12-01-02 23:18
No 385381
I got surprisingly few hits about this in TFSE, and hope some fresh thoughts can be heard on this.
Tartaric acid from cream of tartar (potassium bitartrate): Is it D, L, or DL? I've seen about an equal number of opinions in favour of each. One source suggested that L is what's produced in nature, so I would tend to believe that the stuff on the grocery store shelf is DL, perhaps leaning towards L (thinking that the acid isomerizes somewhat during processing).
If I had no other choice, could I reflux a tartaric acid solution in the hopes of guaranteeing DL, if I had no other way of determining whether it was D or L originally? Any specific conditions? Or should I try harder to find D?
Anyone actually tried sorting crystals of ammonium tartrate?
Add your thread to the rich tapestry of conspiracy...
... and wave hello at the satellites!
(Chief Bee)
12-01-02 23:32
No 385393
The optical form depends on where you live. In some parts of the world (for example in wine districts) the natural form is sold OTC, as it can be bought cheaply from wineries there. In other parts of the world, synthetic (racemic) tartaric acid is cheaper, and there that form is sold. You will never find the optically pure unnatural isomer OTC though, so if you buy it and check for optical activity (or the mp, it's different), then you can determine if it is the natural form or the racemate.
(Stranger)
12-02-02 15:49
No 385648
pure tartaric acid can be found on a very very popular auction website usually for about 5 bucks a pound.
(Hive Bee)
12-03-02 06:44
No 385811
of D and L tartaric acid have different melting points?
That cant be. Enantionmers have the exact same optical activity but opposite, where a racemic mixture would have a net rotation of 0. Enantiomers arent separable by usual physical methods, certainly not by melting points unless you formed diastereomers with the salt, then you could separate by physical methods such as distillation. What do u mean R?
(Hive Addict)
12-03-02 09:24
No 385838
what he said was that the racemate and the enantiomers have
different mp's. but only one enantiomer is commercially
available, so given the mp you can decide whether you have
the racemate or the commercial enantiomer.
anyway, wouldn't it be fascinating, if D- and L-form had
slightly different mp's? it would mean that space is twisted
in one direction, wouldn't it!?
(Hive Addict)
12-03-02 10:15
No 385850
aurelius would argue that given enough stereo-centers, or in crucial enough areas, that the phys. props. of the enantiomers would be different. For example, if melting point is based upon the strength of the crystalline lattice energy, then the orientation of a molecule would have an effect on the crystalline alignment and therefore it's lattice energy. Perhaps, with crucial placement of the stereocenter or many stereocenters, the mp would change- maybe not by any large degree, but a noticable/observable change.
(Hive Addict)
12-03-02 10:59
No 385859
> aurelius would argue that given enough stereo-centers,
> or in crucial enough areas, that the phys. props. of the
> enantiomers would be different.
hmm... but it seems to me you are talking about molecules that are
not exact mirror images. if you have more than one stereo-center, you'd
have to invert them all. such molecules, which are perfect mirror
images, cannot have different mp's, can they? othewise there must be a
law which is not symmetric (in space), i've never heard of any...
(Hive Addict)
12-03-02 11:09
No 385862
doesn't tartaric acid have 3 forms, L,R and meso?
would the racemate contain all 3?
(A Different Title)
12-03-02 11:10
No 385863
L-Tartaric acid: mp 170
D-Tartaric acid: mp 172-174
Possible? I don't know. I think I'll scavenge some polarising filters from somewhere anyway, I don't need much and sorting by hand seems do-able.
Add your thread to the rich tapestry of conspiracy...
... and wave hello at the satellites!
(Hive Addict)
12-03-02 11:20
No 385865
shall that be yet another day with an earthquake in my world view?
there are so much of them it's not funny anymore...
how can two mirrored molecules have different mp's?? sorry but i won't believe
it until i measured it myself
(and even then i will find some excuseto save my worldview...)
(Hive Addict)
12-03-02 11:52
No 385871
> if you had the synthetic (racemic) form, which is a 50:50
> mixture of D-tartaric acid and L-tartaric acid.
how is commercial tartaric synthesised? wouldn't many possible syntheses also produce the meso form?
(Hive Bee)
12-03-02 15:11
No 385923
According to Merck Index L and D-isomers have the same melting points. Of course, one cannot undermine the possibility of a conspiracy.
(Hive Bee)
12-03-02 15:56
No 385945
All I have to say is this:
Racemic: a 50:50 mixture of enantiomers
Optical activity: 0 for a racemic
Enantiomers: Non superimposable images of each other
L-tartaric and d tartaric are enantiomer
Rotation can only be found experimentally
Meso compound: Stereocenters but a molecule with an internal plane of symmetry with the consequence of having 0 optical activity
Tartaric acid has no internal plane of symmetry and isnt therefore a meso.
Enantiomers dont have different physical properties except for their optical rotation. One would have a positive rotation, the other the exact same but opposite. Enantiomers are non superimposable images of each other
In this case the enantiomers are 2R,3R tartaric and 2S,3S tartaric acid
As far as melting points they are the same. A racemic mixture or a pure enantiomer will have the same melting point. Any mixture of enantiomer be its racemic or not will have the same melting point and physical properties(except again for optical rotation)
Diastereomers(which is what you would get using a racemic amphetamine of mdma mixture plus one enantiomer of tartaric acid)have different properties. These are separable and indeed tartaric acid is used as a resolving agent for amphetamines
Rhodium: I misread what you wrote. The natural form would be optically active where a racemic wouldnt like you said. Natural tartaric would only be one enantiomer
(Hive Addict)
12-03-02 23:10
No 386079
maybe meso is the wrong description, but i'm pretty sure that there
_are_ three forms of tatrtaric acid! at least i've got them in my head
right now. if you dont believe me: it has 2 stereocenters => 4 different
possibilties of arranging those. now try making a model of all those and
you will see that only 2 are equivalent, makes 3. (2 of those are mesomers
and the other one isn't, so i guess that would be meso according to your
description!?)
bye... i'm in a hurry, gotta leave..
(Hive Bee)
12-04-02 07:23
No 386197
Tartaric forms:
+ tartarid acid is 2R,3R
- tartaric acid is 2S,3S
A 2R,3S form would be meso youre right about that(sorry for not seeing it before)
I wonder if its present in nature, I doubt it,
+ tartaric is the isomer that occurs most abundantly in nature, it was actually used for determination of absolute configuration
I couldnt find anything about that form, I guess it could exist synthyntically. Anyone know how about they go synthesizing tartaric acid?
(Hive Addict)
12-04-02 09:09
No 386230
hmm... given that alpha-hydroxyacids can be made
from alpha-bromoacids, my first (and naive!) guess would
be bromination of fumaric/maleic acid and then hydrolysis.
if those reactions are stereoselective (i believe bromination is,
the latter can be SN2), i guess(!) that one of those will give
mainly the the racemate and the other one mainly the meso form...
or maybe not...
(Moderator)
12-04-02 17:12
No 386374
From Perkin's Organic Chemistry
Tartaric acid, or dihydroxysuccinic acid, is vegetable acids, and is contained in grapes, in the berries of one of the most commonly occurring species, the mountain ash, and in other fruits; during the secondary fermentation of grape-juice, which takes place in the casks, a considerable quantity of argol or impure potassium hydrogen tartrate, is deposited, and it is from this salt that the tartaric acid of commerce is obtained.
Tartaric acid can be obtained from succinic acid, and, therefore, from its elements, by reactions similar to those employed in the synthesis of malic acid; dibromosuccinic acid is first prepared by heating succinic acid with bromine (2 mols.) and water, and two hydroxyl-groups are then substituted for the two atoms of bromine in the usual way-namely, by heating the dibromo-derivative with water and silver hydroxide.
Tartaric acid may also be obtained synthetically from glyoxal, which, like other aldehydes, combines directly with hydrocyanic acid, the dicyanohydrin thus produced is decomposed by mineral acids, giving tartaric acid, just as cyanoacetic acid yields malonic acid, Tartaric acid is prepared on the large scale from argol. This crude, dark-red deposit is partially purified by recrystallisation from hot water, and its aqueous solution is then boiled with chalk, when insoluble calcium tartrate is precipitated, neutral potassium tartrate remaining in solution, the calcium salt is separated, and the solution treated with calcium chloride, when a second precipitate of calcium tartrateis obtained, The calcium tartrate from these two operations is washed with water, and decomposed with the theoretical quantity of dilute sulphuric acid; finally, the filtered solution of the tartaric acid is evaporated to crystallisation.
The tartaric acid obtained in this way is optically inactive and is a mixture of racemic acid and mesotartaric acid. This product is also optically inactive, and consists of racemio acid only. Tartaric acid forms large transparent crystals, and is readily soluble in water and alcohol, but insoluble in ether; it melts at about 167° but not sharply, owing to decomposition taking place. When heated for a long time at about 150°, it is converted into tartaric anhydride, and several other compounds, and on dry distillation it yields a variety of products, among others, pyruvic acid and pyrotartaric acid.
Tartaric acid, like other dicarboxylic acids, forms both neutral and acid salts, some of which are of considerable importance. Normal potassium tartrate is readily prepared by neutralising the acid, or the acid potassium salt, with potash; it is readily soluble in cold water, in which respect it differs from potassium hydrogen tartrate, which is only sparingly soluble. The latter is precipitated, the precipitation is much hastened by shaking or stirring with a glass rod. On adding excess of tartaric acid to a concentrated neutral solution of a potassium salt (test for potassium), and also on treating an aqueous solution of normal potassium tartrate with one equivalent of a mineral acid, it is known in commerce as argol or cream of tartar. Potassium sodium tartrate, or Rochelle salt, is obtained when potassium hydrogen tartrate is neutralised with sodium carbonate and then concentrated; it forms large transparent crystals, and is employed in the preparation of Fehling's solution.
Calrium tartrate, being insoluble in water, is precipitated on adding a soluble calcium salt to a neutral solution of a tartrate; it is readily soluble in potash, but is reprecipitated on boiling the solution, a behaviour which is made use of in testing for tartaric acid.
Tartar emetic, or potassium antimonyl tartrate, is prepared by boiling potassium hydrogen tartrate with antimonious oxide and water; it is readily soluble in water, and is used in medicine as an emetic, and in calico-printing as a mordant.
The detection of tartaric acid or of a tartrate is based (a) on the behaviour of the neutral solution with calcium chloride (in the cold), and on the solubility of the precipitate in potash; (b) on the behaviour of the neutral solution with an ammoniacal solution of silver nitrate, from which a mirror of silver is deposited on warming; (c) on the fact that the solid compound rapidly chars when heated alone, giving an odour of burnt sugar; it also chars when heated with concentrated sulphuric acid, sulphur dioxide and the two oxides of carbon being evolved.
That the constitution of tartaric acid is expressed by the formula given above is shown by the methods of formation of the acid; it is a dihydroxy-derivative of succinic acid, just as malic acid is a monohydroxy-derivative of the same compound.
On reduction with hydriodic acid, tartaric acid is converted first into malic, then into succinic acid, whereas, when heated with concentrated hydrobromic acid, it, yields dibromosuccinic acid, as was to be expected, It is a remarkable fact that four distinct modifications of tartaric acid are known-namely, dextrotartaric acid (the compound just described), levotartaric acid, racemic acid, and mesotartaric acid. These four compounds have the same constitution-that is to say, they are all dihydroxy-derivatives of succinic acid, they differ, however, in certain physical properties, as, for example, in crystalline form or solubility, but more especially in their behaviour towards polarised light; the salts of the four acids exhibit similar differences. This point is referred to later part
Dextrotartaric acid rotates the plane of polarisation to the right, levotartaric acid to an equal extent to the left.
Racemic acid is optically inactive; it is produced when equal quantities of the dextro- and levo-acids are dissolved in water, and the solution of the mixture allowed to crystallise. It may be obtained synthetically by heating an aqueous solution of dibromo-succinic acid with silver hydroxide, as described above; also from glyoxal. Racemic acid may be resolved into dextrî- and levo-tartaric acids.
Mesotartaric acid, like racemic acid, is optically inactive, but it cannot be resolved into the two optically active modifications; it is formed, together with racemic acid, when dextrotartaric acid is heated for a long time with a small quantity of water at about 165°, and when dibromosuccinic acid is heated with silver hydroxide.
(Hive Addict)
12-05-02 01:20
No 386465
that answers all my questions. so commercial tartaric can be
- natural isomer
- racemic
- racemic & meso
(perkin's seems to be a great book...)
(Stranger)
12-07-02 21:33
No 387367
d tartaric and d,l tartaric for sale cheap to individuals from a source onthe net that sells to individuals no problem--just look a bit