Sciencemadness Discussion Board

strange (?) results from nitrating toluene

kafka - 14-4-2007 at 13:04

80ml of toluene was reacted with 118g 68% HNO3 and aproximetly 120ml of con (rooto) H2SO4 over the course of 1 hour. the mixture was stirred for 1 hour thenallowed to stand for 8 hours. a yellow precipitate formed taking up half of the total volume of the mixture.

in all the toloul reactions i have read there were two liquid layers the mononitrotoulene and the acid. im guessing that the top layer is either DNT or hopefully its precipitated p-nitrotoluene. any ideas? the melting point of p isomer is 51-54 celsius and i believe the melting point of dnt is around 68. so a melting point determination would be best.

if it is DNT any ideas as to what i may have done wrong? i filtered off all the solid and now i have yellow liquid which i have neutralized with KOH solution. no two distinct layers are present yet so im goign to allow it to sit for a little while.

thanks for the help.

Ozone - 14-4-2007 at 13:09

What was the maximum temperature during the nitration? What's this about toluol? If it got too hot you got product, DNT's and *crap*

More detail, please,

O3

Sauron - 14-4-2007 at 13:38

If you allowed temp to rise over 30 C at any point you may have some DNT

What you should have is yellow oil o-nitritoluene in which some p-nitrotoluene is dissolved and just a little m-nitrotoluene.

The approx isomer ratio (o:p:m should be 60:35:5 give or take.

Chill your product to -5 C in ice/salt bath (brine) and after p-nitrotoluene finishes crystallizing out, filter it off.

Seperate the aq acid layer.

What you have left is mostly o-nitrotoluene with some of the other isomers dissolved. If you are SURE temp NEVER got over 30 then you can fractionate the 0-NT off, through a good column, and stop collecting when temp at still head indicates the other isomer(s) are coming.

But if you are NOT SURE do not do this or you can have a little BOOM.

Anyway now that most of the o-NT is out, chill the rest to -5 again, let crystalls form, filter. Repeat process quite a few times until no more p-NT forms. Recrystallize the p-NT until you get a lit. mp. Then you are done.

kafka - 14-4-2007 at 13:50

more detail, of course! i mixed the nitric and sulfuric in an ice bath before hand and let that cool for a good 20 minutes. i then added the toluene TO the acid mixture. im thinkng next time it will be the otherway around. the temperature DID go above 30 for sure, it just about hit sixty once or twice. i follwed a 3 step process for making tnt, im guessing that these procedures are not trying to minamize the amount of dnt created.

so hey, it looks like i have a large amount of dnt, gives me something to do while im making a new batch of nitric acid. thanks for the help you guys, next time around ill keep the temp LOW.

i keep promising myself ill take pictures and good lab notes so i can post a nice step by step procedure with pics, the results of this last nitration serve as reminder to follow directions.

Ozone - 14-4-2007 at 18:29

Sauron has a good point, the reverse addition, in this case, allows for a lot more fudge in the temperature (30 is ok vs 5°C)...and, the excess toluene strongly favors the mono-nitro product.

Yes!

With a thermometer. If you do not exceed 5°-20C, you should get the o,p distribution exclusively. The separation of crude products is readily afforded by recrystallization.

BUT, do not run this thing very cold, viz. dry-ice acetone. The reactant concentration will be very high (with little reaction occuring). With slight warming, it *will* run-away.

Be Careful,

O3






[Edited on 14-4-2007 by Ozone]

Sauron - 14-4-2007 at 20:18

I'd advise adding your cold mixed acids slowly (dropwise) to cold toluene with stirring so that toluene is always in excess.

And monitor temp so that it does not go over 30.

A recommendation is to only use the stoichiometric amount of HNO3 for the mononitration, if you do that and control temp you will not make any DNT.

Nitration of toluene is rapid. You do not need to let it sit for 8 hours. It is 27 times faster by rate than nitration of benzene, which I can assure you is faster than your procedure.

You got proportions about right, just tweak the nitric to exact stoichiometry (the molarity of conc HNO3 you can look up) and watch that thermometer. The reaction IS exothermic. The exact amount of sulfuric acid is less important.

On an 80 ml scale the amount of m-isomer is negligible (<4 g) and not worth working up.

The conversion of toluene should be 96% overall.

You should end up with c.48 g o-NT and maybe 27 g p-NT.

chemrox - 15-4-2007 at 17:16

how are you making the nitric and purifying it? this could be important in figuring the stoichiometrics..

[Edited on 15-4-2007 by chemrox]

Sauron - 15-4-2007 at 19:26

I dunno about how kafka is doing that or if he is buying comml nitric. Those who can't usually make it out of nitrates and sulfuric acid, and as it is an azeotrope 68% 120 C quality control seems like a minor issue. It is self regulating.

kafka - 15-4-2007 at 22:55

nitric acid: distilling as azeotrope from "stump remover" KNO3 and "rooto" sulfuric (unpurifyed) mixture.
apperance: definitely contains NO- golden yellow in apperance.

pictures soon to come (if anyone interested, its been done 1,000,000 times...)

Separating the mono-nitrotoluenes

Aubrey - 27-1-2009 at 11:03

Apologies if this is the wrong thread to reply on, but there were several mentioning mononitrating toluene.

in a 500ml rbf a mixture of H2SO4 and Nitric acid was dropped slowly into toluene keeping the temperature under 30 degrees C. (following ratios mentioned in the library nitro book)

(The first couple of attempts, i tried this without stirring and it managed to go up to 60 degrees. )

The acid in my pressure equalised funnel looked like it didn't completely mix, with the sulfuric at the bottom.

I've attempted to follow the technique of freezing out to seperate the o-nitrotoluene from the p-nitrotoluene. However after 2 days in the freezer, its still an orange liquid. I froze the lighter coloured lower layer, which erowid states is the acid layer and can be disposed of. (http://www.erowid.org/archive/rhodium/chemistry/quaalude.che...)

However this layer is now showing signs of crystallisation,.
since p-toluene is denser than water this may make sense( 1.29 g/cm³)?
Any ideas how i can proceed?

the image on the left (bottom pic) is the result of my first experiment, where the temp went a bit too high, the bottles on the left show the uppermost layer in orange, and the acid /water layer i assume, being much lighter. The pic at the top is before going into the freezer, you might just be able to make out that the darker layer floats

[Edited on 27-1-2009 by Aubrey]

SCIMAD.jpg - 78kB

Sauron - 27-1-2009 at 12:25

If you want to have exclusively mononitrotoluenes you must strictly regulate temperature to below 30 C at all times and employ only the calculated theoretical amount of HNO3 (or KNO3)

To get exclusively 2-nitrotoluene, nitrate p-toluenesulfonic acid and then desulfonate with conc H2SO4/heat. Easy.

To get pure 4-nitrotoluene nitrate o-toluenesulfonic acid

See Fundamental Processes of Dye Chemistry.

JohnWW - 28-1-2009 at 01:14

Of course, by far the most common commercial nitration of toluene is to make 2,4,6-trinitrotoluene, the explosive TNT in wide use, using an excess of HNO3. I believe that even more rigorous conditions can produce pentanitrotoluene.

Sauron - 28-1-2009 at 01:53

Does that come as a surprise to anyone here?

I thought the thread was about what was supposed to be mononitration that was botched.

The problem with normal mononitration is that it is lossy, you get mostly o-isomer, and p-isomer, but a lot of both are trapped in the eutectic from which they are difficult to separate. The usual techniques are fractional crystallization, fractional distillation (only safe is no DNT is present) or complexing with certain amines which occurs with the p-isomer only.

The first is tedious, the second is energy intensive and the third is unacceptable from an industrial hygiene point ov view (the amines are aniline, toluidines etc.)

Hence when pure mononitrotoluenes are required special techniques are employed that avoid isomer mixtures.

TNT

bluemike - 28-1-2009 at 17:05

I made about 100g of TNT when i was in college for the hell of it. I recrystallized it twice and it melted at 80C so I assume it was pure. I never bothered separating any of the isomers until after the final nitration with fuming sulfuric, and everything went fine. I boiled bown the filtered recrystallization solution under vacuum and kept the TNT oil(bad isomers) as a souvonoir(sp?). There are very explicit instructions available from a book that's in this site's library I believe, "The Chemistry of Powder and Explosives." that tell how to make it. The TNT crystals are very pretty; they look like giant snowflakes. I cast my TNT into a tiny statue, and my college girlfriend stole it. I haven't seen either since!

Sauron - 28-1-2009 at 21:36

Maybe she ate it.

DNA - 17-2-2009 at 05:44

Why would you want to seperate the isomers at all when making trinitrotoluene.
Just nitrate it so you get mononitrotoluene and then nitrate your product again to get dinitrotoluene and then nitrate it again with 100% pure nitric acid to get the trinitrotoluene.
Who cares if in the first nitration you will already get dinitrotoluene a little bit.

Nicodem - 17-2-2009 at 06:19

I wonder why nobody wants to answer the specific question instead of posting a bunch of off topic posts?
Quote:
Originally posted by Aubrey
in a 500ml rbf a mixture of H2SO4 and Nitric acid was dropped slowly into toluene keeping the temperature under 30 degrees C. (following ratios mentioned in the library nitro book)

(The first couple of attempts, i tried this without stirring and it managed to go up to 60 degrees. )

Doing exothermic reactions, particularly biphasic ones like such a nitration, without stirring can result in runaways. You can have a small volcano spraying conc. HNO3/H2SO4 out of the flask.
Quote:
The acid in my pressure equalised funnel looked like it didn't completely mix, with the sulfuric at the bottom.

HNO3 and H2SO4 are miscible. Surely you mixed them in a beaker immersed in an ice bath before pouring them in a addition funnel?
Quote:
I've attempted to follow the technique of freezing out to seperate the o-nitrotoluene from the p-nitrotoluene. However after 2 days in the freezer, its still an orange liquid. I froze the lighter coloured lower layer, which erowid states is the acid layer and can be disposed of. (http://www.erowid.org/archive/rhodium/chemistry/quaalude.che...)

That separation is for separating p-nitrotoluene from a mixture of p- and o-nitrotoluene, not about separating p-nitrotoluene from o-nitrotoluene and a bunch of other stuff. You first need to isolate the mixture of mononitrotoluenes and then freeze out the para isomer.
Quote:
Any ideas how i can proceed?

Follow the experimental procedure to the letter. Up to now you did not.

nitric - 14-4-2009 at 07:38

with all may attempts at MNT i get a black, almond odored, liquid

ProChem - 14-4-2009 at 09:09

I would run this reaction in excess of toluene, say 5 mole excess (adding nitric acid the limiting reagent), follow via TLC, evaporate most of the toluene at room temperature then cool to crystalize the product.

[Edited on 14-4-2009 by ProChem]

S.C. Wack - 14-4-2009 at 13:43

I have not found the reaction to require more than a very slight excess of toluene. Or end up black. Red/orange before washing yes, pleasant smelling yes.

I would absolutely not "follow the experimental procedure to the letter", not THAT one. As for freezing, if you read a real experimental procedure, such as the one in Systematic Organic Chemistry, you will see that -20C is suggested for the mixed isomers. As it says, once you fractionally distill (I suggest vacuum) off some o- isomer, then the p- isomer can freeze out at a higher temp.

And though improperly done this can produce lots of DNT, yes which is yellow and of low solubility in certain concentrations of acid, it can also straight-up oxidize the toluene, and it wouldn't surprise me if the resulting benzoic acid came out yellow until put through a simple purification.

[Edited on 14-4-2009 by S.C. Wack]

manimal - 12-7-2009 at 17:06

Quote: Originally posted by Sauron  
If you want to have exclusively mononitrotoluenes you must strictly regulate temperature to below 30 C at all times and employ only the calculated theoretical amount of HNO3 (or KNO3)

To get exclusively 2-nitrotoluene, nitrate p-toluenesulfonic acid and then desulfonate with conc H2SO4/heat. Easy.

To get pure 4-nitrotoluene nitrate o-toluenesulfonic acid

See Fundamental Processes of Dye Chemistry.


Can you provide refs. for these reactions, Mr. Sauron? I couldn't find any in the Dye Chemistry book.