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1 March 2005 Photoreactions of 1,4-Naphthoquinones: Effects of Substituents and Water on the Intermediates and Reactivity
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Abstract

The photochemistry of lapachol and other 1,4-naphthoquinone (NQ) derivatives, e.g. 2-methoxy-1,4-naphthoquinone (MeONQ), 2-hydroxy-1,4-naphthoquinone (2-HONQ) or 5-hydroxy-1,4-naphthoquinone (5-HONQ) and 2-methyl-5-hydroxy-1,4-naphthoquinone (P-NQ) in solution at room temperature was studied by ultraviolet–visible spectroscopy after nanosecond laser pulses at 248 nm. The triplet state and semiquinone radicals were observed for MeONQ, HONQ and P-NQ, whereas for lapachol, intramolecular H-atom and charge transfer processes take place, as in the case of vitamin K1. The photoinduced reaction of NQ into HONQ is initiated by nucleophilic water addition to the triplet state, and for the secondary reactions, a modified mechanism is proposed.

Helmut Görner "Photoreactions of 1,4-Naphthoquinones: Effects of Substituents and Water on the Intermediates and Reactivity," Photochemistry and Photobiology 81(2), 376-383, (1 March 2005). https://doi.org/10.1562/2004-08-11-RA-270.1
Received: 15 July 2004; Accepted: 1 November 2004; Published: 1 March 2005
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