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Author: Subject: Benzene synthesis
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[*] posted on 22-5-2003 at 20:24
and the pressure


The first reference speaks of 40bar pressure and the multiple injection and control of hydrogen in the reactor.

The second one works with even higher temperatures - if there wouldn´t be the necessity of feeding hydrogen which has to be produced in the needed amounts if one wants to come around the storing hassle - also free from any oxygen - I would see it as possible. A slight variation of the ketene lamp could do it.
More exact parameters would be needed in special what are the nono´s in materials used (unwanted catalytic effects), the temperature range and very important the contact time needed, to calculate the flow.

If anyone brings up an hydrogen generator with constant output of oxygen-free H2 under some pressure - then this might be a way. (for the friends of industrial processes at least ;), the "Knights of the hot tube" :D)




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[*] posted on 22-5-2003 at 20:55


What kind of ketene lamp do you mean ?
I make my benzene when i throwing with arrows to diketopiperazine
:D !




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[*] posted on 7-6-2003 at 23:46


Tripopelpamziene decomposition! Thats a favorable way for benzene thats understood - how did you solve the question of collecting it? ;)

And ketene lamp, I thought of the kind which makes ketene. From acetone. Mr. Hurd made one and Mr. Vogel too.
My lamp is more a tube I confess. To be true, it is a tube and no lamp at all.
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[*] posted on 10-6-2003 at 01:57
Benzene from chloramine-B


It works. I had found the information but had forgotten where, lugh at the Hive was so friendly to look it up as he has better library access than I.

All benzylic sulfonic acids get dehydrated by strong mineral acids at elevated temperatures.
Heating chloramine-B with phosphoric acid to about 225°C will yield benzene.
I give it a try tomorrow and report the results. If it works as told it would be the most favorable benzene synthesis up to now here - easy and cheap starting compounds and bearable reaction conditions.




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[*] posted on 22-6-2003 at 17:45
Benzene


Benzene and formaldehyde --> diphenylmethane


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[*] posted on 22-6-2003 at 19:45


That's not relevant to the topic of this thread. This discussion is on the preparation of benzene, not the reactions of benzene.



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[*] posted on 23-6-2003 at 08:55


Do I smell someone showing off?
You seem to be getting a habit of posting irrelevant stuff.




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cool.gif posted on 16-11-2003 at 08:48


My chemistry book says: 3C2H2 (Ni, 70C) =>C6H6. That's not much, but at least Ni is an active catalyst, so a solution of acetylene in acetic acid or any other high-boiling solvent with a bit of Ni powder or NiO (another book says "certain transition metal compounds", so NiO will work, I think) could be heated to 75C (to prevent evaporation of benzene don't raise any further) and eventually give benzene. I personally advise a sealed vessel to stop C2H2 escaping.
For C2H2 see http://www.sciencemadness.org/talk/viewthread.php?tid=1053&p....
For Ni or NiO see http://www.sciencemadness.org/talk/viewthread.php?tid=534&pa...
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[*] posted on 16-11-2003 at 13:52


Chloramine B is said to decompose explosively at 185 C.

The decomposition of sodium benzoate to produce pure benzene is famous for making a fool of some famed chemist (Emil Fischer IIRC) because the test for benzene way back when (colour development with isatin and sulphuric acid (again IIRC)) was really a test for thiophene. Thiophene was always present in coal tar derived benzene and gave a blue colour. Pure benzene doesn't react. Imagine very embarassed Chem. prof. at front of lecture....
Anyway, the reaction should be easy. The products you want (benzene and Na2CO3) are about as stable as you can get so it shouldn't matter too much if you overheat it a bit.
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[*] posted on 21-12-2003 at 17:32


"7.CO + 6.CH4 ==(AlCl3)==> C6H6 + C6H5-CH3 + 15/2.H2O " posted by Ramiel

This reaction looks feasible and relatively simple unless pressurising is involved which seems unnecessary.

Methane just comes off the gas tap at pretty high purity, and CO can be generated by heating a mix of excess conc sulphuric acid with oxalic acid (availiable in most hardwares), or anhydrous formic acid, or a metal-formate. With oxalic acid CO and CO2 are both formed in 1/1 ratios

(COOH)2 --> CO + CO2 + H2O

but shouldn't affect the production of benzene i believe.

The aluminium chloride can just be made from anhydrous HCl on aluminium, since this occurs at much lower temp than pure chlorine. HCl is generated by adding hydrochloric acid to concentrated sulphuric acid.

Put the AlCl3 into a ~2cm wide s/steel pipe and with some basic plumbing skills, one should be able to pass the CO and CH4 over the catalyst "bed" in the heated (to 300degC?) s/steel tube, and duct the vapours of benzene into a condenser or just a glass bottle in iced water...

the temperature of the catalyst could easily be adjusted and experimented with, and if this process works, you could get yourself a lifetime's supply of benzene if required... or just some fun with the practical work involved. The tube could also be used to contain other catalysts to make various chemicals like ethene and acetaldehyde...

seems pretty intriguing for the chemists who really want the practical process of synthesise and experimentation more than product

[Edited on 22-12-2003 by pyroscikim]
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[*] posted on 22-12-2003 at 04:31


AlCl3 s a bit volatile, I think you would lose quite a lot of it with the product.
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[*] posted on 22-12-2003 at 11:16
perhaps:


toluene + Al + Cl2 ->
toluene + AlCl3 -- disproportionation -->
xylene + toluene + benzene

distill off benzene continously and refill toluene to shift the equilibrium to the wanted side.

comments, flames, name me names? ;)




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[*] posted on 23-12-2003 at 21:06


one phrase!

AlCl3 catalysed chlorination:D




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[*] posted on 26-12-2003 at 08:10


one answer:

not as long Al is present - this will react predominantly I would like to believe.

So: excess of Al + Cl2........




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[*] posted on 7-1-2004 at 11:55
Benzene Synthesis from PCBs


You could take PCBs and decompose them to
thier simple benzene construction.
Of course you would also have to break the
bond between the two benzene rings also




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[*] posted on 7-1-2004 at 16:35
possibly unfortunate news


Quote:
Alkyl migrations can be inter- or intramolecular, depending on the conditions and the R group [...] o-xylene treated with HBr and AlBr3 gave a mixture of o- and m- but no p-xylene, while p-xylene gave p- and m- but no o-xylene, and no trimethyl compounds could be isolated in these experiments (exclusively intramolecular rearrangement). Apparently, methyl groups migrate only intramolecularly, while other groups may follow either path.

That's from March, and the references for the xylene experiments are:
Brown; Jungk J. Am. Chem. Soc. 1955, 77, 5579; Allen; Yats J. Am. Chem. Soc. 1959, 81, 5289.

Unless methyl groups migrate intermolecularly under different conditions or with different reagents, this seems to bode ill for easy benzene from toluene.
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[*] posted on 8-1-2004 at 21:05
reduction of benzen diazonium salts


in a practical organic chemistry (in farsi) found two (qualitative) tests for benzene diazonium sulfate which yielded benzene:
1. warm the material in alcohol. a vigorous reaction will take place and the solution turns red. after the reaction subsides add some water an oily liquide will come to surface which is benzene mixed with some phenetol
C6H5N2SO4H + C2H5OH    > C6H6 + N2 + CH3CHO + H2SO4
C6H5N2SO4H + C2H5OH    > C6H5OC2H5 + N2 + H2SO4

2. (this one seems quite more interesting) add 1g of the material in some water and chill with ice, alkalify by adding NaOH solution. now prepare an alkaline stannous hydroxide solution (made by dissolving 3-4 g stannous chloride in twice its weight water and some concentrated NaOH solution is added till the precipitate dissolves) when it cools off add the stannous solution to the benzen diazonium sulfate sol, nitrogen will evolve and benzene comes to surface which is easily separated
C6H5N2SO4H + Sn(ONa)2 + H2O    > C6H6 + N2 + Na2SnO3 + NaOH
Edit: had missed the arrows in last equation

[Edited on 13-1-2004 by KABOOOM(pyrojustforfun)]




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[*] posted on 12-1-2004 at 16:08
well, I was wrong


R. M. Roberst and D. Shiengthong, J. Am. Chem. Soc. 86:2851 (1964) - heating 0.25 mol of p-xylene with .013 mol of AlCl3 at 30 degrees for 2 hours, with stirring, gave 2% benzene, 2% toluene, 94% xylenes, 2% pseudocumene. Repeating the experiment but at 50 degrees gave 12% benzene, 12% toluene, 70% xylenes, 1% mesitylene, 7% pseudocumene. Orgy's proposed method of "mix alkylbenzene with AlCl3, heat, and watch the benzene come over" seems very workable.

And now, since I think he's interested in various Friedel-Crafts catalysts, here's what Carey and Sundberg have to say:

Very active F-C catalysts:
AlCl3, AlBr3, GaCl3, GaCl2, SbF5, MoCl5

Moderately active:
InCl3, LnBr3, SbCl5, FeCl3, AlCl3-CH3NO2, SbF-CH3NO2

Mild:
BCl3, SnCl4, TiCl4, TiBr4, FeCl2

No information about iodides, sadly, but it might be easier to just try than to chase down references.
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[*] posted on 19-1-2004 at 21:39


ketene is required continuously for becnch scale study..so please, let me know the details pertaining the equipment used for the generation of ketene
( if possible support me with a neat sketch)
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[*] posted on 19-1-2004 at 22:56


Quote:
Originally posted by madscientist
Synthesis of benzene seems to be a topic of interest and value, considering that benzene has now been labeled as an "evil scary carcinogen of inevitable death".

Looking at the immense efforts people are proposing to create (what would be) small amounts of benzene, I have to ask Why? Does it possess some amazing properties as a solvent that aren't shared with, say, Toluene? It's not particularly interesting as a synthetic intermediate. It doesn't explode.
Other than the thrill of a few milliters of benzene sitting around in a vial, I say save your energy for more interesting things.

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[*] posted on 20-1-2004 at 08:47
Benzene


Well, for starters benzene has the lowest boiling point for aromatic liquids. And sometimes aromatics fill the void when your aliphatic liquids wont dissolve the solute you want dissolved. Secondly one valuable use of benzene is make absolute ethanol using the terniary azetrope (composition: 7.4% Water; 18.5 % Alcohol; & 74.1 % benzene) which boils 64.9 C leaving 200 proof behind. Also, I am reading here about a very simular terniary azetrope with chloroform that boils at 55C! Trouble is you have to use twice as much chloroform as benzene because the chloroform azetrope it only 3.5 % water:( But with calcium chloride treatment of the chloroform distillate) one should be able to reuse the same chloroform over and over again. :o I might head to the liquor store this weekend for Everclear!

Reference: Lange Handbook 10th Edition 1961

[Edited on 1/20/2004 by chloric1]




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[*] posted on 20-1-2004 at 09:09


Quote:

Does it possess some amazing properties as a solvent that aren't shared with, say, Toluene?


Well benzene holds up much better to oxidizing conditions then toluene or xylene. In addition it is a 'virgin' slate to work with if you're trying to synthesize something. Nitrobenzene, chlorobenzene and others are quite easy to make from the mother benzene but would take in some cases many additional steps to produce from toluene.

Finally, many of the older chemistry books that us home chemists own constantly refer back to benzene as a reference material, they list the solubilities of various substances in it and many of its reactions in detail, also it was one of the solvents of choice back in the day if you want to follow some old reaction to the letter.




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[*] posted on 20-1-2004 at 12:09
not synthetically useful?


Quote:
It's not particularly interesting as a synthetic intermediate.

It's a good starting point for nitrobenzene (and therefore aniline), phenol, bromobenzene, allylbenzene, most sorts of benzene with a single side chain...

How would you make aniline starting with toluene, if not through converting toluene to benzene at some point? I realize that these are all simple molecules, and "just buy it" is probably the easiest answer, but not everybody can just buy what they need for experimentation. Xylene and toluene are more readily available in many parts of the world, hence interest in methods of converting them to benzene.

I must say that Organikum's proposed Friedel-Crafts alkylation/dealkylation looks like the simplest method and it could probably provide substantial quantities of benzene starting from toluene or even xylene.
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shocked.gif posted on 21-1-2004 at 08:00
I was wrong


but not on the Friedel-Crafts but on the AlCl3 in situ using Cl2. KABOOM was right, this would chlorinate the benzene. But It is possible to generate AlCl3 from Al in benzene by using dry HCl-gas instead of Cl2, also a small amount (3%) of AlCl3 is needed to start the reaction - a nice way to produce bigger amounts of AlCl3 btw. ...

The thermal decomposition of chloramine-B seems very interesting too - A quick testtube trial showed that the proposed decomposition takes place and some fumes form which might very well be benzene - I didnt stick my nose into the fumes so thats all I can tell by now. On friday I get some new equipment as the old was all lost including a condensor and then will try it again on a larger scale and condense the fumes - we will see what this is.
The "violent decomposition" is not so violent as I feared it to be and can be rather easily controlled by removing the heat, I just wouldnt try this putside a flask or other vessel as the shit jumps around a little bit, thats it.




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[*] posted on 24-1-2004 at 13:25


Maybe the decarboxylation process would work with benzoic acid.


A Preparation Method for Benzophenone
 

JACS volume 50 page 571 (1928)

A Preparation Method for Benzophenone

It is well known that simple carboxylic acids yield hydrocarbons to a greater or less extent when they are heated with finely divided metals, particularly copper and nickel.

In the case of aliphatic acids the reaction is usually difficult to effect.  Acetic acid, for example, when heated with copper at 390-411°, gives mainly acetone and when nickel is used as the catalyst a considerable portion of the acid is decomposed into complex carbonaceous substances1.  With aromatic acids the decomposition is usually easier but frequently, as with benzoic acid and nickel2, the reaction temperature is so high that the resulting hydrocarbons are largely transformed into other substances.

It has been found that this process of eliminating carbon dioxide from an acid can be used to advantage in the preparation of benzophenone from o-benzoylbenzoic acid.

The yields, 80-90% of the theoretical, exceed the average of those obtained by the Friedel and Crafts synthesis, in which benzene and benzoyl chloride react in the presence of aluminum chloride, by about 10 %.  Furthermore o-benzoylbenzoic acid which is the intermediate in the synthetic anthraquinone process, is manufactured on a large scale and should be obtained without difficulty.  It can also be prepared easily and inexpensively from phthalic anhydride, benzene and aluminum chloride3.  This reaction goes nearly to completion, 95-97%, so that the yield of benzophenone based on the phthalic anhydride is still somewhat better than that obtained when benzoyl chloride and benzene are used, and the cost of the materials is much less. 
     When o-benzoylbenzoic acid is heated alone to about 300° some carbon dioxide is eliminated and benzophenone can be detected among the products.  The yield, however is negligible.  The catalysts which accelerate the reaction most efficiently are metals such as copper, nickel, iron and the o-benzoylbenzoic acid salts of these metals.  It is not necessary that the metals be particularly finely divided as they go into solution in the acid, and the only apparent advantage in having a fine state of subdivision is to increase the rate of solution.  The preferred catalysts are finely divided copper and the copper salt of o-benzoylbenzoic acid.  The later is easily made by adding a copper sulfate solution to a solution of the sodium salt of the acid, washing, filtering and drying the precipitate at 110°.  The velocity of the reaction increases with the amount of catalyst used, but too large a quantity causes inconvenience in getting out the product.   It has been found that a satisfactory ratio is 1-3 g. of copper, or an amount of the copper salt of o-benzoylbenzoic acid containing an equivalent weight of copper, to 100 g. of the acid.  In the presence of these catalysts carbon dioxide elimination begins at about 150° and increases as the temperature rises until 306° is reached, when the reaction mixture begins to boil.  The speed of the reaction below 200° is too slow for practical purposes and above 280° there is decomposition, the formation of anthraquinone and unidentified tarry substances.  The optimum temperature range is about 250-270°.


Preparation Procedure


Three hundred grams of pure o-benzoylbenzoic acid was placed in a distilling flask with a low side tube.  To this was added 20 g. of the copper salt of the acid.  The flask was fitted with a mechanical stirrer arranged through a mercury seal, and a thermometer the bulb of which was immersed in the liquid when the material melted.  The mixture was heated with stirring; carbon dioxide evolution was appreciable at 200°, and it was allowed to escape through the side tube of the flask and to bubble through water, which gave an indication of the progress of the reaction.  The temperature was allowed to rise and was maintained at 260° until carbon dioxide evolution ceased (about four hours).   It is necessary to continue until the carbon dioxide evolution has completely stopped. If a distillation is attempted before this point, a considerable quantity of anthraquinone is formed, which contaminates the product.  The stirrer was taken from the flask, a short air condenser attached to the side tube and the thermometer raised out of the liquid as for distillation.  The crude benzophenone was distilled over until the drops of distillate became dark in color; the weight of this crude product was 209 g., 86.6 % of the theoretical.  One crystallization from 95% alcohol gave pure benzophenone, m. p. 47-48°, in an amount corresponding to 82-84% of the theoretical based on the o-benzoylbenzoic acid.  The crystallization may be replaced by distillation in a vacuum.

1 Sabatier and Senderens, Ann. chim. phys., [8] 4, 467 (1905).
2 Sabatier and Mailhe, Compt. rend., 159, 217 (1914).
3 Cain, “The Manufacture of Intermediate Products for Dyes,” Macmillan and Co., London, 1918, p. 240
 

 

 

[Edited on 24-1-2004 by If_6_was_9]
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