Proper Handling Of Hazardous Iodylarenes

Lukasz Kraszkiewicz, Lech Skulski
Medical University of Warsaw
Warsaw, Poland

Chemical & Engineering News (23 Jan 2006) Vol. 84, No. 4, p. 4.

"Bretherick's Reactive Chemical Hazards Database, Version 3.0" reports that iodylarenes explode above 200 oC. They are generally hazardous compounds, which may explode upon impact, by scratching them with a spatula, or by heating under confinement, for example. When heated in the absence of a solvent, they often detonate; reported melting points are actually explosion points. They should always be handled with care, even during their preparation by oxidative reactions, or when they are purified by recrystallization from boiling water.

A violent explosion occurred during an attempt to recrystallize 2 g of 3-iodotoluene from boiling water with vigorous stirring. The energy of the explosion was such that fragments of the glassware scratched a transparent security shield made of Plexiglas and a nest-shaped electric heater was demolished. No one in the laboratory suffered injuries because of the presence of the shield.

After the accident, we analyzed the possible causes of the explosion. We came to the conclusion that it had been caused by ineffective stirring of the boiling biphasic system. The solid ArIO2 has a polymeric nature, which makes it insoluble in most ordinary solvents, except water. During their preparation and recrystallization, the densely packed, heavy crystals of ArIO2 tend to settle down and adhere to the walls of round-bottomed flasks if the stirring is ineffective. The external electric heating of the flask caused local overheating of the solid ArIO2 that was adhering tightly to the hot walls of the flask; this resulted in the explosion.

Hence, very effective stirrers should be used, such as those of the Hershberg-type (Vogel, A. I. "A Textbook of Practical Organic Chemistry Including Qualitative Organic Analysis." London: Longmans and Green, 1948, page 65), to scrape out and stir the solids clinging to the walls of the vessels. Also during the preparation of ArIO2 from ArI, a very efficient stirring should be applied to keep the heavy ArIO2 crystals in a suspension in the bulk of a boiling liquid phase heated externally.

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