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Near miss with Acetyl Nitrate

A near miss occurred in the lab when consideration of the order of addition was not made, for a nitration reaction using acetyl nitrate.

It is essential when making acetyl nitrate to ensure that the order of additions is correct.  When the addition order is wrong, then the system will pass through a region where the mixture is potentially shock sensitive.

The centre of the shock sensitivity zone is around 70 mole% nitric acid : 30 mole% acetic anhydride and spreads about 20 mole% each side.  Typically the acetyl nitate is made in excess acetic anhydride (thus resulting in about 35 mole% nitric acid), so the correct order is, to start with acetic ahydride, and slowly add the nitric acid.  Thereby the concentration of nitric goes from 0 to 35 mole%, and does not approach the start of the sensitive region.
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