Chan
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Concentration of organic phase without rotovap?
After separation and washing, the non-polar organic phase remains as a hydrochloride solved in dichloromethane.
Since we do not have access to a rotovap, I wonder how it could be concentrated?
Someone suggested simply magnetic stirring (evaporation of DCM over time) which should leave the crude hydrochloride salt. Is this an option?
Since DCM has such a low boiling point (39.2 °C), would heating to 40+ °C while stirring be feasible to accelerate the process?
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Sulaiman
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Provided that your non-polar organic phase does not decompose, form an azeotrope with dcm, or vapourise near 40oC it should be ok
go slowly on the last part, and consider the dcm fumes.
CAUTION : Hobby Chemist, not Professional or even Amateur
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fusso
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Hydrochloride salts should be highly polar. Are you sure the solute in DCM is hydrochloride salt instead of the free base?
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Chan
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Quote: Originally posted by Sulaiman  | Provided that your non-polar organic phase does not decompose, form an azeotrope with dcm, or vapourise near 40oC it should be ok
go slowly on the last part, and consider the dcm fumes. |
Slower is better, I got you. I guess one could try
with a small amount of the solution and would see what happens. Adequate ventilation is important, thanks for the tip.
[Edited on 3-3-2019 by Chan]
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Chan
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| Quote: Originally posted by fusso | | Hydrochloride salts should be highly polar. Are you sure the solute in DCM is hydrochloride salt instead of the free base? |
I am as certain as the authors of the academic paper published in a reputable chemical journal. No more.
Maybe the hydrochloride form of certain organic molecules is non-polar? Would that be possible?
We haven't tried the procedure, and probably never will, we are just thinking it through.
According to the authors, the product will remain as a "non-polar hydrochloride" in the dichloromethane layer. It should be in hydrochloride form
because the phase had been shaken with HCl before what would (according to the paper) convert all still remaining compounds (along with the product)
into hydrochloride form.
The separation of the product (from the remaining unwanted compounds in HCl form) seems to happen because the salt of the product molecule is
non-polar. All the remaining compounds in HCl form (which seem to be polar) would land up in the aqueous layer.
The authors suggest treating the salt of the product with NaOH to get the freebase form, but our experiment would stop at the crude salt (or eventual
recrystallization for purification).
[Edited on 3-3-2019 by Chan]
[Edited on 3-3-2019 by Chan]
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fusso
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So it's the hydrochloride of what (amine)?
[Edited on 190303 by fusso]
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zed
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Yup! As fusso has intimated. The term "Hydrochloride Salt" suggests your product is an amine. Such a "salt", would be polar and as such, would
likely be insoluble in DCM.
Provide a link to, or a transcript of, the original procedure.
Happy to help, if possible, but we need more, and better.... information.
Otherwise, rotovap lacking, slowly injecting such a solution into a vacuum (flash/freeze drying), might serve as a method of concentration.
[Edited on 3-3-2019 by zed]
[Edited on 3-3-2019 by zed]
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Heptylene
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I usually vacuum distill off the solvent for recovery. In the case of DCM, no vacuum, except to dry the product at the end. You don't need a rotavap
for most things, though it makes life easier.
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DraconicAcid
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Dichloromethane is sufficiently polar to dissolve numerous ionic compounds in my experience, particularly ones with huge organic cations.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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fusso
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| Quote: Originally posted by DraconicAcid | | Dichloromethane is sufficiently polar to dissolve numerous ionic compounds in my experience, particularly ones with huge organic cations.
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For example?
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DraconicAcid
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Bis(triphenylphosphine)iminium chloride comes to mind, along with several dozen complexes containing bis(diphenylphosphino)methane ligands (with
chloride, tetrafluoborate or triflate counterions).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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draculic acid69
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Methylamine HCl is insoluble in DCM whereas trimethylamine HCl is soluble.
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Dr.Bob
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I have isolated some lipophilic amine HCl salts in the DCM layer, you need about 4-6+ carbons in the molecule. If you have an amine in DCM then wash
with aq.HCl, dry the organics well, then concentrate the DCM and either cool it or add ether, the salt will often ppt. I was making a
mono-FMOC-protected diamine, which is not stable as the free amine and thus was isolated as the HCl salt. Even better, the unprotected diamine was
water soluble, and the bis-protected did not make the salt, so it did not ppt. Great way to purify it.
You could simply blow air/nitrogen over the DCM solution, preferably then over an ice cold or dry ice trap to recover the DCM, or distill it with a
40C water bath. If the compound is stable, 40C should be fine. In my case, I did it very cold under a good vacuum on the rotovap.
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