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Agent MadHatter
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What does partitioned mean?
I was looking over a text book and it said:
The solvent is removed under vacuum and the residue partitioned between EtOAc (or other suitable solvent) and saturated NaHCO3 (or NH4OH). The layers
were separated and the organics were washed with NaHCO3 (or NH4OH), H2O, saturated NaCl, dried over MgSO4
Im not sure what this means, but I think it means, to use chromatography to purify whatever chemical it was talking about by putting the solution,
baking soda, and a solvent in the column, then the solution was washed with more baking soda and table salt, then dried...
Is this correct? Also, whats the best way to wash something?
I don't know what chemicals it was talking about, I just saw it in my textbook today in class and was curious what it meant.
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crazyboy
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Hmmm not sure but it's possible "the residue" is lighter than saturated NaHCO3 but heavier than ethyl acetate meaning it would form a layer between
the two compounds.
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Agent MadHatter
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But would would you do with that layer? Could would you remove it?
would you use a column filled with silca? Or would you just throw that in a separation funnel?
Also. If your using an Erlenmeyer Flask, how would one remove the substance from the flask?
For example. If I was doing a recrystallization (just watched a video on it) and the crystal reformed in my flask, I pour the water out of it, I'm
left with a glob of crystals at the bottom. How would I remove these?
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Arrhenius
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Performing a partition is a liquid-liquid extraction. The "partition" physically is the boundary between the two immiscible solvents. If you want to
partition between ethyl acetate and aqueous base, it's as simple as placing the two in the flask (with your synthate or analyte of course) and -
presumably - extracting your compound into the organic phase by shaking the mixture to an emulsion and letting the two layers separate back out. The
aqueous layer is discarded here. The organic phase can then be washed - here with base, then water, then brine - dried and evaporated to afford a
product freed of carboxylic acid containing impurities (good to remember bicarbonate can deprotonate carboxylic acids, but not phenols). Doing a
final shake with brine to remove water from the organic phase is, in my opinion, not desirable on a small scale. Typically a separatory funnel is
used to perform a partition. Hope this makes sense.
[Edited on 30-7-2009 by Arrhenius]
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Agent MadHatter
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Thank you so much!
So if I wanted to copy this (I believe this is on my test so I'm trying to get it down)
I'd that the solution, add a mixture of Ethyl acetate saturated with baking soda, then pour out the ethyl acetate, put the original solution back into
a different flask.
Once in another flask after being mixed with the ethyl and the baking soda, I'd pour in water, and baking soda, then add in MgSO4, mix up abit, then
remove the original solution through a sep. funnel. Ending with a pure-er than before, substance?
EDIT: Also, when drying with brine, do I just scoop some into the flask, then shake? How would I remove the brine?
[Edited on 30-7-2009 by Agent MadHatter]
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Arrhenius
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First off, when you read something and a solvent is not given, it's fair to assume it's water. So if I say "saturated sodium bicarbonate solution"
assume it's in water. Or "brine" which is saturated sodium chloride.
Here would be the procedure (leaving out the brine wash):
The synthetic product is diluted in ethyl acetate and transferred to a separatory funnel. Saturated sodium bicarb is added and the funnel shaken,
then the layers allowed to separate. The lower layer (bicarb) is drained off and fresh bicarb is added and the process repeated again with bicarb,
once with water, once with brine (saturated NaCl) and finally the remaining ethyl acetate is drained into a beaker or flask containing some magnesium
sulfate and allowed to stand until clear. The ethyl acetate is decanted or filtered off the drying agent and the drying agent rinsed with a little
fresh ethyl acetate. The ethyl acetate is evaporated to give the product.
Here's a simple hypothetical situation:
Ethyl benzoate is prepared by Fischer esterification of benzoic acid with ethanol. The reaction may not have gone to completion, so we would like to
remove any residual benzoic acid. So, the crude product is diluted in ethyl acetate and subject to the above procedure. The benzoic acid is
extracted into the basic bicarbonate layer, while the ethyl benzoate remains dissolved in the ethyl acetate layer. The final product is ethyl
benzoate free of benzoic acid.
Make sense?
brine
If you want to make brine, just add salt to a bottle of water until you can't dissolve any more and a nice lump of salt remains at the bottom of the
bottle. The liquid is brine.
After performing a partition between ethyl acetate and some aqueous solution, the ethyl acetate will have soaked up a small amount of water and
appears to be a bit cloudy as a result. One way to get rid of some of this water is to add brine and shake/separate as described above. This works
on principles of osmotic pressure. The ethyl acetate should be fairly clear after shaking with brine, though it's not completely dry.
[Edited on 30-7-2009 by Arrhenius]
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Agent MadHatter
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I know some of the chemicals we are using in our labs shouldn't be mixed with water (All the solids are anhydrous, even the solvents are) so are you
sure saturated means a mixture of solid and water?
Other than that, yes it makes perfect sense =) Thank you.
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ammonium isocyanate
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Saturated means that a solution can dissolve no more solute than it already has. A saturated solution is a liquid, and by definition must be
homogeneous (the same throughout).
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Magpie
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| Quote: |
So if I wanted to copy this (I believe this is on my test so I'm trying to get it down)
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What kind of a class are you taking where all of this might be on the test but hasn't already been explained by the instructor?
The single most important condition for a successful synthesis is good mixing - Nicodem
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Agent MadHatter
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Pop quiz. Its the beginning of the semester, its not graded, but I don't want to seem like I haven't done my homework you know?
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Magpie
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How would one synthesize a BOP reagent?
(Benzotriazole-1-yl-oxy-tris-(dimethylamino)-phosphonium hexafluorophosphate)
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Do I understand this correctly?: You want to synthesize the above compound but you don't know what "refluxing" and "partitioned" mean. Seems you
have the cart way before the horse.
The single most important condition for a successful synthesis is good mixing - Nicodem
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crazyboy
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Honeststy will get you much farther than lies around here. First it's
"I just saw it in my textbook today in class and was curious what it meant. "
Then
"Pop quiz. Its the beginning of the semester"
And as mentioned by Magpie you want to synthesize (Benzotriazole-1-yl-oxy-tris-(dimethylamino)-phosphonium hexafluorophosphate) but don't know what
"saturated" means.
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JohnWW
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Actually, ethyl acetate would usually be a very poor choice of solvent to do a liquid-liquid solvent extraction with water or an aqueous solution of
an ionic salt as the other solvent, because it is soluble in water to the extent of 8.5 parts per 100 parts at 15ºC, according to Perrys, and
probably even more miscible at higher temperatures. It is also miscible with ethanol in all proportions. What was the solute that you were trying to
extract?
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Agent MadHatter
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You guys are thinking i'm lying but I'm really not. I'm taking a small organic chem course before the actual school starts to get ahead, and while
flipping through the book I saw some cool reactions I'd love to try at home. But so far, the majority of them require chemicals that only a lab can
buy. For example a BOP. Hence wanting to make it. And just because I was unsure if saturated meant water, or another liquid, doesn't mean I'm not able
to want to try labs at home.
So before you assume I'm lying. Why don't you think alittle bit before you act like assholes.
Its extremely rude. Though I am grateful for the help, the people bashing on me for being curious don't do anything besides flame.
John, I didn't pick the solvent the book used, who knows, maybe its made for a lab in school and ethylacetate is the easiest/safest chemical? I'm not
sure as to what solute they are extracting, it was some extraction, maybe Limonene? Or some alkaloid? I'm not sure.
What other solvents would you recommend?
I'd like to find a lab I can try at home, that covers the basics, distillation, refluxing, TLC, filtering, all that, so when my semester starts I can
get ahead. I'm actually hoping to major in organic chemistry.
[Edited on 31-7-2009 by Agent MadHatter]
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ammonium isocyanate
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Nobody here is trying to flame or degrade you. The simple truth is that these reactions you have posted about are above your current level. The
people here just wan't you to slow down and study up before building up to such reactions so that you don't get frustrated, or worse, hurt.
This would apply to the BOC synthesis especially. I haven't seen the proposed synthesis, but I can almost guarantee I wouldn't try it. And I'm
certain I don't have the reagents (which I'm guessing includes PF5).
We try to welcome new people to home chemistry. Just learn to walk before you try to run. 
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Agent MadHatter
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Well...I can't ask my professor at the time, since he rarely even shows up to class, so I'm forced to look online...then I don't know what half of it
means, so I post on here to get an understanding of how hard it is...then I get told I don't know enough chemistry. So I look for other labs to do.
"If you can say you've never failed, then you arn't pushing hard enough"
Why walk, when you can jog?
Atleast thats my motto in life.
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watson.fawkes
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Overall, this is the right motto,
but be aware that certain failures in chemistry will maim and kill.
Acquire yourself a copy of "The Organic Chem Lab Survival Manual". It's the best compact volume I've seen about how to deal with the gear ordinarily
found in a chemistry lab. It has a whole chapter on extraction and washing (which includes the topic of the original question). It's also the only
place I've come across with a good account about how to keep a lab notebook. (Hint: You are keeping it for your future, memory-impaired self.)
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Arrhenius
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JohnWW: No, you're wrong... sorry. Ethyl acetate is a fine solvent. It's environmentally friendly cheap, and works perfectly fine for aqueous
workups.
Agent Madhatter: Ask as many questions as you want. I don't care how you learn it or what you want to do with it, but I'm happy to share what I
know.
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Agent MadHatter
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Thank you =) I'll get myself that book.
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stoichiometric_steve
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except that it breaks down if you use it to extract highly basic aqueous solutions, and it's (for me) not really any cheaper than standard grade
toluene - which i highly prefer over anything else.
toluene is sufficiently volatile, can dry itself by azeotropical distillation, immiscible with water, does not tend to form emulsions, and its
toxicity is also acceptable. and the recycling is so much easier than for ethyl acetate!
[Edited on 31-7-2009 by stoichiometric_steve]
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Magpie
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I've been usually substituting toluene when benzene is called out for a solvent, because of cost and availability. Steve, have you found any
instances where this is not practical?
The single most important condition for a successful synthesis is good mixing - Nicodem
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JohnWW
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For non-polar and low-polarity organic compounds produced as the result of a reaction in an aqueous solution involving water-soluble reactants which
themselves are only slightly soluble in an organic solvent, toluene or benzene would be an excellent choice of solvent for solvent extraction of such
a compound to separate it from the reactants and water-soluble by-products. They are soluble in water to the extent of only about 0.05 and 0.97 parts
per 100 parts of water at around 20ºC.
PS: As well as its polarity making it partly miscible (up to 8.5%) with water and able to dissolve some polar compounds also soluble in water, ethyl
acetate would also be unsuitable for solvent extraction from aqueous solutions containing concentrated strong acids or alkalis because of its
liability to hydrolysis to methanol and acetic acid (miscible with water in all proportions, and able to dissolve many organic compounds immiscible
with water).
[Edited on 1-8-09 by JohnWW]
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entropy51
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Quote: Originally posted by JohnWW  | | For non-polar and low-polarity organic compounds produced as the result of a reaction in an aqueous solution involving water-soluble reactants which
themselves are only slightly soluble in an organic solvent, toluene or benzene would be an excellent choice of solvent for solvent extraction of such
a compound to separate it from the reactants and water-soluble by-products. They are soluble in water to the extent of only about 0.05 and 0.97 parts
per 100 parts of water at around 20ºC. |
As is dichloromethane, which is non-flammable and easy to remove by evaporation on the Rotovap due to its low BP.
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DJF90
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DCM can also "dry itself" like tolene, as it too forms an azeotrope with water.
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Agent MadHatter
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I looked into this one more time...and I saw Ethanol Acetate can dissolve 8.6g to 100ml of water..
So wouldn't a solution of Baking soda in water, mix with the Ethylacetate? Or does the baking soda make the polarity to wide?
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