US EPA

1705901 

Journal Article 

Nitration of pyridine by dinitrogen pentoxide, a study of the reaction mechanism 

Bakke, JM; Ranes, E 

1997 

Yes 

Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry
ISSN: 0300-9580 

10 

1919-1923 

WOS:A1997YB26100007 

https://xlink.rsc.org/?DOI=a703079g
Exit
 

The nitration of pyridine and substituted pyridines by dinitrogen pentoxide (DNP)has been studied, The reaction of DNP with pyridine in either liquid SO2 or an organic solvent produces N-nitropyridinium nitrate (4), On reaction of this with aqueous solutions of SO2 or NaHSO3 three transient species are formed: N-nitro-1,4-dihydropyridine-4-sulfonic acid (5), N-nitro-1,2-dihydropyridine-2-sulfonic acid (6) and 1,2,3,6-tetrahydro-3-nitropyridine-2,6-disulfonic acid (7). Compounds 6 and 7 may be sulfite esters instead of sulfonic acids, Compound 5 reacts by a first order reaction [Delta H-double dagger = 32(1) kcal mol(-1), Delta S-double dagger = 31(4) cal K-1 mol(-1)] and 3-nitropyridine is formed, Compound 6 is rapidly transformed to 7 which reacts by a first order pH dependent reaction {k(obs) = 1.9(4) x 10(-4) s(-1) + 3.5(2) x 10(-2)[H+] M-1 s(-1)} to give 3-nitropyridine. From the available evidence the reactions were either intramolecular or took place in a solvent cage, Two mechanisms are found to be in accordance with the reported evidence: the nitro group either migrated as a nitronium ion in a solvent cage or by a sigmatropic shift. The results from the nitration of a series of dimethylpyridines support the sigmatropic shift migration mechanism.