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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: levis123 on February 12, 2018, 04:06:07 PM

Title: Diazonium salt foam production problem (Balz-Schiemann)
Post by: levis123 on February 12, 2018, 04:06:07 PM

This was my attempt in a Balz-Schiemann reaction.

In a three neck round bottom flask containing HCl i added a thermometer, a dropping funnel and a powder funnel. The flask was cooled in an ice bath. I slowly added some amount of m-phenylenediamine through the powder funnel. Then, I added drop-wise some aqueous sodium nitrite solution through the dropping funnel. I was careful not to add the reagents too fast. The temperature did not exceed 7 Celsius.

The problem that occurred was that the reaction started to produce massive amounts of foam. The flask overflowed. I tried to make room for the gas to come out but it did not work. I decided to transfer the solution into a beaker. I had to use a lot of water to get all of it out. By this time I had about 5 times more foam than solution.

I added some fluoroboric acid to the solution hoping that i would save the reaction but no crystals were formed. So, I poured the mixture into a crystallizing dish and left it there overnight, hoping that the water will evaporate and i will be left with some benzenediazonium tetrafluoroborate.

Any thoughts?

Title: Re: Diazonium salt foam production problem (Balz-Schiemann)
Post by: Arkcon on February 12, 2018, 04:29:55 PM

Most online sources suggest that this substance is very slightly soluble in water.  So you should have it, if the process hasn't lost it.  This seems likely, since its not very stable.  And lucky, because its explosive.  So win-win.  Try again with a large vessel, if you believe you can handle the substance safely.

Title: Re: Diazonium salt foam production problem (Balz-Schiemann)
Post by: levis123 on February 12, 2018, 05:12:23 PM

Thank you. Producing foam was not mentioned in the patent so I was worried I did something wrong.

I will probably try again using a large beaker so that the gas has a way out.

One more thing, I am not sure what solvent should I use to recrystallize it?

Title: Decomposition of diazonium salt
Post by: levis123 on February 12, 2018, 05:43:11 PM

I want to produce difluorobenzene by thermal decomposition of benzenediazonium fluoroborate. I am following an Organic Sytheses patent DOI : 10.15227/orgsyn.0130046 .

The salt is obviously a solid and when i heated it decomposes to the wanted liquid. I am not sure why the procedure says that three flasks are needed for this. Why shouldnt I just heat the solid in a round-bottomed flask?

Title: Re: Decomposition of diazonium salt
Post by: wildfyr on February 12, 2018, 07:32:09 PM

Quote from: kkoupe01 on February 12, 2018, 05:43:11 PM

Why shouldnt I just heat the solid in a round-bottomed flask?

Because it might explode and blow your hands off.

Title: Re: Diazonium salt foam production problem (Balz-Schiemann)
Post by: kriggy on February 17, 2018, 04:51:58 AM

Why dont you just buy it? Sigma has 10g for like 100 euro