resolution of racemic meth

[hypo]

> More than likely the separation was done not based on visible differences in crystal
> geometry, however done through separation of visible crystals through crossed polaroids.

why?
it should be very easy to separate crystalls in right and left handed ones.
(just like you would be able to separate gloves for the right and for the left hand)

[methyl_ethyl]

why? it should be very easy to separate crystalls in right and left handed ones. (just like you would be able to separate gloves for the right and for the left hand)

I have no idea what you mean by this, in fact you do not even sound like yourself hypo  

My point is under crossed polaroids you will only see in your microscopic field either the d- or l- crystals depending on which way the polarizer is set up.

This makes separating the crystals much easier, than if you had all of the crystals visibly present in your microscopic field and were trying to separate individual crystals based on their geometry.

Take the glove scenario for example, it may be easy to seperate 100 pairs of gloves by looking at the way the fingers are arranged.  But it would be even easier if you put on a pair of glasses that "filter" out all of the left handed ones.  With these spectacles you can just grab any glove that is visible to you, knowing that you are only grabbing the right handed ones.  In essence this is what crossed polaroid microscopy would do in this case (theoretically).

regards,

methyl_ethyl

[Jacked]

Damn I'd hate to be the guy sitting there separating crystals under a microscope for a living.
 Just how would he keep from dragging what he cant see with the ones he can see to one side or the other? In other words how does the guy seeing only left handed gloves keep from accidentally moving a right handed glove along with it because its hidden from his view?
How would this polar filter see a raceamized materal?

[dwarfer]

If you shine a plane polarized light on the crystals,
you can dispense with the polarized spectacles..

anyway,
?
Hmf!: Ignored again.

Damn.

Consider a “Brownian Rachet”
etched in silicon for separation of the isomers.

Although I can’t find it
after 10 minutes of looking at Rhode’s site,
there is a crystalline difference
in the (S)-(+) and the (R)-(+) as I recall,
whihc should be
amenable to the approach..

As regards the (s)-(-) isomer,
if anyone has the MP and other
 conformational data, it would be
appreciated.

Also, if my speculation about temperature dependant precipitation/flocculation in stirred
poor solvency liquids is bunk, please advise.

[hypo]

of course i wasn't suggesting that it's easier to go by geometric
criteria. my point was that it's definitely possible given the right
crystall system and i'm pretty sure that it's what louis pasteur did.

note that this was 1849 and what they called microscope was probably a
better magnifying glass...

[indole_amine]

note that this was 1849 and what they called microscope was probably a
better magnifying glass...

Which makes a perfect reason against separation by geometrical appearance ("left-handed crystals"? Visible with pro-grade, adjustable magnifying glasses? How do d- and l-meth crystals differ in appearance? Why does a racemic crystal modification exist then?   ).
 
But even with a good magnifying glass and cross polarized light and/or filters you can differentiate very well between the different isomers by view...

Your point is (although originally, you said something else   ) that due to lack of good optic instruments, Louis Pasteur worked just based on the performance of these, and distinguished isomeric crystals just by view?

Sorry, but I don't get your point...

It is not possible to differentiate between optically pure isomeric d- and l-crystals unless their crystalline structure differs substantially, which is very uncommon as Rhod pointed out earlier.
Very possible (and applicable to every optically active salt!) on the contrary is the visualization of either the optically active (think about it) d- or l-isomer by simply irradiating with polarized light (a filter permitting only photons swinging up/down or left/right to pass, you know it). And the crystals aren't invisble with the "wrong" polarization: they just appear transparent, whereas the other isomer will appear whitish due to reflecting the light rather than letting it pass. All this assumed you figure out how to make most of the d- and l-salt visible at once: with using two contrary polarized light sources (with different wavelengths?) for example, and varying their positions/angle until you get a satisfying distribution of two differently colored crystal subsets, each consisting of mainly one isomer. You surely are aware of that too (as well as about the fact that it surely ain't got anything to do with entropy in this case   )...

And Pasteur knew it too, I would guess...



_{indole_amine}

[hypo]

> Which makes a perfect reason against separation by geometrical appearance

on the contrary. try separating crystals with tweezers under 20x and 1000x
magnification. my point was:
a) they did not have microscopes with all those fancy polarisation filter features
b) those crystals were rather big, ie. you could handle them with tweezers, so
you could watch them from all sides, which makes this rather easy. (funny sidenote:
i've seen my highschool teacher make a tiny hexagonal crystal stand on the small
side under a microscope. wow.)

> It is not possible to differentiate between optically pure isomeric d- and l-crystals
> unless their crystalline structure differs substantially, which is very uncommon as Rhod
> pointed out earlier.

well, tartaric acid
a) crystallises in pure d- and l- crystals
b) those crystals are handed
and no they don't "differ substantially", they are like mirror images.

but hey, don't take my word for it:

http://www.worldhistory.com/wiki/L/Louis-Pasteur.htm

Pasteur noticed, upon examination of the tiny crystals of tartaric acid, that the crystals came in two asymmetric forms that were mirror images of one another. Tediously sorting the crystals by hand gave two forms of tartaric acid: solutions of one form rotated polarised light clockwise, while the other form rotated light anticlockwise.

or from the horse's mouth:

http://web.lemoyne.edu/~giunta/pasteur60.html

I carefully separated the crystals which were hemihedral to the right from those hemihedral to the left, and examined their solutions separately in the polarising apparatus.

thanks for trying anyway...

[WizardX]

http://www.orgsyn.org/orgsyn/prep.asp?prep=cv5p0932

  R(+)- AND S(-)-a-PHENYLETHYLAMINE

http://www.orgsyn.org/orgsyn/prep.asp?prep=CV9P0387

  Part C.

http://www.orgsyn.org/orgsyn/prep.asp?prep=v76p0023

Part C to D.

[indole_amine]

OK, I'll try to make it short   :


-It begins with this post:

Post 503558

(zero_nrg: "Louis Pasteur used a micrscope and tweezers to", Stimulants)and a followup article posted by Rhodium...


-Methyl_Ethyl a few posts later mentions the use of 2 crossed polarized light sources to distinguish between l- and r-isomeric salts as being superior to the mechanic separation by hand.


-Then you question the use of crossed polarized light with the following words: "why? it should be very easy to separate crystalls in right and left handed ones. (just like you would be able to separate gloves for the right and for the left hand)"


-Then Methyl_Ethyl explains to you that it just is the superior method.


-You answer with (drumroll) "i wasn't suggesting that it's easier to go by geometric criteria" (tadaa - sounded like you at least suggested it "should be very easy", though...), and clarify about having meant that mechanical "per view" separation is possible with some salts, and that Pasteur used this technique. As "proof" you give the bad quality of his microscope..

(there's no logic behind that - it is in fact a proof for crossed polarized light isomer identification and against mechanical sorting at that time, if you think about it...)



Nothing new so far...



-Now I tried to explain that polarized lighting has the advantage of being applicable to all optically active salts (not only tartaric, but also visually not distinguishable hydrochlorides of optically pure d/l-isomers for example). To do so, I explained how polarimetric identification with 2 crossed light sources works.

-You claim that I said something wrong and present hexagonal crystals standing on their small side as an argument. You say that with big crystals, mechanical separation is easy and that tartric acid gives distinguishable crystal modifications (D'oh!)..


OK let me reiterate what I said before in four short sentences:

-crossed polarized light identification is more generally applicable and therefore advantageous compared to visual/manual separation with microscope/tweezers.
-Although seeming not in agreement with what I said, you still have given no reasonable exp. about which novel information you originally wanted to add to this thread?!
-It was already said that tartaric gives crystals with differing physical properties,
-and it was already mentioned that Louis Pasteur used the tedious "by hand" method on tartaric.

So far the important facts I re-checked....


"thanks for trying anyway..."

Well, you're welcome - even more if you try to understand what others write next time, before criticizing them...

(dividing a bunch of salt into optically pure isomeric salt modifications by hand can be a good occupation for the long winter months - hypo sittin there with his giant magnifying glass and a needle, while others just illuminate the scene correctly, take what they want and leave back the remainder - but hey! it's your time...)


_{indole_amine}

[hypo]

1) there was a misunderstanding between me and methyl_ethyl: i thought
she was saying that louis pasteur used polarised light.
2) the misunderstanding was cleared up by me saying that i was only talking
about pasteur and _nothing_ else.
3) you answered to that post adding "And Pasteur knew it too, I would guess..."
making clear that you are talking about pasteur too.
4) you were as usual wrong and have the cheekiness to sneak out of the situation
by misrepresenting facts.

> tadaa - sounded like you at least suggested it "should be very easy", though...

read the whole sentence. i said "very easy given the right crystal system".

> You claim that I said something wrong and present hexagonal crystals standing on
> their small side as an argument.

what? i added that as funny sidenote. this is _not_ presenting something as an argument.
it's becoming pretty obvious that you have a language problem and don't understand what
you are reading.

> To do so, I explained how polarimetric identification with 2 crossed light sources works.

nobody cared, because we knew it already. you just wasted bandwith as usual.

> while others just illuminate the scene correctly, take what they want and leave back the remainder

go ahead, i will make some diastereomer salt with an enantiomeric pure acid and
chromatography the shit. let's see who is the first to separate 10g of product.  

[indole_amine]

Hypo: I still fail to see your intention!

"1) there was a misunderstanding between me and methyl_ethyl: i thought
she was saying that louis pasteur used polarised light.
2) the misunderstanding was cleared up by me saying that i was only talking
about pasteur and _nothing_ else."

So you originally thought Methyl_Ethyl was talking about something, and so you started to ramble; but then you realized that you were wrong, and therefore you "cleared up the misunderstanding" by saying that at least YOU raised the issue?
Strange, at this point my understanding of your motivation becomes drastically diminished...

And "talking about Pasteur and _nothing_ else" is inappropriate as a reply to "I know a technique superior to that of Pasteur's: using crossed polarized light..."

And please don't complain about wrong citations of posts you just edited a few seconds ago...


My comments on the sentences you waste our precious bandwidth with (as usual)...

1) your problem if you misunderstand things, no need to start an argument, hm?

2) well of course you said different things; besides telling us about which method Pasteur used, you also said "my point was that it's definitely possible given the right crystall system" - and that's fine dude. Because noone has ever doubted this. No need to become angry...

3) Yeah, and I meant that Pasteur surely knew too about his separation method being only applicable for optically active salts with big crystal size. So what about it?

4) Sure, I forgot - I is me, and you is HYPO, of course I must be wrong...
(could you please show me where I am actually wrong?)




"what? i added that as funny sidenote. this is _not_ presenting something as an argument. it's becoming pretty obvious that you have a language problem and don't understand what you are reading"

Nobody cared, because we knew it already. you just wasted bandwidth as usual.



"nobody cared, because we knew it already. you just wasted bandwith as usual."

It is becoming pretty obvious that you have an ego problem and don't know when to admit having said something wrong...

(Why do you always become insultive if you can't prove yourself right - have had bad experiences during your childhood maybe?   )



"go ahead, i will make some diastereomer salt with an enantiomeric pure acid and chromatography the shit. let's see who is the first to separate 10g of product"

OK, at last you agree with the tediousness of manual separation (although you promoted it originally   ). Chromatography might be indeed the most practical way to go.

(Finally! hypo as we know him is back! Your unusual lack of logic/sqeamishness almost started to seriously worry me... )



_{indole_amine}

[hypo]

> Hypo: I still fail to see your intention!

the intention was to get historical facts straight:
pasteur used geometric properties, not polarised light.

reread this post, everything is cleared up therein:

Post 534944

(hypo: "eh..., sorry for being so unclear", Stimulants)

> And please don't complain about wrong citations of posts you just edited a few seconds ago...

are you insane? which post did i edit, apart from spelling fixes?
what citation did i complain about?

> could you please show me where I am actually wrong?

at your service! this post:

Post 535028

(indole_amine: "either way round...", Stimulants)
highly implies that pasteur used polarised light to separate the crystals. wrong.

> Why do you always become insultive if you can't prove yourself right

the funny thing is that in our discussions so far i have always been right, as
has been confirmed by other bees, and you always feel offended for no reason.

> don't know when to admit having said something wrong...

i have no problem admitting that. but i don't see anything by me in this thread
that was wrong or not coherent.

> OK, at last you agree with the tediousness of manual separation

i've never said anything different. too bad that you're not capable of understanding the
english language.