Preparation of dinitrogen pentoxide

Dinitrogen pentoxide is a colorless crystalline solid which sublimes without melting at 32.5 °C at atmospheric pressure. Dinitrogen pentoxide is inherently unstable and readily decomposes to oxygen and dinitrogen tetroxide at room temperature as shown in Equation (9.1). The rate of decomposition is temperature dependent with a half-life of 10 days at 0 °C and 10 hours at 20 It is stable for 2 weeks at —20 °C and up to 1 year at temperatures below —60 °C. 

Dinitrogen pentoxide is readily soluble in absolute nitric acid and chlorinated solvents. The polarity of the solvent has a significant effect on the rate of decomposition in solution. The rate is fastest in nonpolar solvents like chloroform and slower in polar solvents like nitromethane. ° The decomposition rate for solutions of dinitrogen pentoxide in nitric acid is very slow and these solutions are moderately stable at subambient temperatures.  

Being the anhydride of nitric acid , dinitrogen pentoxide readily reacts with moisture to form nitric acid. 

In the solid state, dinitrogen pentoxide is ionic, existing as N02+N03 and sometimes called nitronium nitrate. The same is true of dinitrogen pentoxide in polar solvents like nitric acid where complete ionization to nitronium and nitrate ions is observed. In the vapour phase, and in nonpolar solvents, a covalent structure is observed. This dichotomy of behavior in both physical state and in solution means that no single nitrating agent is as diverse and versatile as nitrogen pentoxide. 

Deville first synthesized dinitrogen pentoxide in 1849 by reacting silver nitrate with chlorine gas. This reaction probably involves the initial formation of nitryl chloride and, accordingly, dinitrogen pentoxide can also be formed from the reaction of nitryl chloride or nitryl fluoride with a metal nitrate. These reactions are more of theoretical interest than of any practical value. 

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We have already seen how P4O10 is used to dehydrate nitric acid in the preparation of dinitrogen pentoxide (Equation 11.23). 

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