[sharbeldam]

I always like to be sure before going to my lab from the experts on this site. so this is an experiment to synthesize phenacetin from acetaminophen by williamson ether synthesis, first we reflux acetaminophen with base (k2co3) and methyl ethyl ketone as my solvent. then we add CH3CH2I - alkyl halide to make phenacetin. after 1 hour we add the filtrate and we add NaOH to the filtrate to react the remnants of acetaminophen.

My question is, after i add NaOH , we should get two layers, to know which one is up and which is down, I just looked at densities.
MEK Density=0.8g/ml
NaOH density=1.5g/ml

so organic layer (which is composed of CH3CH2I/MEK/phenacetin/Remnant of acetaminophen-i really hope you assure this is true also) should be up because my organic solvent is less dense right?

Thanks alot

[AWK]

In the vast majority of organic syntheses, the bottom layer is a layer containing water. But in cases where the compounds contain a lot of bromine or iodine, the situation may reverse. Check even the density of the ethyl iodide you use. It is better not to wash the glass before making sure that we have the right product in hand. Surprises happen.

[sharbeldam]

Hmm interesting, I'm confused now since I can't rely on the majority of cases and I thought I'd only compare densities of liquids, since i will add 1.8 grams on ethyl iodide (solid) i didn't even think of it at all.
So i cant know beforehand which layer will be top?
density of ethyl iodide is 1.94g/ml... and adding a solution of NaOH also means it has water in it... so it got complicated now after thinking of ethyl iodide and water. I thought i'd just compare NaOH with Methyl ethyl ketone (my organic solvent vs aqueous solvent)

[AWK]

In chemistry, you have to behave like a car driver - limited confidence in everything. I had the adventure with hydrochloric acid fixanal, which contained sodium hydroxide solution.

[sharbeldam]

After doing some searching on this site, some chemists say that what matters is the density of the organic solvent vs density of water... so in my case methyl ethyl ketone vs water, so organic layer should be on top.

[hollytara]

typically, if you do a diethyl ether extraction: water on bottom, organic on top.  BUT if you do a dichloromethane extraction, organic on bottom, water on top.

HOWEVER - if you have concentrated salt solutions, you can have water on the bottom with dichoromethane. 

My rule (learned by hard experience) is - ALWAYS CHECK THE SOLUTIONS BEFORE YOU THROW ANYTHING AWAY! 

[sharbeldam]

Thank you, what about MEK, do you agree with what i said above? that water should be on bottom (typically)? because it is less dense than water?

[hollytara]

Yes - water is more dense than MEK and should be the lower layer.

MEK is a horrible extraction solvent, as it is too soluble in water.  The solubility is 28 g in 100 mL of water.  So if you have 100 mL of aqueous reaction mixture and extract with 50 mL of MEK, you will get two phases: about 130 mL of aqueous (but about 23% MEK) and about 20 mL of MEK (with probably 5-10% water).  Since both phases are mixtures of water and MEK, partitioning will be poor.  A second extraction with MEK will be a little better (since the aqueous layer is already saturated with MEK), but partitioning will still be poor.  But there is probably a reason they use it.

MEK smells pretty bad also (in my opinion).

[AWK]

NaI is soluble in butanone and this may increase the density of the organic layer.

[clarkstill]

NaI is soluble in butanone and this may increase the density of the organic layer.

But surely many times more soluble in water, so more likely to increase the density of the aqueous layer?

[AWK]

I do not question that Sharbeldam's assumptions about the composition of the phases are not true, but I recommend a lot of restraint on the conclusions.
During the butanone extraction, the aqueous phase contains almost 30% butanone, and the organic phase about 10% water (as Hollytara pointed out). Therefore, all reaction products and unreacted substrates can be in both phases in unspecified proportions, all the more so because sodium or potassium iodide dissolves quite well in butanone.
The aqueous phase has a slight excess of potassium carbonate and sodium hydroxide, which can affect the reduction of the solubility of NaI and KI in water by displacing these compounds into the organic phase. No conclusions can be drawn based on the density of the NaOH solution added, because it has reacted to a large extent to form an additional, although a small amount of water.

[Babcock_Hall]

I sometimes take a single drop of one or the other layer and see whether or not it disperses (with mixing lines) in pure water in a small test tube.  If it does, then it is the aqueous layer.  If it floats or sinks, then it is the organic layer.  Obviously one might not want to do this with a particular precious sample.

I agree with the general points that AWK and hollytara made.  To take a specific example, when one washes with brine (saturated aqueous sodium chloride), one has to remember that the density of brine is not the same as pure water.  I did a quick search and found that the specific gravity is about 1.2.

[AMINATY]

In chemistry, you have to behave like a car driver - limited confidence in everything. I had the adventure with hydrochloric acid fixanal, which contained sodium hydroxide solution.

My question is, after i add NaOH , we should get two layers, to know which one is up and which is down, I just looked at densities.

[AWK]

If we deal with two liquids that cannot mix, the matter is simple.
But if we deal with several substances that are better or worse soluble in both phases, you need to think carefully. I did not write that sharbeldam is wrong but it may not have it because it made the wrong assumption. He added concentrated NaOH, but in the amount needed to neutralize acidic substances, and did not take into account the fairly high solubility of the organic solvent in water. Babcock_Hall gave a practical and effective method to check these doubts.

[kriggy]

I might be late to this but you could easilly add hydroxide to quench the ethyliodide and evaporate most of the butanone and extract with another solvent?