Sciencemadness Discussion Board

What does partitioned mean?

Agent MadHatter - 29-7-2009 at 22:44

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.

crazyboy - 29-7-2009 at 23:00

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.

Agent MadHatter - 29-7-2009 at 23:04

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?

Arrhenius - 29-7-2009 at 23:09

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]

Agent MadHatter - 29-7-2009 at 23:26

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]

Arrhenius - 29-7-2009 at 23:52

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]

Agent MadHatter - 30-7-2009 at 09:13

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.

ammonium isocyanate - 30-7-2009 at 10:27

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).

Magpie - 30-7-2009 at 10:34
Quote:

So if I wanted to copy this (I believe this is on my test so I'm trying to get it down)


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?

Agent MadHatter - 30-7-2009 at 10:40

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?

Magpie - 30-7-2009 at 14:35
Quote:

How would one synthesize a BOP reagent?
(Benzotriazole-1-yl-oxy-tris-(dimethylamino)-phosphonium hexafluorophosphate)


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.

crazyboy - 30-7-2009 at 14:53

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.

JohnWW - 30-7-2009 at 18:02

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?

Agent MadHatter - 30-7-2009 at 22:32



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]

ammonium isocyanate - 30-7-2009 at 22:39

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. ;)

Agent MadHatter - 30-7-2009 at 22:49

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.

watson.fawkes - 31-7-2009 at 07:04

Quote: Originally posted by Agent MadHatter  
"If you can say you've never failed, then you arn't pushing hard enough"
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.)

Arrhenius - 31-7-2009 at 10:32

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.

Agent MadHatter - 31-7-2009 at 12:57

Thank you =) I'll get myself that book.

stoichiometric_steve - 31-7-2009 at 14:18

Quote: Originally posted by Arrhenius  
Ethyl acetate is a fine solvent


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]

Magpie - 31-7-2009 at 14:37

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?

JohnWW - 31-7-2009 at 15:20

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]

entropy51 - 31-7-2009 at 15:31

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.

DJF90 - 31-7-2009 at 16:01

DCM can also "dry itself" like tolene, as it too forms an azeotrope with water.

Agent MadHatter - 31-7-2009 at 20:22

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?

ammonium isocyanate - 31-7-2009 at 21:13

Quote: Originally posted by Agent MadHatter  

So wouldn't a solution of Baking soda in water, mix with the Ethylacetate? Or does the baking soda make the polarity to wide?

As I understand it, the ethyl acetate would tend not to dissolve in the water because of osmotic pressure. I do not believe sodium bicarbonate (baking soda) is soluble in ethyl acetate, and so any water in the ethyl acetate would tend to move into the aqueous phase in order to dilute the bicarbonate solution.

Arrhenius - 31-7-2009 at 21:39

Stoichiometric steve: What organic reactions even exist in which you need to extract hot saturated NaOH? I use ethyl acetate almost every day to partition against 1N NaOH and absolutely never have a problem. The only time hydrolysis becomes an issue is when you leave it in contact with the base for a long period of time... which is rarely the case.

Toluene is not all that good at dissolving moderately polar compounds... it's high boiling, and it smells bad :P I have not once used toluene for extractions... but I guess you can buy it at ACE.

Agent MadHatter: Ethyl acetate and water are immiscible... if you increase the polarity ("osmolarity") of the water by adding a solute (especially ionic salts) it mixes even less with water. I highly suggest that you try performing a partition, as it will quickly make a whole lot more sense how this all goes down.