Sciencemadness Discussion Board

Benzene synthesis

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wayne_m - 22-7-2017 at 16:43

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]

JJay - 22-7-2017 at 17:22

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



clearly_not_atara - 22-7-2017 at 20:48

Benzophenone or triphenylmethanol are my first guesses.

wayne_m - 23-7-2017 at 04:37

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!

digga - 30-8-2018 at 10:03

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.

digga - 31-8-2018 at 12:38

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:



  1. Permatex High Temperature putty works well to seal the glass adapter to the paint can top
  2. It is necessary to hammer the paint can lid in place, or you will get wisps of white carcinogenic vapor creeping out.
  3. I added a small amount of water to the hot pot to flush the system.
  4. Buying the benzene may well be cheaper, but this is way more fun.
  5. Having run out of ring stands, a standalone toilet paper stand weighted with a brick made a creditable stand-in.
  6. Grease every joint.
  7. Did I mention grease?



[Edited on 31-8-2018 by digga]

[Edited on 31-8-2018 by digga]

CuReUS - 1-9-2018 at 06:40

Quote: Originally posted by digga  
Once I have the product gin clear and dry, I will proceed to commit nitrobenzene.
wouldn't it decarboxylate better if you nitrated benzoic acid first ?

Xrpdguy - 1-9-2018 at 09:00

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.

digga - 5-9-2018 at 10:28

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.

digga - 18-9-2018 at 08:52

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.

macckone - 18-9-2018 at 13:12

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.

S.C. Wack - 18-9-2018 at 14:48

Biphenyl...go back 14 years...the lowest heat is best IMHO.

digga - 19-9-2018 at 07:26

Quote: Originally posted by S.C. Wack  
Biphenyl...go back 14 years...the lowest heat is best IMHO.


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]

macckone - 3-10-2018 at 15:51

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.

digga - 4-10-2018 at 10:26

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.


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.

macckone - 4-10-2018 at 15:52

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]

thor.lucas - 13-7-2019 at 02:36

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…

aromaticfanatic - 2-12-2020 at 18:57

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.

sykronizer - 19-3-2021 at 20:40

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.

Jenks - 14-4-2021 at 13:59

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.

Organikum - 27-9-2021 at 02:01

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

macckone - 27-9-2021 at 08:24

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

Organikum - 28-9-2021 at 00:55

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


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.

CwisGons - 1-11-2021 at 14:01

Would distilling PET like how E&I did work?

Tsjerk - 1-11-2021 at 15:43

Who or what is E&I?

[Edited on 1-11-2021 by Tsjerk]

Corrosive Joeseph - 1-11-2021 at 15:56

https://www.youtube.com/c/ExtractionsIre/videos



/CJ

draculic acid69 - 11-4-2022 at 01:46

Quote: Originally posted by not_important  
p-dichlorobenzene + AlCl3 gives mostly a mix of the dichlorobenzene isomers, the chlorines seem happy to hop about on the ring but don't like to jump rings. Careful fractionation of the mix might be able to remove benzene, I've not tried that as several reports stated no ring jumping for Cl although Br has been stated to ring jump.

If the mixed dichlorobenzene isomers are cooled so the much of the para isomer freezes out, the ramaing mix is a useful not-too-reactive solvent.


I know this is an old thread but I'm interested in this mention of
chlorine jumping around on the ring and turning 1,4 dcb into
1,2&1,3dcb is great news if true. If anyone has any experience or
information about the moving around of halogens on the ring please
enlighten me.

MrDoctor - 10-8-2022 at 04:39

I am curious, has anyone ever actually succeeded in using HCl bubbled into toluene with Al+AlCl3?
I have heard 2 claims, firstly that this yields benzene, among other things, and the other, that this yields AlCl3, even if not in quantities alone that justify the reaction as a low temperature route to produce AlCl3.

Frankly it seems too good to be true, that you can have nice cheap benzene AND you end up with more AlCl3 than you started with.

Where i live, benzoate is getting less obtainable for cheap, and more and more industrial chemicals are being pulled from the shelves or their sale is being restricted to businesses/business entities only. a little while ago i had to jump through several hoops just to obtain 50 grams of crystal violet for running a gram stain.


Otherwise the route i had thought of taking would be catalytic oxidation of toluene in a heated quartz tube with vanadium and other metal oxide catalyst. One paper of interest was "Oxidation of Toluene to Benzoic Acid Catalyzed by Modified Vanadium Oxide" Iraqi Journal of Chemical and Petroleum Engineering, Vol.15 No.1 (March 2014) 73- 77

playing around with different mixtures of vanadium, molybdenum and cobalt seems to be able to shift the conversion in favor of benzene sometimes, as does changing the reaction temperature and steam content. Other papers have described greater benzene selectivity, but they require unreasonably high pressure, or unobtainable catalysts, like uranium.

Mateo_swe - 17-10-2022 at 02:11

The sodium benzoate and NaOH method works very good and is the only method i have tried.
For me its enough to make the small amount of benzene i might need.
As benzene is not the healthiest of compounds its usually not used in more modern preparations.
So if you need just a smaller amount, i would do the benzoate/NaOH method.
And 1kg of sodium benzoate on ebay is about 22 Euros, not very expensive.

Texium - 17-10-2022 at 09:27

I use benzene regularly in my research, as the solvent for a radical bromination with NBS/benzoyl peroxide. It still shines in that application, since other common solvents are reactive to radicals.

Keras - 17-10-2022 at 10:11

Quote: Originally posted by Texium  
I use benzene regularly in my research, as the solvent for a radical bromination with NBS/benzoyl peroxide. It still shines in that application, since other common solvents are reactive to radicals.


Interesting. I have a litre of pure benzene, might use it to try anti-markovnikov additions to double bonds. Anything handier than NBS and benzoyl peroxide? Would HBr with peroxyacetic acid work?

MrDoctor - 5-9-2024 at 23:11

Quote: Originally posted by MrDoctor  
I am curious, has anyone ever actually succeeded in using HCl bubbled into toluene with Al+AlCl3?
I have heard 2 claims, firstly that this yields benzene, among other things, and the other, that this yields AlCl3, even if not in quantities alone that justify the reaction as a low temperature route to produce AlCl3.


I dont recall if i originally read someone in this thread or elsewhere had poor results or not, or wasted some days and dry HCl with no result, but i have found something useful. There exists a complex between AlCl3 and benzene refered to as R-AlCl3 or Radzivanovskii-AlCl3, produced by bubbling dry HCl into benzene containing aluminum. the R-AlCl3 forms a sort of brown scum on the metal and functions as a friedel-crafts catalyst. I have not heard though if the benzene can be seperated since it does form a complex, which is something i want to try in the future.

Anyway, if one was to bubble HCl into toluene containing benzene already, it would produce increasing amounts of benzene and AlCl3 as i saw once claimed. The fact it was hit or miss, between people who attempted it, might have to do with whether or not they began with some AlCl3 catalyst to begin with. Although, they have it backwards, since its the benzene the AlCl3 turns the toluene into, that lets the reaction progress, and it might also be that not very much can be produced with heavy dilution, so one wastes an enormous amount of HCl trying to increase the miniscule amount of AlCl3 present, as well as the actual solubility of HCl too in solution, which would be poor. lastly, the composition and physical surface of the aluminum seems to matter too.

I think if one was to first produce a large amount of catalyst just in benzene, then the reaction should play out as claimed/theorized once toluene is added and heated. doing both together might prove unfavorable though
I think it would take many cycles of heating, and gassing, to get a decent build up of the necessary benzene or AlCl3 if you only had a small amount of just 1 to start with.
Attachment: Chem_Abs_45_Friedel_Crafts_with_Al_catalyst.pdf (412kB)
This file has been downloaded 55 times

[Edited on 6-9-2024 by MrDoctor]
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