Sciencemadness Discussion Board

Problems with toluidine synthesis

Ex42k9j - 22-10-2016 at 13:06

Hello, long time lurker, first time poster.

Anyway, I have been playing around with the reduction of nitrotoluene using tin/hcl. Today I tried repeating the synthesis in which I had succeeded previously and it ended in a failure.

I started by adding 60.2g of nitrotoluene (this was made via the mixed acid nitration of toluene and no effort was made to separate the ortho or para isomers) to a rbf containing a stir bar and 98g of freshly cleaned tin metal. A reflux condenser was attached. Finally, to this was slowly added 220ml of 31.45% hcl (in 10ml or so increments).

I initially got the cloudy color change like normal but a reflux wasn't really taking place. I continued adding and the color never darkened like it usually does. It's cold outside so I figured maybe it just needs some heat to kick off. So I heat things up and the reaction proceeds somewhat like normal.

The nitrotoluene kinda stayed suspended on the top despite my vigorous stirring and a good hour in I notice a thickening taking place. So I turn off the heat and let things cool.

Now the solution initially was quite dark (as it usually is) but as things cooled, it started getting thicker and lighter.

So now I am at a loss and wondering if anyone has a clue of why this happened.


Sorry about the external links for images, posting on my phone so I can't resize them right now.

[Edited on 22-10-2016 by Ex42k9j]

[Edited on 22-10-2016 by Ex42k9j]

Metacelsus - 22-10-2016 at 14:51

How did you do it your first (successful) time? Were there any changes?
It's possible your "nitrotoluene" was different this time around, since you didn't check the purity.
What does the reaction mixture smell like? (Nitrotoluene or toluidine?) Don't sniff too much of it, though.

[Edited on 10-22-2016 by Metacelsus]

Ex42k9j - 22-10-2016 at 15:59

I followed the chemplayer video with some minor tweaks such as adjusting the weights for my starting material and whatnot. The reaction seemed to go exactly like what I watched and have read about. Yields seemed spot on, density looked good, turned very dark red/brown when exposed to air for some time, smells skunky, etc

The gunk smells of nitrotoluene and has now turned into this greenish gel. When I squirt some into water it becomes this yellow gel that will sit on the bottom and make the water a little oily.

[Edited on 23-10-2016 by Ex42k9j]

chemplayer... - 23-10-2016 at 01:59

Sounds as though you're getting incomplete reduction. You could work up and steam distill the product anyway - you might get some nitrotoluene coming over as well, but you can then use an acid-base extraction to purify the toluidine (water soluble in acid conditions).

Only reason this could be happening is the quality of your tin metal - is it reagent pure tin shot? Or another source?

Ex42k9j - 23-10-2016 at 05:01

I was thinking it was an incomplete reduction at first. As the reaction started, the nitrotoluene turned pretty green/black while the hcl stayed cloudy and then eventually turned red/black and nearly all the tin metal got consumed. I ended up letting that reflux for a further hour until I noticed that thickening was taking place.

The quality of my tin was probably an issue. They were tin weights (no lead or steel I believe, no magnetic base metals anyway) that I melted down.

unionised - 23-10-2016 at 06:55

The tin will be "consumed" by the acid. That would happen even if you didn't add any nitrotoluene.
But, unless it's well stirred etc the tin won't reduce the nitro group.
So, I suspect the reaction didn't go to completion.

Ex42k9j - 23-10-2016 at 06:58

Understandable. I did encounter stir issues during the reaction. Do you think it would be better to do as chemplayer suggested and proceed or perhaps attempt to complete the reduction?

[Edited on 23-10-2016 by Ex42k9j]

Templar - 1-12-2016 at 21:18

Synthesising toluidine is a serious pain in the ass. Great if you just want to make it, but a pain in the a$$ for anything over 100g. I recommend checking out auction websites for sellers and inquiring if you need more than that. all the best :)

careysub - 2-12-2016 at 07:37

BTW - I was looking at the Perkin's mauve (mauveine, aniline purple) synthesis, a landmark in the history of chemistry, for a colorful experiment.

The recreation described in at the attached file by Scaccia in J Chem Ed calls for both ortho and para toluidine so an isomer mixture should suit quite well. It uses a 1-2 ratio, instead of the 2-1 ratio typical of nitrotoluene, so the ortho isomer will be in excess according to the instructions (but the ratio itself is probably variable, as discussed in attached Sousa article).

Interestingly, the identity of the key condensation products forming Perkin's mauveine was only identified in 1994! And additional isomers have been identified since then (see Sousa).

I was planning on preparing the toluidine mixture myself to run the Perkin mauve preparation, but if anyone has done this and has some isomer mixture lying around I would be interested in acquiring some. The Scaccia demo uses microscale technique (5 mL), but given the tiny amount mauve produced I want to run it at 100 times larger, 500 mL, which requires about 18 g.

Attachment: scaccia1998.pdf (50kB)
This file has been downloaded 295 times

Attachment: sousa2008.pdf (442kB)
This file has been downloaded 252 times

[Edited on 2-12-2016 by careysub]

Dr.Bob - 2-12-2016 at 19:35

If you can make it into tin powder, dust, fillings, or granules, that will be much better than chunks. Iron powder can also work, and is even more messy, but often easy to find iron powder.