Photochemistry of 2-chloropyrimidine.
The photochemistry of 2-chloropyrimidine (ClPy) was investigated by means of nanosecond laser flash photolysis, HPLC, mass spectrometry, polarography and absorption spectroscopy. Two major products were formed on low-intensity UV irradiation (lambda = 254 nm) of ClPy in anaerobic aqueous solution: 2-hydroxypyrimidine (quantum yield approximately 0.01) and a compound identified as 2-chloro-4,2'-bipyrimidine (quantum yield approximately 0.005). Only the former of these products was obtained under aerobic conditions. Investigation by nanosecond flash photolysis revealed the occurrence of efficient intersystem crossing to the ClPy triplet state; the deactivation processes from this state were determined. Photosensitised generation of the ClPy triplet state showed that the triplet is involved in the formation of the bipyrimidine. A reaction scheme is proposed comprising two reaction channels: heterolytic rupture of the C-Cl bond in the excited singlet state of ClPy leading to formation of 2-hydroxypyrimidine, and homolytic C-Cl rupture in the triplet state with creation of pyrimidinyl radicals, which react with excess ClPy to give 2-chloro-4,2'-bipyrimidine.
Lindqvist
Lars
L
Laboratoire de Photophysique Moleculaire du CNRS, Bât. 210, Université Paris-Sud, 91405 Orsay, France. lars.lindqvist@ppm.u-psud.fr
Czochralska
Barbara
B
Fontaine-Aupart
Marie-Pierre
MP
Kawczynski
Wieslaw
W
Tfibel
Francis
F
Douki
Thierry
T