Vitus_Verdegast (Stranger)
01-05-03 20:38
No 395607
      an experiment with DL-lactic acid and HBr  Bookmark   

Yesterday, I prepared a solution of 72 gr KBr in 130 ml dH2O, added 3 icecubes followed by addition of 66 gr 93% H2SO4. The beaker was cooled in an ice bath, and 45 gr (0.5M) DL-lactic acid was added. The mixture sat there for 4 hours, stirring once in a while.

Then I started fucking up (haven't had much sleep latelycrazy), so instead of neutralising the acid with NaHCO3, filtering and distilling the water off, I proceeded to add an excess of ethanol, trying to make the desired ester in situ.

I began to smell the ethyl bromide I've just made blush so I started to neutralize the acid to pH 4 with bicarb. Then the ppt. salt was filtered with suction (quite an amount) and the yelloworange filtrate was distilled. First came a small amount of EtBr, then ethanol, then H2O, and it left a offwhite solid residue in the distilling flask .

It's still in the flask, haven't got around to checking its mp.

 Normally under these conditions lactic acid should brominate, why hasn't it? I used an excess of HBr and H2SO4, according to "Morrison & Boyds Org. Chem." the most desirable way to brominate alcohols, and I kept it well cold to avoid acrylic acid formation. 

Has it been done before using aq. HBr ? any refs?


"There are many things under the sun."
 
 
 
 
    Vitus_Verdegast
(Stranger)
01-06-03 22:36
No 395889
      Found this patent, EP401104 , they treat ...  Bookmark   

Found this patent, Patent EP401104 , they treat l-ethyl lactate with SOCl2, followed by decomposition of the formed chlorosulfite.

"There are many things under the sun."
 
 
 
 
    Captain_Mission
(Stranger / Eraser)
01-08-03 02:30
No 396303
      I have also been looking into ways of making...  Bookmark   

I have also been looking into ways of making the halo acid from lactic acid. A procedure I tought might be worthwile is is voguel 3rd edition, at rhodiums page. Itīs the preparation of ciclohexylchloride from ciclohexanol, using conc. HCl and bubling HCl gas through the mixture.
A hell of a lot better than messing with SO2Cl2, if it works OK.

I think the reason your reaction didnīt work is because the reaction has to be refluxed. Maybe just adding aqueous HBr, distilled from the mixture of KBr and H2SO4, to the lactic acid, and refluxing can give the desired outcome. Not sure about this, just trouwing ideas aroud, but Iīve never seen a esterification that proceeded at such low temperatures.

Actually, making the Chloroacid might be better, I remember someone(barium?)saying that it works better for the darzens reaction.
 
 
 
 
    Vitus_Verdegast
(Stranger)
01-09-03 15:30
No 396671
      acrylic acid  Bookmark   

I was afraid that refluxing would dehydrogenate the lactic acid, hydroxy-acids are easily dehydrogenated when heated in acidic solution. Maybe performing this on ethyl lactate would be a better idea.

"There are many things under the sun."
 
 
 
 
    Captain_Mission
(Stranger / Eraser)
01-10-03 00:27
No 396774
      In Post 346512 thereīs a procedure for ...  Bookmark   

In Post 346512 (moo: "alpha-bromopropionic acid from lactic acid", Methods Discourse) thereīs a procedure for bromopropionic acid from lactic acid, using HBr at high temp, in a glass bomb so i suppose it will stand up to the temperature of the refluxing HBr solution.
The procedure is in german and, when put into a automatic translation software, will give you some very funny sentences but it is understandable. They also mention the production of ethyl-bromopropionate. Hereīs a translation I made:

If lactic acid in a river is heated up by gaseous hydrobromic acid, last to 180 to 200', then something Brompropionsaeure destillirt over. More vortheilhafter it is far, lactic acid up with somewhat more than heating the same Volum of coldly satisfied hydrobromic acid in zugeschmolzenen tubes two to three days in the wasserbad. The Product is then vibrated zweckmaefsig with alcohol-free ether, which destillirt ether solution taken off and after evaporating the ether. With Rectification of the Antheils turning into over 180' one receives with 202 Brompropionsaeure pure to 204'. The lower simmering Theile already contains much Brompropionsaeure, which can be won by repeated Rectification to the Theil. (in Theil simmering with 197 to 200 the ' became with different regulations 50.8 PC. Bromine found.) When opening the tubes one notices sometimes a strong pressure; the escaping gas is pure carbon monoxide, without admixture of carbonic acid. If tube contents are direct destillirt, then some drops of a bromhaltigen, pleasantly smelling liquid turn into with the water vapours, whose nature could not be determined with security. Perhaps a Theil of lactic acid disintegrates after the equation: C3HÕ3 + 2HBr = C2H4Br2 + CO + 2HŌ If one uses available, thus alkoholhaltigen ether for taking the Productes off, then one receives much Brompropionsaeureaether and nearly no acid with distillation; obviously because the Brompropionsaeure is very easily aetherificirt with presence of hydrobromic acid.

"(...)the same Volum of coldly satisfied hydrobromic(...) acid"laugh
Maybe some german speaking person could translate this for better understanting of the procedure.