Natures Natrium
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2-Br Propionic Acid Physical Properties
Recently I attempted an expieriment which yielded what I believe to be 2-bromopropionic acid (aka alpha bromopropionic acid). This was done by
refluxing 82 mmol of calcium lactate in 250 ml of ~45% home made (distilled once) Hydrobromic acid.
The results of this, following attempted extractions with DCM (seemed to work) and petroleum ether (didnt seem to work) and subsequent distillation of
extraction solvents (after drying with dehydrated magnesium sulfate, of course) was 1.5mL of a pale yellow liquid. Using a triple beam the density
was found to be .73 g/mL. The substance did not freeze on prolonged cooling in a conventional freezer (>24h), and distillation was not attempted
because I dont have micro scale glassware.
To make it short, these are the observed properties:
Density: .73 g/mL
Color: pale yellow
mp: not observed
bp: not observed
Smell: A peculiar burnt/tart smell. Very hard to describe.
Has anyone every worked with this compound, either home made or reagent grade? If so, please do me a favor and detail all observed properties
(qualatative and quantatative). Thanks so much. 
Nature's Natrium
PS I am aware that the biggest flaw in my methodology was that I did not include a catalytic amount of sulfuric acid. Assuming my sample is pure (it
isn't), my yield is ~9%. 
EDIT: Oh yea, and I cant remember which thread it was in, but at some point I made the arguement that anhydrous HBr gas could be generated by dripping
concentrated H2SO4 on NaBr. Somebody called me on it, and although I wasn't openly defiant, I did not believe them. Several experimints later I
have confirmed that concentrated sulfuric acid does oxidize hydrogen bromide to bromine to an appreciable extent, making an attempt to prepare
hydrobromic acid in this manner useless. In other words, I was wrong. 
[Edited on 7-5-2005 by Natures Natrium]
\"The man who does not read good books has no advantage over the man who cannot read them.\" - Mark Twain (1835-1910)
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Kinetic
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Some Properties
For some reason I have a kilo of this in my loft. It's a solid.
According to Beilstein it should melt at about 25 C - so, although that in itself may not be a warning your synthesis was unsuccessful (sometimes
things just refuse to crystallise), the density is a giveaway. I'm afraid there's no way you'll ever get an organic compound
containing bromine having a density of 0.73g/ml. It's more likely to be twice that. Actually, it's even higher: approximately 1.7g/ml,
according to Beilstein.
Back to the drawing board, I think.
You may like to check out Justus Liebigs Ann. Chem., 130, 18 (1864). The ancient article, written by Kekule, contains the
synthesis of 2-bromopropionic acid from lactic acid and HBr at 100 C.
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S.C. Wack
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At WD I mentioned that a JCS article on nitroethane manufacture said that the lactic route gave a 13% yield of the acid, though I don't recall
that they said where exactly that figure came from.
I think this is JACS 5805-5807, actually this is only 5806 because this was the only page that I photocopied at the time. It does not give a mp but
does mention a bp that may be of use to someone else. It mentions a couple more Ann. refs. And the preparation, in 76% yield (propionic and
polyphosphoric acids + Br2) is a good one.
Those interested in racemic (I assume) N-methylalanine should look at this as well, alcoholic methylamine is supposed to give good yield on standing
for a couple days at STP.
Attachment: jacs_76_5805_1954.pdf (49kB)
This file has been downloaded 1577 times
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Natures Natrium
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Thanks Kinetic for the information. I didn't have a whole lot of hope for it, but I did have a little. The density information is in particular quite valuable, as I had been unable to obtain that bit of data. I knew the
melting point was 25C, but as you said and my expierence dictates, even a little bit of an impurity can make crystallizing certain organic compounds
virtually impossible.
SC Wack, that is an interesting article. However, according to http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0021 alpha-bromopropionic acid can be formed in 80-85% yields by directly adapting a method for
bromovaleric acid found here: http://www.orgsyn.org/orgsyn/prep.asp?prep=cv2p0093 . This method also seems a little easier on the work-up side of the reaction too.
Thanks for the input guys. I am currently thinking about two possibilities.
First, would be refluxing as before except in the presence of catalytic amounts of sulfuric acid. Second would be the addition of a small amount of
pure zinc powder to the HBr acid before adding the lactic acid and refluxing. The idea for the second came from somewhere (can't find reference)
in which it stated the yield of isopropyl chloride from IPA and HCl was substantially increased by the addition of ZnCl2.
\"The man who does not read good books has no advantage over the man who cannot read them.\" - Mark Twain (1835-1910)
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Kinetic
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Alanine
If you have alanine (which is cheap and OTC), you can use this to make your 2-bromopropionic acid. What's more, you end up with enantiomerically
pure acid when starting with enantiomerically pure alanine (which it would be, if you bought it from a health food shop).
Aniline is diazotised with sodium nitrite and the resulting diazo group displaced by bromide. What is odd about the reaction is that
R-alanine gives R-2-bromopropionic acid. Depending on what you have in mind for your 2-bromopropionic acid, the chirality may be a
benefit, a hindrance or neither.
Here is a general procedure from J. Org. Chem., 50, 1356-1359 (1985):
(R)-2-Bromopropionic Acid (4).
D-Alanine (50 g, 0.56 mol) was dissolved in a mixture of 580 mL of 48% aqueous HBr and 1 L of water, and cracked ice added to give a total volume of 3
L. NaNO2 (104.3 g, 1.51 mol) was added in small portions with stirring, followed by 700 g of Na2S04. When the stirred reaction had warmed to 15 C, it
was decanted from solids and extracted with five 500-mL portions of EhO. Drying over Na2SO4 and then CaCl2, and concentration in vacuo gave 65 g of
oil as residue. This was distilled collecting a forerun from 40-70 C (25 torr) and three fractions distilling at 104-108 C (25 torr) totalling 51.3 g
with [alpha]D 45.6' (neat).
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alchemie
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Here´s another procedure for conversion of alanine to bromopropionic acid. It´s a much better alternative than the above procedure as it needs much
less solvent for the same amount of reactants and doesn't require the addition of insane amounts of Na2SO4 (700g!!!) to the reaction mixture.
Tetrahedron: Asymmetry Vol. 4. pp 1141-1152, 1993
(2R)-Alanine (4.0g, 45 mmol) was added to a saturated solution of KBr (10 ml), followed by the dropwise addition of 15ml of 47% HBr. The resulting
mixture was then cooled to 0C and NaNO2 (6.21g, 90 mmol) was added over 1hr. The reaction mixture was maintained below 5C for a further 1hr and then
allowed to warm to room temperature. The resulting solution was then extracted with et2O (3 X 25ml), the combined ether extracts were then dried over
MgSO4 and concentrated in vacuo to give a pale yellow oil (6.54g) in 95% yield. This was distilled under reduced pressure to give pure
(2R)-bromopropionic acid B.P. 68/70C/0.1 mm Hg.
And there's also a similar procedure for the Chloroacid from
Organic Synthesis wich uses, obviously, the infinitely more OTC HCl instead of HBr.
Depending on the intended reaction this might be a much better alternative to the Bromoacid.
Chloropropionic esters are perfect, for example, to use in the Darzens Glycidic ester synthesis...
Edited the link to the Organic Synthesis procedure
[Edited on 22-5-2005 by alchemie]
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S.C. Wack
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Pretty high yield.
| Quote: | And there's also a similar procedure for the Chloroacid from
Organic Synthesis wich uses, obviously, the infinitely more OTC HCl instead of HBr. |
| Quote: | | Sorry, your query returned no results. |
In which article?
Since this has turned towards preparation from alanine, here is another one. I figure that the difference in yield (the HBr part is about the same
yield as Kinetic's) with similar takes on the old NOCl/NOBr procedure (same yields, less convenient) in these different articles is interesting:
JACS 76, p. 6056 (1954), has 17.8 g alanine with 250 ml 6N HCl, cooling to 0C, and 22 g powdered NaNO2 was added with stirring in small portions over
2.5 hrs., keeping temp below 5C. then it was stirred another 4 hrs @ 0C. It was extracted with ether, dried with CaCl2, ether evaporated, and
fractionally distilled 3X, bp10 77C. Yield 32%. Using 6N HBr and fractionating twice (bp4 78C) gave 60-65% yield.
[Edited on 21-5-2005 by S.C. Wack]
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alchemie
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Sorry, I made a mistake linking to the procedure in my post above. Should work now. In any case if you search the orgsyn acrchive with the keyword
"alanine" and you will find it easily.
The 95% they mention is before distillation, the yield of the pure product should be lower.
The HCl procedure from orgsyn is very similiar to the JACS procedure on your post and they claim yields comparable (58–65%) to the HBr yields of
the JACS article.
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chloric1
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Just curious
Could you do this with glycine (aka aminoacetic acid) with HCl and NaNO2 to make alpha chloroacetic acid?
Fellow molecular manipulator
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Maja
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Is it possible to use other solvents to extract bromopropionic acid instead of diethyl ether ?
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smuv
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I say if you want to know if you have successfully brominated anything in your product I would burn a sample of it; if you get smoke of HBr you know
you have at least halogenated something; make sure there is no DCM in the product before testing.
The density could be misleading if the product is not pure; which it likely isn't; although I don't think your reaction was successful because this
kind of thing is an equilibrium reaction; it is driven forward by distilling off some of the product or allowing the product separate out (ex benzyl
chloride).
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Klute
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Regarding the solvent question, of course Et2o can be replaced by the solvent you prefer, DCM, toluene, ethyl acetate, etc. Pet ether might be less
suitable as it will not dissolve much of this product (too polar). As long as the solubility is in adequate range, and the the bp of the solvent will
not cause the compound to decompose (using vacuum for solvents like toluene is generally advised), any common organic solvents can be used.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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