Sciencemadness Discussion Board


fluffy bunny - 18-2-2003 at 02:59

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!

a_bab - 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.

I am a fish - 18-2-2003 at 08:22

Tin(II) Chloride is available from dyeing suppliers as 'Tin Mordant'.

notagod - 18-2-2003 at 08:33

It is called nascent hydrogen

fluffy bunny - 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.

a_bab - 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]

madscientist - 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.

a_bab - 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.

fluffy bunny - 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.

fluffy bunny - 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.

Polverone - 25-2-2003 at 00:05
You should definitely get this book. Here's the procedure for aniline using HCl and iron filings:

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.

a_bab - 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.

markgollum - 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:.

frogfot - 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?

Making aniline

Endo - 12-1-2006 at 15:51

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?

Darkblade48 - 13-1-2006 at 05:23

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"...

Errr Ooops...

Endo - 13-1-2006 at 05:41

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.


gsd - 13-1-2006 at 05:51

The Fe / HCl reduction is called Bechamp reduction

Darkblade48 - 13-1-2006 at 13:42

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

So it is, so it is :)

Learn something new everyday

Magpie - 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

Esplosivo - 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.

Magpie - 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

Magpie - 8-2-2006 at 17:27

And the Cu ring steam bath (with steam):

[Edited on 30-1-2007 by chemoleo]

Cu.jpg - 52kB

Magpie - 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?

garage chemist - 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]

Magpie - 10-2-2006 at 09:44

GC I was afraid you were going to say that. But I am sort of committed to the steam distillation of both as I have already converted the aniline hydrochloride to aniline. Next time I will try the other method.

You are right about the massive precipitation of SnO2 - it was quite dramatic. When I took the clear honey-colored aniline hydrochloride brew off the steam bath (which worked beautifully BTW) there was this sudden and massive precipitation of white salt as it cooled. :o

I will be making the phenol next. This will be the termination of my planned synthetic route:

Rooto + Detrol + carp bait preservative + fishing lead + Red Devil Lye + Muriatic acid ---> benzene ---> nitrobenzene ----> aniline ----> phenol :D

Magpie - 13-2-2006 at 17:19

My aniline synthesis went OK but the yield was not very good, i.e, about 50%. I have a feeling that all those precipitated Sn hydroxides somehow interfered with the steam distillation.

One of the qualitative tests for aniline was to mix a few drops with 5 mL water then add 0.5g bleaching powder. This gave an immediate and strong purple color. Does anyone know what the purple product is and the reaction that occurs? I was wondering if this might be a chloroaniline.

I also wanted to point out that my aniline did not have much of an odor. Of course I really did not stick my snoot in it as it is highly toxic. But with a lineage of benzene and an amine I expected a strong, aromatic fishy smell.

Today I made phenol with the 6.4 mL of aniline and 5.5g NaNO2 that I had made. I will post results on a phenol thread.

[Edited on 14-2-2006 by Magpie]

ordenblitz - 13-2-2006 at 20:49

I decided to try to simplify the route from benzene to Aniline as much as possible. The aim was to do it easy, fast and use as little glassware as possible. I set out by generally using the procedure for nitrobenzene and aniline outlined in Vogel, but skipping the tedious washing and distilling of the C6H5NO2 and not spending time making sure all the previous residues were removed from the glassware before moving to the next step.

70ml HNO3, 68% and a stir bar were placed in a single neck 1000ml flat bottom flask, resting in an ice cube slush. Next 80ml H2SO4 ~95% was added in several portions over a few minutes. A thermometer was placed just into the liquid and when the mix fell to ~20º, 60ml C6H6 was then added drop wise but fast, over the course of 10 to 15 minutes generally keeping the temperature at least below 40º.
After the addition was complete, the ice bath was replaced with a water bath at 60º and a condenser was affixed for reflux. This setup was maintained for 20 minutes.
The contents were then dumped into 700ml cold water with a little ice. After resting for several minutes the contents were transferred to a separatory funnel and the lower layer was run off and discarded. 100ml cold H2O was added, shaken and the lower layer was run off and then repeated once again. The result was 61ml of wet nitrobenzene, certainly some residual nitrating acid and most likely some di-nitrobenzene, although none was seen to crystallize out upon standing.
19ml of wet crude C6H5NO2 was run out of the separatory funnel leaving 42ml remaining which is what I needed for the reduction using iron and HCL.

The 1000ml flat bottom used above was rinsed two times with water and into it was placed 80ml DI-H2O, 60gm 200 mesh iron powder and 5ml 34% HCL.
The thermometer was placed back in loosely and while holding the flask in my hands I began the reaction by running 3 or 4ml of nitrobenzene from the funnel into the flask. Upon swirling the contents a temperature spike was noted but it never reached the intended 80º so I placed the flask on a hotplate until it was nearing ~80º. I then removed it and swirled by hand again. C6H5NO2 was added in ~4ml portions usually when the temperature had fallen below 80º which would then immediately cause a temperature rise.
As noted in Vogel it was sometimes necessary to alternate the flask between a cool water bath and a hot plate to keep the temperature between 80º and 90º. After all the nitrobenzene had been added the flask was left on the hotplate and a condenser was affixed while maintaining a gentle reflux and continued for 20 minutes. It was then removed from the hotplate and cooled as fast as the glass would allow. After reaching room temperature, 10 grams of potassium carbonate was added slowly. The flask was then returned to the hotplate and setup for steam distillation.
On the flask was placed an angle adapter with a thermometer port that was fitted with a glass tube where the thermometer would be. A length of hose connected the tube to another flask with boiling water and a few boiling stones.
A condenser and collecting flask was attached and the distillation begun. A turbid distillate begun to collect after a while and was continued until it ran clear. This process took roughly 30 minutes. A total of 250 ml was collected and then the crude wet aniline was then placed into the separatory funnel with 50 grams sodium chloride and shaken to dissolve the salt.
Two layers politely formed and the lower run off and discarded.

The salted out crude aniline was placed in a 250 ml round bottom set up for distillation.
The heat was applied and after some time the temperature reached 100º and water began coming off which was collected in a beaker and discarded.
Shortly after the temperature quickly rose to 180º whereupon the heat was shut off and the flask pulled from the mantle to cool. The adapter and condenser were removed and rinsed of the remaining water with acetone and forced to dryness with a hot air gun. The setup was reassembled and the heat turned on again.

The distillation proceeded very smoothly with no trouble to just dryness where upon the flask was quickly removed from the mantle and the collecting flask was removed.

The result was 31.22 grams of a lovely golden aniline oil. I think the yield could have been better but I lost some with the first water coming over and subsequent glassware drying.

I too did not smell the fishy odor as was reported in vogel and other texts. There was a faint amine smell and other somewhat pleasing notes similar to nitrobenzene but different. I will run a sample on the FTIR and report the findings when I have more time.

[Edited on 14-2-2006 by ordenblitz]

Magpie - 14-2-2006 at 09:31

Ordenblitz your streamlining of the synthesis of aniline is outstanding. I would be embarassed to compare the hours I spent getting my aniline.

Could you please calculate your %yields for both nitrobenzene and aniline? I will sheepishly provide mine once my phenol is made.

[Edited on 14-2-2006 by Magpie]

Drunkguy - 19-10-2006 at 05:14

I followed the procedure in Vogel using granulated tin that I made myself using wire clippers. The tin obviously dissolves as the reaction procedes using magnetic stirring the whole time to keep the two immiscible layers in close contact. A few pointers:

*Making nitrobenzene, the reaction became dark and fuming so I stopped early. Be careful not to over heat this although I was lucky that there was a healthy amount of nitrobenzene at the end of the reaction though not as much as there would have been. I got the amount necessary for all the tin I had available to me which was the limiting reactant (111g). [The reaction lightens upon diluting with water as the nitric oxide goes back into solution].

*I did the reduction as in Vogel except I just streamlined it and used a little bit over to compensate. The nitrobenzene was a turbid opaque color but I added a 2ml test aliquot that I had left over to some CaCl2 and it does clear up on standing.

*Vogel says to pour the acid down the condenser. I have a Graham condenser and found this retarded. It's much better if you have a Claisen head and a pressure equalising addition funnel. You dont need to cool this reaction at all as long as you dont add the acid too fast. I also doubt what effect heating it on the water bath has but I did this 1/2 hr just because it said to.

*Steam distillation was actually just distillation of the water until the white scum (aniline) floating on the surface of the boiling mixture stopped coming over. You can play it by eye if you like. I think I added about 250mL additional water thoughout the boil although im not 100% to what extent this is actually necessary.

*The aniline is colorless. However traces of nitrobenzene in the sep funnel gave it a yellow tinge. The yield was 37.5ml aniline from 62g PhNO2 (I added 64g since it was emulsified). Didnt bother using ether either.

Im drying it over NaOH pellets now. I cant imagine it being anything other than very pure although its probably worth distilling it just in case.

Zinc - 15-11-2006 at 09:07

At my school chemistry lab I found an old (20-30 years) bottle of aniline. It was never opened before and is was tightly sealed. What suprised me is that the aniline is dark red and I have never heared before of dark red aniline. Is that possible?

Nicodem - 15-11-2006 at 09:40

Aniline can be anything from just yellowish to intense orange or reddish. It all depends on how much oxidation products it contains. Mind that the oxidation products of aniline are the polyanilines which are a black dye (worth a fortune in the old days, but just an annoyance nowadays). You can purify it if you think it is worth the fuss (by vacuum distillation or steam distillation followed by drying).

garage chemist - 15-11-2006 at 14:00

I have an old bottle of analytical grade aniline and it is dark red as well. The aniline is perfectly fine, the red stuff is just an impurity of oxidised aniline which is strongly colored.
A simple distillation again yields nearly colorless pure aniline- it says so on the bottle.

The reduction of nitrobenzene with metals is an antiquated method of aniline synthesis. There are much more convenient methods available both for industry and lab that don't make such a mess upon basification with all the metal hydroxides.
I am especially thinking of catalytic transfer hydrogenation (CTH) using formate salts or straight formic acid as the hydrogen donor. Any common metal hydrogenation catalyst such as raney nickel, palladium or platinum on activated charcoal or similar carriers can be used.
Look here to see how truly easy, versatile and high- yielding this method is:

I am in the process of getting some palladium. When I have it, I plan on preparing some Pd/C catalyst and doing such a hydrogenation with a formate salt and an aromatic nitro compound (probably a nitrotoluene isomer, as I already have enough unsubstituted aniline). Maybe I'm going to document it here how it went.

[Edited on 15-11-2006 by garage chemist]

Zinc - 16-11-2006 at 06:17

At I have read that potassium permanganate in neutral solution oxidises aniline to nitrobenzene. Has aniline to perform that reaction be dissolved in water in its pure form or in the form of its salts?

[Edited on 16-11-2006 by Zinc]

Kahlil27 - 16-11-2006 at 23:34

While on the topic of aniline- what could one do with aniline HCl to produce a desired substance??:

Drunkguy - 17-11-2006 at 00:58

Aniline can be used to make azodyes. p-DiMe-phenyl-azobenzene gives brightly yellow colored crystals whereas p-OH-phenyl-azobenzene is orange colored.

Sulfanilamide is also made from aniline.

pantone159 - 17-11-2006 at 12:23

Aniline can also be used to make mauve (not sure if this is an azo-dye or not), you also need p,o-toluidine.

Zinc - 18-1-2007 at 11:19

I know that aniline reacts with acids to form salts. I am planning to react aniline with HNO3 (60%) to make aniline ntrate. Is the HNO3 enoguh concentrated to perform the reaction?

Also does anyone know some properties of aniline nitrate?

Sauron - 18-1-2007 at 22:19

Some comments:

Nitrobenzene is now regarded as a serious carcinogen suspect.

Aniline is a serious hepatotoxin.

You should be working in a fume hood.

You should be using goggles and gloves.

Get yourself Vogel's 3rd ed. and/or the Org.Syn. procedures for the aniline reduction.

Once you have aniline, purified by distillation, and want to take it to the next step, you have a lot of technique to learn before attempting diazotization.

Temperature control is paramount.

You need starch-iodide paper.

Diazotization is a highly versatile reaction, which benzene derivative are you trying to make?

not_important - 18-1-2007 at 22:41

Originally posted by Zinc
I know that aniline reacts with acids to form salts. I am planning to react aniline with HNO3 (60%) to make aniline ntrate. Is the HNO3 enoguh concentrated to perform the reaction?

Also does anyone know some properties of aniline nitrate?

More than enough. Aniline and nitric acid tends to give oxidation products, nitration of the ring, and hair pulling. Treat the nitric acid with a small amount of urea just before reacting with the aniline, the urea removes traces of nitrous acid and NOx.

A better route is through the reaction of aniline hydrochloride with ammonium nitrate in a water-alcohol solution (or water solution followed by addition of some alcohol) followed by filtering to remove the ammonium chloride. Alternative is to use sodium nitrate in water solution.

Aniline nitrate is very soluble in water and alcohol.

These might be of interest:

Sauron - 18-1-2007 at 23:06

It's rather the long way round the course to make phenol this way, the short toute is sulphonation then fusion with alkali then liberation of the phenol from the phenoxide salt.

But learning to diazotize is a nobel goal.

Zinc - 19-1-2007 at 07:10

Originally posted by not_important
More than enough.

Should I dilute it?
If yes to what concentration?

garage chemist - 19-1-2007 at 07:16

Diazotization is really simple if the important conditions are met, like enough acid, low enough temperature (best attained by putting ice in the reaction mix itself) and diazotization to an end point with KI/starch paper or the like.

I made iodobenzene and it worked marvellously. Upon addition of the KI solution to the diazonium salt solution, it turns deep red and nitrogen is being given off for several hours, making it look like if it was fermenting. The product seperates as a black very dense oil (the black color is due to oxidised aniline compounds, the iodobenzene becomes colorless upon distillation).

Zinc - 24-1-2007 at 09:06

Is aniline nitrate explosive (If it is I am not going to make it)?

[Edited on 24-1-2007 by Zinc]

Magpie - 25-3-2007 at 13:09

I usually don't post too much about my failures, but this one is really bothering me, so I'm seeking your comments:

I attempted to make aniline a few days ago using powdered iron (from United Nuclear), a little HCl, water, and nitrobenzene. I had made it before successfully using tin instead of iron. I wanted to use iron this time as it is cheaper, and just to try something new.

I used the method in Vogel's 3rd. Add 40 mL of water, 30g of iron, 2.5mL of conc HCl, and 21 mL of nitrobenzene. The nitrobenzene is added a little at a time to keep the exothermic reaction under control.

There wasn't much heat evolved. In fact I had to place the RBF in a hot water bath to get the temperature up to 80C. After all the nitrobenzene had been added I attached a reflux column and placed the RBF on a heating mantle. Occaisionally I would shake the flask for mixing. [I initially tried to use a mag stirrer but this failed due to the magnetic properties of the iron (duh).] Once the flask got hot enough I could see some bubbles forming and took this as H2 and as a very good sign. This became fairly active with much more bubbles and heat generation. I gave the flask a little cooling in a cold water bath when it looked like it might start to boil. I don't think I heated it much after the reaction subsided.

I added Na2CO3 to bring to basic pH (10) and then steam distilled. Following this I added the NaCl. This is when I knew I had a failure as no aniline floated to the top. Instead there was a reddish-orange layer at the bottom of the separatory funnel. I took this as unreacted nitrobenzene and terminated the procedure.

Your critique is sought, please. What do you think went wrong?

S.C. Wack - 25-3-2007 at 14:17

Maybe you'd like to try using more heat to start with, and different addition strategy such as in Cumming or Cheronis:

60 ml of water and 120 g of iron powder are placed in the reduction pot, agitation being maintained during the addition. The pot is then heated to 90-95°, and 10 ml conc. hydrochloric acid (d 1.18) are poured in; 100 g nitrobenzene are then added, a few ml at a time. The temperature must be held at 100°, and this can be conveniently done by regulating the addition of the nitrobenzene. When all the latter has been added, the reduction is continued at about 100° until no smell of nitrobenzene remains, or until a sample dissslves completely in dilute hydrochloric acid.

If the agitation is not powerful enough to carry through this process, the following may be adopted: 100 g of nitrobenzene and 60 ml water and 10 ml of conc. hydrochloric acid (d 1.18) are heated in the pot up to 95°. 120 g iron powder are then added carefully, the temperature being maintained at about 100°. After all the iron has been added, the temperature is maintained at 100° by external heat, and agitation continued until all the nitrobenzene has been reduced.

Steam Distillation.--If direct steam can be led into the reduction pot, this process is simplified, for, by merely altering the condenser to the usual sloping position, the aniline can be distilled off. If direct steam cannot be led into the reduction pot, the contents, after the reduction is finished,, are poured into a large round-bottomed flask, and steam from a steam generator led into it, the products of vaporisation being condensed in the usual way.

Separation.--The condensate is poured into a separating funnel and allowed to stand until separation into two layers is complete. This may be assisted by applying heat or by adding salt. The aniline is then poured off, dried over solid NaOH and distilled.

Yield.-95% theoretical (70 g). bp 184°


In a 500 ml round-bottom or Florence flask place 30 ml (35 g) of nitrobenzene, 5 g of Bentonite clay, 120 ml of water, and 20 ml of concentrated hydrochloric acid. Heat to boiling, remove the flame, and after a minute or so lift the cork which holds the condenser, and add all at once 36 g of iron powder. Replace the cork at once and allow the vigorous reaction to proceed for 2-3 minutes, then resume heating. Boil briskly for 2 hours. Cool the reaction mixture, and add 50 ml of water and 8-10 g of sodium carbonate. The carbonate is added gradually to avoid frothing. Set up a steam distillation apparatus, and steam-distill the reaction mixture until the distillate is perfectly clear. Saturate the distillate with 30 g of commercial sodium chloride, and extract with three 50-ml portions of ether. Dry the combined ethereal solutions with 6-8 g of sodium hydroxide pellets. If an aqueous solution forms on shaking, decant the ether solution into another dry flask and add a fresh amount of sodium hydroxide. Allow the ether to stand overnight. Pour one-half of the ether solution into a 125-ml distilling flask and distill off the ether from a water bath. After most of the ether has distilled, add the remaining portion, and continue the distillation until all the ether has been removed. Remove the water bath, wipe off the outside of the flask, and heat the flask with a small free flame. When the temperature of the vapor reaches 120°, disconnect the water in the condenser and allow the jacket to drain, thus converting it to an air condenser. The fraction which boils at 180-185° is collected in a tared flask or bottle. The yield is 20-23 g.


I've found some old block tin things here and there with help from people who don't know the worth of scrap tin. Very easy to melt and the little pieces of tin that go flying everywhere upon adding molten tin to water are lots of fun.

Edit: It is interesting that neither Cumming above (whose experiments seem sometimes not based upon the experience of the authors and their students; but in this case probably is) nor Fieser (the eminently trustworthy but unscanned Experiments in Organic Chemistry 2nd ed.) basify before steam distillation.

[Edited on 25-3-2007 by S.C. Wack]

Magpie - 25-3-2007 at 16:06

Thank you S.C. Wack. It seems like insufficient temperature for a long enough time is likely the culprit based on your submittals.

I wanted to blame the iron powder, thinking that it was excessively oxidized. But I really don't think I can justify that. I've attached a picture of my iron. The colors seem accurate.

Yes, I've melted tin myself and dropped it into water to form a "mossy" tin with more surface area. It is indeed fun. I'm going to have to be on the lookout for cheap sources as you have done.

I don't like wasting my precious nitrobenzene in an effort to find out what I did wrong, so if I have enough tin will likely just use that for now. I really do want to find out what went wrong, at some point in my mad science career, however.

Fe powder.jpg - 56kB

UnintentionalChaos - 25-3-2007 at 17:32

Just a random thought. If you had some time and tin on your hands, you could reduce it to dust by putting it in the freezer and leaving it there for a while, converting it into the alpha allotrope (gray tin) which should be incredibly easy to powder.

I get my tin from fishing sinkers at Walmart. It runs me roughly $6.86 US a pound, or the truly important figure $1.80/mol. Purity is unknown, but likely higher than 95%

[Edited on 3-25-07 by UnintentionalChaos]

Magpie - 25-3-2007 at 17:55

S.C. Wack says:


Edit: It is interesting that neither Cumming above (whose experiments seem sometimes not based upon the experience of the authors and their students; but in this case probably is) nor Fieser (the eminently trustworthy but unscanned Experiments in Organic Chemistry 2nd ed.) basify before steam distillation

I noticed that too in the 1st procedure. I don't see how you could steam distill the aniline if it had not been basified to the free base. It would still be in the aniline HCl form, a salt.

The 2nd procedure uses sodium carbonate to basify.

I had Fieser & Fieser's text for my organic course in the 60's and liked their style. I have nver seen a copy of Experiments in Organic Chemistry. But as you say I would definitely trust Louis Fieser.

Nicodem - 25-3-2007 at 23:58

Since HCl is only used to start up the reaction (FeCl3 can be used instead) and Fe is in large excess, the side products are only Fe hydroxides (very slightly basic buffer) and chlorides (only slightly acidic). Thus the post reaction medium is more or less neutral and the aniline can be steam distilled even without basifying. However, perhaps I'm wrong but I would expect aniline to somewhat complex with the dissolved Fe(III) ions, though this is probably of little importance where only little HCl is used and besides the complex is probably not particularly stabile anyway.

Magpie - 26-3-2007 at 10:20

Nicodem says:


Since HCl is only used to start up the reaction (FeCl3 can be used instead) and Fe is in large excess

This is also something that I have wondered about. In the procedures using tin a great deal of HCl is used whereas with the iron only a minor amount of HCl is used. Since the purpose of the metal in both cases is to generate nascent hydrogen (I think) it appears that most of the H2 from iron must be from its reaction with water. But in the case of tin the reaction would be more with HCl. Is this true?

Eclectic - 26-3-2007 at 11:29

You might try brake turnings to get better exposed surface area and less compaction. Also they are cheap (free) and may be more reactive than pure iron powder.

Magpie - 29-3-2007 at 14:56

I remade my aniline this time using tin. Everything went well and I got the 80% expected yield, if not a little more. I never saw any hydrogen bubbles. I assume that was because the hydrogenation was very efficient.

I must have 5 or 6 procedures for making aniline using either tin or iron laying around in various books. Yesterday I stumbled on one that I had forgotten about, ie, that in Brewster, 4th edition. It gives two procedures, one with tin and one with iron. It is interesting that for the one using iron it says "If iron powder is selected as the reducing agent, the use of an efficient stirring apparatus is imperative." I think that was my downfall. My iron powder just hung on the bottom.

Also I would much rather work with tin than iron. Iron powder gets into any crevice and stains everything. Tin is well behaved.

It was also interesting that Brewster's 4th ed (1977) said that reduction via catalytic hydrogenation using a nickel or platinum catalyst was an option for "interested students." This used elemental hydrogen as supplied by a Parr hydrogenator (drool) like the one owned by NERV. I think garage chemist also mentioned this method in a previous post.

chemrox - 1-4-2007 at 21:15

Originally posted by a_bab
One interesting thing about aniline is that it was recognised as carcinogen only about 20 years ago or so...

I don't think this is right...aniline's carcingeneity has been known from before 1970. Computers were mainframes and ran Fortran 4 and Cobal. The calculator as we know it was just being born. Chemists used slide rules.

chemrox - 6-4-2007 at 21:04

Bravo Magpie! That is the same steam genrator I use .. I use a trap with it to catch water. Why do you run it into the wall? presumably it comes right back out and into the flask? Through a water trap? Otherwise you're distilling from a mixture of your product and boiling water .. a way to do steam distillation but inferior to live steam which you've got from the P cooker and a trap...

Magpie - 7-4-2007 at 09:14

from chemrox:


Why do you run it into the wall?

This is merely a way of not consuming valuable real estate inside my fume hood (other side of that wall). I also keep my water supply sump & pump for condenser cooling water outside of the hood for the same reason.

When using the copper plated steam bath shown I don't use a steam trap as the condesate just drains harmlessly into the bottom of the bath. But when doing steam distillations I definitely use a steam trap.

Yes, the pressure cooker works pretty good as a steam supply. Condensate tends to build up in the Tygon line low spots and then get pushed out in slugs. I think this actually helps as it builds a little back pressure thereby providing slightly superheated steam when it breaks through.

Zinc - 27-2-2008 at 12:45

A lot of time ago I added aniline to a NH4NO3/H2SO4 mix. When I added the aniline after several seconds it boiled violently and aniline was converted to some tar. I think that it happened because I added too much aniline whit out proper cooling. I wanted to make nitroaniline. Can it be even made that way or is something else produced?

PHILOU Zrealone - 28-2-2008 at 02:34

Originally posted by Zinc
A lot of time ago I added aniline to a NH4NO3/H2SO4 mix. When I added the aniline after several seconds it boiled violently and aniline was converted to some tar. I think that it happened because I added too much aniline whit out proper cooling. I wanted to make nitroaniline. Can it be even made that way or is something else produced?

Following wich nitroanilline you wish to do, you have or to use diluted acids (meta) , or to protect the amino group by acetylation (ortho-para).
Too high a HNO3 concentration or heat, will result in parabenzoquinon oxydation.
C6H5-NH2 -ox-> O=C(-CH=CH-)2C=O
The later can react to polycondense with aminogroup of aniline resulting in brown-black tar like polymer.

grind - 28-2-2008 at 20:50

Distilling aniline in vacuum in the presence of sodium gives a colorless product that darkens only very slowly even when stored in the light.

Zinc - 1-3-2008 at 12:17

Originally posted by PHILOU Zrealone
Following wich nitroanilline you wish to do, you have or to use diluted acids (meta)

How much should I dilute? I will be using NH4NO3 or NaNO3 and H2SO4.

PHILOU Zrealone - 4-3-2008 at 07:21

Originally posted by Zinc
Originally posted by PHILOU Zrealone
Following wich nitroanilline you wish to do, you have or to use diluted acids (meta)

How much should I dilute? I will be using NH4NO3 or NaNO3 and H2SO4.

Add 30-50% water to the mix

merlic79 - 26-10-2008 at 18:20

Has anyone ever tried using lead-solder as their source of tin? The stuff I have is of 95% purity. The rest is made up of small amounts of antimony, copper, and silver. Would these trace metals somehow adulterate the tin if used for a nitrobenzene reduction?

kclo4 - 26-10-2008 at 19:13

Lead solder that is 95% tin, with the rest being made up of antimony, copper, and silver?
Dang! whats going on?
haha, perhaps you meant Tin solder?
The copper and silver might cause some problems since they don't react with HCl, but you could try it to find out I guess.