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Author: Subject: Benzene synthesis
sargent1015
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[*] posted on 6-2-2014 at 20:26


Try this?
http://www.youtube.com/watch?v=iGTq43-2V_I




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[*] posted on 7-2-2014 at 09:45


KMnO4 isn't available for me. I could make it, but when one needs 3-6 times the amount of that for 1 part of toluene, that's just way off scale.

How about this?

Benzoic acid is produced commercially by partial oxidation of toluene with oxygen. The process is catalyzed by cobalt or manganese naphthenates. The process uses cheap raw materials, and proceeds in high yield.

Should it need pressure, temperature? Max pressure I can reach is maybe 40-50bars with refrig. compressor. Could normal Cu salts catalyst work, or what is the role of napthenate in here?

EDIT

This looks most promising:

https://www.google.com/patents/US3210416

Essentially one will need a steel reactor pot where toluene is inserted with cobalt or manganese catalyst and possibly a promoter, and then the vessel is pressurized to 15-20bar and heated to 175-200C. Probably it should be mixed by jerking the pot around. This should be quite possible to produce with common fridge pump with one-way valve and copper pipes, a needle-relief valve and a pressure meter and thermoprobe on top.

But how does this differ from Dow Process of making phenol from toluene by oxidation (Toluene + 2 O2 = phenol etc.)?

[Edited on 7-2-2014 by testimento]
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[*] posted on 7-2-2014 at 10:13


Pressurizing vessels at home seems... Bad? Anyways, don't blow a hand off

Also, KMnO4:
2 pounds for $20

-Sarge




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[*] posted on 7-2-2014 at 13:48


I have more experience in that area than in chemistry. :) Permanganates are banned in my country.

I read the patent now fully and it states much of the following:

Of total mass of toluene:
1 % manganese acetate
0.5 % ammonium bromide (i've got only sodium)
10-14bar pressure
140-180C temperature
Air bubbled inside

With high flow air it should form benzoic acid quite fast. In patent it is reported to produce several tons per hour with the specs mentioned. I think I could use ordinary compressor because the pressure range is from 4 bars to 20 bars. 8-10 bars should be pretty enough and since the reaction goes very fast, I can directly adjust the air flow with needle valve to compensate the consumed air(which should be mostly lack of oxygen).

Heating should be concerned, since the device is essentially a pressurized bomb which contains both oxidizer and fuel and it might go up pretty nice if it were to get fire. So electric heating should be preferred instead of gas burner, and the exhaust gas, which certainly contains vapors of toluene and other gunk, must be led into water trap or vented safely elsewhere or ignition may occur.

Attached picture for reactor.

The achieved benzoic acid could be turned into benzene or decarboxylated into phenol. What else could benzoic acid be used into?

potty.png - 14kB

[Edited on 8-2-2014 by testimento]
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[*] posted on 17-4-2014 at 16:44


I just had the opportunity to get 80 ml of toluene by distilling the non-aqueous layer of an old varnish can. The first test I wanted to do is catalytic oxidation. It was just a first try using this principle.

I mixed 0.1 ml of bromine, a pinch of cobalt carbonate, and 30 ml of glacial acetic acid, I then added 20 ml of toluene and put the mixture in a 100 ml two neck flask. After the bromine addition the mixture was of a orange color. One neck was used to pass air using an aquarium pump in the mixture, and the other had two condenser inline setup for reflux. Heating was started and the mixture slowly turned dark red, up to a point it suddenly shifted to pink and air was passed in when the mixture suddenly changed color. Two condenser did not seem to be enough, as plenty of vapors could go all the way out of the apparatus. At some point, white fog formed on the glass which I presume is sublimed benzoic acid.

I runned it for an hour, and then I stopped. I still have yet to find a way to extract the benzoic acid without diluting the acetic acid, as it is quite hard to make/get in quantity.




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[*] posted on 26-4-2014 at 12:21


Here’s an exploratory experiment on benzene preparation from sodium benzoate and sodium hydroxide dry distillation.

30 g of sodium benzoate and 9 g of sodium hydroxide were ground into a fine powder with a granite mortar and pestle and loaded into the following ad hoc apparatus (here post reaction):



Because I’m not keen on using open flame with a highly flammable reaction product and rubber stoppers as sealant/connectors, I first tried heating on full on my electrical hot plate. No product came over.

Medium propane Bunsen heat immediately caused the reagent mix to char and orange distillate to form. I reckon this needs at least 400 C to get benzene to form. Also some white smoke that didn’t seem to want to condense formed. I kept heating somewhat intermittently until almost no white reagent mix could be seen. The large rubber stopper had by then also suffered badly and it was time to stop.

In all I got about 25 ml of orange product with the unmistakable smell of benzene.

Here’s a close up of the reactor, post reaction: mostly black gunge with some white material too;



For a larger scale test, a metal reactor or expendable glass reactor, will be needed. I think some of the above commenters are right about heat transfer: it appears difficult to heat the whole mass through.




[Edited on 26-4-2014 by blogfast25]




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[*] posted on 26-4-2014 at 14:27


I'd specifically recommend Pyrex 4620/4680 dime a dozen flask auctions, and not exposing rubber stoppers to benzene, but this like everything else will just be ignored in 3 months if not now, so there's not much point to saying anything any more.

Charring = too hot, organic chemistry = low and slow.




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[*] posted on 27-4-2014 at 01:32


S.C.:

The glass I used was cheap and I think it will be recoverable.

Rubber stoppers: agreed but this wasn't an occasion where ground glass was available to me. I'll be using another type of sealant next time, possibly EPDM rubber with a much higher temperature/aromatics resistance.

Slow may be best but at an estimated 250 C (max setting on electrical plate) I got nothing whatsoever.

I think this preparation calls for a long, tubular type reactor geometry, placed on its long side and with gradual heating from one side to the other. This would also prevent thermally overloading the sealant.

[Edited on 27-4-2014 by blogfast25]




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[*] posted on 27-4-2014 at 13:12


Quote: Originally posted by Magpie  
Benzene making, 1st picture:

<img src="http://www.scimad.org/scipics2/Na_Benzoate_+_NaOH%20_2).JPG" width="800" />

<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: reduced image size(s); hosted image(s) at scimad.org/scipics2/]

[Edited on 12.12.13 by bfesser]


Can anyone restore these photos?




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[*] posted on 29-4-2014 at 08:21


I doupt so, did you re-distilled the crude benzene blogfast?



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[*] posted on 29-4-2014 at 09:06


Quote: Originally posted by blogfast25  
Quote: Originally posted by Magpie  
Benzene making, 1st picture:


<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: reduced image size(s); hosted image(s) at scimad.org/scipics2/]

[Edited on 12.12.13 by bfesser]


Can anyone restore these photos?


I attempted to find these 2 photos on my hard drive but they are not there.

It appears that bfesser moved them from this thread to scipics for some reason. When I go to scipics I find that the domain is for sale. Does this mean that we have lost all the pictures on scipics forever?

[Edited on 29-4-2014 by Magpie]




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[*] posted on 29-4-2014 at 11:41


@plante: not yet, as the volume is so small and this was just about 'feeling the water'.

@magpie: where is bfesser when he needs a b*ll*cking? ;-)

Any chance of simply describing your set up?

I'm now thinking of a largish (30 mm OD), tubular reactor (boroglass, a large test tube in essence, I may have found just the thing on eBay), horizontally clamped with an EPDM rubber stopper and glass tube at the neck leading to the condenser. Charge to no more than half capacity, leaving 'head room' for the expanding charge. Gentle heating by moving a propane Bunsen flame along the tube, until crude benzene starts coming off.

I'm not keen on the many Utoob metal cans + 'some sealant' + copper tube: leakage of benzene could have very serious consequences with that set up...


[Edited on 29-4-2014 by blogfast25]




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[*] posted on 29-4-2014 at 12:09


Quote: Originally posted by blogfast25  

.....
I'm not keen on the many Utoob metal cans + 'some sealant' + copper tube: leakage of benzene could have very serious consequences with that set up...

[Edited on 29-4-2014 by blogfast25]


The point is that a standard thread of iron watertubing, you may know the conical one, fits snuggly into the opening of a solvent can where the plastic was removed. Some good amount of PTFE tape gives a sure seal. Just as always whe using PTFE tape -dont use force or youdestroy more then you seal.

I am now not going into details of your suggested nonsensical setup which is so prone to failure that it hurts only reaing it. Sorry, but its true.

If you want the last edge on saftey then fit a aspirator at the receiving vessel and run it just for a little suction. Cool receiver with ice, maybe a small condrensor with icewater on the flask before the aspirator connection.
This will speed things up and push yields a bit what will be lost by the aspirator again, but most important: no benzene nowhere never in the air.

If thats just a contest to suggest the most byzantine ways this might be implemented as the best ways are already known and just too simple, then I apologize.
I instead will consider to contribute in this sense myself.

regards
/ORG




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[*] posted on 29-4-2014 at 12:16


I think that a 30mm borosilicate glass tube 1/2 filled will work just fine. Keep in mind that the decarboxylation doesn't really go until the NaOH melts. Mp for NaOH is 318°C, so this will severely corrode the glass tube. But the tube can be reused, likely for several runs (5-10 maybe).

I don't make benzene anymore - I buy it. But if you just want to make it for education/fun I understand.




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[*] posted on 29-4-2014 at 12:32


@Magpie:

Hmm... the decarboxylation works also with Ca(OH)2 and that doesn't really melt.

The glass reactor I used was unaffected by the NaOH and after washing was 'as new'. This may be due to the emanating volatiles protecting the glass somewhat. Glass always has one advantage: you can see through it.

I'd gladly buy the benzene if I found a seller. No luck so far.

@Organikum:

"I am now not going into details of your suggested nonsensical setup which is so prone to failure that it hurts only reaing it. Sorry, but its true."

From your hyperbolic reaction I deduce you don't seem to understand what it is that I'm proposing. You owe it to me to explain what it is you believe that can go wrong with this 'nonsensical setup'.

Thanks for the tips on using cans, threads and Teflon.


[Edited on 29-4-2014 by blogfast25]




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[*] posted on 3-5-2014 at 10:25


I tested the idea of a tubular reactor today, using an old Nessler tube, OD about 30 mm and nominal capacity of 150 ml:



The charge was the same as in my first experiment: 30 g sodium benzoate and 9 g sodium hydroxide, ground up (about 50 ml), spread out over the length of the tube to allow easy heat transfer (only a thin layer of charge) and avoiding excessive expansion of the reagent mix.

I wanted to use a specially ordered black EPDM rubber stopper (better heat resistance) but it hadn’t arrived yet. So instead I used the usual (SBR?) orange stopper but this time wrapped carefully in Teflon gas tape. There’s several cm distance between the right hand side of the charge and the stopper, to try and keep the stopper as cool as possible.

I heated very carefully, constantly moving a medium propane Bunsen flame from one side of the charge to the other and back. But to get actual distillate (as well as white smoke also reported by Magpie) ultimately more heat was needed. I collected about 12 g of orange distillate, a yield based on benzene of 74 %. It doesn't appear to be possible to obtain benzene without charring the charge, at least not within reasonable time frames.

Here’s the tube after reaction:



Black patches, white patches and orange condensate on the top side.

I need to check the state of the rubber stopper to see if the Teflon wrap provided any protection.

The Nessler tube will be cleaned by soaking the inside in 30 % NaOH solution.


[Edited on 3-5-2014 by blogfast25]




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[*] posted on 3-5-2014 at 10:45


http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/48_2...
The paper above states that, at 450º C, Sodium Benzoate may decompose to form a variety of producrs, including Triphenylmethane, wich is used to make a large number of dyes, the Triarylmethane dyes (http://en.wikipedia.org/wiki/Triarylmethane_dye).

This is a long shot, but is there any possibility that the Triphenylmethane is reacting with other products, thus making an orange dye? Anyway, most Triarylmethane dyes can be used as pH indicators because they change colour depending on the pH. Perhaps you could try to increase and lower the pH of your product to see if it changes colour?
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[*] posted on 3-5-2014 at 13:01


HgDinis25:

Quite a bit of work has gone into identifying the orange material, higher up in this thread. I can't remember the outcome, sorry. Thanks for the paper.

I'll take you up on the pH/colour idea but my hopes aren't high.

On a more mundane level, my Teflon wrapped stopper hadn't sustained any damage worth mentioning. That worked even better than hoped for.

[Edited on 3-5-2014 by blogfast25]




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[*] posted on 3-5-2014 at 13:34


Quote: Originally posted by blogfast25  
It doesn't appear to be possible to obtain benzene without charring the charge, at least not within reasonable time frames.


Perhaps you're doing it wrong. For me there was a colorless distillate and no charring, until the heat was turned up when things tapered off, which did nothing worth doing and should not have been done.




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[*] posted on 4-5-2014 at 04:56


Quote: Originally posted by S.C. Wack  

Perhaps you're doing it wrong. For me there was a colorless distillate and no charring, until the heat was turned up when things tapered off, which did nothing worth doing and should not have been done.


I didn't see your contribution in this thread, point to it if you will?

The first drops came over clear and colourless but at an interminably slow rate. Even at higher rate it still took about 15 min for 12 ml. At that rate one is inclined to go full throttle at the expense of purity.

If I'm doing it wrong everyone else here, bar you (no sarcasm intended), seems to be too.

It would help greatly if someone could establish some rate-temperature relation for this reaction(s).


[Edited on 4-5-2014 by blogfast25]




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[*] posted on 4-5-2014 at 10:42


I also had a quick stab at the reduction of phenol with zinc powder. Using the same set up as above but slightly tilted so that the Nessler’s bottom was pointing downwards a bit. 10 g phenol and 8 g ultrafine Zn powder were then loaded into the Nessler tube.

I assume this reaction is supposed to go as:

Phenol + Zn === > Benzene + ZnO

Edit: hydrogen deleted as per deltaH (ta!)

I heated and got bubbles but no benzene. At higher heat the phenol started to distil over and froze in the condenser:




The zinc appeared also unaffected, still a grey dark powder.

It appears this reduction needs leading vapours of phenol over 400 C zinc granules or turnings, as mentioned in Wikipedia.

[Edited on 4-5-2014 by blogfast25]




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[*] posted on 4-5-2014 at 11:15


Quote: Originally posted by deltaH  

I don't think the hydrogen should be there, one hydrogen needs to go in the place of the -OH group


Oooopsie. You're right of course.

[Edited on 4-5-2014 by blogfast25]




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[*] posted on 4-5-2014 at 14:22


You may want to try to pass phenol vapors over an heated tube containing zinc dust which would be heated using a bunzen.



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[*] posted on 5-5-2014 at 05:18


Quote: Originally posted by plante1999  
You may want to try to pass phenol vapors over an heated tube containing zinc dust which would be heated using a bunzen.


Sure, but it's a lot less practical as a lab preparation than a dry distillation: it requires quite a bit of engineering to do it safely, like condensing very hot benzene for instance. The latter would require a copper coil, I think. Any unreacted phenol would have to be dealt with too, in a separate cold trap.

Later on I'll have a quick test tube stab with aluminium powder.


[Edited on 5-5-2014 by blogfast25]




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[*] posted on 5-5-2014 at 06:39


blogfast, can you please ellaborate how you expect these reductions to proceed as I have a major concern:

Phenol is weakly acidic, so a reaction between phenol and an electropositive metal would most likely initially yield the metal phenate (presumable a solid) and produce hydrogen and heat, for example:

2Ar-OH(l) + Zn(s) => Zn(O-Ar)2(s) + H2(g) + heat

Idealy, one would reflux this to prevent phenol boiling off.

The problem is that further pyrolysis of the phenate is unlikely to yield benzene because you're now short the hydrogen having previously driven it off.

You might make diphenyl ether on pyrolysis, which would, nevertheless, be an interesting result :D

?? Zn(O-Ar)2(s) + heat => Ar-O-Ar(g) + ZnO(s) ??

Note that diphenyl ether is very high boiling (258°C), so it may condense near the pyrolysis heating zone.

Apparently it smells weakly of geraniums, though I doubt a pyrolytic product would smell very pleasant :o

****

I found this obscure and dated text about pyrolysing calcium phenates (not sure if phenolate or phenate is correct, the authors referred to it as phenate, so I'll stick to that). According to them, phenol yields an 'unusual' calcium phenate hydroxide 'half salt' upon reaction with calcium hydroxide which simply regenerates the phenol upon pyrolysis and forms CaO as co-product.

They also say that the pyrolysis of alkali phenates like sodium or potassium phenate yields only char and gas, but no volatile organic products (as per the finding of others, see references in article). That could be on account of the high basicity of those salts, so maybe some hope for zinc and aluminium to make something else?

See: https://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/28_...

[Edited on 5-5-2014 by deltaH]




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