mnick12
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bromoacetic acid synthesis
So...
I have bee wanting to try out the Reformatsky reaction for quite some time, but one thing stood in my way, bromoacetes. One of my chem books outlines
the basics of the reaction. So I was planning on using ethyl bromoacetate as my halo-ester, but none of my suppliers carry it. So I thought hey I will
just chlorinate some GAA and do a simple esterification -right?Wrong! I tried to chlorinate 15ml of GAA with a massive excess of chlorine in the
presence of a small amount of sulfur as a catalyst. With this I was able to chlorinate less than a ml of the GAA, and I am not even sure it is the
mono-chlorinated acid.
That was a few months ago and I have been thinking.
Then I stumbled upon my next idea.
I thought I would go straight for bromoacetic acid rather than chloroacetic-> bromoacetic acid. So I figured I would try a free-radical bromination
of GAA. This was a few weeks ago, and looking at my notes I will try to explain my set up as best I can.
Reactants:
15.00gr of GAA
25gr of KBr (excess)
H2O2 35gr of 30%
50ml of water
Everything was mixed in a 3 necked 500ml flask, except the H2SO4. Then the H2SO4 was added drop-wise using a addition funnel. As each drop fell it
dissolved forming HBr which was oxidized to Br2. While this was happening I cooled the mix to prevent the Br2 from evaporating. Then after the
reaction was complete I added the contents to a 250ml media bottle. I then screwed on the cap tightly and left it in direct sunlight for a few weeks.
Nothing really noticeable happened over that time period, but when I opened up the bottle my eyes began to sting and I had a little troubled
breathing. Though that could just be the Br2.
I then separated the elemental bromine using a separatory funnel. Next under a slight vacuum I distilled off most the water. Then I added 20ml of dry
ethanol and 1ml of H2SO4 and set the whole thing up for reflux. I am currently waiting for results, but I doubt I will be able to get a yield.
So my question is does anyone know how to synthesize bromoacetic acid?
I can get ethyl chloroacetate, but my supplier only carries it in 1kg quantities which is much much more than I need or want.
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Picric-A
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Try seperating the bromine, drying it then adding it to pure GAA followed by leaved it in bright sunlight.
From your write-up it looks like you left just added GAA to your reaction mixture
e and i am sure this will stop radical bromination...
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DJF90
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If using a halogen carrier the reaction is not a radical one. Vogel illustrates a method using a small amount (0.5ml) of pyridine as a halogen carrier
and from what I recall it is almost quantitative. If you're planning on doing a reformatski then you'll need to isolate a bromoacetate ester, so it
may be beneficial to start with ethyl acetate, form the "enolate" and halogenate with bromine or other, nicer source of electrophilic bromine.
Alternatively Vogel also gives a high yielding esterification of the bromoacetic acid on the same page (at least from memory anyway).
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not_important
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That's in Vogel's 3rd edition, the 5th doesn't have it. It uses acetic anhydride with pyridine as a transacetylation catalyst; acid ahhydride,
halides, and even esters are easier to alpha-halogenate than the free acid. Similarly a small amount of an acid chloride or bromide added to the free
acid to be halogenated will work, the acids swap -Cl and -OH between them. The old standby of adding a bit of red phosphorous to the acid and the
adding Cl2 or Br2 does the same thing, making a small amount of the acid halide.
The 5th ed. just has the acid halide method using either PCl3 or thionyl chloride to convert all the acid to halide; in that case excess Br2 could be
evaporated/distilled off, and EtOH added to form the ester without isolation the a-Br acid.
Using the halogen in excess generally means producing some poly-halo acid.
Treatment of alpha-amino-acids with nitrosyl chloride or bromide give reasonable yields of the corresponding alpha-halo-acid. Thus treating the ethyl
ester of glycine with nitrosyl bromide would give ethyl bromoacetate.
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click the edit post button.
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Picric-A
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Thanks not_important, i must be going blind...
I have made chloroacetic acid form EtOOH + Cl2 with a small amount of red P (catalyst) however i did not get much larger yields than EtOOH + Br2 +
sunlight ( i used a halogen bulb). Use the acid in slight excess to avoid the production of higher brominated acids which are harder to remove than
the plain acid itself.
P.s- I only use red P as i have a lot of the stuff and no other use for it however Sulphur works just as well (P.J.DURRANT)
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Methansaeuretier
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Can someone provide a link to the synthesis of bromoacetic acid with pyridine?
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DJF90
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Picric: Wtf is EtOOH?! You mean acetic acid, AcOH right? I hardly doubt you'll be doing anything with ethyl hydroperoxide...
Methansaeuretier: Procedure is in the 3rd Edition of Vogel (in english), p 429. Enjoy.
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S.C. Wack
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Bull Soc. chim. 7, 364 (1892):
http://books.google.com/books?id=rSvOAAAAMAAJ&pg=PA364
100 parts acetic acid and 5 parts sulfur are heated to boiling in a flask with condenser, and 110% of the theoretical amount of bromine is added
dropwise, the excess due to loss of bromine by the evolved HBr, which may also carry enough bromoacetic acid to clog the condenser. After the bromine
has been added, the bromoacetic acid is distilled. From 300 g. of acetic acid were obtained 655 g. (theoretical yield 700 g.).
Doubling the amount of bromine, refluxing at 150C, gives dibromoacetic acid in good yields.
The same procedure gives a-bromopropionic acid, 95 g. from 50 g. propionic acid (theoretical yield 104 g.). A similar procedure by a different author
is on page 359.
An alternative is polyphosphoric acid (yield 67.6%, other acids in higher yield) as in JACS 76, 5805 (1954):
Preparation of a-Bromoacetic Acid.-In a 50-ml. 3-neck
round-bottom flask were placed 6 g. (0.1 mole) of acetic
acid, 10 ml. of polyphosphoric acid (PPA) and 1 ml. of
H2O. The flask was fitted with a condenser, a dropping
funnel and a mechanical stirrer. The mixture was heated
with stirring for 45 minutes. The acetic acid became miscible
with the PPA and the solution turned a light yellow.
Eighteen and seven-tenths grams (0.117 mole) of bromine
was then added dropwise with stirring while the reaction mixture
was maintained at 80-100". The addition required
1 hour and the mixture was allowed to stir for an additional
two hours until the evolution of hydrogen bromide from the
condenser had ceased. The reaction mixture was transferred
to a distilling flask and the volatile material removed
in vacuo. The fraction distilling 100-105° (30 mm.) was
collected. This material was redistilled and solidified upon
cooling.
From sodium acetate (you'll have to copy/paste the link; the horror!): http://dx.doi.org/10.1016/0883-2889(89)90157-3
[Edited on 31-5-2010 by S.C. Wack]
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mnick12
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Thank you everyone for your replies.
I like all of the suggested ideas, and I especially am interested in the synthesis that uses sulfur as the catalyst. Also must the bromoacetic acid be
purified by vaccum distillation? The reason why I ask is I do not think my aspirator can do 30mmHg.
Also that bromopropionic acid synth looks interesting, and I have some propionic acid which I made from n-propanol.
I will try at least on of these methods out next week, and I will post my results and mabe even some pics.
Thanks everyone
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mnick12
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Sorry for the double post everyone, but I am giving an update.
So instead of trying a free radical halogenation like I wanted to do earlier. I have decided to try a different aproach. I am currently attempting to
hydrolyze trichloroethylene using H2SO4 and water. I have a small test going right now and if it works I should end up with chloroacetic acid and HCl.
I have a paper somewhere which mentions the formation of the bromoester using chloroacetic acid, KBr, H2SO4, the alcohol, and toluene as a solvent. If
I remember correctly the yields are over 90%, if I can find the paper I will go ahead and post a link.
Stay tuned
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Panache
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fine iron wool, with a grit size `~1000 or greater suffices as a halogen carrier if using bromine or iodine, use similar amounts as per red
phosphorous.
The CL2/red p method works for dry refluxing propionic acid
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Mindchemist
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Another route you could try is the hydrolysis of trichloroethylene with a sulfuric acid catalyst. This will give you chloroacetic acid, you can treat
it with sodium bromide to get bromoacetic acid.
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entropy51
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Quote: Originally posted by Mindchemist  | | Another route you could try is the hydrolysis of trichloroethylene with a sulfuric acid catalyst. This will give you chloroacetic acid, you can treat
it with sodium bromide to get bromoacetic acid. |
Got a reference for that one?
Better to remain silent and appear a fool than to open your mouth and remove all doubt.
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Mindchemist
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http://en.wikipedia.org/wiki/Chloroacetic_acid
http://onlinelibrary.wiley.com/doi/10.1002/14356007.a06_537/...
[Edited on 3-27-2011 by Mindchemist]
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