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]

Some Properties

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.

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).

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]

Just curious

Could you do this with glycine (aka aminoacetic acid) with HCl and NaNO2 to make alpha chloroacetic acid?