Wolf-Aalude
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O-Toluidine purification
Background;
I have supposedly created o-toluidine (and p-toluidine) via a zinc / ammonium formate reduction of the respective nitro compounds.
Excerpt from 'Cheapskate':
to get the newly created o-toluidine out of the flask is by steam distillation.You can try separations, neutralization, etc. They won't work.
Believe me, lots of attempts to do this have been tried, but none of them work.
My first thought was - b.s. Why would a simple aniline not be easily separated from the resulting mixture?
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1st Idea is cheapskate doesn't have a pH meter/paper, he never neutralized (or basified) the nitration solution, and thus his organic extraction was
null.
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2nd idea is that strong acids and bases form complexes with zinc & the anilines, thus making it difficult to separate
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Following my initial thoughts, I carried out a basification of the nitration solution, followed by an extraction of the o- & p-toluidines with
ethyl acetate.
What I Recieved was quite odd;
1st pull of ethyl acetate yields dark brown/orange organic layer.
2nd pull yields lime green organic and aqueous layer (both turn the same color)
I left the green organic and aqueous layers aside and concentrated the original brown organic solution, to recieve a very dark solution that smelled
nothing of nitro-toluene.
Questioning if various zinc complexes and other unwanted parts were still dissolved, I ran the steam distillation. Very clear yellow oil comes over,
and the water is extremely cloudy.
Upon letting the water sit overnight, it becomes crystal clear, and the oil separates to the bottom.
However, addition of MORE water to the now clear biphasic system totally disrupts it and it becomes cloudy again.
Summarizing questions.
1. Why is it that a simple A/B extraction of the toluidines can't be done (even if isomer separation doesn't happen?)
2. Why would a clear biphasic system become MORE cloudy on addition of additional water?
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Nicodem
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Thread Moved
16-1-2014 at 10:02 |
Hitachi R1200
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Aromatic amines can be appreciably soluble in water, so it is best to add NaCl to the steam distillate until saturation and extract with a low boiling
solvent such as ether or dichloromethane.
The separation of these isomers are very difficult at this stage of the game. I would recommend fractional vacuum distillation of the intermediate
nitrotoluene mixture and crystallization of the material in the still pot in a freezer after about 50% of the mixture has distilled. The lower boiling
fraction should be distilled again, since considerable amounts of the p-isomer are still present from my experience.
This may be interesting to try:
o-Toluidine (2-methylaniline) [95-53-41 M 107.2, f -16.3O, b 80.1°/10mm, 200.3°/760mm,
d 0.999, n 1.57246, n25 1.56987, pK25 4.45. In general, methods similar to those for purifying
aniline can be used, e.g. distn from zinc dust, at reduced pressure, under nitrogen. Berliner and May [J Am
Chem Soc 49 1007 19271 purified via the oxalate. Twice-distd o-toluidine was dissolved in four times its
volume of diethyl ether and the equivalent amount of oxalic acid needed to form the dioxalate was added as its
soln in diethyl ether. (If p-toluidine is present, its oxalate pptes and can be removed by filtration.) Evapn of the
ether soh gave crystals of o-toluidine dioxalate. They were filtered off, recrystd five times from water
containing a small amount of oxalic acid (to prevent hydrolysis), then treated with dilute aqueous Na2C03 to
liberate the amine which was separated, dried (CaC12) and distd under reduced pressure.
p-Toluidine (4-methylaniline) [106-49-01 M 107.2, m 44.8O, b 79.6°/10mm, 200.5O/
760mm, d 0.962, n 1.5636, n 59.1 1.5534, pK2’ 5.08. In general, methods similar to those for
purifying aniline can be used. It can be separated from the 0- and m-isomers by fractional crystn from its melt.
p-Toluidine has been crystd from hot water (charcoal), EtOH, *benzene, pet ether or EtOWwater (1 :4), and dried
in a vacuum desiccator. It can also be sublimed at 30° under vacuum. For further purification, use has been
made of the oxalate, the sulfate and acetylation. The oxalate, formed as described for o-toluidine, was filtered,
washed and recrystd three times from hot distd water. The base was regenerated with aq Na2C03 and recrystd
three times from distd water. [Berliner and May J Am Chem Soc 49 1007 1927.1 Alternatively, p-toluidine
was converted to its acetyl derivative which, after repeated crystn from EtOH, was hydrolysed by refluxing (50g)
in a mixture of 500mL of water and 115mL of conc H2SO4 until a clear soln was obtained. The amine sulfate
was isolated, suspended in water, and NaOH was added. The free base was distd twice from zinc dust under
vacuum. The p-toluidine was then recrystd from pet ether and dried in a vacuum desiccator or in a vacuum for
6h at 40O. [Berliner and Berliner J Am Chem Soc 76 6179 1954; Moore et al. J Am Chem Soc 108 2257
1986.1
Citation: Purification of Laboratory Chemicals 5th Edition, 371.
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