[Borek]

You, organikers, you may be able to help an old timer with short memory

Many years ago during organic lab I was doing some experiment, some kind of synthesis. It required an ice bath for preparation of unstable intermediate, after that I had to add some solution - iodide? - and things went awry at that moment, with whole mixture exploding and staining everything with iodine.

What could that be? I guess that was some more or less standard synthetic method of replacing some functional gruop with iodine.

[stewie griffin]

Haloform reaction? Iodohydrin formation?

[sjb]

Now, now you know we don't discuss explosives here

Could be all sorts of things - do you remember anything about your other reactants?

[Borek]

Unfortunately not much, that was about 25 years ago. Somehow I think the reason of the explosion was not highly energetic reaction, but rather fast decomposition with evolving gas (nitrogen?) - but I can be wrong.

[tmartin]

An unstable intermediate, an "explosion" and evolution of nitrogen... perhaps a diazo compound? 

[408]

I must agree about potentially being a diazonium reaction.  I have had one get out of hand when not cold enough and adding iodide too fast.

[nj_bartel]

Sandmeyer maybe?

[Borek]

Yep, these obviously fit things that I remember. Wiki states that diazonium salts are unstable above 5 °C - and that sounds like something I may have read about the reaction at the time.

Unfortunately, I don't remember much more.

From what I read Sandmeyer reaction requires presence of some copper (I) halogen - but I think addition of iodide solution was the final operation before separation and purification of the product.

[nj_bartel]

Most do, but iodination just requires an iodine salt.  Wiki says there's apparently another method for iodination of benzene by refluxing benzene, nitric acid, and I₂, but I don't really know anything about that.