bluamine
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Seperating "PARA" & "ORTHO" nitrochlorobenzene
Hi everyone
I'm working on the nitration of chlorobenzene and I have two separate thses two products.
What would you suggest to do it?
I found that their boiling points are 242°C and 245.5°C respectively for Ortho and Para, but using some solvents may be s good idea as well
What do you think guys?
[Edited on 19-9-2022 by bluamine]
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Boffis
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Hi bluamine,
I haven't worked with the nitrochlorobenzene but I have worked extensively with nitrobromobenzenes. These compounds can be separated by
recrystallisation from ethanol or IPA to give a fairly pure 4-nitrobromobenzene. After a second recrystallisation the Mp is pretty good. Evaporating
the liquor down give further crops of less pure material which must be repeatedly recrystallised to obtain further pure 4-nitrochlorobenzene; a 50%
yield is readily obtainable with a bit of patience and care.
The residue is evaporate by warming in stages and after each evaporation of about 20-25% of the original volume, cooled and any fine needles of the
4-nitrobromobenzene filtered off and the process repeated. This 4-nitro compound is impure and must be recrystallised again (I add it to the next
batch of fresh nitro compound). This operation is repeated until quite suddenly the nitro derivative separates as an oil. When this happens carefully
decant the alcoholic liquor at about 20 C and chill separately. The oil is very rich in the 2-nitro isomer but I haven't found a good solvent for the
recrystallisation of this fraction yet. The alcoholic liquor when chilled deposits crude 4-isomer which is again recycled. This process is repeated
until the volume is unworkably small.
I did make an interesting observation recently while drying the solvent from a batch of 2-nitro isomer. The solidified oil was placed on a filter
paper on a watch glass in a warm place. Much to my annoyance it melted and soaked into the filter paper. On close examination some material didn't
melt and remained on the filter paper. I brushed off these crystals and recovered the 2-nitro isomer by extracting the cut-up filter paper with
alcohol. TLC shows that this material has a high 2-nitro isomer and contains very little of the dinitro isomers. This suggests that a "zone refining"
technique may possible for the enriched 2-isomer.
In some of the earlier batches I used an excessive amount of nitric acid in the original nitration and got a lot of dinitro material present (by TLC).
I discovered that after the recovery of the first few crops of 4-nitro isomer the residual material can be partially converted into nitro anilines by
fusion with urea, 2,4-dinitro and 4-mononitro bromobenzenes are converted quickly into their respective anilines but the 2-nitro isomer reacts more
slowly and forms an oil when the mixture is leached with water. This observation suggest another possible separation method but it needs some more
work on it. I did, however, managed to recover the 2-nitro isomer from the last melt batch with petroleum spirit and then separate the nitroanilines
with dilute HCl.
Hope this helps you! There is no easy route that I can find but fractional crystallisation offers a route for the patient and those working on
reasonable sized batches.
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j_sum1
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Bmoore recently separated para and ortho nitrophenol by column chromatography. You could watch his (excellent) yt vid and see if anything could apply
to your synth.
(Edit. I think it was nitrophenol. It's been a big day.)
[Edited on 19-9-2022 by j_sum1]
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bluamine
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Quote: Originally posted by Boffis  | Hi bluamine,
I haven't worked with the nitrochlorobenzene but I have worked extensively with nitrobromobenzenes. These compounds can be separated by
recrystallisation from ethanol or IPA to give a fairly pure 4-nitrobromobenzene. After a second recrystallisation the Mp is pretty good. Evaporating
the liquor down give further crops of less pure material which must be repeatedly recrystallised to obtain further pure 4-nitrochlorobenzene; a 50%
yield is readily obtainable with a bit of patience and care.
The residue is evaporate by warming in stages and after each evaporation of about 20-25% of the original volume, cooled and any fine needles of the
4-nitrobromobenzene filtered off and the process repeated. This 4-nitro compound is impure and must be recrystallised again (I add it to the next
batch of fresh nitro compound). This operation is repeated until quite suddenly the nitro derivative separates as an oil. When this happens carefully
decant the alcoholic liquor at about 20 C and chill separately. The oil is very rich in the 2-nitro isomer but I haven't found a good solvent for the
recrystallisation of this fraction yet. The alcoholic liquor when chilled deposits crude 4-isomer which is again recycled. This process is repeated
until the volume is unworkably small.
I did make an interesting observation recently while drying the solvent from a batch of 2-nitro isomer. The solidified oil was placed on a filter
paper on a watch glass in a warm place. Much to my annoyance it melted and soaked into the filter paper. On close examination some material didn't
melt and remained on the filter paper. I brushed off these crystals and recovered the 2-nitro isomer by extracting the cut-up filter paper with
alcohol. TLC shows that this material has a high 2-nitro isomer and contains very little of the dinitro isomers. This suggests that a "zone refining"
technique may possible for the enriched 2-isomer.
In some of the earlier batches I used an excessive amount of nitric acid in the original nitration and got a lot of dinitro material present (by TLC).
I discovered that after the recovery of the first few crops of 4-nitro isomer the residual material can be partially converted into nitro anilines by
fusion with urea, 2,4-dinitro and 4-mononitro bromobenzenes are converted quickly into their respective anilines but the 2-nitro isomer reacts more
slowly and forms an oil when the mixture is leached with water. This observation suggest another possible separation method but it needs some more
work on it. I did, however, managed to recover the 2-nitro isomer from the last melt batch with petroleum spirit and then separate the nitroanilines
with dilute HCl.
Hope this helps you! There is no easy route that I can find but fractional crystallisation offers a route for the patient and those working on
reasonable sized batches. |
Hi Boffis
I think I can try this method although it sounds complicated and a little bit hard to
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bluamine
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| Quote: Originally posted by j_sum1 | Bmoore recently separated para and ortho nitrophenol by column chromatography. You could watch his (excellent) yt vid and see if anything could apply
to your synth.
(Edit. I think it was nitrophenol. It's been a big day.)
[Edited on 19-9-2022 by j_sum1] |
Do you mean this video in the link below?
https://youtu.be/Q18jSxmcoSw
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j_sum1
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That would be it.
Not everyone has the same access to analytical gear. But the purification procedures I think could be followed with reasonable effect.
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bluamine
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| Quote: Originally posted by j_sum1 | That would be it.
Not everyone has the same access to analytical gear. But the purification procedures I think could be followed with reasonable effect.
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I would like to try fractional distillation first and see how much the yield would be
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