill straight after reflux, cut off the low boiling lead, start collecting main product in the low 70s,
and cut off around 80.
Methanol/Ethanol is zeotropic, so I expect little more than traces of water in my final ethanol, after distilling over hydroxide, which should get you
down to a few tens of ppm H2O. [Bradley, Williams, Lawton, J. Org. Chem., 2010, 75 (24), pp 8351–8354]
MSDS of Klean Strip Green Denatured Alcohol shows little else besides methanol and EtOAc. (Which doesn't, however, mean there isn't more in there...)
Nevertheless, I would not expect MeIBuK, or anything much else liable to aldol condensation, unless there's some contamination.
http://www.co.vermilion.il.us/MSDS/SDS-EMA/85-Kleanstrip%20D...
[Edited on 2/11/17 by PirateDocBrown]
[Edited on 2/11/17 by PirateDocBrown]
alking - 11-2-2017 at 14:21
That's what I would have thought too, that 2 hours would be plenty. As I said earlier though at this point, and counting the distillation time into
the reflux time, I've distilled it twice, refluxed for over 24 hours (I assume anyway), and have gone through 200g of NaOH. Both times the mixture was
totally black within an hour of refluxing.
I'm obviously removing some of it as I've collected a bunch of black sludge at this point, maybe 25-50ml, possibly 100ml, it's hard to tell since it's
mixed in water. It's definitely not the NaOH, it's very pure food grade iirc, I've used it for numerous other things and never noticed any such
anomalies.
That is strange about the msds. I wonder if it has changed? I got the msds off of the klean strip website, but checking now it is the same. I
referenced it a few times though and I would almost bet money that on the acetic acid/ethyl acetate line it said:
Acetic acid, ethyl ester {Ethyl acetate}, methyl isobutle ketone <1.5%
Checking now however it says:
Acetic acid, ethyl ester {Ethyl acetate} 1.5%.
Very strange. The amount of polymerized crap is definitely greater than 15ml though regardless. I really don't trust msds of industrial chemicals
anyway, they just throw random waste products in there and outright lie to consumers. So far half the things I've bought at the hardware store based
on the msds were just plain wrong, the last thing I got was some naptha listed as 60-90c, yet it didn't even start boiling until 115C and a bunch of
black tar crashed out early on. This stuff is sold as a cleaning solvent. Why would I clean something with such a high boiling point and that is going
to leave a residue of fuel oil or something behind?