Sciencemadness Discussion Board

Preparation of Mononitrotoluenes (o-, p-)

Magpie - 22-2-2014 at 17:45

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)
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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.

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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.

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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

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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.


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Preparation of Mononitrotoluenes (o-, p-) (continued)

Magpie - 22-2-2014 at 18:58

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)
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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]

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S.C. Wack - 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.

Magpie - 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]

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S.C. Wack - 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]

Magpie - 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]

DJF90 - 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.

Magpie - 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]

AvBaeyer - 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!

Magpie - 26-2-2014 at 10:05

Thank you AvBaeyer and welcome to the forum.

smaerd - 23-3-2014 at 07:36

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

Magpie - 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]

Waffles SS - 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 ?

Magpie - 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]

CuReUS - 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

Metacelsus - 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.

careysub - 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.

Magpie - 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.

CuReUS - 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:(

Metacelsus - 13-10-2014 at 07:11

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

CuReUS - 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

DJF90 - 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.

CuReS

careysub - 14-10-2014 at 03:43

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

Oh well.

:cool:

CuReUS - 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)

Metacelsus - 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]

UnintentionalChaos - 5-11-2014 at 11:55

Quote: Originally posted by CuReUS  
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?


o-toluenesulfonic acid is unfavorable due to sterics. Importantly, though, is that the reaction is readily reversible and at the high temps used for sulfonation of toluene with concentrated sulfuric acid, the less stable ortho-product desulfonates/resulfonates into the more stable p-isomer readily. Nitration is not, to my knowledge, readily reversible.

You might see considerable o-toluenesulfonic acid if you used oleum at low temperatures where the reaction is not so readily reversible and the much greater sulfonating power of oleum makes up for the lack of heat.

The nitration of the p-toluenesulfonic acid would require moderate conditions, because it is possible for a nitro group to displace the sulfonic acid moiety on the ring. This is the case for TNT, where some preps specify treatment of dinitrotoluene with oleum before adding the final amount of nitric acid.

[Edited on 11-5-14 by UnintentionalChaos]

CuReUS - 5-11-2014 at 19:27

Quote: Originally posted by UnintentionalChaos  


o-toluenesulfonic acid is unfavorable due to sterics. Importantly, though, is that the reaction is readily reversible and at the high temps used for sulfonation of toluene with concentrated sulfuric acid, the less stable ortho-product desulfonates/resulfonates into the more stable p-isomer readily. Nitration is not, to my knowledge, readily reversible.


that's great ,if even a small group like methyl can cause the sulpho group to go to para ,think of how many reaction could be controlled by this method


Quote:
The nitration of the p-toluenesulfonic acid would require moderate conditions, because it is possible for a nitro group to displace the sulfonic acid moiety on the ring. This is the case for TNT, where some preps specify treatment of dinitrotoluene with oleum before adding the final amount of nitric acid


iirc ,moderate conditions of nitration is conc nitric acid/sulphuric acid at 100'c but then you say that the nitro group will replace the sulpho group at high temp(that's also the method to make picric acid;) ) .so what should we do.

Hellafunt - 4-4-2015 at 09:26

so, I attempted this procedure a while ago and it went pretty well. During the nitration process, which I did by following a friend's advice by adding the toluene to the mixed acids, after each addition, the toluene turned dark, and then turned yellowish in a minute or two. I had to take water out of the ice bath a few times and add fresh ice to maintain a cold enough temp. It turned out well.
Recently, I tried this again. This time, anticipating having to keep adding ice to the water bath, the night before I froze a few inches of water in the bottom of the water bath vessel. When I added the reaction flask and some water, it maintained a cold (18C) temp easily. It seemed like maybe it was too cold, I would add toluene to the reaction, and it never turned dark at all, and it didnt heat up at all. I was able to add all the toluene without it ever really heating up.
I figured it was all done, so I stepped away for less than 10 minutes. When I returned, there was brown gas evolving from the reaction, I put in a thermometer and it was still climbing at 60C when I yanked it out, and put a whole lot of ice and cold water around the RBF this was happening in. I was prepared to run, but it cooled down. Later, I thought it was done but when I poured it into a sep funnel, there was still nitrogen dioxide coming off it, so I put it back in the RBF and let it react another hour. In the end, the finished product looked ok, maybe a little darker than the first time. I thought perhaps there was some NO2 dissolved in it causing the darker color, like the way it does in Nitric acid.
Now, a few days later, the nitrotoluene has separated in the storage bottle, with the top third appearing as the normal , yellow, thick liquid and the bottom two thirds being a darker, thinner liquid. Whats the deal? Id like to make o-toluidine from this. Is it usable?

S.C. Wack - 4-4-2015 at 09:54

Quote: Originally posted by S.C. Wack  
...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.


Surprised that no one mentioned COPAE:

A mixture of 294 grams of concentrated sulfuric acid {d. 1.84) and 147 grams of nitric acid (d. 1.42) is added slowly from a dropping funnel to 100 grams of toluene in a tall 600-cc. beaker, while the liquid is stirred vigorously with an electric stirrer and its temperature is maintained at 30° to 40° by running cold water in the vessel in which the beaker is standing. The addition of acid will require from an hour to an hour and a half. The stirring is then continued for half an hour longer without cooling; the mixture is allowed to stand over night in a separatory funnel...

Tabun - 17-4-2015 at 11:20

Did you see the procedure in Science and Technology of Explosives-Urbanski?They say that this procedure gives o- and p- free of m-.The nitrating composition is 68% acetic anhydride and 32% nitric acid with an exces of 10% acid,made at 10 degrees Celsius over a period of 2 hours.It also says that you can reduce the m- quantity by adding sodium nitrite....Here's a SS:

http://i.imgur.com/yP6gxT2.jpg


Texium - 16-11-2015 at 20:23

I'm planning on attempting this synthesis soon, but I just wanted to clarify- what concentrations are the nitric and sulfuric acids that you used? I'd guess ~63% and 98% respectively, but I wanted to make sure before I go throwing stuff together so I'll know to do stoichiometric corrections as needed.

Sorry if I missed something, but I didn't see exact concentrations mentioned anywhere in the thread.

Magpie - 17-11-2015 at 09:23

There are many contributions to this thread, but I'm assuming you are asking me.

My con H2SO4 is whatever Rooto supplies: probably about 96%.
My con nitric acid is the azeotrope which IIRC is about 68%.

Good luck.

edit: I see that in my procedure I specify nitric acid of density 1.44, which corresponds to a 77wt% acid. I likely took this from Cumming. Normally I don't have this so likely used an equivalent amount of 68%. Unfortunately I didn't say anything about this in my notebook.

[Edited on 18-11-2015 by Magpie]

Texium - 18-11-2015 at 07:22

Alright, thank you! I may try this synthesis today if I have time.

Nitrotoluenes

Aromatik - 6-2-2020 at 05:33

Dear Colleague,
Reviewing your procedure for toluene mononitration, kindly let me ask you if reverse addition has been experienced.
See attached ref. frm Urbanski about it.
Rgds,
Rod
:)

Attachment: Addition_Urbanski.pdf (60kB)
This file has been downloaded 605 times


Aromatik - 6-2-2020 at 09:04

Quote: Originally posted by Tabun  
Did you see the procedure in Science and Technology of Explosives-Urbanski?They say that this procedure gives o- and p- free of m-.The nitrating composition is 68% acetic anhydride and 32% nitric acid with an exces of 10% acid,made at 10 degrees Celsius over a period of 2 hours.It also says that you can reduce the m- quantity by adding sodium nitrite....Here's a SS:

http://i.imgur.com/yP6gxT2.jpg


Has anybody checked the 88% o-NT distrubution informed in references cited by Urbanski?
Rod
:o

Solidified nitrotoluene while washing?!

basement - 28-3-2020 at 01:40

I hope to find some help from the wise people of sciencemadness.

I performed the nitration of toluene largely based on the procedure described here by magpie. Along the way I took the following notes:

Quote:

A 100-mL Erlenmeyer flask was equipped with a stir bar, a thermometer and a dropping funnel, sitting on a magnetic stirrer, surrounded by an ice-salt bath. Toluene (23.04 g, 27 mL, 0.25 mol) was placed in the flask and a previously chilled mixture of sulfuric acid (35.76 g, 20 mL, 96%, 0.35 mol) and nitric acid (25 g, 18 mL, 75%, 0.30 mol) was placed in the dropping funnel. With vigorous stirring, the mixed acid solution was dropped in very slowly (about one drop every 3 seconds), keeping the internal temperature below 20 °C during addition (around 0 °C most of the times). The color faded from an initial dark red color to an orange yellow color during addition. After complete addition (about 60 minutes), the ice bath was removed and an air-cooled reflux column was attached to contain splashes. The reaction mixture was stirred vigorously for further 3 hours (2 hours is enough, it stirred longer because I wasn’t around) without heating or cooling (the reaction is still exothermic on its own). After 3 hours, the reaction mixture was at room temperature and the color was still brightly yellow. The yellow-colored turbid upper layer, containing the product, was separated and washed with water (50 mL).


The first deviation I encountered was the color of the post-reaction mixture. Mine was yellow and magpies was red. I supposed this is a good thing and that I've rendered less side products. The major deviation and reason for this post is an odd phenomenon. After addition of water as described above, the whole lower layer solidified (containing the nitrotoluene). I let everything stand over night and the next day, the separated acid layer also partly solidified i.e. nitrotoluene precipitated from it. This was heavily diluted with dH2O and filtered through a coffee filter.
The fear of polynitration came in mind. Technically it makes no sense as temperature was controlled carefully.

I attached some pictures which hopefully help you to understand and solve my confusion.

The apparatus (missing a stirbar in the picture):
apparatus.jpg - 142kB

The flask after complete acid addition:
rxn-mixture-after-addition.jpg - 190kB

The flask after further 2 hours of vigorous stirring (the white crust is at the outside, presumably sodium chloride):
post-rxn-mixture.jpg - 220kB

The sep funnel after removal of the lower aqueous acid layer and the addition of 50 mL dH2O:
sepfunnel.jpg - 128kB

The filtered precipitate from the separated aqueous acid layer:
acid-precipitate.jpg - 295kB



TLDR; The questions:
1) What happened? I really am puzzled.
2) How could I differentiate between mono-, di- and trinitrated products? AFAIK they behave very similar in mp, color and solubility. Is there a noticeable odor difference e.g. polynitrated toluol doesn't smell sweet?
3) How would you further proceed? Until now, everything rests as described. I isolated the precipitated product from the acid layer to test its 'properties'. I'd like to further dry it at room temperature, place a few mg in a test tube and heat it. In case it's trinitrotoluene, it should explode shouldn't it? Are dinitrotoluenes explosives?
Regarding the primary workup I thought of two ways: Heating the sep funnel with a heating gun in order to melt the solidified phase and continue as described by magpie OR transfer the contents of the sep funnel to a beaker and simply wash the solids. In theory the washings should separate in two layers, one contaning the liquid ortho-nitrotoluene?

I'm interested in any kind of feedback, constructive criticism and help!

Ty, basement

[Edited on 28-3-2020 by basement]

[Edited on 28-3-2020 by basement]

mackolol - 28-3-2020 at 02:10

I think it's just p nitrotoluene that may solidify, as it has really high melting point. Maybe your water was very cold or you performed the separation in cold room.

I have performed this reaction a few times and never had situation like this.
Just freeze out the rest of p toluene and enjoy your products.

sulfuric acid is the king - 3-7-2020 at 11:41

If we use freezing method, why do we have (in liquid phase) o- mixed with m-, when m- melts at 16C,and we are lowering below -10C in the freezer?
Colligative properties?
How far we can go with freezing?My fridge is -20 :D

Is there any way to remove unreacted toluene in the nitration process?
Something better than boiling?

Of course my goal is o- .

fdnjj6 - 11-8-2020 at 16:09

Quote: Originally posted by sulfuric acid is the king  
If we use freezing method, why do we have (in liquid phase) o- mixed with m-, when m- melts at 16C,and we are lowering below -10C in the freezer?
Colligative properties?
How far we can go with freezing?My fridge is -20 :D

Is there any way to remove unreacted toluene in the nitration process?
Something better than boiling?

Of course my goal is o- .


If I were you I'd look into the DCM nitration of toluene. It favors the ortho product highly and you would have a lot less impurities.

fdnjj6 - 11-8-2020 at 16:21

I also tried this nitration. It's a success so far, I'll be crystallizing the para product tonight. I used 75mL of toluene I extracted from a carb cleaner can and distilled.

I also had to titrate the dilute nitric acid I made. ~58%. I decided to pretend as if it was 50-55%. I did the math and used a slight molar excess of nitric acid. I needed 1.5 hours for the additions and kept the temps below 15C the entire time. I swapped the ice bath for water at 20 ish C and began very light heating. It was kept at 35C (+-5C) for about 1 hour and 15 minutes. Then I let the layers separate, and decanted the top layer. Washed with multiple water washes and sodium bicarbonate solutions. The mix of isomers is a nasty fucking mess. Oily, likes to spill (probably my fault), is volatile, toxic, and carcinogenic. Even after washing glassware with water and acetone a few times, the smell was still there. I just let it sit outside for a day or two and the smell is gone. I still hate working with it though. It also likes to stain stuff. The gloves were put in a trash bag and thrown away and it made the whole trash can smell of it if you opened the lid. I just dried the isomer mix and it has become much clearer. Beforehand it was very wet. I used Damp Rid calcium chloride to dry it.

To separate the isomers, I'll make a regular ice bath and cool the mix to around 0C. Two days ago I put a saturated salt water solution into the freezer and it's at -20C now. After the isomers are at ice bath temps, I'll swap the ice bath for the salt water solution and let it chill to as cold as I can get it. I'll set up a gravity filtration (despite it being oily, it filters very quickly, at least with my filters) and filter off the crystals. I have around 50-55mL of the isomer mix which should theoretically weigh about 55 grams, so I can expect an absolute maximum of about 22 grams of para product. I highly doubt I'll get that much but I'll be more than happy with 10 grams of para product.

S.C. Wack - 11-8-2020 at 19:37

Quote: Originally posted by sulfuric acid is the king  
If we use freezing method, why do we have (in liquid phase) o- mixed with m-, when m- melts at 16C,and we are lowering below -10C in the freezer?
Colligative properties?
How far we can go with freezing?My fridge is -20 :D

Is there any way to remove unreacted toluene in the nitration process?
Something better than boiling?


Rotary evaporation with vacuum? I assume there is still an azeotrope with vacuum and this will dry the product too. The m is in the p.

I like the smell of o-nitrotoluene.

The picture is not quite the curdy milkshake like product mentioned in the main thread, that was thought to be due to oxidation and/or dinitration, but could it actually be the result of bad toluene that needs purification?

[Edited on 12-8-2020 by S.C. Wack]

fdnjj6 - 11-8-2020 at 23:07

Quote: Originally posted by S.C. Wack  


I like the smell of o-nitrotoluene.


[Edited on 12-8-2020 by S.C. Wack]


Me too haha. It smells like cherries to me. Too bad it's so toxic. Every time I smell it I right away stop smelling it by exhaling all the way, moving away, putting on the respirator, etc. This usually only happens when I don't expect the MNT to still be present. Like some will have spilled onto the wood plate I'm working on and then when I go to pick up one last thing and I go near it, I smell it and right away stop haha. During the reaction and most of the cleanup I have a fan and respirator and even then smell sometimes leaks in from a non perfect seal that is made if I move my mouth or something. Right away exhale and reseal. If it weren't carcinogenic and toxic, I'd huff that stuff all dayyyy. I'd make it one of those car scent thingies haha. Although I haven't smelled a really large dose or deeply inhaled some but the very slight exposure I get through inhalation smells soooo good. I'd like to keep exposure to that level or less haha.

[Edited on 12-8-2020 by fdnjj6]

fdnjj6 - 11-8-2020 at 23:13

Also for people like me who don't have a dedicated lab freezer and don't want to put a carcinogenic and toxic liquid into their food freezer, use compressed air turned upside down and get a nice liquid bath going. Only do this for lab glass. I tried using the method of salt water in the freezer but it just didn't work very well and was a hassle. I only managed to get like half of a gram of para product out. I should be expecting 10-22 grams not 500mg haha. So I'll be using compressed air bath tomorrow. It boils at around 20 ish Celsius so it's perfect for this application. I don't want to use my vacuum filter for this, any recommendations for how to keep the filter and liquid cold during gravity filtration?

I'll be doing multiple rounds of crystallizing and filtering to get the max amount out. Hopefully I don't overshoot and begin crystallizing out the ortho product. I guess once I feel like I got around 10 grams, I'll store that separately from what comes over next. If at some point it doesn't crystallize anymore due to the mixture having a much lower melting point or something, I'll collect as much as I can. The absolute maximum I should be able to get is 22 grams. It'd be perfect if I got 15-20 grams but I'm not sure how much para product is actually able to come out before either staying as a liquid mix or having the ortho product crystallize out.

Tsjerk - 12-8-2020 at 03:47

You don't have to worry about crystallizing the ortho isomers, the para and or meta impurities drop the melting point so far I wasn't able to crystallize the ortho isomer after several days at - 20 degrees.

CouchHatter - 12-8-2020 at 19:52

By tweaking this reactions conditions, it is very easy to get a very different isomer makeup. Sounds like you used a higher concentration of nitric acid than Magpie, that's all I can see. Maybe it's simply the subtleties in temp control vs time.

I'm not sure of any shortcuts for isomer separation. I'd be curious as to how much of each isomer you got though, basement. Could you be more specific about your reactants?

I used 96-98% Rooto sulfuric, 52% dist. nitric, and tech-grade toluene. My results never meaningfully deviated from OP.

I let several people smell it, and they likened it to those bubble-straw kids toy from the early 2000s. Not unpleasant.

S.C. Wack - 3-3-2021 at 16:47

Attached here is part of the uncredited reference of COPAE and quite likely also Cheapskate for nitrotoluene. Both halve the amounts, but Cheapskate "doubles" the beginning temperature given from 9 to 18C...who cools anything just to 18C?

Cheapskate does use the procedure recommended (even though it takes longer than the normal way!) by the author for mononitrotoluene...if you're making TNT, as it's not really MNT at all, being 37% DNT and a Bureau of Mines document not produced for the unsavory likes of those here to make methaqualone. Cheapskate glosses over that bit; people are surprised to get a milkshake on workup.

Some postwar Germans follow different nitration directions (e.g. 5-10C) than everyone else, probably reflecting a fear of runaway nitrations in student hands rather than optimization. Compare the directions for nitration of benzene and naphthalene in the Organikum to Vogel; it's not just nitrotoluene. Perhaps there was An Incident. The Organikum's Vigreux usage is wise; the o cpd. being distinctly more volatile, and the distillation hardly needs to be perfect and long.

At a certain point, there's no further reason to use a column, unless one wants to use a good one later for a final step. And no requirement for fear. One may expect to launch any parts of the apparatus not firmly clamped down only if they're spacing off while running too hot and too long and too dark and too dry. One may just decide to wash and extract the last once the pot temp gets uncomfortably warm.

There's a sensitive test for dinitrotoluene not made from m-nitrotoluene. The 2,4 cpd. in acetone (or ketamine, rohypnol in alcohol etc.) turns blue with aq. alkali.

Attachment: hoffman1916.pdf (405kB)
This file has been downloaded 441 times

[Edited on 4-3-2021 by S.C. Wack]

S.C. Wack - 5-3-2021 at 06:43

Quote: Originally posted by S.C. Wack  
The m is in the p.


JCS (Transactions) 121, 270 (1922) deals with freezing points for nitrotoluene mixtures. Increasing the amount of the m isomer lowers freezing points considerably, which could hardly happen if it all crystallized out first.

So it depends on how one goes about collecting and cooling and warming and all. Partial crystallization is partially meaningless if one doesn't know when one thing has crystallized as much as it will and whether the next thing has already started or finished coming out too. They do not bother to mention the composition or temperature (probably around -17C) of this eutectic:

When commercial nitrotoluene is cooled, the initial crystallisation point is rather difficult to determine, as it is not very far removed from the eutectic and there is a great risk of overcooling. The second crystallisation point is well defined, however, as the eutectic represents about 85 per cent. of the mixture.

S.C. Wack - 16-4-2021 at 16:35

It looks like most of the MNT preparations over 110 years old use just nitric acid, sometimes quite a lot, heated up to 60C. No one worries about excess acid causing dinitration, with just azeotropic HNO3. Which leads me to wonder if sulfuric acid is needed outside of industrial batches, when fractionating the water from waste acid isn't a big deal.

BTW dark brown waste acid is magically converted to clear colorless waste acid after adding water to it...or the reverse (you know what I mean dammit)...precipitates a fair bit of purish p-NT...best to reuse the acid for the next run as is...but some nifty long needles (after a milky phase) can be obtained by dilution.

It's interesting how the "usual" (BTW Cumming et al. appear to have ripped The Manufacture of Intermediate Products for Dyes) process gives no DNT (BTW IPA also gives a nice blue with DNT, which soon darkens...these color reactions happen because the m-dinitro group is particularly activating) at all, none, but using the same weight of nitric acid of 60% conc. <30C (instead of d1.44 acid under warmer conditions) gives some DNT and much unreacted toluene. Small changes can be big here.

[Edited on 17-4-2021 by S.C. Wack]

Fery - 17-4-2021 at 07:42

Here they suggest HNO3+H2SO4 at very low temp, -10 to +5 C:
https://www.oc-praktikum.de/nop/en/instructions/pdf/1001_en....
they still use excess of HNO3 and the DNT is obtained by vacuum distillation as a remainder in distillation flask after distilling out mononitro.
I did the same and the dinitro recrystallized from ethanol few times, I got quite pure 2,4-DNT with nice m.p.
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...
the MNT is still waiting for vacuum distillation through column (I got yet a little of para by crystallization after cooling to -15 C).


[Edited on 17-4-2021 by Fery]

S.C. Wack - 17-4-2021 at 19:28

Not a big fan of overcautious modern German directions that give DNT or 60% yield. Temperatures over 30C might lead to a darker color of the raw product, and over 40C there can be some nitrous vapor in the system, but even so the industrial method (or large excesses of azeotropic HNO3, apparently) does not dinitrate, with proper stirring. Everything is as Cumming says except where they didn't notice that the distillation in Cain's text is with vacuum.

BTW n-propanol is good at separating dirty, mixed NT crystals; 91% IPA might be better.

Fery - 17-4-2021 at 22:49

S.C. Wack do you mean using 91% IPA for recrystallization of mixture of dinitrotoluene isomers, or recrystallization of 4-nitrotoluene?
For removing unreacted toluene I suggest vacuum distillation, without vacuum you have to heat the mixture much higher than b.p. of toluene which caused darkening of obtained dinitrotoluenes. For separation of mono and dinitro the distillation in vacuum is must to go, literature claims that in industry explosion disasters were reduced when heating dinitro only upto 190 C (and b.p. of mononitro isomers are in range approximately 220-230 C at atmospheric pressure). It would be nice to have lab. scale preparation without dinitro formation. I do not see usefulness of 2,4 dinitrotoluene in home lab - maybe oxidation with dichromate+H2SO4 to 2,4 dinitrobenzoic acid, then decarboxylation into meta dinitrobenzene (which could be synthesized form nitrobenzene but the nitration requires fuming nitric acid so this preparation is not trivial) and then reduction to 3-nitroaniline.

S.C. Wack - 18-4-2021 at 14:55

IPA from the store is so good at crystallizing things with little solubility in water (usually better than other alcohols) that I've run out of it and have to buy some more. I had 4 separate solid layers and good crystals with the 60% acid product but have not taken the mp's. It's mostly p-NT. I have an idea for oxidation with Cr to try out.

If one has little toluene left, with good vacuum it can be difficult to condense, ending up in the pump. For sure the SOC direction can be followed even if one substitutes the 1.44 acid with weaker acid (without increasing the sulfuric) or adds toluene to acid, as it also calls for distilling only the first 40%.

PS the relevant part of Houben-Weyl (vol 10 part 1) (BTW this mononitration of monoalkyl aromatics section starts out talking about 1 eq HNO3 in mixed acid of 10-15% water at 20C, not the 20% water of the Belgian reference 2 that starts this and does not give that yield with that nitric ratio IME...PS2 note the workup hint):

houbenweyl.gif - 54kB

[Edited on 19-4-2021 by S.C. Wack]

S.C. Wack - 21-4-2021 at 15:19

Quote: Originally posted by S.C. Wack  
It's mostly p-NT.


I'm beginning to doubt this, as a large fraction recrystallized 3x from n-propanol has a mp of 66C (2,6 dinitrotoluene)...all the less solubles give a strong positive for DNT...It's entirely possible that the 91% IPA gave a positive DNT test because of acetone in it...not sure if it was made from acetone or what...not sure what caused dinitration either, maybe with the water and magnetic stirring, the nitrotoluene was better able to dissolve in the acid than the toluene. If I had nothing else to do I'd try adding something to get better contact and see what that does.

Fery - 22-4-2021 at 00:53

S.C. Wack - I have some mixture of dinitrotoluenes from mother liquor after etanol recrystallization of 2,4 dinitrotoluene (identified by m.p. which is the same as lit. m.p.). So do you suggest to recryst my remainder mixture from 1-propanol to obtain 2,6 dinitrotoluene which is enriched in my mixture (after I obtained 2,4 dinitrotoluene)? Or 91% IPA?

S.C. Wack - 22-4-2021 at 14:03

It's rather hard to say as I don't have any IPA, or mixtures of isomers it seems...the entire less soluble fraction has a mp of 66C regardless of how many times it's been crystallized, whether it's (faintly) chlorine yellow or brown. It should be mentioned that these odorless needles are insoluble in water with or without base, the thermometer was tested with boiling acetone, (PS the toluene was pretreated per Vogel, probably unnecessarily) and the mag stirring was as intense as mag stirring can be...it is the 2,6 version, and a lot of it. This explains why there was no o-NT in the waste acid, and not much anywhere else; it was nitrated preferentially over the p. A hint for why this might be was found in IEC 785 (1955) (Mononitration of o and p-nitrotoluene), where it is said that both are nitrated with ease, but not so much the p-NT, with smaller amounts of sulfuric acid.

[Edited on 23-4-2021 by S.C. Wack]

S.C. Wack - 2-5-2021 at 13:22

PS: 91% IPA (still more expensive than 2 years ago, could be permanent) + refrigeration gave better crystals than n-propanol under the same conditions, especially p-nitrotoluene. That slight brownness to my DNT was cleared up perfectly by boiling for a couple minutes in IPA with decolorizing carbon. This gave long and hair-thin, colorless (until it turned chlorine yellow on drying in the window) transparent needles. The p-NT, already melting correctly and yellow, gave considerably thicker and slightly longer needles, which are also different than the DNT in being pretty much white (opaque), with the slightest hint of chlorine yellow, without decolorizing. And of course the strong smell of MNT.

With second thoughts about using sulfuric acid as solvent for oxidizing the p-NT (w/ Cr+6) because of all the OS warnings already with more dilute acid, KMnO4 was used...the o- would be more convenient either way, as some solid p-NT will be found in cold reflux condensers...Zn/bisulfite will be tried for PABA. (edit: wow...that was easy; the whole off-topic sequence from after isolating the p-NT to before isolating the PABA)

[Edited on 3-5-2021 by S.C. Wack]