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!

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?

Quote: Originally posted by Pinkhippo11

"This shit is reagent grade man, I'd bet my dick on it."

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

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.

Quote: Originally posted by ScienceHideout

Sorry I am sure other people might feel the same, too.