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Author: Subject: Preparation of Mononitrotoluenes (o-, p-)
Magpie
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[*] posted on 22-2-2014 at 17:45
Preparation of Mononitrotoluenes (o-, p-)


February 22, 2014

This procedure takes ideas from many sources but is principally an adaption of that found in Cumming et al (ref 1), at ½ scale. Since the Cumming procedure is sparse in detail, and there are some points at which I (and others) have experienced difficulties, I thought that a procedure providing more guidance would be of value. My difficulties are presented in the Discussion section below.

Attachment: nitrotoluenes.tif (32kB)
This file has been downloaded 1446 times

CAUTION
Nitrotoluenes are poisonous and possibly carcinogenic. NOx vapors are poisonous. Use adequate ventilation and wear gloves.

Excessive temperatures can produce dinitrotoluene and/or trinitrotoluene, which can be explosive. Keep the temperature under 30°C during the acid addition.

A. Chemicals
50g (57.5 mL) toluene
75g (40.2 mL) con sulfuric acid
75g (50.4 mL) nitric acid (density = 1.44) This was an error on my part. The correct amount of nitric acid is 50g (34.7 mL)

Na2CO3 (or NaHCO3)
petroleum ether (or similar)


B. Equipment
2-neck 250 mL round bottom flask
magnetic stirrer (or other mechanical stirrer)
50° C thermometer
p-e addition funnel (or Pasteur pipette)
separatory funnel
fractional distillation apparatus*
source of vacuum
large ice-water bath (a notched 1-gallon plastic ice cream bucket works well for the bath)
freezer, or -20°C salt bath (82.5 g NaCl + 250g ice)
small Buchner funnel
turkey baster

*my column was 600mm x 12.7mm ID, packed with a ss scrub pad. A shorter column may also be satisfactory.

C. Procedure
1. Setup a 2-neck 250mL RBF in the ice-water bath placed on a magnetic stirrer. Install a p-e addition funnel in the center neck, or leave the center neck open for use of a Pasteur pipette. Place a magnetic stir bar in the ice-water bath.
2. Install a 50°C thermometer in the side neck.
3. Place a magnetic stir-bar and 57.5mL of toluene in the RBF.
4. Separately prepare an ice-water cooled, mixed acid consisting of 50.4mL of nitric acid and 40.2mL of con sulfuric acid. If not using a Pasteur pipette place this in the p-e addition funnel (valve closed!). Leave the p-e funnel open to the atmosphere.
5. With the toluene vigorously stirred, run in the mixed acid very slowly. Do not let the temperature rise above 30°C. Maintain temperature by raising or lowering the water level in the ice-water bath as required. A turkey baster can be used to remove water. The acid addition will take ½ hour or a little more.

Attachment: phps3rzVS (66kB)
This file has been downloaded 1521 times
all acid added - temperature 13°C

6. After all the acid has been added the temperature is allowed to rise to 50°C (it probably will be necessary to remove the water in the bath.) This temperature is maintained for 2 hours with the vigorous stirring continued.

Attachment: phpVwHwhO (72kB)
This file has been downloaded 1436 times
2 hr hold at 46°C

Note: The condenser was placed on top of the RBF as shown in the above picture only to contain spattering caused by vigorous stirring.

7. Separate the NT oil from the waste acid using a separatory funnel. The acid will be the bottom layer.

separation of NT and mixed acid.JPG - 67kB
separation of NT and mixed acid

8. Wash the NT with 50mL of water, 50mL of 5% aqueous sodium carbonate, and lastly with 50mL of water. For these washes the NT will be the bottom layer (density = 1.16).

NT plus 1st water wash.JPG - 62kB
NT plus 1st wash water

Attachment: php2cWEEH (66kB)
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NT plus 5% Na2CO3 wash water

NT plus 2nd water wash.JPG - 57kB
NT plus 2nd wash water
9. Drain the NT into a 125 Erlenmeyer flask, add a scant teaspoon of CaCl2, cork and set aside to dry.
10. The dried NT is then separated from the CaCl2 granules by filtering through a small cotton plug.

dried nitrotoluene.jpg - 68kB
filtering the NT dried over CaCl2

11. Place the dried NT in a freezer set at ~ -20°C. Or use a -20°C salt bath. After freezing, the solid p-nitrotoluene is separated from the o-nitrotoluene liquid fraction by Buchner funnel filtration. (The Buchner funnel can be pre-cooled in the freezer to minimize any redissolution of the p-nitrotoluene.) Save the filtrate as it contains the o-nitrotoluene.

p-nitrotoluene (1st batch)

12. Wash the crystals on the filter with a little petroleum ether.
13. Let the crystals dry at room temperature. Determine the melting point. The literature value is 51.7°C. (My yield = 6.7g, mp = 51-52°C)

p-nitrotoluene crystals.jpg - 69kB
1st batch p-NT crystals

o-nitrotoluene
14. Using a vacuum fractionating column collect the low boiling fraction from the filtrate obtained above. If the pressure is 1mmHg the condensate will be collected at 60-63°C. This will be o-nitrotoluene.

vacuum distillation of o-nitrotoluene.JPG - 76kB
vacuum fractionation apparatus

See next post for procedure continuation.


[Edited on 23-2-2014 by Magpie]

[Edited on 23-2-2014 by Magpie]

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[Edited on 23-2-2014 by Magpie]

[Edited on 26-2-2014 by Magpie]




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[*] posted on 22-2-2014 at 18:58
Preparation of Mononitrotoluenes (o-, p-) (continued)


This is a continuation of the above post.

Bennert vacuum indicator.JPG - 76kB
Bennert manometer

o-nitrotoluene (2nd).JPG - 72kB
o-nitrotoluene


p-nitrotoluene (2nd batch)
15. The NT remaining in the pot from the fractional distillation is primarily p-nitrotoluene. Freeze this and recover a 2nd batch as prescribed above. (My yield = 5.8g, mp = 50°C)

2nd batch of p-nitrotoluene.jpg - 90kB
2nd batch of p-nitrotoluene

p-nitrotoluene thrown on ice.JPG - 65kB
2nd batch of p-nitrotoluene thrown on ice

D. Results

Expected yield (Cumming): almost theoretical
65-70% o-nitrotoluene, ie, 48 - 52g
30% p-nitrotoluene, ie, 22g
4% m-nitrotoluene

author:
o-nitrotoluene yield = 30.6g; % yield = 63.8%
p-nitrotoluene yield = 12.5g; % yield =57.3%

No attempt was made to recover the m-nitrotoluene.

E. Discussion
As indicated above, this preparation can have its difficulties. The first one is that of temperature control during the nitration. On my first attempt I used a 500mL RBF, did not provide adequate cooling, and ran in the mixed acid too fast. The temperature rose to 45°C during the addition. In an attempt to reach the 50°C hold temperature I heated with a mantle, overshooting, and the temperature rose to 66°C! During the washing process a whitish waxy solid appeared and I feared that this was dinitrotoluene, which can be explosive. At that time I aborted the run. In my second run I took strong measures to keep the temperature under control and consequently it never rose above 14°C during the ½ hr acid addition. Following this the water in the bath was removed and the temperature came up to 46°C on its own. I then left it unheated/uncooled for the 2 hour hold period. At no time during the subsequent washes did solids appear.

The second difficulty was that of removing contaminant char from the 2nd batch of p-nitrotoluene. To remove any unreacted toluene from the NT batch following drying with CaCl2 I attempted to perform a simple distillation. No toluene came over. Instead I created some char, turning my NT batch black. I must have heated the batch near boiling which would be in the 225-238°C region. The char was tough to remove as the product would oil-out when dissolving in a 1:1 ethanol:water solvent. I sacrificed a small part of this oil as a char scavenger. The remainder of the NT, dissolved in about 100mL of the solvent, was thrown onto a beaker of crushed ice. This produced a very fine white solid with a pale yellow cast. Its mp was 50°C (lit. 51.7°C). Therefore the procedure presented above omits any simple distillation step.

In my attempt to learn more about this synthesis after my first attempt failed, I surveyed what literature I could find including the experiences of Stefan and Ameisensulfat on versuchschemie.de. A comparison of parameters drawn from this survey is shown in the attached EXCEL file (ref 2).

F. References
1. “Systematic Organic Chemistry,” revised 4th ed, 1950, by Cumming, Hopper, & Wheeler, Preparation 226, p. 277-278. (forum library)
2. EXCEL file comparing parameters:
Attachment: nitrotoluene synthesis parameter comparison.xls (23kB)
This file has been downloaded 867 times

G. Useful Data

bps:
o-nitrotoluene: 225°C
p-nitrotoluene: 238°C
m-nitrotoluene: 230°C

mps:
p-nitrotoluene: 51.7°C
m-nitrotoluene: 16°C
o-nitrotoluene: -10.6°C (alpha phase); 4.1°C (beta phase)

density:
o-nitrotoluene: 1.163
m-nitrotoluene: 1.157





[Edited on 23-2-2014 by Magpie]

[Edited on 23-2-2014 by Magpie]

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[Edited on 23-2-2014 by Magpie]

[Edited on 26-2-2014 by Magpie]




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[*] posted on 22-2-2014 at 19:54


Systematic Organic Chemistry uses an equal weight of nitric acid and toluene! Maybe the temperature control problem (not that there isn't exotherm obviously) is from additional nitration. Which is all the more alarming given the later charring and suspected high temperatures:
https://www.sciencemadness.org/whisper/viewthread.php?tid=10...
Although condenser-based launches are impressive and memorable mentally if not physically, it isn't something you want going on in the house.
NaOH washing might be preferable to carbonate:
https://www.sciencemadness.org/whisper/viewthread.php?tid=10...
followed by hydrodistillation, drying, vacuum fractionation.

I haven't bothered to do the math lately, but numbers run much earlier indicated that the standard industrial procedure (equimolar amounts of nitric acid and toluene or maybe a very slight excess of one or the other, maintaining 25-40C during the acid addition, then rising to 60C) uses a nitrating mixture of around 28% nitric acid, 16% water, and 56% sulfuric acid, that comes out to 1 part toluene, 1 part 68% nitric acid, and 1.42 parts 96% sulfuric acid.




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[*] posted on 22-2-2014 at 21:04


Quote: Originally posted by S.C. Wack  
Systematic Organic Chemistry uses an equal weight of nitric acid and toluene!


50g of toluene and 75g of nitric acid are not equal wts. Did you look at the EXCEL spreadsheet - it shows a mole ratio of HNO3/toluene of 1.11.

Quote: Originally posted by S.C. Wack  

Although condenser-based launches are impressive and memorable mentally if not physically, it isn't something you want going on in the house.


If you are referring to the condenser on the RBF I put that on there after all the acid had been added to prevent some spattering due to vigorous stirring & reflux any acid formed by evolved NOx. I know it is hard to see but that picture was taken in the 2-hr hold period when the temperature had reached 46°C and I had removed all of the ice-water from the bath. I don't think there was any chance of a temperature excursion at that point.

The charing did not occur during the nitration. It occured later when I attempted to remove any unreacted toluene by simple distillation.





[Edited on 23-2-2014 by Magpie]

[Edited on 23-2-2014 by Magpie]

[Edited on 23-2-2014 by Magpie]




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[*] posted on 23-2-2014 at 07:57


I probably wouldn't open .xls attachments even if I could at home...and don't care how your condenser is hooked up; didn't even look at your pictures so sorry, I'm sure it's fine...The condenser mention references what I have seen myself, ergo, what I said...yeah charring during distillation not nitration "225-238°C region" is exactly what I was thinking about not sounding good...the suggested NaOH washing and steam distillation may eliminate that, there could be problems if it doesn't...attachment is the relevant Systematic Organic Chemistry pages...equal weights of nitric acid of d 1.44 and toluene are used...

my spreadsheet...
50 g. 68%(69%) nitric acid = 34(34.5) g.
/ 63.01 = .5396(.5475)
+
50 g. toluene / 92.14 = .5427
..equal weight sure does look good for not overnitrating, as long as the acid is added to the toluene with extreme stirring etc...

...maybe no dinitrotoluene is formed using excess nitric acid if the temperature is low enough and there is enough sulfuric acid to compensate for the water...maybe that isn't how it goes. AFAIK it isn't recommended.

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[Edited on 23-2-2014 by S.C. Wack]




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[*] posted on 23-2-2014 at 08:58


You are correct! I inadvertantly used 50% too much nitric acid! This is likely the reason I observed so much NO2 being given off during the 2 hour hold period at 46°C. This may also explain why there was no unreacted toluene.

Just how much dinitrotoluene I made I don't know. It seems, however, not much. I saw no solids during the washes. Also (thankfully) there was no explosion when I heated the NT up to the 225-238°C region. My first batch of p-NT is quite pure by mp (51-52°C). The 2nd batch was reasonably pure also by mp (50°C). I can only guess at the purity of my o-NT based on its bp of 60-63°C at P=1mmHg.

As you say a mole ratio of HNO3/toluene of 1.67 is certainly not standard procedure, although not without precedent (Amiesensulfat, Davis). I will flag this error in my procedure. Thank you for pointing it out!

[Edited on 23-2-2014 by Magpie]

[Edited on 23-2-2014 by Magpie]




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[*] posted on 25-2-2014 at 12:48


I really like that you've documented this as I've been wanting to do this for a long time now. I could not find any previous attempt that detailed the separation of the o- and p-nitro toluenes. I'd suggest however that you re-crystallise your p-nitrotoluene to ensure it is free from any m-nitrotoluene.

As a side note I find p-nitrotoluene has a pleasant cherry/almond odour reminiscent of benzaldehyde or piperonal. The two nitrotoluenes you've obtained are useful substrates for further elaboration and other interesting projects.

Let me finish by congratulating you on your success.
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[*] posted on 25-2-2014 at 14:11


Thanks. I think the reason we haven't seen any posts on isolation of the o- isomer is that the bp difference between the o- and p- isomers is only about 13°C. This is a challenge for fractional distillation unless you have a sufficiently long column.

In the thread referenced above by S.C.Wack I believe garage chemist mentions that he attempted a vacuum fractionation but ran into column flooding problems. I too had some flooding but backed off on the heat and it seemed to go away. I couldn't really tell what was going on in the column, except at the top, because I had the column fully insulated. GC then said he tried fractionation at normal pressure. But this would require temperatures in the 225-238°C region where I experienced severe charing.

It was also brought out in this thread, I believe, that if residual toluene (if any) is not removed from the NT product the p- isomer will not crystallize out properly by freezing.

I regret that I inadvertantly used 50% too much nitric acid. But I still wanted to post the results as I felt that they would be useful to others.

[Edited on 26-2-2014 by Magpie]




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[*] posted on 25-2-2014 at 19:51


The predominance of the ortho-isomer is a very useful outcome as it is a good starting point for heterocycles such as indoles and quinolines. From an old retired chemist, nice job!
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[*] posted on 26-2-2014 at 10:05


Thank you AvBaeyer and welcome to the forum.



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[*] posted on 23-3-2014 at 07:36


Fantastic job. What kind of vacuum fractionating column is that?



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[*] posted on 23-3-2014 at 11:56


Quote: Originally posted by smaerd  
Fantastic job. What kind of vacuum fractionating column is that?


Thank you. My column is 600mm x 12.7mm ID, packed with a ss scrub pad. It is a Hempel column with ground glass end fittings. This is available from Eagle Scientific Glass. At the top of the column is mounted a Hennion type still head which allows control of the reflux ratio.

[Edited on 23-3-2014 by Magpie]




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[*] posted on 24-3-2014 at 00:32


That is great Magpie.
I have some questions:
How you provide 1mmhg(do you use diaphragm vacuum pump or double stage oil vacuum?)
This is possible to separate O isomer only by Fractional crystallization ?
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[*] posted on 24-3-2014 at 07:49


Quote: Originally posted by Waffles SS  

How you provide 1mmhg(do you use diaphragm vacuum pump or double stage oil vacuum?)
This is possible to separate O isomer only by Fractional crystallization ?


My vacuum pump is merely a one-stage oil pump: a $100 cheap pump from Harbor Freight. I, too, am a little surprised that it pulls such a good vacuum.

I think one procedure says that by removing the p-isomer by repeated crystallizations the remaining component is essentially the o-isomer. Then by steam distillation the p-isomer can be separated from the small amount of m-isomer. I would have to go back and find that procedure to confirm this, however.

---------------------------------------------------------------------------

Edit: The procedure I was referring to can be found in the forum library, as was pointed out by garage chemist. It is the book on TNT by G. Carlton Smith. Here is the excerpt that provides for separation of o- and p-nitrotoluenes without the use of fractional distillation:

"A possibly better method of separating the isomeric
mononitrotoluenes is one used by the firm of Meister,
Lucius & Bruning. This consists in cooling the
mixed nitrotoluenes to —4 to —10 °C and removing
the liquid portion after about one-half the mixture has
crystallized. The separation may be effected by a
centrifuge. The liquid obtained by one crystallization
is practically pure ortho nitrotoluene. The resulting
mixture of meta and para nitrotoluenes may be
separated by steam distillation. The para is very
volatile with steam, while the meta is but slightly so."

I have not tried this. Basically I went right to vacuum fractional distillation based on the experience of garage chemist.


[Edited on 25-3-2014 by Magpie]

[Edited on 25-3-2014 by Magpie]




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[*] posted on 12-10-2014 at 02:49


magpie
could we increase the yield of the ortho isomer by sulphonating toluene first(oleum or boiling in sulphuric acid for sometime) and then adding nitric acid only, to the mix(no need to extract the p-methylsuphonic acid),the extra sulphuric acid will help form nitroniu ion and help in nitration
mostly while sulphonating toluene ,the -HSO3 will go to para ,but even if it goes to ortho
the -NO2 will enter the ring otho to the methyl group rather than going near to -HSO3(those two are the positions available due to meta directing nature of -HSO3)

or will the -HSO3 group get substituted for -NO2

also can para-methyl sulphonic acid be alkylated using friedel craft
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[*] posted on 12-10-2014 at 05:44


Quote: Originally posted by CuReUS  

also can para-methyl sulphonic acid be alkylated using friedel craft


Sulphonic acids are strongly deactivating. Friedel-Crafts alkylation will fail.




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[*] posted on 12-10-2014 at 08:30


Quote: Originally posted by Magpie  
Quote: Originally posted by Waffles SS  

How you provide 1mmhg(do you use diaphragm vacuum pump or double stage oil vacuum?)
This is possible to separate O isomer only by Fractional crystallization ?


My vacuum pump is merely a one-stage oil pump: a $100 cheap pump from Harbor Freight. I, too, am a little surprised that it pulls such a good vacuum.
[Edited on 25-3-2014 by Magpie]


According to the HF website it is good to 0.075 torr. I have been looking at the HF two stage for vacuum distillations (and a little carbon fiber vacuum bagging) which is good to 0.022 torr.

I think this mononitration can be done with really cheap reagents - drain cleaner acid (94% H2SO4) and fertilizer KNO3. This would make optimization for position selectivity moot, just crank out a larger batch.
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[*] posted on 12-10-2014 at 08:47


CuReUS: I would not want to speculate on the efficacy of your proposed scheme as I do not know that much about it. But how do you propose to remove those extraneous -HSO3 groups following the nitration?

I agree with careysub and would just make a larger batch. Your approach just seems like unnecessary complication. Like many organic syntheses the devil is in the separation of product from by-products and unreacted reactants.




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[*] posted on 13-10-2014 at 05:11


magpie -actually removal of the sulpho group is very easy and the sulphonation process is actually reversible
read this under mechanism http://en.wikipedia.org/wiki/Aromatic_sulfonation
they talk about how to remove the -HSO3

cheddite cheese -i agree that sulphonic acid is deactivating,that's why i have put a methyl group ,are you saying it will still fail:(
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[*] posted on 13-10-2014 at 07:11


Yes. The sulphonic acid is a much stronger deactivator than the methyl group is an activator.



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[*] posted on 13-10-2014 at 07:35


i dont want to ask this ,but since alkylation will fail ,acylation will also definitely fail?
what about a gatterman-koche reaction of the p-methylsulphonic acid
gatterman -koche reaction http://en.wikipedia.org/wiki/Gattermann_reaction
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[*] posted on 13-10-2014 at 21:55


I've looked into doing just as you suggest, Careysub, and previously found an old reference for the nitration of p-toluenesulfonic acid. I don't recall the details though I have the paper saved on my pc at home. Other reaxys results used TsCl as the substrate, but that is less friendly. The idea was to improve the selectivity for o-nitration as it would be required in a larger quantity than the p-nitrotoluene, although both are useful and interesting.
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[*] posted on 14-10-2014 at 03:43
CuReS


Hmm... I could have done the "Breaking Bad" thing with my username here and be known as CaReYSUB.

Oh well.

:cool:
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[*] posted on 14-10-2014 at 03:59


DJF90
so nitration on sulphonated ring is possible .but while sulphonating wont the sulpho group go to ortho as well as para position because the methyl group is not such a bulky molecule?

careysub
yes ,Br Ba was the best show there WAs,there IS and there will B (you could also use Be:D)
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[*] posted on 18-10-2014 at 10:57


I think I'll give this a try, on a larger scale. I plan to use 200 g nitric acid (135 mL), 300 g sulfuric acid (165 mL), and 200 g toluene (230 mL). Because of the greater scale, I will add the acids very slowly to keep the temperature down.

I'm adding the acid at a rate of roughly 1 drop per second. I will try to keep the temperature below 20 C at all times. It currently is at 15.

The addition of the acid is finally complete (total time 4 hours 10 minutes). I will let it react for another half hour, then collect the product. The maximum observed temperature was 27 C (my ice ran out); not ideal, but acceptable.

First crop of p-nitrotoluene crystals: 28.7 g. 225 mL of nitrotoluene mixture remains.

Yield of o-nitrotoluene after fractionation (fraction 65-70 C): 128.1 g. I was using the same type of Harbor Freight single stage pump that Magpie used, actually.

I'm freezing the remaining portion to recover more p-nitrotoluene.
I got 10.1 more grams of p-nitrotoluene.

[Edited on 26-10-2014 by Cheddite Cheese]




As below, so above.
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