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Author: Subject: Very exothermic rxn: bromine & pyridine

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Registered: 23-7-2011
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shocked.gif posted on 19-8-2011 at 11:59
Very exothermic rxn: bromine & pyridine

Several weeks ago the unexpected did happen. My aim was to halogenate pyridine under UV-light.

I slowly added a few drops of pyridine and it was clear that this was a really exothermic reaction at 20°C. I repeat the whole process several times again until the reaction suddenly stopped.

A closer look to the reaction mixture provide me the information why it didn't react further, while a lot of pyridine had to be added to the bromine to obtain a dilute solution of pyridine and monobrominated pyridine.

I used a thermometer to break this mysterious layer, under this layer was still a layer of unreacted bromine, but above this layer I added a lot of pyridine with the idea that it might quench the reaction.

The reaction was so strong that the mixture bubbled out of my recipients. A toxic yellow gas was escaped.. Once this gas was cooled down, it formed a brown solid waxy substance. The only solvent to remove this was acetone.

But, what was happened. What substance was formed?
So far, I even didn't find the answer in literature. Even not in safety books about chemical reactions.

Can someone help me, so that these dangerous situations don't happen again when some other members try it...

Thanks in advance

Good to be wrong
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[*] posted on 19-8-2011 at 12:40

First thing; if you're trying to generate radicals from Br2, no need for UV light. An incandescent or even fluorescent bulb will do it.

Were you adding neat pyridine to neat Br2? If not, could you provide a few more details?
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[*] posted on 19-8-2011 at 14:43

Could you provide concentrations and volumes used? What were you mixing in and did you have a stir bar inserted to prevent the formation of the crust/layer?
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International Hazard

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[*] posted on 19-8-2011 at 20:10

you brominated it, alpha to the nitrogen. The 2 position is quite activated.

"Titanium tetrachloride…You sly temptress." --Walter Bishop
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