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Author: Subject: Improvement in the yield of racemic PPA*HCl via Akabori reaction (35 % molar)
turd
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[*] posted on 31-8-2010 at 14:42


Sorry for off-topic, but please help a complete OC-idiot:
Quote: Originally posted by Ephoton  
hmmm goodbye darzen :(

How do you make phenylpropanolamines via Darzens? I figure benzaldehydes, halopropionic acid alkyl esters and base give epoxides. But then - ring opening with ammonia or via PAC (phenylacetylcarbinol)? Or are you talking about a different Darzens? I don't get it. :(

PS: Thanks for the experimental details!
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[*] posted on 31-8-2010 at 14:53


Quote: Originally posted by turd  
Sorry for off-topic, but please help a complete OC-idiot:
Quote: Originally posted by Ephoton  
hmmm goodbye darzen :(

How do you make phenylpropanolamines via Darzens? I figure benzaldehydes, halopropionic acid alkyl esters and base give epoxides. But then - ring opening with ammonia or via PAC (phenylacetylcarbinol)? Or are you talking about a different Darzens? I don't get it. :(

PS: Thanks for the experimental details!


Hey turd thanks for dropping by :cool:

Im far from being an authority in this whole area but Im fairly sure those interested in the Darzens condensation, as an alternative to the work presented here, are looking forward to obtain the product of the catalytic dehydrative deamination of PPA;). No amino-alcohol will ever be involved in their scheme.

My bet is benzaldehyde condensed with a given 2-halopropionate alkyl ester followed by hydrolysis of the glycidic ester and decarboxylation/rearrangement of the epoxide .

QD
[Edited on 1-9-2010 by Quantum_Dom]Typo

[Edited on 1-9-2010 by Quantum_Dom]




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[*] posted on 1-9-2010 at 10:41


Oh, I see. Thanks for clearing that up.
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Melgar
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[*] posted on 1-9-2010 at 21:56


A bit off-topic, but are there any good ways of getting benzaldehyde from benzyl alcohol? I found one that uses DMSO and HBr, but it recommends like 5 times as much DMSO as benzyl alcohol, and DMSO and benzaldehyde have similar boiling points so it seems they'd be hard to separate.
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[*] posted on 1-9-2010 at 22:32


Quote: Originally posted by Melgar  
A bit off-topic, but are there any good ways of getting benzaldehyde from benzyl alcohol? I found one that uses DMSO and HBr, but it recommends like 5 times as much DMSO as benzyl alcohol, and DMSO and benzaldehyde have similar boiling points so it seems they'd be hard to separate.


Thats actually a very good question and usually people who havent spent a great time tackling it will claim facile and high yielding conversion with gentle oxidizers and conditions or two-steps procedures via hydrolysis of benzal chloride or oxidation of benzyl chloride to name a few.Well all I can tell you is that I guess it depends if youre looking for a preparative scale procedure, in order to obtain a decent amount for various future experiments, or is it simply on a pure interest of synthesizing a little benzaldehyde.

The latter procedures involve cumbersome work-ups, a great amount of work for a less than modest payoff IMHO. Especially for the direct oxidation of benzyl alcohol as it is rather a pain to separate it from benzaldehyde. And people that will recommend you to use the bisulfite adduct procedure, when youre working almost on a molar scale, just dont know any better ;). This is why I wouldnt recommend benzyl alcohol as a facile and worrieless substrate for benzaldehyde. IIRC Klute predicted high yields using catalytic amount of 4-oxo-TEMPO (from triacetonamine) with an oxidizer such as an hypochlorite salt or TCCA but cant figure out where I saw him say that :(. Ill look and let you know if you want.


Im curious about your proposal, dont think I ever heard of it. Do you have any references or a link to a thread here ? It sure is a lot of DMSO if you want to work on a preparative scale though.:o

QD

[Edited on 3-9-2010 by Quantum_Dom]




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[*] posted on 2-9-2010 at 01:29


Quote: Originally posted by Quantum_Dom  

Please try to work on the quality of your post and avoid posting half-ass information and gibberish. This thread is not about any diastereomers of ephedrine either.

Tasting an isolated compound in hoping to characterize it is absolutely irresponsible and dangerous :mad:. If you are proning such methods, I have no desire to discuss this procedure with you.

[Edited on 31-8-2010 by Quantum_Dom]

Please calm down and dont Disrespect
I dıd this reaction several time according to another threat on this site(i forget link)i know chemistry of drug and i know tasting small amount of ppa is not dangerous also i know PPA has bitter taste but my PPA(by akabori reaction) is sour.
İ think impurity is amino acid.i dont want to make ephedrine and as you wrote before I just referred to maknig N-methyl-alanine from Pyruvic acid




Chemistry=Chem+ is+ Try
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Quantum_Dom
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[*] posted on 2-9-2010 at 16:33


Quote: Originally posted by hector2000  

i know chemistry of drug and i know tasting small amount of ppa is not dangerous also i know PPA has bitter taste but my PPA(by akabori reaction) is sour.

No, tasting (regardless of the quantity involved) a product you do not know the nature or idendity makes you a cook, not a chemist.

Quote: Originally posted by hector2000  

İ think impurity is amino acid.i dont want to make ephedrine and as you

No, again you do not know as you havent characterized the said impurity with valid chemical analysis techniques.




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Melgar
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[*] posted on 2-9-2010 at 19:41


I attached the paper where they oxidize benzyl alcohol to benzaldehyde with DMSO. Seems the end products are dimethyl sulfide (which has a low boiling point) and water. But maybe the huge excess of DMSO can be avoided?

Attachment: dmso_oxidation.pdf (25kB)
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[*] posted on 2-9-2010 at 19:43


Quick question... On the previous page methyl_magic posted a picture of his reaction mixture after several toluene washes and addition of NaOH... please correct me if I am wrong (I am having difficulty finding information on DPEA freebase), but it looks as though the DPEA is prone to forming some sort of emulsion with the aqueous phase, or at least it is not as quick as the PPA freebase to separate from the aqueous phase.. or it has a greater specific gravity than water... If any of these is the case, could a number of repeated washes with water and shaking be used en lieu of a chlorinated solvent or distillation?
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[*] posted on 3-9-2010 at 12:00


QD you're a lifesaver as i have a bitch who suffers badly from incontinence.
i will give one recommendation but this is some fine chemistry
that Aq phase holds some ppa mayb e 5g/100ml
i would suggest you salt it while it's warmed until it can hold no more salts and add ipa and separate the ipa after 30 seconds of stirring or so.
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Methyl.Magic
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[*] posted on 5-9-2010 at 13:27


Hi !

I am a bit late sorry but Im just back from france. So here is the last part of my workup. I have not the final yield yet.

After let the solution for 1 night, the white scum dissapeared. The solution is extracted with 3x100ml 1x50 ml of toluene. The solvent is rotavapored off and the resulting brown oil is dissolved in 3 times its volume of acetone, then titrated with 37% HCl. White crystals immediatly formed. The flask is put in the freezer for a few days.

The brown PPA freebase


Crystallisation with conc. HCl


The aqueous solution is extracted with 3x50ml DCM. This latter is dried over MgSO4 and boiled off. The resulting yellow/orange oil is dissolved in 3x its volume of acetone and is titrated with conc HCl to give tiny amount of white crystals.

After removed DCM


second crystallisation (in acetone/DCM)


The first crop is filtrated through a buchner and the cake is washed with 2x30ml acetone. The crystals are still drying in an oven at 80°C.



The second crop is filtrated, washed and dried separately. The expected yield is poor. Im waiting for the results before posting comments.

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[*] posted on 5-9-2010 at 16:53


Hi Methyl.Magic :)

Thanks for reporting back, I must say Im very suprised the white suspension you obtained went back into solution, but again I never did a work-up without reducing the water extracts by at least half the initial volume. I hope you kept you aqueous layer, if you did I would recommend to reacidify the latter untill pH 2-3 and evaporate slowly the water to a maximum and repeat the acid/base extraction. You should be able to extract the remainings but they will be contaminated. It would interesting IMO to establish a separation method of PPA*HCl and DPEA*HCl.

Thanks again for the lovely images :cool: (nice rotavapor, im jealous :P)
QD

[Edited on 6-9-2010 by Quantum_Dom]




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[*] posted on 6-9-2010 at 05:28


Hey !

I was also surprised the scum went back into the solution... There was another strange thing, too : When I shaked the solution with toluene for the first time, the toluene layer was slightly yellow. I let the solution in the funnel overnight. The next day, the scum dissapeared. The yellow toluene was separated out and the aqueous solution was extracted again with toluene. Now the toluene is brown...

The main reason why I didnt concentrated the water solution is I thought PPA freebase is much more soluble in toluene than water and the aqueous layer contains plenty of NaCl formed when I neutralised with 25% NaOH.

I have no idea about separating DPEA from PPA. But when I washed the cake with acetone, some crystals went away with acetone. I have no idea about the solubility of PPA HCl in acetone but I think it can be like ephedrine (poor solubility).

I think the main mistake I did was while the extraction of tar with HCl. You used DCM which dissolved the tar and makes it more "extractable". My tar was extremely sticky and it was difficult for the acidic water to go through. The PPA could clutch at the tar and couldnt be protonated and solubilised in acidic water even with the several days stirring I've done.

Another mistake is I didnt check the reflux temperature during the first step.

The main problem with this method, beside poor yield, is benzaldehyde must be used in large excess (6 eq.). BA (not BnO ! ) is the most expensive reagent here and despite of its large excess it's difficult to recover it (did you try ??) because of the tar. Distillation is not possible, maybe you should form the bisulfite adduct if not many tar.

Next time I'll try again, like you can see in the picture of my report, the condensation of nitroethane with BA then reduction with H2SO4/Zn HCOOH/Zn or HCl/In.
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[*] posted on 6-9-2010 at 06:16


Quote: Originally posted by Methyl.Magic  

The main reason why I didnt concentrated the water solution is I thought PPA freebase is much more soluble in toluene than water and the aqueous layer contains plenty of NaCl formed when I neutralised with 25% NaOH.


Its understandable as I too was not too keen in vaporizing all that water at first. But I assure you that a great deal of material was left in that aqueous phase when you treated it with NaOH.

Quote: Originally posted by Methyl.Magic  

I have no idea about separating DPEA from PPA. But when I washed the cake with acetone, some crystals went away with acetone. I have no idea about the solubility of PPA HCl in acetone but I think it can be like ephedrine (poor solubility).


Very interesting, I dont have data regarding solubility in acetone of either compound. Was the acetone thoroughly dry and cold ? Was it evaporated to isolate the material that it solvate ?

Quote: Originally posted by Methyl.Magic  

I think the main mistake I did was while the extraction of tar with HCl. You used DCM which dissolved the tar and makes it more "extractable". My tar was extremely sticky and it was difficult for the acidic water to go through. The PPA could clutch at the tar and couldnt be protonated and solubilised in acidic water even with the several days stirring I've done.


Im not sure I understand what step you are referring to, Im confuse. Im having a hard time understanding if you are talking about the DCM wash of the HCl extracts or the hydrolysis step right after the decarboxylation.

Quote: Originally posted by Methyl.Magic  

Another mistake is I didnt check the reflux temperature during the first step.


Yes I think this was a bit too much, the decarboxylation does not need to reach reflux. Leaving it at that temperature for so long also (8 hrs) is too long IMO and might have contributed in the great amount of tar you obtained.


Quote: Originally posted by Methyl.Magic  

The main problem with this method, beside poor yield, is benzaldehyde must be used in large excess (6 eq.). BA (not BnO ! ) is the most expensive reagent here and despite of its large excess it's difficult to recover it (did you try ??) because of the tar. Distillation is not possible, maybe you should form the bisulfite adduct if not many tar.


Indeed, it is wasteful in benzaldehyde, especially if the latter is hard to obtain for an experimenter. Even if its readily available and cheap, the yield of PPA*HCl will always be low. So in terms of efficiency, there is no doubt in my mind that the reaction will never be viable. If my reactional parameters are use, the np layer after hydrolysis needs to be washed with diluted aqueous sodium carbonate 3-4 times. Then one can vacuum distill a fair amount of benzaldehyde back. Again, I guess the main reason you couldnt claim any back was the rather high temperature you used and reaction time too. An awful lot must have polymerized. I also remember that it was contaminated with benzoic acid, maybe it could be a factor too.


Quote: Originally posted by Methyl.Magic  

Next time I'll try again, like you can see in the picture of my report, the condensation of nitroethane with BA then reduction with H2SO4/Zn HCOOH/Zn or HCl/In.


Ah now I understand ;). Did you took a melting point of your produt ? TLC ? Any attempt to characterize ? It will be nice to compare with a sample obtained via condensation/reduction of benzaldehyde and nitroethane.

Thank you very much for sharing data Methyl.Magic:)

QD




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[*] posted on 6-9-2010 at 10:46


Just some ideas here: would this reaction be inhibited by either benzoic acid or benzyl alcohol? If so, which one would inhibit it more? Also, what would be a better ratio to use if trying to maximize yield with respect to alanine?

I've made benzaldehyde before by ozonolysis of styrene, and also by oxidation of benzyl alcohol. It's kind of tricky to purify though.
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[*] posted on 6-9-2010 at 11:42


Quote: Originally posted by Melgar  
Just some ideas here: would this reaction be inhibited by either benzoic acid or benzyl alcohol? If so, which one would inhibit it more? Also, what would be a better ratio to use if trying to maximize yield with respect to alanine?


Good question, of course I will only speculate but if the media is fairly acidic, this could influence the reaction greatly as an intermediate carbanion is formed in the mechanism and would be quenched by an acidic media. Theyre is also the influence on the reactivity of alanine as the amino group will be protonated in sufficiently acidic media. The list goes on and I cant really speculate much without actual data. The only way of figuring out the optimal benzaldehyde ratio, without overkilling it, would be to establish an experimental design where yields of PPA are calculated with respect to the variation of initial benzaldehyde equivalents used. Thats the only way.

Quote: Originally posted by Melgar  

also by oxidation of benzyl alcohol. It's kind of tricky to purify though.


You did ? Which procedure did you used ? I thought you never tried it before as you said earlier you were looking for a procedure to do it ? Sorry, I surely misunderstood you ;) Thanks for the DMSO paper by the way :) (I dont think it is a viable way but its just a hunch).




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[*] posted on 6-9-2010 at 19:10


Actually, I was more interested in optimizing yield based on benzaldehyde, since alanine is really easy to get here but not so for benzaldehyde. Right now I'm trying to oxidize benzyl alcohol by stirring it with chlorine bleach. It definitely has the benzaldehyde smell, but we'll see if the Cannizzaro reaction plays a major role with those reagents. I'm interested in knowing if adding alanine slowly to the benzaldehyde could improve yields, since there would be a high aldehyde/amino acid ratio at the beginning, theoretically improving yields. But maybe it doesn't matter at all? Once I get the benzaldehyde I'll have to give it a shot.
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[*] posted on 7-9-2010 at 13:16


Hi,

I've just done the melting point test... It starts melting at 255°C and totally melted at 280°C ...

Litterature : PPA = 190-200°C

I think we got the wrong product... Did you analyse yours ?
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[*] posted on 7-9-2010 at 13:17


oh I forgot the yield...

total amount is 3.6g ... A big Deception :(
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[*] posted on 7-9-2010 at 14:30


Quote: Originally posted by Methyl.Magic  
Hi,

I've just done the melting point test... It starts melting at 255°C and totally melted at 280°C ...

Litterature : PPA = 190-200°C

I think we got the wrong product... Did you analyse yours ?


Methyl.Magic, have a look at the third paragraph in my original post for product characterization.

Your product is too contaminated to make an assumption, but it seems like its mostly benzylamine *HCl

Identification
Name Benzylamine hydrochloride
Synonyms Benzylammonium chloride
Melting point 262-263 ºC
Water solubility SOLUBLE




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[*] posted on 7-9-2010 at 14:46


The erythro isomer: hydrochloride mp = 172-194 °C, free base mp = 100-105 °C
The threo isomer: hydrochloride mp = 171-173 °C, free base mp = 71-105 °C
These are actually just some averages from several sources, because there are very different data, particularly for the free bases (some as low as 50 °C). In essence, for both diastereoisomers, the melting points are similar, except maybe a bit higher for the erythro isomer.

The hydrochloride of the 1,2-diphenylethanolamine erythro isomer has a mp = 215-216.5 °C.

I see that some people still did not bother to learn the theory of liquid-liquid extraction. The solubility is not directly correlated to the partition coefficient - contrary to what some here believe. I'm not going to repeat myself, so I will just point to another thread: http://www.sciencemadness.org/talk/viewthread.php?tid=12017
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[*] posted on 7-9-2010 at 16:32


Quote: Originally posted by Melgar  
I'm interested in knowing if adding alanine slowly to the benzaldehyde could improve yields, since there would be a high aldehyde/amino acid ratio at the beginning, theoretically improving yields. But maybe it doesn't matter at all? Once I get the benzaldehyde I'll have to give it a shot.


Sorry I missed out your post earlier on. I also was considering, in my previous work prior to the one posted here, introducing slowly the amino acid within the reaction flask in order to keep the ratio of benzaldehyde/alanine high in all times. But the side reactions do not involve a too high concentration of alanine. The main points that are favoring side-reactions are rather related to the stability of the different intermediates involved in the mechanism. The main reason for large excess of benzaldehyde is to make sure that the intermediate carbanion reacts with another equivalent of aldehyde rather than with water (see illustrated mechanism).


Edit: I would also like to bring your attention to this study. It reports that when an equimolar amount of a (un)substituted benzaldehyde is dripped in a slurry of amino acid refluxing in DMF, large amounts of the corresponding benzylamine can be isolated. On the other hand, when 4 equivalents are used the corresponding alkamines (amino-alcohols) are rather obtained.

QD

[Edited on 8-9-2010 by Quantum_Dom]

Attachment: A Novel Synthesis of Benzylamines.pdf (619kB)
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[*] posted on 10-9-2010 at 14:35


Reaction was prepared á la original Quantum Dot with some modifications as listed below.

1. LG 500 mL Benzaldehyde and and LG 50g D,L Alanine were stirred for 20 min before being heated on a 150 C bath for 3 hours.

[CO2 was observed evolving after 20 min of heating. After 3 hours, solution was not black but more a dark golden yellow. Assumed less by-products were present.No distillate was collected. ]

2. Solution cooled before 150 mL of 5% AcOH in Toluene was added. Stirred 20 min. 500 mL of 15% HCl added.

3. Gently refulxed for 3 hours.

[Mixture appears identical to figure 2 of the QD write up]

4. Left to cool slightly before being separated warm.

[On separating, aqueous phase is a lot less orange in color than in figure 3 of QD but tar layer is similar colour]

5. Washed aqueous with 3x 100 mL of DCM.

[NP solution dark brown, aqueous slightly yellowish]

6. Reduced aqueous solution through vaporising by 1/5

[No fume hood available and the vapor was yuk so stopped earlier than would have liked]

7. Washed with 3x 100 mL DCM

[NP solution very light dark brown, aqueous still slightly yellow, almost clear]

8. Treated aqueous with saturated NaHCO solution, followed by aqueous NaOH until strongly basic

[Strong aqueous basic solutions were added. NaHCO resulted in lots of fizzing. Took a lot of base to make basic ~ 500 sat. NaHCO and 500 mL very strong NaOH. Upon approaching basic, a white cloudy fraction appeared in the bottom of the beaker and spread through out on additional base additions. No oily fraction was observed as in figure 7.]

9. Extracted aqueous phase with 4 x 200 mL of DCM.

[no brown colour was observed in DCM fraction]

10. Removed DCM via evaporation overnight.

[Approximately 5 g of white solid with distinctive green tinge remained after all DCM had been removed]

All solutions have been kept. Any suggestions on where the PPA is (if there is any) and how to get it out would be much appreciated.

Lots of love,

Francis
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[*] posted on 10-9-2010 at 17:24


Quote: Originally posted by Francis Crick  
Reaction was prepared á la original Quantum Dot with some modifications as listed below.


My user is Quantum_Dom

Quote: Originally posted by Francis Crick  

1. LG 500 mL Benzaldehyde and and LG 50g D,L Alanine were stirred for 20 min before being heated on a 150 C bath for 3 hours.

[CO2 was observed evolving after 20 min of heating. After 3 hours, solution was not black but more a dark golden yellow. Assumed less by-products were present.No distillate was collected. ]


Dont know if I understand right but did you keep stirring while the decarboxylation was performed ? It is critical.


Quote:

6. Reduced aqueous solution through vaporising by 1/5


Only a 1/5 of the initial volume? It is not enough. I reduced the volume by half and it was the bare minimum IMO.

Quote:

Treated aqueous with saturated NaHCO solution, followed by aqueous NaOH until strongly basic

[Strong aqueous basic solutions were added. NaHCO resulted in lots of fizzing. Took a lot of base to make basic ~ 500 sat. NaHCO and 500 mL very strong NaOH. Upon approaching basic, a white cloudy fraction appeared in the bottom of the beaker and spread through out on additional base additions. No oily fraction was observed as in figure 7.]


So if I understand correctly, you reduced the volume of the aqueous acidic extracts to only rediluted them later by adding aqueous solution of base ??? Is that correct ? If it is, it does not make much sense as the sole purpose of reducing the volume of water is to force any material to separate from the latter in the first place.


Well all I can suggest is that youre material is still in the aqueous phase since you omitted to reduce the latter properly and rediluted it by adding aqueous alkaline afterwards. The alkaline material (NaHCO3 and NaOH) needs to be add as is, not in solution regardless of the concentration.

Hope it helps,

QD





[Edited on 11-9-2010 by Quantum_Dom]




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thumbup.gif posted on 10-9-2010 at 19:35


Sorry about the naming issue QD, brain must have been skim reading your name for a while :o your work is very much admired from these parts

Yes, the aqueous was reduced then aqueous base added to it as it was thought a LOT less base would be needed than was required.

If there is indeed still PPA present in the aqueous, would one expect to see the freebase rise to sit on top as the volume reduces? Or would it be better to acidify with HCl, reduce volume then basify again to get at the freebase?

And is the freebase actually brown or that just a result of byproducts present in the sample prior to the crystallization?
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