TY  - JOUR
A1  - Fudickar, Werner
A1  - Linker, Torsten
T1  - Photooxygenation of naphthalene
JF  - ChemPhotoChem
N2  - The photooxygenation of naphthalene to the corresponding endoperoxide (EPO) under various conditions is described. Substantial conversion is only observed at -10 degrees C and after more than two days, indicating that the [4+2] cycloaddition of singlet oxygen to this acene proceeds much more slowly than corresponding reactions of substituted naphthalenes, a rate constant of k = 5.4 +/- 0.3 M(-1)s(-1) was determined by competition kinetics. Another problem is the thermal lability and photochemical cleavage of the naphthalene EPO. We investigated the mechanism of this radical process depending on the light source and sensitizer in comparison to known cyclohexadiene EPO. Thus, bisepoxides and keto epoxides are formed after homolysis of the O-O bond by irradiation with sodium lamps or blue LEDs and subsequent cyclization. This process is accelerated by the sensitizers methylene blue and 9,10-dicyanoanthracene, indicating an electron transfer mechanism. Finally, the cleavage of the peroxidic bond is inhibited with red LEDs, and photooxygenation under such conditions affords 20 % EPO. Thus, we could demonstrate that contrary to literature statements singlet oxygen does indeed react with naphthalene.
KW  - naphthalene
KW  - photooxygenation
KW  - reaction mechanisms
KW  - reactive
KW  - intermediates
KW  - singlet oxygen
Y1  - 2021
U6  - https://doi.org/10.1002/cptc.202100097
VL  - 5
IS  - 11
SP  - 1004
EP  - 1008
PB  - Wiley-VCH
CY  - Weinheim
ER  -