ScienceHideout
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Sandmeyer Benzene Production
We've all used the Sandmeyer reaction to make cool stuff, like phenol and halo-benzenes and stuff like that 
A less common thing to do with the sandmeyer reaction is to use it to make benzene.
We are all interested in making benzene, right? Most of us who make it, though, go to extreme measures mixing hydroxides and benzoates and distilling
at high heat, only to ruin your apparatus for a disappointing yield.
Now, I understand that for the sandmeyer reaction, one needs a little bit of aniline. I realize that aniline is hard to obtain, but my response is a)
it is easier to obtain than benzene, and b) some of us have a lot of it! I myself have a very old bottle of aniline from Merck- about 500 ml, and it
is full, and surprisingly still quite good! The only thing I use it for is the production of acetanilide. I would certainly have no opposition to use
an ounce or so to make benzene.
Now, I cannot find much information at all about this particular reaction, however it seems that the only thing that needs to be done is to add
phosphorous acid to the diazonium compound.
The problem: I lack phosphorous acid.
Now, the question is- is there a substitute? My answer: Maybe.
Phosphorous acid is used most commonly as a reducing agent. I'd imagine that it is used as a reducing agent in this reaction, because the diazonium
group comes off the benzene ring and a hydrogen goes on. Not to mention, diazonium salts are electrophiles, 'electron lovers' and therefore can be
reduced.
I then decided to look this up. What is actually going on when phosphorous acid is added? There is a special word for it: dediazonization.
So, perhaps it is possible to simply add a reducing agent to a diazonium salt and get benzene. Maybe it is not that simple. Perhaps the reaction works
with only phosphorous acid. Maybe there is some sort of anomaly where the phosphite will catalyze the reaction the same way aluminum will not replace
copper unless Cl- are present. But for right now, perhaps we should assume the best.
So, the next question is, what reducing agent should we try out? It would be so simple to just start with the big guns- LiAlH4 or NaBH4.
Unfortunately, we don't have endless supplies of either of these chemicals. And, if we don't work our way up we will lazily work our way down. If
there is one lesson I learned about the scientific method by watching "Mythbusters" since the day it aired 10+ years ago, it is to start small scale,
then jump to the big guns 
A quick search to wikipedia seemed promising. Wikipedia provided a list on the "Reducing agent" page. Looking at it, I think it would be safe to
imagine that it goes in order from best reducer to better reducer to good reducer. I hypothesized this by looking at LiAlH4 on the top, borohydride in
the middle, carboxylic acids farther down, and carbon near the bottom. Phosphorous acid- 15th on the list. That means there are at least fifteen
reducing agents stronger than H3PO3, and therefore, 15 or more that could work.
Some of these, the ones ranked just above H3PO3, are the carboxylic acids I previously mentioned. Oxalic, formic, ascorbic, etc.
Others are sulfites. Perhaps sulfurous acid would work? It has a lot in common with phosphorous acid- both are multi-protic acids, rather weak, end in
-ous...
Another awesome one is hydrazine. However, I am just wondering, what the heck will happen to all the nitrogen!?!
Sn2+ is also a reducer. I am worried about this one, too, because it is a metal ion. I know that the diazonium salts react with copper compounds- will
adding stannous chloride form chlorobenzene?
I guess that I would like to propose a problem we all can solve... we are all interested in benzene, why don't a couple of us look into this? I would
myself, but I don't know where to start!
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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Zephyr
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If you can find Foliar spray containing potassium phosphite this old hive post may help you.
http://chemistry.mdma.ch/hiveboard/crystal/000456171.html
The procedure is sketchy and I am not as sure of the purity as the author is "This shit is reagent grade man, I'd bet my dick on it." But after some
modifications to the procedure and a few recrystalizations it may be of high enough quality.
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Boffis
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Phenyl diazonium salts can be reduced to the parent hydrocarbon with either hypophosphorous acid or warming with ethanol. Hypophosphorous acid of
adequate purity can be prepared from sodium hypophosphite and HCl. If you make the hypophosphorous acid first you can us it to carry out the
diazotization and reduction simultaneously. I am pretty sure that information on this procedure has been posted before on this forum.
Sulphite cannot be used as the product is phenylhydrazine sulphonic acid which decomposes to phenylhydrazine; this is the general procedure for the
preparation of phenylhydrazines.
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ScienceHideout
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 Wow, someone has been reading some organic chemistry books lately
Thanks a lot, Boffis... What really interests me is this 'warming with ethanol.' This seems too easy- is there a catch?
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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BromicAcid
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Sounds like something out of an old ACS journal.
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Nicodem
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Thread Moved
10-7-2014 at 22:34 |
blogfast25
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Quote: Originally posted by ScienceHideout  | If there is one lesson I learned about the scientific method by watching "Mythbusters" since the day it aired 10+ years ago, it is to start small
scale, then jump to the big guns
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Really? Most myths the 'busters' bust can be busted with a piece of paper and a pencil, i.e. with simple, pure reason and no experimentation.
Nor do I really recall them starting at small scale.
For the most part MB is a veneer of quasi-science designed to dress up big 'KABOOOOMs!!!', large things spectacularly collapsing and
other 'kewl, dude!' stuff. Quite anally retentive, IMHO... But it sure generates revenue...
More to the point of benzene, have you considered the decarboxylation of sodium benzoate (very OTC) with sodium or calcium hydroxide? See organic
section, sticky thread.
[Edited on 11-7-2014 by blogfast25]
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ScienceHideout
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by ScienceHideout | If there is one lesson I learned about the scientific method by watching "Mythbusters" since the day it aired 10+ years ago, it is to start small
scale, then jump to the big guns
|
For the most part MB is a veneer of quasi-science designed to dress up big 'KABOOOOMs!!!', large things spectacularly collapsing and
other 'kewl, dude!' stuff. Quite anally retentive, IMHO... But it sure generates revenue...
More to the point of benzene, have you considered the decarboxylation of sodium benzoate (very OTC) with sodium or calcium hydroxide? See organic
section, sticky thread.
[Edited on 11-7-2014 by blogfast25] |
Lol, yes, Mythbusters is VERY quasi-scientific, but our first taste of science has to come from somewhere. The show aired first ten years ago. I was
eight. of course now I realize they are not really scientific, but scientific or not, it inspired me to like chemistry.
Yes, I have read the pages about the decarboxylation of benzoic acid. As I have stated above in my long post, it just seems too difficult for me.
After I track down an OTC source of sodium benzoate, I then have to create some sort of crazy apparatus that will hold up during the distillation,
only for a few mL. I have oodles of aniline for my lab. I just would rather work at non-extreme temperatures in the comfort of my lab with my standard
glassware than have to go out of my way to create one chemical. Sorry  I am sure
other people might feel the same, too.
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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plante1999
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Some *legitimate* over sea supplier will sell benzene to anyone with about 60$ to spare for 500 ml.
I never asked for this.
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Boffis
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If you check out Vogel's Textbook of Preparative Organic chemistry 3rd Ed (downloadable from the internet) there are three experimental procedures for
deamination of amines via diazonium compounds and in the chapter intro there are descriptions of three techniques using hypophosphorous acid, sodium
stannite (SnCl2 in strong NaOH) and ethanol. One of the experimental procedures is for the preparation of toluene from p-toluidine which should be
readily modified to suit aniline.
A procedure using alcohol is also described for 1,3,5 tribromobenzene from the equivalent aniline.
I also found a paper that describes the deamination of 5-aminotetrazole to the simple tetrazole using hypophosphorous acid:
"An improved procedure for the deamination of 5-aminotetrazole to tetrazole JACS Henry & Finnegan 1953; vol. 79; p290. (this paper also describes
some experiments with other amines including various anilines.)
Hypophosporous acid can be prepared by adding the sodium salt to 36% HCl in appropriate ratio, partial volume reduction to reduced the water content,
cooled and the then filtered to remove the crystalline salt. Further purification is not required if the acid is to e used for the reduction of
diazonium salts. I am pretty sure that my procedure came from this forum so try a search.
Hope these are helpful.
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S.C. Wack
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Pages 210 and 223 of the 1909 Gattermann at the library.
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blogfast25
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Well, I do too (although you exaggerate the difficulties with benzoate + NaOH).
But I don't have oodles of aniline. Do report back if you've managed something based on aniline. It's ridiculous we have to scavenge around for
something so basic now. A plague on both their houses...
Will have a look at SC's reference now.
@plante: who's the mystery supplier?
[Edited on 11-7-2014 by blogfast25]
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