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2‐(2,4‐Dinitrobenzyl)pyridine (DNBP): A Potential Light‐Activated Proton Shuttle
Author(s) -
Goeschen Catrin,
Herges Rainer,
Richter Josef,
Tokarczyk Bogdan,
Wirz Jakob
Publication year - 2009
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200900191
Subject(s) - chemistry , protonation , tautomer , aqueous solution , pyridine , flash photolysis , titration , proton , reaction rate constant , enamine , photochemistry , medicinal chemistry , organic chemistry , kinetics , catalysis , ion , physics , quantum mechanics
The well‐known photochromic tautomerism of 2‐(2,4‐dinitrobenzyl)pyridine ( 1 ; CH; Scheme 1) was re‐investigated by flash photolysis in aqueous solution in view of its potential application as a light‐activated proton pump. Irradiation of 1 yields the enamine tautomer NH ( λ max =520 nm) that rapidly equilibrates with its conjugate base CNO − ( λ max =420 nm). The pH–rate profile for the first‐order decay of NH and CNO − provides a direct determination of the acidity constant of NH, p K $\rm{ {_{a,c}^{NH}}}$ =5.94±0.12 ( I =0.1 M ) and serves to clarify the mechanisms of proton transfer prevailing in aqueous solutions. The acidity constant of protonated 1 (CHNH + ), p K $\rm{ {_{a,c}^{CHNH}}}$ =4.18±0.02, was determined by spectrophotometric titration.