carbonic
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Black solution in glycerol + oxalic?
Some dude I met on another board told me that the glycerol+oxalic method of formic yields low. He also mentioned that his solution turns black as the
temp reaches 140C under 75 or so torr - anyone have comments on this from your experiments?
My comment to him was if the temp got past 100C under that much vacuum, he had long since passed the stage where formic would be distilling. He
agreed that he did not stop after CO2 evolution died off and continued heating with only the one addition of oxalic.
But the question I could not answer is why the glycerol solution went black? It seems that 140C is not hot enough to get to the allyl alcohol stage,
so we were both puzzled as to why the solution would discolor at all. He mentioned that it had a long "tan" phase, then the change to black was
quicker - in just a few minutes.
For those who have run this, can you comment on whether blackening is expected or if it signifies scorching of the glycerol or something...?
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chemoleo
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Not sure I understand - what is 'glycerol+oxalic method of formic yields low'?
Please be a bit more clear in your description!
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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carbonic
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That was just a side note that he found the yield of formic acid was a little low. Not a big concern, since I think he did not use enough oxalic
acid.
The real question is whether the solution naturally darkens as the temperature increases near the conversion to allyl alcohol? Or was this telling
him that something was going wrong and the mixture was turning to tar?
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chemoleo
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So you are saying that heating glycerol with oxalic acid yields formic acid?????? Or what were you trying to make?
Please say in the beginning what the reaction is about!!!!
Generally dark colour in such reactions can be either
- suspended carbon (i.e. sugar heated above its decomposition point)
- polymeric compounds, such as seen when heating acetone with acids...
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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not_important
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A classic reaction.
How pure was the glycerol? Even a bit of some contaminates will trigger dehydration and polymerisation. Can't say for sure, but some of the
reactions could be autocatalytic, taking place at an ever accelerating rate as the products build up. And it doesn't take a lot of condensed gorp to
make a mix look black.
While the 'cook' sits have more modern, higher yield procedures, here' are some older ones
heating glycerol and oxalic acid to get formic acid:
http://books.google.com/books?id=tawEAAAAYAAJ&pg=PA822&a...
heating glycerol and oxalic acid to get allyl alcohol
http://books.google.com/books?id=MAA5AAAAIAAJ&pg=PA149&a...
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carbonic
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Yes, heating glycerol and oxalic acid is supposed to produce formic acid. I expected anyone who has done the reaction to know what I meant when I
said glycerol + oxalic. I'll be more clear in the future.
Further heating after the formic distills off, is supposed to reduce the glycerol formate (correct? who knows..) to allyl alcohol. But that
temperature is very high and I don't think this guy heated it that far.
I assume the reagents were ACS grade, but I will check with him.
So n_i: You think that the glycerol reaction should not turn black, all the way up to allyl? Have you seen it in action, or just estimating?
My guess is that something is going wrong, but I wanted to double check it here with some experts.
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Ozone
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I need to do some more research before posting on this too deeply...
I know that heating glycerol at 140°C (with acid catalysis) on up with acid is asking for brown crap (acrolein, first purple crap, actually). I also
know that heating glycerol with a carboxylic acid at 140°C (nevermind 260, whoo) will give polyester.
At 280°C it decomposes, without catalyst into acrolein, so the method as cited for allyl alcohol (the thing is in C, the 97°C BP checks out) running
at 260°C is on the fringe (without catalyst). I can see why the yield would be shite.
The up-side, I suppose, is that the feed is dirt-cheap.
I love these old reactions, thanks for bringing it up!
Cheers,
O3
[Edited on 27-2-2008 by Ozone]
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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not_important
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Ozone has it - it's real easy to get hot glycerol plus acids or other stuff to start going brownish, then black. In many cases it doesn't hurt it for
the use you have, I've run the allyl alcohol method with low grade glycerol that you couldn't see through after it was first heated. However the way
you're doing it doesn't match the procedures that I'm used to.
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carbonic
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not_important,
Thanks for the info, I will let him know that blackening is probably not a disaster but rather means that it's heated way past the formic stage. BTW
- what's the procedural errors you saw? Vacuum? That came from the allyl writeup I think, as a faster way to get the formic off.
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j_sum1
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Glycerine and oxalic acid
I thought I would post here rather than start a new thread: even though my contribution is somewhat tangential to the discussion above:
I got to thinking about esterification and polymerisation the other day (ie, polyesters) and got to thinking about the reagents in my lab and what I
might accomplish. The only dicarboxyllic acid I possess is oxalic. And the only di-ol I have is... well I don't have any, but I do have glycerol.
So my thoughts turned to performing a Fischer on the two with the possibility of creating a horribly cross-linked glumpy polymerised mass -- probably
with a bunch of unreacted matter (and maybe the odd stir-bar) caught in its voids.
So, I was naturally surprised on searching to discover that oxalic acid and glycerine is a standard method for making formic acid.
I would love some enlightenment. Was I completely wrong about the possibility of polymerisation? If I added H2SO4 as a catalyst, would I favour the
esterification or would I have two competing reactions? Or, as I suspect, would the products be highly dependent on temperature?
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Texium
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Well, the reaction forming formic acid works because it goes through an unstable glyceryl oxalate intermediate that quickly decomposes to formic acid,
carbon dioxide, and glycerol, (basically, glycerol acts as a catalyst for decomposing the oxalic acid). Because of that, it seems very unlikely that
glyceryl oxalate would be isolable.
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blogfast25
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Anybody got a recipe for formic acid from glycerol + oxalic acid?
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Boffis
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@Blogfast
Google - search- split second later I got:
JCS 1914 p151-156 (paper on reaction of oxalic acid with glycerol)
JCS 1915 p407-410 (prep of allyl alcohol from this reaction)
Plus many other hits on erowid, various practical chemistry books etc. which are largely reworking of these papers.
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S.C. Wack
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Shirley there must be more relevant threads for that discussion. Safe to say, not heating to 140C with aspirator vacuum. But I want to mention this
book (again. Hey Marvin here it is, and a much better and more complete scan than mine.) because I'm strangely fond of it and Noyes is the sort of
good cookbook from 1897 this would naturally be in.
https://books.google.com/books?id=woMMAQAAIAAJ&pg=PA61
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blogfast25
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Thanks Boffis.
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