cyberzed
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Azeotropical distillation of a mixture
Hi, i don't know if i'm allowed to put this question on this board, so if someone feels offended, just ignore my post, i also don't want to give the
impression that i'm throwing a bone to go fetch, but due do my little knowledge it will probable give that impression, so here it goes.
One is trying to distill a mixture which is consisting of the following compounds:
Ingredients Weight% BP°
ethyl formate 30 - 60 54
nitroethane 30 - 60 114
n-butanol 1-5 118
ethyl acetate 3-7 77
2-phenoxyethanol 3-7 247
After collecting the boiling fraction at 114 ° which should be the nitroethane, one did a small test with NaOH which was completely unreactive.
Can i find out if this mixture is forming an azeotrope, and how would one find this out? Are there existing tables for this?
I did do some reading about breaking the azeotrope which deals with adding a third compound which woulld then lower the boiling points, but this is
for a mixture with two components that form the azeotrope. But what with a mixture like this one, could someone point me in the right direction?
[Edited on 31-10-06 by cyberzed]
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solo
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Here is something which may help you...........solo
https://sciencemadness.org/talk/viewthread.php?tid=5158#pid5...
File contains :
Table of Azeotropes and Nonazeotropes
L. H. HORSLEY,
AZEOTROPIC DATA FOR BINARY MIXTURES
http://rapidshare.com/files/1477614/azeotropes.zip.html
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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Magpie
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Is one after the nitroethane? If so distillation might not be the best initial separation process. Check on the solubilities of the components in
water. (I'm assuming nitroethane is insoluble.) What I'm saying is look into solvent extraction for your 1st crack at this mixture.
(In my local library is Gmehling's Azeotropic Data. This is a huge two volume list of azeotropes. About 95% are binary, a few % are
ternary, and <1% would be quaternary and above. So finding useful information based on a mixture of 5 components might be just luck. I wouldn't
count on it. But I'll admit I don't have a lot of experience in this area.)
The single most important condition for a successful synthesis is good mixing - Nicodem
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not_important
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Magpie has a good idea, but it may fail in this case. Both ethyl format and n-butanol are soluble in roughly 10 parts of water, and the resulting mix
will dissolve some amount of organics that aren't particularly water soluble. It may be a rather ugly mixture to separate.
While checking the references first is the smart way to go, if they don't yield the needed data - as is quite possible in this case - then you may
have to determine if there are azeotropes on your own. Distill a moderate sized sample, using a fractionating column if you've one, at a fairly slow
rate. Note temperature at the reflux point and the amount of distillate per time slice, and plot distillate volume vs temperature. Peaks of high
distillation rate that don't match that of the components indicate azeotropes; of course an azeotrope with a boiling point close to a component will
be hard to notice, although the volume collected may clue you in. You can do some simple analysis of the fractions to get an idea of their makeup, the
esters should react with aqueous sodium carbonate or bicarbonate to give ethanol and the salt of the acid, or with strong ammonia to give alcohol and
amide.
If you don't really care about the esters, pre-treatment with warm aqueous NaHCO3 should hydrolize them fairly quickly. This reduces the number of
omponents by one, and changes the nature from ester to alcohol.
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cyberzed
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Hey, thanks all for the reply's, i was actually expecting that someone would shoot this thread ....
One tried the pre-treating by making a 100 ml warm saturated mixture of NaHCO3 and dH2O and added this to the sep funnel together with 100 ml of the
original mixture where two layers where visible, this was allowed to stand for 10 mins and the aq layer was removed, this was done a second time and
the resultant solution was distilled with the following distillation results.
Time ..temp oil bath....temp distillate.ml collected..vessel
0......26...............20
5......84...............24
10.....85...............60
15.....89...............64
20.....89...............65..............15,5..........1
25.....94...............67..............12............1
30.....95...............69..............10,5..........1
35.....93...............68..............8,5...........1
40.....95...............69..............6,5...........1
45.....102..............72..............9.............2
50.....106..............76..............9,5...........2
55.....102..............76..............8,5...........2
60.....105..............78..............5,5...........2
65.....109..............78..............4,5...........2
70.....114..............88..............7.............3
75.....114..............88..............5.............3
80.....115..............90..............2,5...........3
85.....127..............97..............5.............4
90.....126..............99..............7,5...........4
95.....126..............100.............3,5...........4
100....124..............100.............1,5...........4
105....135..............107.............5,5...........5
110....136..............108.............6,5...........5
115....130..............108.............4,5...........5
120....135..............109.............2,5...........5
125....145..............112.............8.............6
130....145..............114.............7.............6
135....144..............114.............6.............6
140....145..............114.............6.............6
145....145..............114.............5.............6
150....148..............114.............2,5...........6
155....156..............115.............6.............6
One did stop the distillation after that on which there was some 20ml left in the flask. (2-phenoxyethanol, yellow colored ??)
One did a test with all the reaction vessels by presenting the distillates to a little of NaOH, but all where unreactive.
Shouldn't nitroethane react with NaOH?
One wanted a second opinion in wheter the boiling fraction in reaction vessel 6 (the 112-116 fraction) should indeed contain nitroethane, one did this
as follows:
2 test tubes where prepared
one with 2 ml dH2O, 2 ml EtOH and 0.1 g NaOH + 1ml of the distillate
one with an aq solution of Fe III chloride
In a third test tube there was added 1 drop of the first tube and 3 drops of Fe III chloride solution, there was a red colorisation noticable.
Should one conclude from this test that there is indeed nitroethane in the distillate?
Is it possible that this distillate still containt some water which can be cleaned of with a drying agent like CaCl2?
[Edited on 1-11-06 by cyberzed]
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Magpie
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Forgive my ignorance, but what is supposed to happen when NaOH is added to nitroethane?
The single most important condition for a successful synthesis is good mixing - Nicodem
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cyberzed
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Well i have read somewhere that it shoud react violently with NaOH and that it automatically should catch fire.
I did this test outsides just to make sure.
The place where they discussed this where talking about nitromethane, but they thought it would be the same for nitroethane.
It's not my intention to make a bomb though 
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not_important
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Nitroalkanes for slats with strong bases, and the dry salts can ignite and possibly explode. But I don't think that the small scale mixing is going to
be too exciting, the Nef reaction starts with forming the salt of a nitroalkane and then treating that with acid to yield a carbonyl and hyponitrous
acid. That might be a better test, as acetaldehyde should be recognisable by smell in small quantities.
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