2,4-dinitrophenylhydrazine (2,4-DNP)

Wednesday 2 November 2016

Years ago when I first started teaching at Atlantic College I came across a bottle of picric acid in the store room. It had completely dried out and posed a considerable risk of explosion as friction can cause the dry solid to detonate. My way of dealing with it was to carefully add water dropwise as it is stable when wet. It appears now that I should have called in the bomb disposal squad!

Several schools and universities in Wales have had to have controlled explosions to get rid of  both picric acid and 2,4-dinitrophenylhydrazine which is also potentially explosive when dry. 

Swansea University in South Wales where a controlled explosion to destroy picric acid took place on 27 October 2016.

Many schools do still have 2,4-DNP (sometimes also known as 2,4-DNPH) as until recently it appeared on the syllabus of many 16-18 chemistry courses as a way of identifying aldehydes and ketones as they undergo addition-elimination reactions with 2,4-DNP to give orange crystals each with a characteristic melting point. For example it was covered under Assessment Statement H.8 on Further Organic Chemistry on the old 2003- 2008 IB programme

and under G.4.1 on the 2009 programme (the last exam on this syllabus was in November 2015). Nowadays spectroscopic data (Topics 11.3 and 21.1 on the current programme) provide a much easier way to identify aldehydes and ketones.

It may be worth you checking to see whether you have any dry 2,4-DNP in your store cupboards. However do not fall into the same error present in the BBC article which confuses 2,4-DNP with the diet supplement pills DNP (dinitrophenol)!! 


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