Benzene synthesis

Quote: Originally posted by Jor

Whoever it was, rest in peace!

Quote: Originally posted by S.C. Wack

IIRC he mentioned a terminal lung cancer diagnosis (he was a smoker) in passing in his deliberately last post there in a threat --- about 5 months before his last post here. Note how the last login here is much later. IDK if he said anything in whimsy here that no one noticed, if he hated the RIP Halfapint thread at the-hive, or what the deal is. Anyone that knows for sure isn't saying.

Quote: Originally posted by BASF

Do you have more information on the decarboxylation of benzoic acid? Decomposition temp. and similar things? I think the decarboxylation of benzoic acid would be very attractive for the home chemist due to the widespread use of benzoic acid in the food industry, and therefor it should be easy to get and not that expensive. I still have some 100-200g of benzoic acid from a drug store. HLR

Quote: Originally posted by amazingchemistry

It might be possible to form benzene via decarboxylation of benzoic acid.

I don't see a reason to abandon the current route either (after all, we know it works). However, as far as I know, no experiments have been done to explore whether the above route or other routes would be feasible, or perhaps even better than the current one. I'm interested in the route described above because both ascorbic acid and sodium benzoate are cheap and readily available, and because the procedure described in the paper amounts to little more than 'mix and heat.' If that doesn't work, maybe we can learn something from it. We're chemists after all, and most of the stuff we do doesn't work

Quote: Originally posted by amazingchemistry

...procedure described in the paper amounts to little more than 'mix and heat.'

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?



[Edited on 8-2-2014 by testimento]

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]

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]

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?

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]

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]

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.

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 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]

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

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.

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

?? 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

****

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]

Ah ok I understand now, I was thinking of it in too simplistic terms, you are right, at high temperatures in the gas phase, it might be a different ball game altogether.

However, that said, I can't shake the feeling that beside for the reductive abilities of the metal, its ability to transfer the hydrogen or more specifically, its kinetic ability to work with hydrogen is important. In that sense, I don't think zinc is particularly known to be catalytic with hydrogen nor form hydrides AFAIK, so may not be the best choice here (note, not saying it doesn't work ).

In this regard, I think something like commercial titanium hydride powder might work well. My thinking here is that unlike titanium powder, which is probably too kinetically inert, the hydride is much more amorphous and active and so provides both hydrogenation ability and strong reducing ability in one package. I know that you don't theoretically need the extra hydrogen stoichiometrically, but I think for kinetic reasons, it would help a lot to have an excess for this reaction.

That said, I don't think benzene itself would hydrogenate (forming cyclohexane for example) as that is particularly tough and probably needs specialised hydrogenation catalysts like palladium or platinum.

Thus the reaction I'm thinking of would be:

2Ar-OH(l) + TiH_2-x(s) => 2C₆H₆(g) + TiO₂(s) + (1-x/2)H₂(g) + heat

This reaction could be very aggressive (if it proceeds at all) and take note H₂ produced, so be careful if you try it. For one thing, no ignition source anywhere near the outlet

I'm hoping this could similar to the chlorothermal reactions, start it with a little heat (but beware; H₂ formed!) after which it should be self sustaining, almost aggressive.

I think a setup with condenser here is a must, for one thing to lead the hydrogen away from the source producing it. At least no chance of plugging it with solids this time

Also, please be aware, hot phenol gives TERRIBLY nasty burns if it gets on you. REALLY take this threat seriously! If your apparatus cracks or pops and splatters the phenol and it gets on you face... well I've seen what that does. Needless to say, a $10 plastic face shield (not just goggles), gloves and long sleeve plastic overcoat makes ALL the difference when working with phenols. Please implement these, a technician in a lab I was working in was badly injured with a phenol experiment before implementing this basic safety protocol.

Dratz, I've gone and rambled too much again, kinda useless as you probably don't have titanium hydride powder

[Edited on 6-5-2014 by deltaH]

Yes agreed and as I feared

[Edited on 6-5-2014 by deltaH]

Quote: Originally posted by blogfast25

I really don't know and only go by a reference in wiki.

Quote: Originally posted by p2e3r4f5e6c7t8

has anyone tried this method. http://m.youtube.com/?#/watch?v=S8rtyRnZZMU Sodium benzoate + Sodium hydroxide heated to decompose and vapour condensed & collected ,then distilled & dried.

Quote: Originally posted by p2e3r4f5e6c7t8

So why then are newbees fuckin a round with soke of these more complex methods when this method is easy and dosent require any fancy glassware ?

Quote: Originally posted by Bert

If you are interested in learning as much as possible and acquiring skills in a wide variety of techniques, you might take a more indirect path. Just for the practice in lab technique, and to validate your grasp of theory. Most people here are interested in gaining knowledge and proficiency?

absolutely correct
by trying indirect routes ,chemists learn about new reagents,new reactions ,and new rearrangements (for example,see synthesis of vitamin B-12)

by the way, why cant we try fenton's reagent(H₂O₂ + FeSO₄) on benzoic acid to make it benzene

Quote: Originally posted by p2e3r4f5e6c7t8

And that is also very true cureus

but i dont think we could use fenton's reagent directly,it is too powerful an oxidising agent and might break the ring(it is used to clean glassware and remove stains) .we might have to alter the proportion of peroxide to Fe ions for doing the decarboxylation

Quote: Originally posted by HgDinis25

http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/48_2...

Quote: Originally posted by CuReUS

by the way, why cant we try fenton's reagent(H2O2 + FeSO4) on benzoic acid to make it benzene

Quote: Originally posted by BromicAcid

Quote: Originally posted by CuReUS   by the way, why cant we try fenton's reagent(H2O2 + FeSO4) on benzoic acid to make it benzene Fenton's reagent can add -OH groups directly to the ring via radical reaction, you'll end up with a mix of phenols and such.

Quote: Originally posted by aga

You mostly get HCl, Carbon, and a small amount of brown gunk that makes a huge mess of the glassware.

what about the large number of carcinogenic chemicals like dioxins etc.

but no one tried the method posted by this guy,maybe it was too crazy
http://www.sciencemadness.org/talk/viewthread.php?tid=508

[Edited on 2-1-2015 by CuReUS]

Quote: Originally posted by CuReUS

... what about the large number of carcinogenic chemicals like dioxans etc. ...

Quote: Originally posted by Awesomeness

Quote: Originally posted by CuReUS   ... what about the large number of carcinogenic chemicals like dioxans etc. ... As stated by aga, the PVC method isn't practical. But while on the topic of dioxins, thermolysis may be a good way to get rid of these compounds. Run the gas stream into the bottom of a hot fire to decompose any undesirable waste.

My Recent Attempts:

Hi guys!

This week I tried three different possible routes to benzene. They all failed, but are worth noting.

Firstly, I know some of you are bound to think that I have been sniffing too many of my reagents. I promise you that I am sane. The most likely reason why you would be led to such a hypothesis is because of the fact that I am using rather odd reagents to do such reactions. The reason is that I prefer not working with mixtures of ungodly hot hydroxides and benzoic acid... just something I prefer to stay away from. So here, as follows, are my recent experiments, and also one of my ideas

1) REDUCTIVE DE-AMINATION A couple days ago I wanted to try to make it from aniline. I took about 2 mL of aniline and added to it a stoiciometrically correct amount of HCl to produce a required amount of HNO2 when a nitrite is added in situ. I then made the nitrite solution and added it to get a diazonium salt. After the salt was made, I tried reducing it with a HUGE excess of NaBH4. Borohydrides have four working hydrides, so I figured a fourth of an equivalent should work, but I doubled it and chose to do a 2:1 molar ratio of diazonium salt to NaBH4. As I added it, it made a fizzing sound but no other change was noted. I got, instead, a black tar in the reaction vial and it didn't smell like benzene, so I disposed of it. The tar was soluble in most polar organic solvents, though.

What went wrong?: I considered for a moment that the BH4- might have been reacting with the water instead of the diazonium, but I know that borohydrides react with water slower than it reacts with other chemicals. Maybe a hydride just won't react well with this, I can't find a mechanism. Plus, see my note for the next step.

2) In this experiment, conducted the first steps very similarly (on a somewhat larger scale, .1 mol) but I tried warming the diazonium salt with EtOH instead of borohydride. I noticed the tar forming again, but in addition I saw many more bubbles than the previous reaction, so I thought it was working. Cool oily patterns were forming on the surface of the liquid. I dumped it in a sep funnel after it was done bubbling, but saw no separation like I expected. Instead, the crappy oil came out dropwise and made clean-up a disaster.

What went wrong?: I have no idea. It is either me or my reagents. The bottle of aniline I have is VERY old and has a sort of brown tinge... It also doesn't smell as pungently as I imagined it would (I inherited this chemical, it came from Merck originally. Must be about 60+ years old. Is there any way to test it and see if it is still good?

3) ZINC REDUCTION. Here I took .05 mol of phenol and melted it in a 5 mL reaction vial. I added .05 mol of zinc and attached a hickmann still head with a condenser at the top. I ramped up the heat until it started boiling and collected the distillate. I stopped the distillation just before it ran dry. I then took it apart and got the distillate. It crystallized. I just distilled the phenol. Not what I was after, but if anyone wants the purest phenol in town you are more than welcome to come to my house and scrape it out of the head!

What went wrong?: Maybe I should've refluxed it? I really don't know. A couple sources say it should've worked

WHAT'S NEXT? How about BENZENE from DOLLAR STORE CHEMICALS!
All you need is some para-dichlorobenzene mothballs, magnesium, ether from engine starting fluid and water! Tell me if you guys think it will work, I attached the mechanism, but I am very terrible at grignard-type radical mechanisms so please let give me your critiques!

Thanks for the response, Morkva!

1) The copper sounds like it would be a good idea, I am just confused as to how I can get those ions in there without introducing any Br- or Cl- that would cause just a normal sandmeyer reaction. I find it interesting that you bring up the hypophosphite, because every source online uses phosphorous acid to do the reaction, which is very hard to obtain. I was unaware that it involves a radical mechanism, though. I thought it would be polar. Perhaps this is why I couldn't figure out how to draw the darn thing

2) I found many sources that describe passing vapors over red hot zinc dust, but a couple more questionable ones about plain distillation over zinc. Chemists are lazy; I just had to try the easier (and more practical) of the two! I assume that this is some sort of radical reaction, as well. Maybe the transition state is too high in energy? In which case, maybe an added catalyst would work.

3) Thanks for the [somewhat comical] link! I will study this! What you said, though, about not having to form grignard reagents in ether or anything though seems so... simple! I would've thought if it was that easy, others would've already done it...

Rain today, so tried out the benzene synthesis by dry distillation of 50g sodium benzoate & 14g sodium hydroxide.

(Benzene is the last item required to attempt Magpie's Congo Red synthesis)

Initially a 'golden syrup' tin was used as the reaction vessel, with the remaining distillation glassware (the rest was in the wash).



Using just a small spirit burner, this actually worked (kind of) and gave a tiny, yet totally clear product which smelt distinctly like i always thought benzene smelled.



A blowtorch was then used to raise the temperature and speed up the reaction. Perhaps doing that caused the next distillate to become orange ?

Unfortunately the metal tin seal began to leak, also the lid, which led to to small benzene fire which was immediately extinguished.

Undeterred, the contents of the tin were extracted and around half was loaded into a 100ml RBF. They're the cheaper to replace than the 250ml+ sizes.



Again the spirit burner was used, this time with aluminium foil for insulation.

The product came over after 8 minutes at a rate of 1 drop every 3 seconds.

The gas escaping from the pot appeared as 'threads' in the condenser.



The result of this distillation was a yellow/orange liquid which clearly has two layers.



The rest of the reagents will be distilled soon, the products combined, then re-distilled to work out the yield.

[Edited on 26-11-2016 by aga]

This all went a bit wrong and destroyed a 100ml and a 250ml RBF on cooling, as expected.

All of the available sodium benzoate was used (~80g) resulting in about 37ml of orange liquid, still to be re-distilled to get any actual product.

The spread of heat appears to be vitally important.

In an RBF one can see the area affected by the flame becoming black and bubbling, while the rest of the white powder remains unaffected.

With a naked flame (spirit burner) this can be moved to target an unaffected area, which seemed to squeeze out a brief run of more drops of distillate each time the flame was moved.

A steel conical flask with a huge bottom surface area might work, so that the powder remains in a very thin layer and gets heated enough for the reaction to complete.

Maybe a steel reactor where an inert atmosphere is super-hot and the powder gets fed in somehow, while allowing the benzene gas to escape.

Edit:

The products were redistilled and a cloudy liquid came over between 71 C and 75 C, the orange stuff stayed in the boiling pot.

Yield at this point is 24.1g = 56.7%

Probably needs drying so that % will reduce

[Edited on 28-11-2016 by aga]

Quote: Originally posted by aga

This all went a bit wrong and destroyed a 100ml and a 250ml RBF on cooling, as expected. All of the available sodium benzoate was used (~80g) resulting in about 37ml of orange liquid, still to be re-distilled to get any actual product. The spread of heat appears to be vitally important. In an RBF one can see the area affected by the flame becoming black and bubbling, while the rest of the white powder remains unaffected. With a naked flame (spirit burner) this can be moved to target an unaffected area, which seemed to squeeze out a brief run of more drops of distillate each time the flame was moved. A steel conical flask with a huge bottom surface area might work, so that the powder remains in a very thin layer and gets heated enough for the reaction to complete. Maybe a steel reactor where an inert atmosphere is super-hot and the powder gets fed in somehow, while allowing the benzene gas to escape. Edit: The products were redistilled and a cloudy liquid came over between 71 C and 75 C, the orange stuff stayed in the boiling pot. Yield at this point is 24.1g = 56.7% Probably needs drying so that % will reduce [Edited on 28-11-2016 by aga]

Quote: Originally posted by JJay

Quote: Originally posted by aga   This all went a bit wrong and destroyed a 100ml and a 250ml RBF on cooling, as expected. All of the available sodium benzoate was used (~80g) resulting in about 37ml of orange liquid, still to be re-distilled to get any actual product. The spread of heat appears to be vitally important. In an RBF one can see the area affected by the flame becoming black and bubbling, while the rest of the white powder remains unaffected. With a naked flame (spirit burner) this can be moved to target an unaffected area, which seemed to squeeze out a brief run of more drops of distillate each time the flame was moved. A steel conical flask with a huge bottom surface area might work, so that the powder remains in a very thin layer and gets heated enough for the reaction to complete. Maybe a steel reactor where an inert atmosphere is super-hot and the powder gets fed in somehow, while allowing the benzene gas to escape. Edit: The products were redistilled and a cloudy liquid came over between 71 C and 75 C, the orange stuff stayed in the boiling pot. Yield at this point is 24.1g = 56.7% Probably needs drying so that % will reduce [Edited on 28-11-2016 by aga] I made my benzene in steel solvent cans. I punched a hole in the top and attached a brass compression fitting, which I connected to a copper tube that ran through a thermometer adapter into a condenser. I loaded a powdered mixture of sodium hydroxide and sodium benzoate into the cans, and heated I heated the cans over a propane stove. This resulted in an orange distillate, which was washed, dried, and fractionated. Each can is good for several runs. The yield was far from quantitative, but the reaction is easy to do, and the reactants are cheap and readily available. I was very careful not to breathe any benzene; I'm not really sure how severe a carcinogen it is, but it has been proven to actually cause certain cancers. [Edited on 27-2-2017 by JJay]

Exactly the way I did it. Stainless biscuit barrel, tank connector and some 15/22mm copper pipe plus fittings. Yield not great but better than nothing. I got the same orange distillate which I then redistilled in a glass setup