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wayne_m
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Has anyone ever figured out just what the orange gunk from the benzoateNaOH reaction is?
I can confirm that it is not phenol red (I had heard it proposed as an answer.) I added bromine to my latest batch, which would have turned it into
bromophenol blue, but it certainly wasn't that.
Whatever it is, I hope there is a good use for it. I'm growing quite a stock of it in my benzene waste container.
Also, in this last batch, I noticed that the distillate from refining the crude product came over at 73, which indicates an azeotrope of benzene and
acetonitrile. (Could be something else, but that's the exact number I found for that mixture.)
I distilled my benzene before washing it with water this time.
I'll wash it out with water and try to isolate it, then post my findings.
[edit]
Apparently not. Acetonitrile should be soluble in water, and 100cc benzene mix + 100 cc water shaken vigorously and allowed to separate yielded: 100
cc of benzene mix and 100 cc of water.
Anyone have any ideas ideas what might have made the BP of the benzene mix so low?
[Edited on 23-7-2017 by wayne_m]
[Edited on 23-7-2017 by wayne_m]
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JJay
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Benzene has an azeotrope with water at 69.3 C.
I'm not quite sure what the pyrolysis reaction between benzoic acid and sodium hydroxide is, but it's something like this:
PhCOOH + 2 NaOH -> PhH + Na2CO3 + H2O
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clearly_not_atara
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Benzophenone or triphenylmethanol are my first guesses.
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wayne_m
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I actually had two temperature rests; one at 68, which stayed there for several minutes, and one at 73.
I didn't bother fractioning at this point, since it was just to get the crude separated into low-boiling and water / high-boiling components. I
stopped it at 85 C, and a lot of yellow came over, which seems to indicate that it isn't any of the really high boiling things.
I suppose it could be something like benzophenone, if it evaporates readily in boiling benzene, somewhat like a steam distillation. I don't have any
experience with it, so I don't know.
I doubt it's or triphenylmethanol, or tetracene, considering that the leftover tar has a melting point well under 100 C, but given the unknown
impurities, there's no way to be sure. It solidifies at room temperature.
Could tricene form the dye Alizarin in the benzoate reaction? It seems unlikely, but you never know until you know.
I'll dry the tar and try dropping some of my potassium in it. (I'll warm it just until it melts, and wait a bit to see if it runs away before applying
any more heat! Made that mistake the other day and lost a stopper - I think it's in the neighbor's swimming pool.) If it turns blue or purple, it
should confirm benzophenone. If not, then I'll try something else until an answer is found!
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digga
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I just ran the NAOH decarboxylation of Sodium Benzoate last night. I used a paint can over a Walmart camping stove as a vessel. I sunk a glass 24 40
adapter into the lid with high temp putty and used the usual glassware to collect and condense. I got a strongly orange colored cloudy product. ( I
intend to run several times and then purify the commingled results.) I noticed some orange solid collected at the top of the condenser where the
joint had loosened for a short time. (the 3 way is stuck to the adapter in the can lid now, and the joint is orange.)
I believe that the orange gunk IS Chrysene/Tetracene, and that it forms an azeotrope with benezene, thus boiling below its advertised melting point.
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digga
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Ran another batch. Similar results ~60 ml of orange "Tang". Worked the temperature control more carefully to try and keep the white vapor just
spilling over into the condenser.
Next step is the purification of the commingled batches. Once I have the product gin clear and dry, I will proceed to commit nitrobenzene.
Some observations:
Permatex High Temperature putty works well to seal the glass adapter to the paint can top
It is necessary to hammer the paint can lid in place, or you will get wisps of white carcinogenic vapor creeping out.
I added a small amount of water to the hot pot to flush the system.
Buying the benzene may well be cheaper, but this is way more fun.
Having run out of ring stands, a standalone toilet paper stand weighted with a brick made a creditable stand-in.
Grease every joint.
Did I mention grease?
[Edited on 31-8-2018 by digga]
[Edited on 31-8-2018 by digga]
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CuReUS
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wouldn't it decarboxylate
better if you nitrated benzoic acid first ?
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Xrpdguy
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Benzene can be obtain if you melt solid benzoic acid (dry sample) with solid calcium-oxide also dry and few grains of sodium hydroxide.
The mixture in the vial after some time of heating will get the smell of benzene and it can be destiled.
The second method of obtaining a benzene from benzoic acid is melting benzoic acid and citric acid, but i didnt try it.
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digga
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Did a third run. I have been able to reuse the same 1 quart paint can each time. The NAON/Sodium Benzoate method leaves a hard deposit of sodium
carbonate which dissolves when the can is heated on the stove with water added.
What I like about this method is that the lid can be re-used over a series of paint cans.
Washed the product with 100 ml of distilled water, then set to dry over a layer of calcium chloride which clumped up. Now it is orange and clear.
As for decarboxylating nitrated benzoic acid, this had not occurred to me. But I also wanted to have some benzene on the bench for the odd task.
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digga
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I took the three combined runs of raw orange benzene, washed them with distilled water and dried them over calcium chloride, which clumped
immediately. I poured off the remaining liquid and distilled off about 4 ounces of clear benzene, which came over around 90o C. I stopped
the distillation with about 15 or 20 ml of orange liquid remaining in the round bottomed flask This was transferred to a beaker and allowed to dry at
ambient temperature and humidity for several days.
What remained was 4 grams of shiny orange crystals. They had a strong aromatic odor. I am positing that they are primarily tetracene (napthacene)
with chrysene impurity.
I am thinking about purifying the tetracene by sublimation or chromatography. A uv lamp is on order. I will check the fluorescence.
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macckone
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If your are getting tetracene in the final product before careful redistillation, there is probably naphthalene and anthracene as well other
conformers. Short of repeated fractional distillation these would seem to be difficult to avoid.
Obviously on the first run everything is getting condensed.
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S.C. Wack
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Biphenyl...go back 14 years...the lowest heat is best IMHO.
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digga
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Makes sense. As the temperature rises, the activation energy requirements for more reactions are satisfied. I suspect that for each product formed
in a heat catalyzed decarboxylation, the equilibrium is way to the right.
For example, once you have napthalene, it will not go back to benzene. Once napthalene goes to anthracene, it doesn't go back to napthalene.
BUT, if the process cannot, for some reason, proceed past a certain compound - like tetracene or its isomer chrysene, that compound will tend to
accumulate.
[Edited on 19-9-2018 by digga]
[Edited on 19-9-2018 by digga]
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macckone
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I did a little research on the permatex high temp putty.
Looks like it is clay with sodium metasilicate and possibly some aluminium.
They say 'inert material 40-60%'.
This looks like it would be easy to formulate.
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digga
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Quote: Originally posted by digga  | I took the three combined runs of raw orange benzene, washed them with distilled water and dried them over calcium chloride, which clumped
immediately. I poured off the remaining liquid and distilled off about 4 ounces of clear benzene, which came over around 90o C. I stopped
the distillation with about 15 or 20 ml of orange liquid remaining in the round bottomed flask This was transferred to a beaker and allowed to dry at
ambient temperature and humidity for several days.
What remained was 4 grams of shiny orange crystals. They had a strong aromatic odor. I am positing that they are primarily tetracene (napthacene)
with chrysene impurity.
I am thinking about purifying the tetracene by sublimation or chromatography. A uv lamp is on order. I will check the fluorescence.
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update: The orange solid product fluoresces bright orange under UV light. The solution in acetone under uv light fluoresces the same as a picture of
a tetracene sample I saw. btw, the uv light ALSO shows just how that stuff spreads all over my bench.
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macckone
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Pentacene, higher compunds and analogs/confomers are probably not making it out of the reaction chamber in significant quantity due to the high vapor
phase temperature.
The following paper also suggests injecting steam to reduce crosslinking.
Dabestani, R., Britt, P. F., & Buchanan, A. C. (2005). Pyrolysis of Aromatic Carboxylic Acid Salts: Does Decarboxylation Play a Role in
Cross-Linking Reactions? Energy & Fuels, 19(2), 365–373. doi:10.1021/ef0400722
That study provides some good insights. It is done in a sealed environment at 450C for sodium benzoate. Water reduced crosslinking and at 450C. The
reaction took 4hrs to decarboxylate 30% of the sodium benzoate.
In a non-sealed environment with added sodium hydroxide as has been used, I would expect cross linking to still take place and higher yields are being
reported with slightly lower temperatures since the added hydroxide should have a catalytic effect.
If the chamber top is below 372C then no pentacene should be escaping. This gives a narrow range of 357C - 372C where we expect benzene production
since we are getting tetracene (BP 357C) but not pentacene (wiki listed sublimation point 372C) however the lower portion of the chamber could be much
hotter.
If steam is introduced in this temperature range, there should be a higher yield. But I don't have the equipment to feed in temperature regulated
steam.
[Edited on 5-10-2018 by macckone]
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thor.lucas
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| Quote: Originally posted by subsecret | Just a note:
JB Weld will does not withstand the effects of dry distillation of sodium benzoate and sodium hydroxide. I sealed a copper tube into a paint can with
it, but several minutes after I applied heat, it began to flake and leak benzene vapor. |
Shit! I should have read this before I JB welded the hell out of my paint can…
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aromaticfanatic
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Has anyone looked into the overly complicated and wasteful synthesis of benzene from anthranilic acid? You can perform a diazotization reaction on the
acid and that forms benzyne. I think you can hydrogenate the benzyne. It is an overly sensitive reaction and no idea if it would work. It seems like
there is no proper literature and it is definitely not practical. Just wondering.
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sykronizer
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Benzene from Benzoic acid salt pyro decarboxylation: This is one reaction that I have done a few times, on a electric stove top, it behaves itself
and does not offer up any unwelcome horror moments. Sodium, or calcium or potassium Benzoate, an easily obtainable food preservative from many online
suppliers, is usually obtained as tiny granules, these are crushed and mixed with either Sodium or potassium hydroxide, of approximately equal
particle size , and heat is applied inside your can. The can is easily made, just a one liter clean paint tin, with the press on lid type. You can
punch a small hole in the center of the lid, and insert about a 30 cm length of copper tubing into it, leave about 1 or 2 cm on the inside of the lid.
Inside diameter of copper tubing anywhere from 3 to 8 mm is O.K. Most of us may not have a big grunty 200 watt soldering iron, so what I did was
leave the lid and it's length of copper tubing sitting on the hotplate, just over position 1 on the heat setting is enough to get some heat into the
thing, THEN you can use your piddly little electronics soldering iron and some normal flux cored solder to sweat on a nice circular seal around the
pipe and lid , I soldered mine on both sides of the tin lid. When you set up to do this, you can just lead the copper tube into your Liebig glass
condenser, with cooling from the kitchen sink of course. Doing this in your kitchen may sound er, you know, but it really is well behaved. You have to
sink a fair amount of heat from the element into this to get it going, but at no time ever did it get hot enough at the top at the center of the lid
to melt the solder. From memory I made about a Liter or thereabouts in two runs, and after a final distillation for cleanup the final product was
perfect.
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Jenks
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If the point of making benzene is to further derivatize it ... consider possibly starting with aniline and derivatizing it. At this moment on eBay,
aniline sulfate is available. But sulfanilic acid is also available for 1/3 the price/g, which could be hydrolyzed to aniline. Even this could lead to
benzene, via reduction of the diazonium salt with phosphorous acid, but consider the possibilities. Sulfanilic acid could be modified (e.g.,
brominated), desulfonated and then diazotized to give many possible benzene derivatives. So unless the benzene is sought as solvent, perhaps aniline
derivatives would be a more versatile starting point.
But while I am here I wanted to throw in a thought relevant to this thread. The Friedel-Crafts reaction is reversible. And a simple Friedel-Crafts
example is reaction of benzene with methyl chloride to yield toluene. But this reaction is reversible, so that toluene treated with aluminum chloride
should produce benzene and methyl chloride. But also, toluene and aluminum chloride should give xylene, and that, ultimately, should give the
thermodynamic product, mesitylene. If toluene were allowed to equilibrate with aluminum chloride, without the release of methyl chloride gas, it
should eventually equilibrate to a 1:2 mixture of mesitylene and benzene, and the benzene, of course, could be isolated by distillation, with a
theoretical yield of 67% based on toluene. I don't know if aluminum chloride is the best catalyst for this, but it always seemed like this pathway was
a beautiful option.
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Organikum
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| Quote: Originally posted by Jenks | ......
But while I am here I wanted to throw in a thought relevant to this thread. The Friedel-Crafts reaction is reversible. And a simple Friedel-Crafts
example is reaction of benzene with methyl chloride to yield toluene. But this reaction is reversible, so that toluene treated with aluminum chloride
should produce benzene and methyl chloride. But also, toluene and aluminum chloride should give xylene, and that, ultimately, should give the
thermodynamic product, mesitylene. If toluene were allowed to equilibrate with aluminum chloride, without the release of methyl chloride gas, it
should eventually equilibrate to a 1:2 mixture of mesitylene and benzene, and the benzene, of course, could be isolated by distillation, with a
theoretical yield of 67% based on toluene. I don't know if aluminum chloride is the best catalyst for this, but it always seemed like this pathway was
a beautiful option. |
Naturally this option was discussed before and it was also tried but it did not really
work as hoped what may well have been to blame on the lacing skills of the experimenters or water or other contamination.
Anyways I remember that it was suggested and evenrually tried with far better success to bring forth the rearrangement of Toluene by using Aluminium
Triiodide prepared in situ what besides providing better results also adds a lot to the comfort and safety what is possibly just a way of saying it is
better suited for lazy sloppy fucks. 
This all is posted as IIRC, one thing seems to me obvious though: To prevent all possible variations of being formed and being broken up and reforming
again it is for sure advantageous to distill the benzene out of the reaction as it is formed saving a lot of time and improving yields.
/ORG
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macckone
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The friedel-craft reaction to disproportionate toluene into benzene, xylene and mesitylene is well known.
the benzene-xylene ratio is 1:1
the benzene-mesitylene ratio is 2:1
but mesitylene will disproportionate with toluene to yield xylene as well.
http://nopr.niscair.res.in/bitstream/123456789/26478/1/JSIR%2060(4)%20319-327.pdf
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Organikum
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| Quote: Originally posted by macckone | The friedel-craft reaction to disproportionate toluene into benzene, xylene and mesitylene is well known.
the benzene-xylene ratio is 1:1
the benzene-mesitylene ratio is 2:1
but mesitylene will disproportionate with toluene to yield xylene as well.
http://nopr.niscair.res.in/bitstream/123456789/26478/1/JSIR%2060(4)%20319-327.pdf
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Sure, it is the industrial process and hundreds of thousands of tons are produced with it. But in the end I would recommend the benzoate dry
distillation for the ease of workup and the superior quality of the benzene produced in the reaction. To get a similar quality from a Friedels Crafft
one would have to labor for some days with distilling, re-distilling through columns with many plates whilst here a simple water wash followed by
distillation and drying suffices.
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CwisGons
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Would distilling PET like how E&I did work?
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Tsjerk
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Who or what is E&I?
[Edited on 1-11-2021 by Tsjerk]
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