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Author: Subject: Benzene synthesis
blogfast25
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[*] posted on 5-5-2014 at 10:13


DeltaH:

I really don't know and only go by a reference in wiki. Reduction of phenol with Zn has also been briefly discussed higher up. It's a question of Delta G, I think: the route leading to ZnO and not Zn phenolate is more exergenic. And w/o water phenol must be a poor proton donor: in molten (or gaseous) phenol no H<sup>+</sup> can probably exist in significant amounts.

Refluxing phenol would be awkward because of its MP (but not impossible).

I briefly contemplated phenolates too but there's that hydrogen problem...


[Edited on 5-5-2014 by blogfast25]




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


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) + TiH2-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 :o

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]




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blogfast25
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[*] posted on 6-5-2014 at 04:47


DeltaH:

Not sure about TiH2 and as you say: I don't have any. It would become rather expensive way to prepare small amounts of benzene though...





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[*] posted on 6-5-2014 at 05:06


Yes agreed and as I feared :(

[Edited on 6-5-2014 by deltaH]




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[*] posted on 7-5-2014 at 04:07


Other methods for benzene preparation have been proposed here:

http://www.sciencemadness.org/talk/viewthread.php?tid=4902

No one seems to have followed up on anything other than benzoate/hydroxide though.




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[*] posted on 11-5-2014 at 09:49


Just finished a quick test tube test on Al + phenol.

A quarter of a teaspoon of phenol was loaded into a test tube and heated to BP. A long, thin strip of aluminium was then lowered into the boiling phenol. No reaction was observed. No discernible damage was sustained by the tip of the aluminium.




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[*] posted on 11-5-2014 at 10:35


amalgamated aluminium should prove to be reactive in such a medium.



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[*] posted on 13-5-2014 at 07:55


I was reading the Wikipedia article on 'decarboxylation' and found this oddity at the bottom:

Quote:
In beverages stored for long periods, very small amounts of benzene may form from benzoic acid by decarboxylation catalyzed by the presence of vitamin C[8]


[8] http://www.cfsan.fda.gov/~dms/benzdata.html

Unfortunately, this is a dead link. While not practical, I was merely curious how vitamin C catalyses the decarbonylation of benzoic acid to benzene at near room temperature -- even in "very small amounts"!?




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[*] posted on 13-5-2014 at 08:19


@blogfast

Amalgamated aluminium will also work when not into aqueus solution is used as an oxygen reductor, and not an hydrogen one needed to reduce alkanes or nitro group.




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[*] posted on 15-5-2014 at 10:31


Quote: Originally posted by blogfast25  
I really don't know and only go by a reference in wiki.

The scientific literature is there to be used when doing scientific experiments. Reviewing the literature is the most important part of designing the experiment.

Prof. Baeyer: Ueber die Reduction aromatischer Verbindungen mittelst Zinkstaub
Journal für Praktische Chemie, 1867, 100(1), 46–47.
DOI: 10.1002/prac.18671000110

S. Marasse: Untersuchungen über das rheinische Buchenholztheerkreosot
Justus Liebigs Annalen der Chemie, 1869, 152(1), 59–87.
DOI: 10.1002/jlac.18691520105

E. Müller: Ueber pyrogene Zersetzung von Gasöl, Phenol und Kreosot
Journal für Praktische Chemie, 1898, 58(1), pages 1–50.
DOI: 10.1002/prac.18980580101

See also the review in DOI: 10.1002/ange.19290421404.

Attachment: 10.1002jlac.18691520105.pdf (1.1MB)
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Attachment: 18661400306_ftp.pdf (79kB)
This file has been downloaded 541 times




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[*] posted on 18-5-2014 at 14:30


I have only made benzene by dry distillation of Benzoic acid and Sodium Hydroxide. It is simple to me. I bought a threaded pipe on both ends, bought two end caps and tapped one cap to fit a 1/4" compression fitting with about a 3' 1/4" copper line. Load up the vessel and flame that thing. I also took the burner part off of a portable deep fryer and connected it to a propane tank. I get approximately 250 mL of benzene. set up and distill and get very reasonably pure benzene. Simple.

[Edited on 18-5-2014 by organicchemist25]
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[*] posted on 20-5-2014 at 13:55


Would it be insanely stupid to try an aluminium vessel/setup rather than glass ?

[Edited on 20-5-2014 by aga]




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[*] posted on 20-5-2014 at 14:14


Sodium Hydroxide + Aluminum = Yes that would be stupid to try. You will most likely end up with benzene vapor/liquid going everywhere.
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[*] posted on 18-6-2014 at 10:54


Oh that was a long long time ago....lol

Found an article which fits in snuggly here I thought an here it is, hope it wasnt already posted, a quick search showed nothing though.

The guys actually wanted to make benzoic acid from CO2 and benzene but to get the direction they researched the decomposition of benzoic acid first and catalysts which can be used.
In short: Zn-Cu-Cr oxide catalyst gives 95% benzene in 100 hours at 290°C to 300°C, with additional MnO2 85% in 10 hours.

What might PAA and GAA do under the conditions. Hmmm...

/ORG



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[*] posted on 1-10-2014 at 06:14


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.
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[*] posted on 1-10-2014 at 08:11


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.


Yes. This method is featured on several other threads. The improvised equipment and dry distillation method shown in that video is functional.




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[*] posted on 2-10-2014 at 01:58


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 ?

some simple distilation glassware is required, and that just makes things a little easyer.
when i first started out intersted in chemistry it was for all the wrong reasons untill i learned the hard way (goal), Now its the case of all those wierd funny looking symbols and the like that looks intersting ,& the fact that you can make something from nothing so to speak.
Anyway back on topic , benzene is soooo simple to make and only requires otc chems to synthesis it from scratch witch is the best way to learn about the reaction.
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[*] posted on 2-10-2014 at 07:11


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 ?


Organic chemistry presents a LOT of possible paths to a target substance...

If the goal is PRODUCTION, for some other use- The quickest/simplest/cheapest path is the obvious choice.

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?




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[*] posted on 3-10-2014 at 23:48


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
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[*] posted on 6-10-2014 at 04:08


hmm, you make a good point bert.
And that is also very true cureus
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[*] posted on 6-10-2014 at 04:26


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;)
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[*] posted on 1-11-2014 at 09:54


Quote: Originally posted by HgDinis25  
http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/48_2...


Britt and Buchanan published a later version of the above, attached, and other similar things such as
DECARBOXYLATION OF SALTS OF AROMATIC CARBOXYLIC ACIDS AND THEIR ROLE IN CROSS-LINKING REACTIONS
http://web.ornl.gov/~webworks/cppr/y2000/pres/109540.pdf

These all lead to perhaps endless somewhat-interesting-DOE-reference chasing, e.g. Manion who does somewhat interesting things in naphthalene with substituted benzoic acids etc., and/or decarboxylation agents in this same journal; probably no one ever uses NaOH and benzoate in a soup can though.

Note that the attachment's "Commercial Calcium Benzoate" (7% water) at 500C produced almost pure benzene, while "Vacuum-Dried Commercial Calcium Benzoate" and dried "Synthesized Calcium Benzoate" gave mostly benzophenone, but in much lower yield, in line with the 30% yield of benzophenone from the dried calcium salt in Systematic Organic Chemistry. The quoted article mentions that water is very favorable for producing benzene from sodium benzoate, for whatever reason(s).

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[*] posted on 1-11-2014 at 11:08


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.




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[*] posted on 2-11-2014 at 05:59


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.


yes you are right ,but the yield of phenols is very small .i only suggested the idea because fenton's reagent is used in oxidation of sugar and suppose you have an aldose ,it oxidises the terminal aldehyde to carbon dioxide and converts the next secondary alcohol in the chain(6 carbons in a chain) to aldehyde

btw,as fenton's reagent produces hydroxyl free radicles and the mechanism of NBS allylic bromination is a free radicle one,can we do allylic hydroxylation using fenton's reagent
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[*] posted on 29-11-2014 at 20:41


Could the benzoate to benzene be done in a microwave?

I'm getting started with microwave chem and wondered why this couldn't be applied. Sodium hydroxide and sodium benzoate will both absorb MW. It will solve the problem organikum got, the sticky layer which was caused by uneven heating.

Perhaps the MW can do a whole lot of other high temp destructive distillations. I really don't want to mess with flames and that's the only other reasonable way.
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