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?

I’m not familiar with the reaction in a hands on sense, but the obvious thing to do would be to use a bigger flask.