new-b
Harmless
Posts: 15
Registered: 12-2-2006
Member Is Offline
Mood: No Mood
|
|
D-tartaric acid
Hi everybody,
I've red somewhere I don't remember that it's possible to get a racemic solution of d-tartaric acid and l-tartaric acid from
l-tartaric acid in hot aqueous KOH solution. (Probably by the formation of the "enolate"and a subsequent protonation of the enolate on both side...)
My question is what do you think would be the best way to isolate these enantiomers?Chromatography (silica, what solvent)? Cristallization? Is there a
enantiomeric molecule who can only cristallize the D-tartaric acid?
|
|
|
Eclectic
National Hazard
Posts: 899
Registered: 14-11-2004
Member Is Offline
Mood: Obsessive
|
|
You can try to grow very large crystals and the separate them visually. AIR, you get mirror image crystals of pure isomers.
|
|
|
Nerro
National Hazard
Posts: 596
Registered: 29-9-2004
Location: Netherlands
Member Is Offline
Mood: Whatever...
|
|
Is it feasable to try to grow large single crystals from a racemic mixture? (large = >1 cm)
#261501 +(11351)- [X]
the \"bishop\" came to our church today
he was a fucken impostor
never once moved diagonally
courtesy of bash
|
|
|
Eclectic
National Hazard
Posts: 899
Registered: 14-11-2004
Member Is Offline
Mood: Obsessive
|
|
I seem to recall that tartaric acid was one of the first compounds separated into optically pure isomers, with the aid of a magnifying glass and a
pair of tweezers. 
Oh yeah, some obscure old fart named Louis Pasteur, in 1847.
[Edited on 8-4-2007 by Eclectic]
|
|
|
new-b
Harmless
Posts: 15
Registered: 12-2-2006
Member Is Offline
Mood: No Mood
|
|
From what i read :
The tartaric acid sodium-ammonium salt is unusual among racemic mixtures in that during crystallization it can separate out into two kinds of
crystals, each composed of one isomer, and whose macroscopic shapes are mirror images of each other. Louis Pasteur was thus able to separate the two
enantiomers by picking apart the crystals.
So now how to you do a sodium-ammonium salt. Never heard of a mixed salt?????
|
|
|
Nicodem
Super Moderator
Posts: 4230
Registered: 28-12-2004
Member Is Offline
Mood: No Mood
|
|
Indeed it was a stroke of luck that Pasteur choose a compound that forms aglomerates instead of racemic compound crystals. Less than 10% enantiomeric
compounds have this property.
| Quote: | Originally posted by new-b
So now how to you do a sodium-ammonium salt. Never heard of a mixed salt????? |
I would assume it is as easy as to neutralize tartaric acid with 1/2 eq. NaOH and 1/2 eq. NH3 and crystalize the double salt.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
|
|
|
Eclectic
National Hazard
Posts: 899
Registered: 14-11-2004
Member Is Offline
Mood: Obsessive
|
|
The sodium-potassium salt (Rochelle salt) will easily grow large crystals...
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
Chromatography would be no help unless you are going to apply chiral chromatography on a prep scale in which case you are pretty much on the cutting
edge.
The serendipitous physical seperation of tartaric acid's enantiomers manually notwithstanding, the usual more general methid is to make a salt of the
racemic tartaric acid with an optically pure base (often an alkaloid) and then you can seperate the two salts by conventional physico-chemical
methods.
Naturally occuring tartaric acid is optically pure. The unnatural enantiomer is available commercially but a lot more expensive.
By the way D and L do not mean the same thing as d and l. One refers to the absolute configuration and the other to the optical rotation (+) or minus
(-) as determined on a polarimeter. The polarimeter is of course the only way to tell just how optically pure something is (we talk in terms of ee
(enantiomeric excess) and the reading on such an instrument depends on solvent, temperature, concentration, and length of optical path in sample tube.
Great fun! especially with a plain jane optical model rather than a fancy schmancy digital instrument with a LED or LCD display.
|
|
|
new-b
Harmless
Posts: 15
Registered: 12-2-2006
Member Is Offline
Mood: No Mood
|
|
Any interesting ideas about an OTC optically pure base who could serve the purpose of separating the D-tartaric acid from the L-tartaric acid?
Or, do you think D-tartaric acid is a watched substance and suspicious to order for any reasons?
What do you think about sciencelab.com they say they sell to individuals :
http://www.sciencelab.com/page/S/PVAR/SLT3046
|
|
|
Eclectic
National Hazard
Posts: 899
Registered: 14-11-2004
Member Is Offline
Mood: Obsessive
|
|
Order from a brewing and winemaking supply. MUCH cheaper.
|
|
|
pantone159
National Hazard
Posts: 590
Registered: 27-6-2006
Location: Austin, TX, USA
Member Is Online
Mood: desperate for shade
|
|
I think that Pasteur was additionally lucky, in that his compound only formed the chiral crystals at specific temperatures, which just happened to
match those on his windowsill (or whatever).
I've never used ScienceLab.com, but I have heard multiple bad things about them. There is a thread about them on this board somewhere.
|
|
|
new-b
Harmless
Posts: 15
Registered: 12-2-2006
Member Is Offline
Mood: No Mood
|
|
| Quote: | Originally posted by Eclectic
Order from a brewing and winemaking supply. MUCH cheaper. |
I wanna get the pure D-tartaric acid not the L.
|
|
|
Eclectic
National Hazard
Posts: 899
Registered: 14-11-2004
Member Is Offline
Mood: Obsessive
|
|
I thought you might want to try making it from the racemate.
The sodium ammonium salt crystallized below 28 C seems the only useful one for physical separation. If you get good seed crystals of each enantomer,
you should be able to get good separation by slow evaporation of a racemic solution using one seed of each.
There are also organisms that consume the natural form of the ammonium salt, and leave the other in the ferment.
|
|
|
new-b
Harmless
Posts: 15
Registered: 12-2-2006
Member Is Offline
Mood: No Mood
|
|
What if you use only one seed crystal of the D form???You'll get one big crystal of the D form plus lots of small crystals of the L form. Am I right?
|
|
|
new-b
Harmless
Posts: 15
Registered: 12-2-2006
Member Is Offline
Mood: No Mood
|
|
| Quote: | Originally posted by Eclectic
I thought you might want to try making it from the racemate.
The sodium ammonium salt crystallized below 28 C seems the only useful one for physical separation. If you get good seed crystals of each enantomer,
you should be able to get good separation by slow evaporation of a racemic solution using one seed of each.
There are also organisms that consume the natural form of the ammonium salt, and leave the other in the ferment. |
Do you know the name of these organisms?
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
And why do you want D-tartaric acid, exactly?
And why are you worried about whether or not it is watched?
I mean, just because it is specifically mentioned in the literature as being the resolving agent of choice for various optically active organic bases
that just happen to be optically active?
What a coincidence!
|
|
|
new-b
Harmless
Posts: 15
Registered: 12-2-2006
Member Is Offline
Mood: No Mood
|
|
it's the best way to isolate optical molecule. That's it
|
|
|
Eclectic
National Hazard
Posts: 899
Registered: 14-11-2004
Member Is Offline
Mood: Obsessive
|
|
Google "Pasteur tartaric-acid isomers separation"
If you don't seed with a good crystal of each enantomer, you won't
have any control over where crystallization of the unseeded enantomer starts crystallizing. Ideally, you want one large crystal of each with good
physical separation
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
It's ONE way to resolve SOME optical isomers.
It is not the be all and end all of such resolutions.
The pharm industry is being forced to go to chiral chromatography so that field is making leaps and bounds.
There are also enzymatic methods - certain enzymes, for example papain, will hydrolyze the anilide os some amino acids selectively, leaving the free
L-acid while not touching the D-form anilide, the two are then easily seperable.
Not all optically active compounds are bases, and thus, the tartaric acid enantiomers are not useful for them. The alkaloids are by definition
nitrogenous bases. By sheer coincidence the amphetamines are too.
So what are you wanting to resolve?
Optical resolution by crystallization, is laborious and tedious. But, hey, knock yourself out.
|
|
|
ergoamide
Harmless
Posts: 33
Registered: 16-7-2006
Member Is Offline
Mood: No Mood
|
|
Alkaoids are more than just nitrogenous bases though, amphetmine is NOT one. To be an alkaloid it must be found naturally, i.e in plants generally
although most animals have them but much lower concentrations.
Oh and your local supermarket will have what you are after. Also learn what chemicals are watxhed and what is not. I mean asking if THIS is watched
screams lack of knowledge and is a very obvious clue your doing something your not supposed to be.
[Edited on 6-8-2007 by ergoamide]
|
|
|
Sauron
International Hazard
Posts: 5351
Registered: 22-12-2006
Location: Barad-Dur, Mordor
Member Is Offline
Mood: metastable
|
|
I am well aware of what an alkaloid is and isn't. But thanks.
The local supermarket certainly does not have D-tartaric acid, all they will have is the L-isomer, the natural one.
|
|
|
new-b
Harmless
Posts: 15
Registered: 12-2-2006
Member Is Offline
Mood: No Mood
|
|
| Quote: |
I mean asking if THIS is watched screams lack of knowledge and is a very obvious clue your doing something your not supposed to be.
[Edited on 6-8-2007 by ergoamide] |
The fact that I'm asking if it's a watched substance doesn't mean by itself that I'm obviously doing something wrong. I was just asking about it
because I don't want to get hasstle by ordering a watched substance.
|
|
|
solo
International Hazard
Posts: 3975
Registered: 9-12-2002
Location: Estados Unidos de La Republica Mexicana
Member Is Offline
Mood: ....getting old and drowning in a sea of knowledge
|
|
| Quote: | Originally posted by Sauron
I am well aware of what an alkaloid is and isn't. But thanks.
The local supermarket certainly does not have D-tartaric acid, all they will have is the L-isomer, the natural one. |
.........needless to say he naturally occurring form of the acid is L-(+)-tartaric acid or dextrotartaric acid. Note, that the dextro and levo
prefixes are not related to the D/L configuration (which is derived from the reference D- or L-glyceraldehyde), but to the orientation of the optical
rotation, (+) = dextrorotatory, (− = levorotatory...........source,
http://en.wikipedia.org/wiki/Tartaric_acid
While on on the subject there is a patent I'm looking for that resolves the l-isomer to d,l.....using Palladium.......solo
[Edited on 27-4-2008 by solo]
It's better to die on your feet, than live on your knees....Emiliano Zapata.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
