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Author: Subject: Aniline
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[*] posted on 18-2-2003 at 02:59
Aniline


I have recently synthesized about 25g of nitrobenzene and wish to form aniline by reduction, and then diazotize that, and hydrolyse the product to phenol.

I have a few questions.

What is the optimum reducing agent? Tin and hydrochloric acid is used on Megalomania's site. But i don't know where i would get fine tin powder other than buying it from a chem supplier (such a simple chemical yet still hard to get :mad: )

In an encyclopedia they have said that it is made by reduction with iron fillings and hydrochloric acid. Is this a good method? And does anyone have a detailed synthesis, using this method, i couldn't find one searching organic synthesis?

Also i was just curious of what the mechanism for diazotisation of amine aromatics is?

Thanks for any help!
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[*] posted on 18-2-2003 at 03:19


The iron fillings method is a good one. Actually the HCl will form hydrogen in the prezence of Fe, but the H will be atomic (well, I don't know the exact term-"new born" ?! ), and very reactive.
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[*] posted on 18-2-2003 at 08:22


Tin(II) Chloride is available from dyeing suppliers as 'Tin Mordant'.
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[*] posted on 18-2-2003 at 08:33


It is called nascent hydrogen
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thumbup.gif posted on 18-2-2003 at 12:40


Great thats really helpful, thanks.
But does anyone have an actual detailed synthesis with quantities? That would be greatly appreciated.
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[*] posted on 18-2-2003 at 17:11


I'll be able to post the actual process next week if you are patient.
One interesting thing about aniline is that it was recognised as carcinogen only about 20 years ago or so, due to the computers (statistics).

[Edited on 19-2-2003 by a_bab]
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[*] posted on 18-2-2003 at 17:26


Note: this has not been tested. What follows is only me speculating as to what I would do if I were in your shoes.

Add your 25g nitrobenzene to 600mL of 38% HCl solution. Proceed to gradually add 115g of Fe powder or steel wool, with stirring. Boil down the solution; crystals of ferric chloride and aniline hydrochloride should remain. Now add NaOH solution (9g NaOH dissolved in 50mL water). Aniline should float to the surface, ready to be decanted or separated with a separation funnel. 100% yield would be 17.9g (that's 17.5mL) of aniline.

As for the diazotation, here is more speculation:

Carefully add 15g of cold sodium nitrite to 81mL of cold 38% HCl, keeping the temperature below 5C at all times. That will prepare a solution of nitrous acid. Now add that to 17.9g of aniline (I'm assuming a 100% yield in the previous reaction, which will not happen, so you will have to adjust the ratios accordingly), and, while stirring, gradually begin to heat up the solution until fizzling (that's nitrogen gas being released) ceases. You now have a solution of phenol. Proceed to boil it down, heat, and pour the molten phenol through a filter to filter out crystals of sodium chloride.




I weep at the sight of flaming acetic anhydride.
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[*] posted on 19-2-2003 at 05:34


The HCL and Fe is FAR too much in my opinion. I'll post on weekend the good verified quantities.
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[*] posted on 20-2-2003 at 21:29


thanks for your help madscientist, and everyone else, and i'd really appreciate it if you wrote up that method a_bab. Hopefully i'll be able to do some experiments on the weekend.
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[*] posted on 24-2-2003 at 23:24


A_bab, if you could please post that synthesis of aniline whenever you get a chance, i would really appreciate it.
I am really looking forward to doing some experiments with aniline.
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[*] posted on 25-2-2003 at 00:05


http://www.rhodium.ws/chemistry/vogel3.html
You should definitely get this book. Here's the procedure for aniline using HCl and iron filings:

Quote:
Place 40 mL of water and 30 g of grease-free iron filings in a 750 or 1000 mL round-bottomed flask and 25 g (21 mL) of nitrobenzene in a small beaker or conical flask. Warm the former on a water bath at about 60 degrees. Add 1 mL of nitrobenzene and 2.5 mL of concentrated hydrochloric acid, and shake well; the temperature will rise appreciably. In the subsequent reduction maintain the temperature inside the flask at 80-90 degrees by alternate heating on a water bath or cooling the flask in running water as may be necessary. Add the nitrobenzene 1-2 mL at a time over a period of 20-30 minutes. Test for completeness of the reaction (when the smell of nitrobenzene can no longer be detected at the mouth of the flask) by removing a small portion and diluting it with dilute hydrochloric acid; the odour of nitrobenzene should be absent and a clear solution should be formed. (If nitrobenzene is present, warm on a water bath under reflux and with frequent shaking until the reduction is complete.) Render the reaction mixture alkaline by the cautious additon of 5 g. of anhydrous sodium carbonate, and steam distill until the steam distillate is no longer turbid and a further 100 mL of clearr liquid passes over. Measure the total volume of the distillate, transfer it to a separatory funnel, add 20 g of commercial salt for each 100 mL of liquid present and shake vigorously until the salt dissolves. The aniline may be isolated, if desired, by ether extraction as in Method 1. An alternative procedure is to carefully separate the upper layer and pour it into a 50 or 75 mL distillation flask. Use the assembly shown in Fig. II, 12, 1 and heat the flask either on a wire gause or in an air bath (Fig. II, 5, 3). A little water comes over first; collect this separately. When aniline commences to distil, stop the distillation. Run out the water from the condenser, dry the inner tube, and continue the distillation. Collect the aniline at 180-184 degrees (2). The yield is 18 g.

Want to know what Method 1 was, read about the ether extraction, or consult the diagrams? Download the book.
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[*] posted on 25-2-2003 at 01:21


My quantities as taken straight from a chemistry manual are:
In a round flask of 500 ml add 15 grams iron filings and 15 grams (13 ml) nitrobenzene. Than 70 ml of HCl are added gradually in 1-2 ml portions. The reaction is exothermic and if too violent should be cooled down in a water bath. After all the HCl is added, the mix is heated 3-4 hours in a boiling water bath. Then after the cooling is done 25 ml of water should be added. Aniline is extracted from the it's clorhidrate by the addition of 40 grams NaOH dissolved in 50 ml of water.

Well, then there's a long purification process, and in the end you'll get 5 grams of aniline in theory.
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[*] posted on 3-10-2004 at 21:16


How’s this for a OTC synthesis of aniline?.
It involves three steps
1. Esterification (benzoic acid > ethyl benzoate ) (methyl benzoate might be better).
2. Ammonolysis of ester ( ethyl benzoate + NH3 > ethanol + benzamide) (in alcoholic solution).
Or perhaps ammonium benzoate could be decomposed instead, similar to the decomposition of ammonium acetate?
3. Hoffman degradation of amide (benzamide + OCl- + 2 OH- > aniline + H2O + Cl- + CO3 2- ) (in aqueous solution) again, written in a more intelligible way C6H5-CONH2 + NaOCl + 2 NaOH > C6H5NH2 + NaCl + Na2CO3

Unfortunetly I don’t think that dimethylaniline could be made by substituting dimethlamine for ammonia due to the reaction mechanism.
If the reaction conditions aren’t too difficult to obtain and the yields are good then this should be a great, cheap way to aniline or other amines.
I say this because textbooks almost always make a reaction sound easier and simpler than it really is:mad:.
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[*] posted on 5-10-2004 at 02:42


Checked some preps on nitrobenzene reduction. With Sn/HCl they get 90-95% yield and with Fe/HCl they get 96%.. so they give pretty same yields..

I've mentioned that route through benzamide on E&W, but I couldn't find any methodics on Hoffman degradation of benzamide.. any info on this? There are one book (March? ..don't remember) that told this reaction gave good yields but there were no references..

As for benzoate ester + NH3, reaction seems to go faster in aqueous ammonia than in alcohol soln of ammonia.. and it's a bit hard to make a totally dry alcohol solution of ammonia at home..
Sofar I could get about 40% yield with 25% ammonia while stirring the reaction mix for several days.

Btw, amidation is usually made in 50/50 soln of water/dioxane.. would it be worth to try this out?

How about decarboxylation of m-nitrobenzoic acid? Anyone got preparation references to this?? I only know that yield should be 92% nitrobenzene if it's heated with copper powder.. Have actually tested this but since this was on a small scale I couldn't calc the yield. Then the reaction mix chars, so one have to find a suitable solvent (glycerine?).

Another interesting route is to make aniline directly from benzoic acid by HN3/H2SO4.. dunno much about this except that it's quite hazardous route.. do anybody have more info on thisone?
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[*] posted on 12-1-2006 at 15:51
Making aniline


I recently got some NaNO2 and now I just need a good target to play with...

I would like to make some aniline but it seems like a lot of work to go from benzoic acid---heat---> benzene
Nitration with HNO3+H2SO4 to nitrobenzene,
Hoffman reduction to aniline(Fe+HCl)...

Why would the NH3 + H2SO4 +benzoic acid route be so hazardous?
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[*] posted on 13-1-2006 at 05:23


Quote:
Originally posted by Endo
I recently got some NaNO2 and now I just need a good target to play with...

I would like to make some aniline but it seems like a lot of work to go from benzoic acid---heat---> benzene
Nitration with HNO3+H2SO4 to nitrobenzene,
Hoffman reduction to aniline(Fe+HCl)...

Why would the NH3 + H2SO4 +benzoic acid route be so hazardous?

I'm not too sure whether benzoic acid --heat--> benzene is a viable method of obtaining it (benzene). Though theoretically it looks like it will work if your final product you want is aniline (though yield will most likely be quite low, as you have many steps). Is it not possible for you to find a source of nitrobenzene? It would make things much easier :)

On another note, I wasn't aware that this particular reduction (Zn, Sn, Fe in HCl) was known as a Hoffman reduction. Guess I still learn more things even after taking organic chemistry in university ;)

As for the NH3, H2SO4 and benzoic acid, what is your proposed synthesis? Obviously, you can't just add the NH3, H2SO4 and benzoic acid into "one pot"...
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[*] posted on 13-1-2006 at 05:41
Errr Ooops...


I looked at my reference books and you are right... I guess when I get to messing with amines the whole Hofmann elimination thing just got stuck in my head. I don't see that the reduction is a name reaction anywhere. Thanks for pointing that one out...

I was reading about making benzene from benzoic by dry distallation in a previous thread.

I am still doing some research into what the H2SO4 +NH3 method would take.

Thanks
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[*] posted on 13-1-2006 at 05:51


The Fe / HCl reduction is called Bechamp reduction
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[*] posted on 13-1-2006 at 13:42


Quote:
Originally posted by gsd
The Fe / HCl reduction is called Bechamp reduction

So it is, so it is :)

Learn something new everyday
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[*] posted on 7-2-2006 at 20:38


I have also chosen to make phenol via aniline. I finished my nitrobenzene synthesis today. So aniline via reduction using Sn + HCl is next.

When I bought my tin the advertisement said "shot." So I expected it to look like the shot I'm used to seeing in shotgun shells, i.e., BB size or less. Wrong! - each piece of "shot" looks like a full bullet - about 5 g each.

Since my procedure calls for granulated tin I thought well, I'll just grind it up with a coarse file. Wrong again, that stuff is hard. So I decided to make mossy tin using Ammen's method as I did for mossy Ag. Tin melts at 232C so it wasn't much work for my muffle furnace.

Here's a picture of the mossy tin. Some of the pieces look very much like sponge.



[Edited on 30-1-2007 by chemoleo]

mossy.jpg - 58kB




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[*] posted on 8-2-2006 at 07:43


Tin is somewhat expensive here, especially from lab suppliers. I managed to reduce nitobenzene to aniline using steel wool (which, at least in my case, is composed almost completely of iron, with other impurities which cannot interefere with the reduction) instead of tin using the same procedure. Much cheaper and more OTC, at least in my case.



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[*] posted on 8-2-2006 at 15:23


Yes, Explosivo, tin is expensive in the US also. I bought it as my procedure calls for it, but mostly as I wanted to play with it some, having never had any in a bulk state before. My next synthesis of aniline (if needed) would be with iron as you have done.

I ended up taking a pair of side-cutters to further size reduce my mossy tin. The biggest pieces are about 3mm in diameter now and I hope that will be small enough.

I'm playing with my wife's old pressure cooker today :D. Rigging it up as a steam generator for an old-style copper steam bath I found on eBay some time ago. I plan to use this in my aniline systhesis per procedure.

Here's a picture of the steam generator. Next post will have a picture of the steam bath. This bath may be rare nowdays with the advent of electric heating mantles and I thought some of the younger members might like to see it. This is what we used in the old days for heating flammable solvents, especially diethyl ether.



[Edited on 9-2-2006 by Magpie]

[Edited on 30-1-2007 by chemoleo]

steam.jpg - 79kB




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[*] posted on 8-2-2006 at 17:27


And the Cu ring steam bath (with steam):

[Edited on 30-1-2007 by chemoleo]

Cu.jpg - 52kB




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[*] posted on 9-2-2006 at 19:50


I made the aniline with tin today. The reduction of the nitro group to the amine group is strongly exothermic. So is the conversion of the aniline hydrochoride to aniline.

My procedure now calls for steam distillation to simultaneously remove the aniline and unreacted nitrobenzene from the product matrix. An older procedure I have removes the unreacted nitrobenzene by steam distillation prior to conversion of the hydrochloride to aniline. I wonder which is the superior method?




The single most important condition for a successful synthesis is good mixing - Nicodem
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[*] posted on 10-2-2006 at 03:31


I think that the latter is the preferred method. Keep the solution acidic to have the aniline as the nonvolatine anilinium ion and then steamdistill the nitrobenzene.

Do you have a clear solution or is there a lot of SnO2?

Something I have noticed while running a diazotation with aniline (preparation of iodobenzene) is that the sulfate salt of aniline has strongly temperature dependent solubility.
I added the aniline to hot dilute H2SO4 to get a solution of the sulfate salt, and the aniline dissolved rapidly upon stirring and heating.
However, on cooling, huge masses of the solid anilinium sulfate crystallised out. I had like about 20g aniline (weighed as freebase) in 300ml water, and the crystals filled the entire liquid!
(The diazotation still worked, after the calculated amount of NaNO2 solution was added the crystals had dissolved)

So if you have a clear dilute aqueous solution of aniline and wonder how to isolate pure aniline from this, consider heating, adding H2SO4 and cooling with ice to precipitate the sulfate.
The sulfate is more convenient for storage of the aniline, since it is a crystalline solid instead of an oily liquid like aniline freebase.
And most of the time, like for diazotations, the aniline is required as a salt anyway.


Another thing: when making phenol, keep closely to a procedure from a book. The method from madscientist doesn't seem right to me. When boiling an aqueous phenol solution the phenol escapes since it is volatile with steam.
That's actually how the phenol is isolated from a solution obtained by heating a benzenediazonium salt solution: steam distillation.
The distillate is then extracted with ether several times, the exracts combined, dried with Na2SO4, the ether removed by distillation and the phenol distilled into a separate receiver.

You can find the complete procedure in Gattermann from 1982.


[Edited on 10-2-2006 by garage chemist]
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